Gl@ssary

AA 
see reaction to fire

Absorptance 
the proportion of incident solar radiation absorbed by the glass, expressed as a fraction (see solar properties).

Absorption 
an alternative word for absorptance, expressed as a percentage.

Acid etching 
a process whereby the polished surface of glass is etched by exposure to hydrofluoric acid to produce patterns, designs or obscuration – see Information on Pilkington Optifloat™ Opal and on Pilkington Oriel Collection.

Acoustic laminate 
a laminated glass with special interlayers with better acoustic performance than ordinary laminated glass. See Product Data sheet on Pilkington Acoustic Laminate Pilkington Optiphon™ and Technical Bulletin "Glass and Noise Control".

Acoustic performance 
simply how much noise does a product stop. It is the properties of a glass or glazing product which describe its airborne sound insulation, as measured by the reduction or attenuation of sound, at specific pitches or frequencies, in decibels (dB), or by sound reduction indexes, such as the mean sound reduction index (R_m), the weighted sound reduction index (R_w) or the road traffic sound reduction index (R_tra).

Activ™
Pilkington Activ™ is the brand name for the world’s first self-cleaning glass. Its unique dual action uses the forces of nature to help keep the glass free from organic dirt, giving you not only the practical benefit of less cleaning, but also
clearer, better-looking windows.

A Frame
a rack or stillage that is A shaped in profile.

Air Mass 1
a particular definition of the solar spectrum. See also relative spectral distribution.

Air Mass 1.5
a particular definition of the solar spectrum. See also relative spectral distribution.

Air Mass 2 
a particular definition of the solar spectrum. See also relative spectral distribution.

Airborne sound insulation 
the correct term for the type of sound insulation given by glass. See also acoustic performance. See Technical Bulletin "Glass and Noise Control".

Air Gap
an alternative term for cavity in an insulating glass unit.

Airspace 
an alternative term for the cavity in an insulating glass unit.

Annealed glass 
another term for "ordinary" glass, most commonly used for float glass but Pilkington Texture Glass and Pilkington Pyroshield™ 2 are also annealed glass. Glass that immediately after it has solidified into the required form, while still at a high temperature, is slowly cooled in order to minimise the internal stresses in the glass. The resulting glass can be cut by scoring and snapping and worked. It is, in fact "ordinary" glass as taken from the production line and stored in stock plates. Annealed glass, when broken, gives large fragments with sharp edges and so is not usually classifiable as a safety glass.

Anti-bandit glazing 
a form of security glazing resistant to manual attack. See Product Brochure on Safety/Security Glass.

Antisun™ 
An old brand name for Pilkington Optifloat™ Tinted, our tinted float range of solar control glass.

Applied Bevel 
a bevelled piece of glass that is stuck on to another piece of glass or insulating glass unit with a UV curing resin.

Applied Film 
an organic (plastic) film stuck onto glass to give it additional properties, e.g. safety film.

Applied Leading 
strips of lead adhered to both surfaces of a pane of glass to give the appearance of a leaded light.

Arctic™ 
Arctic™ is a design of one of the glasses in the Pilkington Texture Glass range (see customer leaflet The Pilkington Texture Glass Range) of patterned glass.  Arctic™ has an obscuration level of 4. 

Arctic Blue™
Arctic Blue™ is a one of High Performance Tints.

Armed attack 
an attack using firearms. See Product Brochure on Safety/Security Glass.

Armourclad™ 
Pilkington Armourclad™ was an old brand name used for spandrel panels. We now refer to these products as Pilkington Sprandrel Glass.

Armourfloat™ 
an old brand name used for Pilkington Toughened Safety Glass.

Armourlight™ 
an old brand name for Pilkington Heat Strengthened Glass.

Armourplate™ 
an old brand name used for Pilkington Toughened Safety Glass.

Armourscreen™ 
an old brand name for Pilkington Screen Printed Glass.

Arrissed edge 
an edge finish to the glass where the sharp corners of the edge have been removed.

Arrissing 
a process of edge finishing where the sharp edges of a piece of glass are removed.

Aspect ratio
the ratio of the long edge of a pane to the short edge.

Attenuation 
the reduction of either sound (see acoustic performance) or electromagnetic radiation (see electromagnetic shielding).

Audioscreen™ 
Pilkington Audioscreen™ was an old brand name for Pilkington Acoustic Laminate Pilkington Optiphon™.

Autoclave 
a large pressure vessel that Polyvinylbutyral PVB laminated glass is heated in, to bond the layers of glass and PVB together.

Autumn™ 
Pilkington Autumn™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Autumn™ has an obscuration level of 3.

Backing paint: 
a form of opacifier, see also spandrel panels, or a protective coating applied to mirrors.

Balustrade: 
a term commonly used for a barrier, protecting a drop, which comes up to about waist height.

Barrier: 
structures designed to either guide the direction of pedestrian traffic or to provide a guarding to the edges of drops.

Base glass: 
a term used to describe the glass, which is subsequently processed, e.g. acid etching, sand blasting, or coated glass.

Bead: 
see glazing bead.

Bent glass: 
an alternative term for curved glass.

Bevelling: 
decorative process, of grinding a portion off the edge of the glass, to form a shallow angled face, which is subsequently polished.

Blast resistance: 
The ability of a particular type of glass to either withstand explosion pressure waves without breaking or to remain in position if broken.

Body Tinted Float: 
see tinted float.

Bomb Blast:
strictly the high pressure wave of gases (the blast wave) that move rapidly away from an explosion. However bomb blast will often refer to the damage caused by the blast wave and by any fragments associated with the bomb. These fragments can be part of the bomb, any container or vehicle it was carried in and any material that was carried along by the blast wave.

Borosilicate glass:
Glass with increased amounts of Boron. This means that the glass melts at a higher temperature than conventional soda lime silicate glass. Pyran from Schott Glass is an example of a Borosilicate Fire Resistant Glass.

Bow: 
a form of distortion of toughened glass or heat strengthened glass. Bow may vary depending on the glass type/thickness, size, aspect ratio and other factors. It is measured with the glass in the vertical plane and supported at quarter points. The maximum deviation from a straight edge is measured on the concave surface.

BR1: 
EN1063 classification for bullet resistant glass to withstand .22 Rifle

BR2: 
EN1063 classification for bullet resistant glass to withstand 9 mm Parabellum Handgun = G0

BR3: 
EN1063 classification for bullet resistant glass to withstand .357 Magnum Handgun = G1

BR4: 
EN1063 classification for bullet resistant glass to withstand .44 Magnum Handgun = G2

BR5: 
EN1063 classification for bullet resistant glass to withstand 5.56mm Rifle = R1

BR6: 
EN1063 classification for bullet resistant glass to withstand 7.62 mm Rifle = R2

See also Brochure on Safety/Security Glass.

Brass Plating:
a term sometimes used when a customer buys bulk loads of a product through a merchant, who then arranges for the factory to deliver direct to his customer. The merchant usually does not see the glass involved all he does is raise an invoice.

Break Safely: 
see safe breakage.

Brewster’s Fringes: 
an effect like a rainbow visible under certain lighting conditions, produced in an insulating unit when the two panes of glass are almost exactly parallel to each other.

Brilliant cutting: 
the manufacture of a decorative polished V-shaped notch in the surface of the glass. The notch may be straight or curved.

Brise soleil: 
a partial shading device, usually above a window on the exterior of the building.

Brocade™: 
Pilkington Brocade™ is the brand name for one of the Pilkington Oriel Collection range of acid etched decorative glass.

BS#: 
stands for British Standard #. BS 6262 part 4 is a safety glazing standard. A full list of glass related British Standards appears at the back of this guide.

Bubble:
depending on context this could be:

• a bubble of air trapped between interlayers in a laminated glass, or
• a gas bubble that has become trapped within a piece of glass during manufacture.

Bullet Resistance: 
the ability of a particular type of glass to withstand armed attack using a particular type of weapon not just by stopping the bullets, but also in terms of the spall ejected from the opposite face by the impact. classification is explained in EN1063 standard see BR1 – BR6. See also Brochure on Safety/Security Glass.

Bushes: 
nylon or hard fibre ferrules used round the shanks of bolts in bolted connections, to prevent direct contact between the bolt and the glass. Often used in the Balustrades and in the Pilkington Planar™ System (see Pilkington Architectural Information on CD-ROM for further details.)

Butt joint: 
a joint between the edges of adjacent panes, which have no frame, but are filled with adhesive sealant, commonly silicone sealant.

Canopy:
an overhead device to keep rain off can also is used to provide shading on southerly facing glazing.

Canterbury™:
Pilkington Canterbury™ is the brand name for one of the Pilkington Oriel Collection range of acid etched decorative glass.

Cap: 
an abbreviation for end cap.

Capping:
a term used in glazing, depending on context it can mean:

• a glazing compound that has been applied to protect another material, for example a silicone sealant that is applied to protect an intumescent compound from the weather;
• a metal glazing bead in a patent glazing system.

Cast-in-place (CIP): 
a type of interlayer used in the manufacture of laminated glass, by pouring a liquid resin between two panes of glass and curing it either chemically or by exposure to UV light. 

Cathedral:
Competitor textured glass pattern, Pilkington Minster™ should be offered as a substitute.

Cavity: 
the gap between the panes of an insulating glass unit also know as the airspace. 

Ceramic coating: 
the enamel finish applied to toughened glass to manufacture Pilkington Spandrel Glass Enamelled. 

Chantilly™ 
Pilkington Chantilly™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Chantilly™ has an obscuration level of 2.

Class O: 
see reaction to fire.

Class A: 
see safety glass.

Class Ao: 
see safety glass.

Class B: 
see safety glass.

Class Bo: 
see safety glass.

Class C: 
see safety glass.

Class Co: 
see safety glass.

Clear float: 
untinted float glass (normal window glass) called Pilkington Optifloat™ Clear. 

Coated glass: 
a base glass to which an inorganic coating has been applied, either a pyrolytic coating, usually applied on-line (i.e. during the manufacture of the float glass) or a sputtered coating applied off-line to stock sizes or cut sizes.

Cold radiation: 
a description of the apparent effect felt when sitting near to a cold window surface, e.g. single glazing in cold weather.

Coloured film: 
decorative applied film stuck on to the glass, usually in conjunction with applied leading to give the appearance of a leaded light.

Comfort: 
see thermal comfort.

Comprehensive surface stress: 
see toughened glass.

Condensation: 
the formation of water droplets on cold surfaces. Condensation is regularly seen on the room surfaces of single glazing, but its incidence is reduced by the use of insulating glass units and particularly those that contain Low E glass. (See also external condensation.)

Conduction: 
one of the methods of heat transfer through glass or through the gas in the cavity of insulating glass units.

Conduction heat gain: 
the transfer of heat from outside the building to the inside when the external air temperature is hotter than the internal air temperature.

Containment: 
the ability of a glass or glazing product to prevent persons who accidentally fall against it from falling through. (See also guarding and barriers.)

Convection: 
one of the methods of heat transfer by the gas in the cavity of an insulating glass unit.

Cotswold™:
Pilkington Cotswold™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Cotswold™ has an obscuration level of 5.

Critical locations: 
those areas of a building, e.g. doors, adjacent to doors, or low level glazing, where glazing is most vulnerable to accidental human impact and which may require the use of safety glass. These areas are defined in BS 6262 part 4:1992 Accident Human Impact.

Cross bar: 
a support for the lead cames in large traditional leaded lights.

Cullet:
a term used for broken glass. Cullet is often mixed with the other raw materials (see glass) and recycled in glass manufacturing because it takes 50% less energy to melt cullet.

Curtain Slider:
a type of delivery vehicle that has sliding curtains along the sides to protect the load from the weather.

Curtain walling: 
a glazing system in which the complete façade is glazed into frames attached to the building structure. The glazing may include both vision areas and spandrel panels.

Curved glass: 
glass, which has been heated past its softening point and formed into a curved shape, usually by draping the softened glass over or into a mould. The shaped glass is subsequently cooled slowly to form annealed glass or it may be rapidly chilled to form toughened glass.

Cut sizes: 
panes of glass cut to the final size for glazing.

Data protection: 
the electromagnetic shielding of computers either to prevent scanning of the radio waves emitted by computers or to prevent corruption of data by interference from outside radio or radar sources.

Datastop™: 
Pilkington Datastop™ is the brand name for a range of laminated glass and insulating glass units that have been specifically designed to give increased electromagnetic shielding for computers and offices.

dB: 
see decibel.

dBA:
a weighted measure of sound that is designed to stimulate that of our ears. The international standard for this measure is called the 'A' Weighting Curve. Measurements made with this facility are, therefore, termed 'A' weighted decibels or, more concisely, dBA, to discriminate from those made in plain dB, which do not depend directly on human reaction.

Decibel (dB): 
the scale used to measure or describe:

• Loudness of sound, or
• Sound insulation and sound reduction indexes (see acoustic performance), or
• Attenuation of radar and radio waves (see electromagnetic shielding).

Deep Flemish™:
is the brand name for an old Pilkington patterned glass, which is no longer manufactured. It had an obscuration level of 2.

Deflection:
how much something moves out of true plane when a load is applied. Glass can bend when a load like snow or wind is applied. Deflections can be calculated in advance and the correct glass for the application specified.

Desiccant: 
a chemical drying agent that dries and helps remove any organic vapours from the air or gas trapped inside the cavity of an insulating glass unit. It is sometimes called a molecular sieve.

D.G.U.: 
double glazing unit.

Diamond Leading: 
a style of leading copying a traditional leaded light.

Diffusing: 
randomly scattering the incident light while still allowing transmission. Usually applied to the effects on light of acid etching, sand blasting and 3065 white tinted interlayers. (See also translucent.)

Diffusion: 
see diffusing.

Dimensions: 
the length and width or other appropriate descriptions of the size of a pane of glass. The glass thickness is not usually referred to as a dimension of the glass.

Direct transmittance: 
the proportion of a solar radiation, which goes straight through the glass without being absorbed. (See also solar properties)

Distance pieces: 
sections of material used to space the pane of glass away from the upstand of the rebate in a frame, in order that an appropriate face clearance and an appropriate amount of sealant is present between the glass and the frame.

Double glazing: 
depending on context:

• term often used for a replacement window,
• is also used for secondary sash glazing,
• and for insulating glass units.

Double glazing unit: 
an alternative name for insulating glass units comprising of two panes of glass.

Double window: 
a window containing two panes of glass in the same vision area, but which are glazed separately, not formed into an insulating glass unit. It is sometimes described as secondary sash glazing.

Drained and ventilated glazing: 
drained glazing where the rebates are deliberately ventilated so that external air circulates around the edge of the glass to assist in keeping the edges dry.

Drained glazing: 
a glazing system in which any lodged water is channelled out of the rebates.

Driftwood™:
is the brand name for an old Pilkington patterned glass, which is no longer manufactured. It had an obscuration level of 5.

Drying agent: 
another name for desiccant or molecular sieve.

Dual seal system: 
the edge seal of a high performance insulating glass unit, which comprises primary seals between the spacer bar and the panes of glass and a secondary seal between two panes outside the spacer bar. Pilkington Insulight™ Units are made with a dual seal system.

E:
EN 357 classification for integrity, fire resistant glass.

Eclipse™:
Pilkington Eclipse™ is our brand name for a range of hard coated, solar control glasses.

Edge clearance:
the distance between the edge of the pane and the frame in which it is glazed. The clearance is required to allow for tolerances, avoid contact between the glass and it's framing and, in the case of drained glazing, to give sufficient room for water to drain away.

Edge cover:
the amount of glass within the rebate, i.e. covered by glazing bead. This is required to ensure the pane is effectively secured (i.e. a mechanical requirement) and also to ensure the edge seal of an insulating glass unit is protected from the weather.

Edge seal:
the hermetic seal around the edge of an insulating glass unit, designed to limit the rate at which water vapour penetrates into the cavity. The better performing edge seals are usually dual seal systems. These are used in Pilkington Insulight™ Units.

Edge Work:
any extra work carried out to the edge of a piece of glass. This can be arrissed edge, a flat ground edge or a polished edge. It may be used to refer to bevelling the edge of the glass.

Effective U value:
sometimes called the energy balance value, a measure of the performance of glass as an energy saving wall construction when its ability to let in useful solar heat gains is combined with its capability for thermal insulation as described by the U_g value.

EI:
EN 357 classification for Insulation, fire resistant glass.

EKO Plus:
hard coated, Low Emissivity Glass produced by St Gobain. Pilkington K Glass™ should be offered as a substitute.

Electromagnetic attenuation:
see electromagnetic shielding.

Electromagnetic radiation:
a technical expression for all the wavelengths of electrical or magnetic activity. The full spectrum from cosmic and gamma rays with very short wavelength, through X-rays, UV light (generally described as 280 to 380 nanometre (nm) wavelength), visible spectrum (generally described as 380 to 780) and infra-red, to radio waves with very long wavelength.

Electromagnetic shielding:
the use of a Faraday Cage to reduce or prevent the passage of the longer wavelengths of electromagnetic radiation, usually at the frequencies of radar and radio waves. The electromagnetic attenuation give by the Faraday Cage is measured in decibels.

Emissivity:
the ability of a surface to absorb or emit electromagnetic radiation. In terms of glass, emissivity is only important with respect to long wavelength radiation (in the range 5000 to 5000 nm) produced as radiated heat by objects at around room temperature. Glass naturally has a high emissivity. However, when made into low emissivity (Low E Glass), the glass surface does not absorb the radiated heat, but reflects it back into the room, enhancing the U_g value of the glazing. Pilkington K Glass™ and Pilkington Optitherm™ are examples of Low Emissivity Glass. 

EN#: 
European standard #.  

Enamel:
a glassy material, which is melted into the surface of the base glass at high temperatures to form a ceramic coating.

Enamelled glass:
glass with enamel applied. Used as Pilkington Spandrel Glass Enamelled.

End Cap:
wooden boxes held onto the ends of a pack of glass with metal banding. One of the standard methods of delivery for larger quantities of glass.

Energy Balance Value:
also known as the effective U value.

Environmental control:
a term used to describe a glass or glazing product which is used for particular effect on the environment inside a building. Often used as a euphemism for solar control it could also refer to sound insulation, thermal insulation, and the control of lighting levels or a combination of all of these.

Everglade™:
Pilkington Everglade™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Everglade™ has an obscuration level of 5.

EW:
EN 357 classification for partial insulation or reduced heat radiation, fire resistant glass. 

Explosion resistance:
see blast resistance.

Ext. AA:
see reaction to fire.

External AA: 
see ext. AA.

External applications:
applications where glass or glazing products are used in positions exposed to natural weather.

External condensation:
condensation forming on the external face (surface 1) of glazing with very low U_g values. The effect requires particular combinations of high external humidity, average temperatures and exposure of the glass to clear night sky.

Façade:
the face of a building, or the cladding covering it.

Façade element:
a part of the façade, such as a window or spandrel panel.

Face clearance:
the distance between the glass and the rebate upstand. This is usually filled with a gasket or sealant.

Fanlight:
the glazing immediately above the door.

Faraday Cage:
a complete electrically conducting earthed screen around a volume of space, across which electrical fields, including electromagnetic radiation, cannot pass. In terms of data protection, this requires all the surfaces of a room to contain a metal mesh or be made from electrically conducting materials.

Film:
see applied film.

Fin:
an alternative term for glass mullion.

Fin box:
the glazing system used at the ends of glass mullions to retain them.

Fire barrier:
an element of construction, such as a wall, partition or glazed screen, which gives an appropriate level of fire resistance.

Fire performance:
the length of time an element of construction, such as a wall, partition or glazed screen, continues to give fire resistance when tested under simulated fire conditions according to BS 476: Part 20.

Fire propagation:
see reaction to fire.

Fire protection:
the action of a fire barrier in containing a fire.

Fire resistance:
the ability of an element of construction, such as a wall, partition or glazed screen, to maintain integrity and / or insulation when tested under simulated fire conditions according to BS 476: Part 20.

Fire resistant glass:
a glass that in an appropriate glazing system, allows the glazed screen door to achieve fire resistance for more than 30 minutes. The fire resistant glass may be a non-insulating glass, i.e. it satisfies only the integrity requirements of BS 476 for the time recorded during the test, or it may be fully insulating glass, i.e. it satisfies both the integrity and insulation requirements of BS 476 for the time recorded during the test.

Fire safety:
see fire protection.

Fired-on transfer:
an applied transfer containing ceramic material or enamel, which is melted into the glass surface at high temperature.

Fixing:
depending on the context this may mean either:

• the method of retaining the glass in position on the building, or
• the action of installing the glass (glazing it).

Flat Bed:
a type of lorry, which has a flat open area to stand the load on. This sort of vehicle might be used for delivering end caps or stillages.

Flat ground edge:
a glass edge, which has been completely flattened by a grinding machine, after which the sharp corners are arrissed. The surface appearance is similar to sand blasting.

Flemish™:
Pilkington Flemish™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Flemish™ has an obscuration level of 1.

Flexible compound:
a type of glazing material or sealant, which remains permanently elastic, such as polysulphide or silicone sealant.

Float glass:
glass, which has been manufactured by floating the molten glass on a bed of molten tin until it sets, producing a product with surfaces which are flat and parallel. Pilkington invented this process in the 1950's. The first product became commercially available in 1959.

Florielle™

Pilkington Florielle™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Florielle™ has an obscuration level of 5.

Flush glazing:
glazing which has no fixings or parts of the glazing system protruding beyond the outer surface (surface 1) of the glass.

Floatliner:
specially adapted lorry for carrying Jumbo sheets of glass on a stillage.

Fragments:
pieces of broken glass.

Frail:
a rack or frame for supporting or securing glass to. They are often found inside glass delivery vehicles or can be mounted outside the vehicle when they are known as a side frail.

Framed:
supported by a frame along the full length of an edge. Typical descriptions of glazing systems would be 4 edge framed or 2 edge framed.

Frameless:
nor supported by a frame on any of the edges. The alternative to framing is by using bolted connections, which could be described as structural glass. The Pilkington Planar™ range of products is an example of this type of system.

Framing system:
the type of material and the design of the frame supporting the glass. (See also glazing system).

Free path:
the distance, which a person can move directly towards a barrier. This is used as a measure of how much energy can be developed by accidental impact in order to determine the appropriate containment level for glass in the barrier.

Free standing glass protective barrier :
a balustrade in which the glass performs all the mechanical functions. There are no posts or balusters; the glass is cantilevered from the floor and has a continuous handrail mounted on the top edge.

Frequency:
the rate of vibration of a sound wave in Hz (Hertz), also know as the pitch, or the rate of vibration of electromagnetic radiation, particular radio waves, usually in MHz (Mega Hertz).

Frit:
depending on the context can be:

• a term used in float glass manufacturing for the raw materials fed into the furnace,
• an alternative name for enamel,
• sometimes also used to describe screen printed glass patterns.

Fritted:
glass that has had a screen printed glass pattern applied.

Galleria™:
Pilkington Galleria™ is our brand name for a rolled glass, which is designed for picture framing. The rolled surface diffuses the reflections from the surface of the glass and so enhances the visibility of the picture.

Gaskets:
solid, preformed glazing materials used to separate glass from other parts of the fixing or frame.

Georgian Bar:
a grid of bars fixed inside an insulating glass unit in order to make it appear from a distance as though the insulating glass unit is composed of smaller panes. Bar are usually white though Gold and other colours are available.

Georgian Wired:
the old generic name for the Pilkington Pyroshield™ range, see also Pyroshield™.

Georgian Wired Cast:
the old generic name for Pilkington Pyroshield™ Textured.

Georgian Wired Polished:
the old Generic for Pilkington Pyroshield™ Clear.

Glare:
excessive illumination or excessive contrast between lit and unlit areas, which causes difficulty with vision.

Glare reduction:
the ability to reduce glare problems, either by reducing the overall illumination or by diffusing direct light or a combination of both.

Glass:
Glass is a liquid that has cooled to a rigid state without crystallising. It is sometimes described as a supercooled liquid, which it is not. A supercooled liquid is still a liquid at a temperature below that at which is would normally solidify. Glass is actually a solid with an amorphous random or non-crystalline structure. The use of the term supercooled liquid suggests the idea of flow, but in fact glass is too rigid to flow at normal temperatures however long a force is applied to it. Glass consists of a network of silicon-oxygen-silicon bonds. These are randomly modified by the presence of calcium and sodium. This arrangement is completely random as it would be a liquid, it is not orderly or regular like the molecules in a crystal of sugar or ice. Because of this random network glass is non-ductile (it cannot be beaten or worked like say copper) and it is this that sets it apart from most other materials. The raw materials we use to make glass are Sand (SiO₂) 72.6%. The sand we use at St. Helens is dug from the Cheshire countryside near Sandbach. Soda Ash (Na₂CO₃) 13%, Limestone (CaCO₃) 8.4%, Dolomite (MgCa(CO₃)2) 4%, Salt Cake (Na₂CO₃) 1%. We like to mix as much clean cullet as we can with these raw materials because we use 50% less energy to melt cullet than we do raw materials.

Glass fin:
another name for a glass mullion.

Glass mullion:
a mullion support for glass panes made entirely from glass or from glass beams splice jointed with metal connectors. Usually fixed at a 900 angle as a brace and support. Also know as a fin.

Glazing:
depending on the context it is either:

• the complete element of construction comprising the glass, the glazing materials and the fixing or frame, or
• the glass or glass product itself, or
• the act of installing the glass or glass product.

Glazing attenuation:
see attenuation.

Glazing bead:
the common mechanism used to retain glass in a frame.

Glazing compound:
a glazing material, which is soft and pliable, such as putty or silicone sealant and can be used as a gap filler.

Glazing factors:
another term for radiometric properties, i.e. solar properties and optical properties.

Glazing fin:
another name for a glass mullion.

Glazing materials:
the gaskets, glazing tapes, glazing compounds, bushes, sealants and other items required for the purpose of glazing a glass product.

Glazing platform:
the horizontal leg of the rebate in a frame, upon which the glass sits (on setting blocks) when it is glazed.

Glazing seal:
another term for glazing compound or sealant.

Glazing spacer:
a small separator placed between the glass and frame. See also location blocks and setting blocks.

Glazing system:
the frame and the design or method of fixing the glass into the frame.

Gothic:
Competitor textured glass pattern, Pilkington Warwick™ should be offered as a substitute.

Greenhouse effect:
the retaining of solar heat by glass, for two reasons. Firstly, the presence of the glass prevents the wind removing the heat rapidly. Secondly, the glass lets through the short wavelength radiation direct from the sun, but is opaque to the long wavelength radiation emitted by the warmed items inside the greenhouse, so the heat takes a lot longer to escape than it does to enter the greenhouse, resulting in the greenhouse getting warm inside. (See also effective U value).

Guarding:
the prevention of persons falling, by means of barriers and balustrades. Any glass glazed into or forming such a barrier or balustrade is required to give containment.

G.W.C.:
stands for Georgian Wired Cast, the old name for Pilkington Pyroshield™ Textured and Pilkington Pyroshield™ Safety Textured.

G.W.P.P.:
stands for Georgian Wired Polished Plate, the old name for Pilkington Pyroshield™ Clear and Pilkington Pyroshield™ Safety Clear.

Hand-ball:
a term for loading or unloading glass from a vehicle by hand.

Handling:
all the activities involved in transferring the glass from factory to the site and into position in the building ready for glazing.

Hard-coating:
a term for a coating, which is durable, i.e. resistant to abrasion. It is a term usually applied to pyrolitic coatings. Pilkington K Glass™ is a typical example of a hard-coated glass.

Hazardous areas:
an alternative term for critical locations.

Heat gain:
see solar heat gain.

Heat soaked toughened glass:
toughened glass, which has been heated for a period of time (after the glass has been toughened), at moderately high temperatures to reduce the possibility of spontaneous fractures in service. Heat soaking is recommended where toughened glass is specified for use in roofs, structural glazing and some commercial contract applications.

Heat strengthened Glass:
glass which has been heated past its softening point and chilled rapidly to increase its strength and make it thermally safe, but which breaks like annealed glass.

Heat transfer coefficient:
a measure of the rate at which heat can cross a boundary or surface (whether it is by conduction, convection or radiation). The heat transfer coefficients at surface I and surface 4 of an insulating glass unit, as well as the heat transfer coefficient across the cavity, are required to calculate the U_g value of the insulating glass unit.

Hermetic Seal:
an edge seal, which is designed to prevent gas passing. The edge seal of an insulating glass unit is a hermetic seal to minimise the rate at which water vapour can penetrate into the cavity.

Hi-ab:
a lorry with its own crane, which is used, for delivering stillages or end caps to customers who don't have a crane.

High Performance:
See Suncool™

Hot box:
a devise, which is used to measure the U_g value of insulating glass units or the overall U value of windows, including the frame.

Horizontally Toughened Glass:
glass, which has been toughened in the horizontal position supported on rollers. Most toughened glass is produced by this method including Pilkington Toughened Safety Glass.

Although the glass is kept moving during the process, when it is soft it tends to sag between the rollers. The final product shows traces of this sagging as a phenomenon called roller wave, which may manifest itself as a regular distortion of images reflected in the glass surface.

HP:
High performance see Suncool™.

Hydrofluoric Acid:
This is the acid used in acid etching. It is the only acid that will attack glass and has to be stored in special plastic containers. It is also extremely hazardous to human beings.

I.G.U.:
Insulating Glass unit.

Impact performance:
the impact resistance of a safety glass when tested according to BS 6206. See also brochure Safety/Security Glass.

Impact resistance:
the classification according to BS 6206. See also brochure Safety/Security Glass.

Impact resistant:
a euphemism for being a safety glass.

Impact safety:
an alternative term to impact resistance.

Inclined glazing:
glazing which is either horizontal or sloping up to 750 from the horizontal. Glazing within 150 of vertical is defined as vertical glazing.

Incombustible:
an alternative word for non-combustible.

Infill panel:
depending on the context, this could mean:

• an alternative term for spandrel panel, or
• a panel underneath the handrail in a barrier.

Inner glass:
see inner pane.

Inner leaf:
see inner pane.

Inner pane:
the pane on the room side of an insulating glass unit or double window.

Installation:
depending on the context this is either:

• the act of glazing, or
• the finished glazing.

Insulated panel:
a spandrel panel with insulation in the form of organic foam or mineral wool attached to the rear face to lower the U value.

Insulating glass:
a fire resistant glass, which gives both integrity and insulation for a specific period of time greater than 30 minutes. The Pilkington Pyrostop^® range of products is insulating glass. Do not confuse insulating glass with insulating glass units.

Insulating glass unit (or I.G.U.):
Commonly known as a double glazing unit (D.G.U.) a construction consisting of two or more panes of glass spaced apart with spacer bars to form a cavity between the panes. An edge seal is applied around each cavity to form a hermetic seal, minimising the ingress of the moisture into the cavity. A desiccant is incorporated in the spacer bar to dry up any residual moisture. Insulating glass units are assessed in their effectiveness at resisting moisture penetration by BS 5713. The air in the cavity can be replaced by another gas to give the unit specific thermal insulation or sound insulation properties. An insulating unit does NOT normally have any fire resistance properties unless it incorporates at least one pane of fire resistant glass and is glazed into an appropriate fire tested system.

Insulation:
depending on the context, this may mean either:

• the material applied to the back of spandrel panels to increase the thermal insulation of the panels, or
• an alternative word for thermal insulation, or
• the length of time that a construction can give fire resistance in relation to the passage of heat, as defined in BS 476: Part 20.

Insulight™:
Pilkington Insulight™ is the brand name for high quality, high performance, dual sealed, insulating glass units, which are only produced by NSG Group.

Integrity:
depending on the context, this may mean:

• the ability of the glass to hold together after fracture, or
• the length of time that a construction can give fire resistance in relation to the passage of flames and smoke as defined in BS 476: Part 20.

Integrity only glass:
another term for non-insulating glass, see also fire resistance and integrity.

Interlayer:
the material used to separate and bond the plies of glass in laminated glass. The interlayer can be polyvinylbutyral, cast-in-place or intumescent.

Internal applications:
applications where the glass or glazing products are not exposed to natural weather.

Interstitial condensation:
literally means condensation occurring in narrow gaps, cracks or crevices. It is usually found where condensation occurs inside porous structures such as walls.

Intumescent:
capable of expanding. In terms of glass and glazing, intumescent means specifically that the material expands with heat.

This term is applied to glazing materials as well as the interlayers of Pilkington Pyrostop^® and Pilkington Pyrodur^®.

Intumescent interlayer:
an interlayer which intumesces in fire conditions, not only holding the laminated glass together, but also creating an effective barrier to smoke, flames and heat.

ISO range:
the part of electromagnetic radiation, which is UV light according to the ISO definition (between 280 and 380 nm).

Jumbo: 
The largest size of glass we supply e.g. 6000 mm x 3210 mm. Usually delivered in 20 tonne loads on a special glass-carrying vehicle called a floatliner.

Kappafloat™:
is the old name for our first off-line coated, low emissivity glass. It is now called Pilkington Optitherm™.

K Glass™:
Pilkington K Glass™ is the brand name for our pyrolitic coated low emissivity glass. See Pilkington K Glass™ product page.

K value:
In some parts of the world, thermal transmittance is referred to as the K value. The units of K value are usually W/m²K, although it is sometimes quoted in kcal/hrm²°C. The latter unit is slightly larger, which may make K values appear smaller. To convert from kcal/hrm²°C to W/m²K, multiply by 1.163.

Laminate:
another term for laminated glass.

Laminated glass:
laminated glass is produced by combining layers of glass with plastic (PVB) or resin (CIP) interlayers to form sandwiches of material with specific design properties.

Laminated toughened glass:
laminated glass made with all the panes in toughened glass. This is often specified for overhead and structural glazing applications.

Laurel™:
Pilkington Laurel™ is the brand name for one of the Pilkington Oriel Collection range of acid etched decorative glass.

Lead cames:
the lead used in traditional leaded lights to hold the individual small panes of glass in position. The lead cames are relatively flexible, so large leaded lights may need additional support from cross bars attached at intervals to the lead cames.

Leaded glass:
an alternative name for leaded lights.

Leaded light:
glazing which is formed either:

• in the traditional manner by using lead cames to fix small panes of glass, or
• by sticking applied leading on to the surface of a single pane.

Lehr:
terminology used in float glass manufacturing. The annealing Lehr is the cooling area on a float line. Glass leaves the float tank and passes for several hundred yards down the Lehr where it is cooled in a carefully controlled way to prevent stresses being set up in the glass. See also annealed glass.

L.E.S.:
Lehr end size. Sheets of glass that are the width of the annealing lehr. Normally 3210 mm by another dimension.

Light diffusion:
see diffusing.

Light reflectance:
the proportion of the visible spectrum, which is reflected by the glass, expressed as a fraction. (See optical properties).

Light reflection:
an alternative term for light reflectance, expressed as a percentage.

Light reflection can be described as low (< 15%) medium (15-25%) or high (> 25%).

Light shelf:
a reflective device (possibly a partial mirror), placed in a position near the upper edge of a window, which redirects light from the sun and sky onto the ceiling or towards the back of the room, in order to improve the natural illumination within the room.

Light transmittance:
the proportion of the visible spectrum, which is transmitted by the glass, expressed as a fraction. (See optical properties).

Light transmission:
an alternative term for light transmittance, expressed as a percentage. Light transmission can be described as low (<25%), medium (25-50%), or high (>50%).

Lighting conditions:
the level of illumination, specifically the illumination on the public side and the private side in relation to one-way vision effects.

Linkon™:
Pilkington Linkon™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Linkon™ has an obscuration level of 4.

Linseed oil putty:
the traditional glazing compound for single glazed timber windows. Linseed oil putty is NOT suitable for insulating glass units or laminated glass.

Location blocks:
small separators placed between the frame and the edge of the glass to maintain the edge clearance between the glass and the frame. The separators are called location blocks when positioned on the vertical and top edges of the pane. At the bottom edge their equivalents are setting blocks. Location blocks are not required in every instance, but are commonly used in opening windows, where there may be a tendency for the glass to move in the frame.

Long wavelength energy:
an alternative term for long wavelength radiation.

Long wavelength radiation:
that part of the electromagnetic spectrum (i.e. from 5000 to 50000 nm wavelength), which is produced by objects at around room temperatures. Glass is opaque to this radiation so short wave radiation from the sun is trapped by the glass, giving the green house effect. It is possible to design coatings which are transparent to visible light, but which are highly reflective, i.e. have a low emissivity, to long wavelength radiation. Glass with such a coating is called Low E Glass, Pilkington K Glass™ and Pilkington Optitherm™ are examples.

Long wave shading coefficient:
see shading coefficients.

Low E Glass:
see low emissivity glass.

Low emissivity glass:
simply a glass that keeps more heat in the building than ordinary glass. Glass is coated with a special metallic coating. To be a Low emissivity glass it has to have an emissivity less than 0.2 in the long wavelength radiation part of electromagnetic radiation. Uncoated glass has an emissivity of around 0.9. by comparison. The purpose of Low E glass is to reduce the radiation component of heat transfer across the cavity of an insulating glass unit. Since radiation is a significant component of the heat transfer across a cavity, insulating glass units incorporating Low E glass have much improved thermal insulation properties when compared to units without Low E glass (30% better insulation). Building Regulations across Europe are being tightened to make the use of Low E glass mandatory. Further information is available on Pilkington K Glass™ and Pilkington Optitherm™ product pages.

Low level glazing:
glazing which is wholly or partly within the critical location up to 800 mm from finished floor level.

LR:
Low reflectance see Suncool™.

Luxaclair:
This is the brand name for special blinds fitted inside a Pilkington Insulight™ unit.

LWSC:
long wave shading coefficient.

Magnetron sputtering:
a technical term to describe the process used in off-line coating. This involves passing the glass into a vacuum chamber. Argon gas is then introduced and electrical currents are then passed into a series of special coating beams in the roof of the chamber. The current causes small amounts of metal oxides to "sputter" onto the glass below and form a thin uniform coating.

Manifestation:
making panes of glass, whose presence may not be immediately obvious, easily visible by the application of permanent patterns, logos or other markings, in order that persons should not walk into them without noticing.

Manual attack:
attack using manually held implements or thrown objects, but not firearms.

Marked:
having a permanent inscription indicating the performance of the product and other information. The most common marks are those related to safety glass classification, fire performance and to insulating glass unit performance.

Marking:
the permanent inscription marked on the glass.

Mayflower™:
Pilkington Mayflower™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Mayflower™ has an obscuration level of 4.

Mean sound reduction index (R_m):
the average of 16 sound insulation values over the frequency range 100-3150 Hz (see acoustic properties).

Metal casement putty:
the traditional glazing compound for single glazed steel windows. Metal casement putty is NOT suitable for insulating units or laminated glass.

M.G.U.:
Multiple glazing unit.

Minster™:
Pilkington Minster™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Minster™ has an obscuration level of 2.

Mirage:
The old brand name for an on line coated one way vision mirror. This is no longer made but Pilkington Mirropane™ is the product we now offer as a one way vision mirror.

Mirropane™:
Pilkington Mirropane™ is our one-way vision mirror.

Mirror:
a glass, which is highly reflective and opaque. Silvering followed by an application of backing paint form the commonest type of mirror.

Molecular sieve:
another name for desiccant.

Mullion:
a vertical dividing bar between panes of glass in a window or a door.

Multi-laminated:
containing more than two plies of glass in the laminate.

Multi-pane:
a term applied to fire resistant glazing which has been tested with more than one pane of glass in the assembly. It does NOT indicate double windows or insulating glass units.

Multiple glazing unit:
an alternative term for insulating glass unit comprising two or more panes.

Negative Image:
a term used in sand blasting and acid etching. It refers to the area of glass that has been eroded by the sand or acid.

Newton's rings:
a fault occasionally found in insulating glass units caused by exceeding the maximum recommended size. If a large insulating glass unit is made with a narrow cavity it is possible that the two panes of glass can deflect and touch, causing a cold bridge. This can lead to a ring of condensation forming at this point.

Nickel sulphide inclusion:
small impurities in the glass that can cause spontaneous fracture of toughened glass some time after toughening. Enquiries about this problem should be addressed to Pilkington Technical Advisory Service.

Noise attenuation:
an alternative term for sound insulation.

Noise control:
see acoustic properties.

Non-combustible:
see reaction to fire.

Non-insulating glass:
a fire resistant glass which gives integrity for at least 30 minutes, when glazed in a suitable screen, but which does not give insulation for 30 minutes. Pilkington Pyroshield™ is an example.

Non-loadbearing element:
an element of construction, which plays no part in supporting the building structure or part of the structure. Glazing is very rarely used in a structural capacity.

Obscuration:
in addition to its obvious meaning, it is also a classification for Pilkington Texture Glass see also patterned glass. See Pilkington Texture Glass consumer literature for obscuration levels for each pattern.

Obscuration level:
the measure of how much you can see through Pilkington Texture Glass. A level 1 pattern is least obscuring, Level 5 is most obscuring.

Observed side:
see public side.

Observing side:
see private side.

Octaveband:
the range of sound frequencies over which the frequency is doubled, e.g. 200 to 400 Hz.

Off-line coating:
see coated glass.

On-line coating:
see coated glass.

One-way vision:
an optical effect resulting from the relative luminance of transmitted and reflected light, which allows vision through a window from only one side. Typically a 7:
1 lighting ratio is required for this effect to work properly. See also Pilkington Mirropane™ product page. This phenomenon is often used for discrete observation in security situations.

Opacified:
made opaque by the application of a backing paint or other backing material, a term related closely to spandrel panels.

Optical properties:
the light transmittance and light reflectance of glass products.

Optical quality:
the presence or absence of visual distortion or small blemishes in the glass.

Optimirror ™ Plus:
Pilkington Optimirror ™ Plus the brand name for our silvered glass. This product is more environmentally friendly than traditional silvered glass. That is because there is no copper backing used and no lead in the upper backing paint coat.

Optiwhite™:
Pilkington Optiwhite™ is our brand name for float glass with a reduced Iron Oxide content. This results in a glass that is less green in appearance than Pilkington Optifloat™ of a similar thickness. This product is used in thicker versions of Pilkington Pyrostop^®.

Oriel:
Pilkington Oriel Collection is the brand name for our collection of acid etched decorative glasses. See Pilkington Oriel Collection product page.

Outer glass:
see outer pane.

Outer leaf:
see outer pane.

Outer pane:
the pane on the external side of an insulating unit or double window.

Overall U value:
the U value of a window, i.e. the combination of glass and frame.

Overhead glazing:
sloping glazing or horizontal glazing, usually in roofs.

P1A:
EN 356 classification for manual attack.

P2A:
EN 356 classification for manual attack.

P3A:
EN 356 classification for manual attack.

P4A:
EN 356 classification for manual attack.

P5A:
EN 356 classification for manual attack.

P6A:
EN 356 classification for manual attack.

P7A:
EN 356 classification for manual attack.

P8A:
EN 356 classification for manual attack.

Pack:
a bulk quantity of glass, around 1-1.5 tonnes in weight often used to describe an end cap. The number of sheets in a pack will depend upon the thickness and size of the glass. 55 sheets for 4 mm SSS, 35 Sheets for 6.4 mm Laminated SSS. LES sizes are also sold in packs but typically 20-30 sheets depending on thickness.

Pallet:
a packaging method for transporting and storing glass. See also rack and stillage.

Pane:
a piece of glass.

P.A.R.:
Polished All Round. All the edges of a piece of glass are polished for decorative effect.

Parry Moon range:
the part of electromagnetic radiation, which is UV light according to the Parry Moon definition (between 300 and 400 nm). This is a stricter definition of UV light than the ISO range. In order to meet Parry Moon it is necessary to use products from the laminated glass range.

Partial Insulation:
Fire resistant glass that does not achieve give 30 minutes insulation required in BS 476 is often referred to as a partial insulation product. Pilkington Pyrodur^® is an example of this. European Standard EN 357 will have a partial insulation category for products that give 15 minutes insulation or more. This will be referred to as reduced heat radiation or EW.

Patent glazing:
a system of drained glazing which is formed from lightweight framing sections incorporating a built-in gutter in the rebate, commonly used for roof glazing.

Patterned glass:
glass manufactured by passing between two rollers (hence it used to be called rolled glass), one of which rollers forms an impression or pattern into the glass. It is known as Pilkington Texture Glass.

Peg:
regional term for a pack or end cap of glass.

Pelerine™:
Pilkington Pelerine™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Pelerine™ has an obscuration level of 5.

Photovoltaic:
literally producing electricity from light. Sometimes also called solar panels. These are special panels designed to convert light into electricity. A solar powered calculator has a photovoltaic panel, the 'A' Weighting Curve.

Pinhole:
a small defect where part of a coating, enamel or backing paint is missing. Acceptable standards are defined in relevant Product Data Sheets.

Pitch:
the frequency of a sound.

Planar™:
Pilkington Planar™ is our brand name for a range of frameless glazing solutions. The product is no longer offered.

Planarclad™:
Pilkington Planarclad™ is our brand name for a high performance cladding system incorporating the well known features of the Pilkington Planar™ concept. The product is no longer offered.

Planitherm:
Soft coated, Low emissivity glass, produced by St Gobain. We would offer Pilkington Optitherm™ as a substitute. Planitherm II is sold as a soft coated glass that can be toughened, we don't have a substitute for this product at present.

Plateau™:
Simply, extremely flat glass. This is the brand name for specially toleranced glass for use in the cast-acrylic industry. It is available in annealed and toughened forms.

Polarised light:
light waves which are vibrating in a specific orientation, either after passing through a polarising filter, or after being reflected from a surface or from the sky.

Polished Edge:
the edge of a piece of glass that has been first flat ground and is then polished to a high lustre. If all of the edges are polished it may be described as P.A.R. (Polished all round).

Polished wired glass:
a generic name for Pilkington Pyroshield™ 2 Clear. Wired cast glass which has subsequently been ground and polished on both surfaces to make it transparent, i.e. Pilkington Pyroshield™ 2 Clear and Pilkington Pyroshield™ 2 Safety Clear.

Pyran:
Competitors brand name for a Borosilicate glass, which is a clear, fire resistant glass. This product is produced by Schott glass; we have no direct substitute available.

Pyrobel:
Clear, Insulation, fire resistant glass made by Glaverbel. Pilkington Pyrostop^® should be offered as a substitute.

Pyrobelite:
Clear, Partial Insulation, fire resistant glass made by Glaverbel. Pilkington Pyrodur^® should be offered as a substitute.

Pyrodur^®:
Pilkington Pyrodur^® is the brand name for our clear (without wires), partial insulation, fire resistant glass.

Pyroshield™:
Pilkington Pyroshield™ is the brand name for a range of fire resistant glass with a welded steel mesh incorporated within the body of the semi-molten glass and formed by passing between two rollers, one of which forms an impression or pattern into the glass. This product is translucent and is called Pilkington Pyroshield™ 2 Texture. The surface can be polished to make it transparent: this is called Pilkington Pyroshield™ 2 Clear. It is sometimes referred to as Georgian wired. It is an integrity only glass. A safety version to meet BS 6206 Class C is also available.

Pyrostop^®:
Pilkington Pyrostop^® is the brand name for our range of high performance, clear fire resistant glass. The products in this range all give insulation for a minimum of 30 minutes.

Polyvinylbutyral (PVB):
a type of interlayer used in the manufacture of laminated glass, by placing a sheet of the material between two panes of glass and curing under heat and pressure. This is the interlayer used in most laminated glass. In its unprocessed form PVB is opaque. It becomes tr4ansparent in the autoclave due to heat and pressure used, driving moisture from the interlayer.

Positive Image:
a term used in sand blasting and acid etching. It refers to the area of glass that has not been eroded by the sand or acid.

P.P.E.:
Personal Protective Equipment. The amount and type of P.P.E. required will depend upon the hazards likely to be encountered.

Primary seal:
see dual seal system.

Private side:
the side of a one-way vision glass from which the other, public side is clearly visible.

Profile:
a term used by window manufacturers to describe bar lengths of P.V.C. window section.

Public side:
the side of a one-way vision glass from which the other, private side is not visible.

PV:
an abbreviation for photovoltaic.

PVB:
see polyvinylbutyral.

Pyrolitic:
applied at high temperature. In relation to glass, this term describes coatings applied on-line when the ribbon of float glass is around 500 to 600°C. Pilkington K Glass™ and Pilkington Eclipse™ are examples.

Queen Anne leaded: 
A style of applied leading.

Quench: 
The part of a toughening line where glass is cooled rapidly, usually by blowing high pressure cold air at the hot glass. This is done to set up surface stresses in the glass. See toughened glass.

Radiation:
depending on the context it could mean:

• one of the methods of heat transfer across the cavity of an insulating glass unit, or
• electromagnetic radiation;
• one of the forms in which heat from a fire gets through non-insulating glass.

Radiative combustion:
see reaction to fire.

Radiometric properties:
the combined sets of optical properties and solar properties of a glass product.

Rebate:
the part of a frame, which holds the glass.

Rack:
a packaging method for transporting and storing glass. See also pallet and stillage.

Ravenna™:
Pilkington Ravenna™ is the brand name for one of the Pilkington Oriel Collection range of acid etched decorative glass.

Reaction to fire:
the way in which a material or product behaves in a fire situation. There are four major classifications used to define the behaviour. Radiative combustion relates to whether fire can pass through a material when used as a roof covering subject to heat from an adjacent fire. Glass generally (1) obtains the highest rating, described as AA or Ext. AA. Materials are also classified by surface spread of flame, the ability or otherwise of a fire to spread along its surface. Glass generally (1) obtains the highest rating.  Materials are also assessed for being non-combustible, i.e. that they do not burn, and for their fire propagation, i.e. whether they contribute to a fire.

Glass is non-combustible, except for laminated glass, which generally (1) achieves the highest rating for fire propagation. Materials, which are non-combustible, or achieve the highest rating for fire propagation, are designated Class 0 according to Building Regulations.

Note (1) Cast-in-place laminated glass has not been tested.

Rebate depth:
the depth of the rebate in a frame, being the sum of the edge clearance and the edge cover of the glass.

Rectangular leading:
a style of applied leading.

Reduced heat radiation:
EN 357 classification EW for partial insulation fire resistant glass.

Reduced spall:
see spall.

Reeded™:
is the brand name for an old Pilkington patterned glass, which is no longer manufactured. It had an obscuration level of 1.

Reflectafloat™:
was the old brand name for Pilkington Eclipse™ Clear 33/53 (replaced by Pilkington Eclipse Advantage™ Clear). It is an on-line coated, highly reflective solar control glass that under certain conditions looks like a mirror when viewed from outside.

Reflectance:
the proportion of incident light or solar radiation reflected by the glass, expressed as a fraction. (See optical properties and solar properties).

Reflection:
an alternative word for reflectance, expressed as a percentage.

Reflective glass:
glass with a coating which reflects light or short wavelength infra-red radiation,e.g. Pilkington Suncool™ Silver, Pilkington Eclipse™ Silver.

Reflex:
The brand name for an on-line coated, mirror, which we no longer manufacture.

Refraction:
the distortion of the path of light as it passes through a glass/air interface.

Relative spectral distribution:
a specific description of the solar spectrum used to determine the radiometric properties of glass.

R_m:
mean sound reduction index. See also Technical Bulletin "Glass and Noise Control".

Robustness:
the ability of a pane of glass to resist breakage (under accidental human impact).

Rolled glass:
an old name for patterned glass.

Roller wave:
This is a visual distortion encountered in horizontally toughened glass. When glass is heated to a high temperature it becomes soft and it can sag between the toughening plant rollers this is called roller wave distortion. This can give a very slight waviness to things viewed through the glass, which varies with glass thickness and the pitch of rollers.

Rough cast:
is the brand name for an old Pilkington patterned glass, which is no longer manufactured. It had an obscuration level of 4.

RS:
reduced spall.

R_tra:
traffic sound reduction index. See also Technical Bulletin "Glass and Noise Control".

R value:
Heat losses are sometimes quantified in terms of thermal resistance, abbreviated to R value. This is the reciprocal of the U value. R value = 1/U value, m²K/W (or ft²hr°F/Btu) this means that a glass with a U Value of 1.9 would have an R value of 0.53 (1÷1.9 = 0.53).

R_w:
weighted sound reduction index. See also Technical Bulletin "Glass and Noise Control".

Safe breakage:
either cracking without producing large openings or separate large sharp edged pieces (i.e. in a manner similar to laminated glass), or cracking into many small fragments (i.e. in a manner similar to toughened glass). Safe breakage is precisely defined in BS 6206. Depending on the context, this may be either:

• the ability of glass to reduce the possibility of piercing and cutting injuries when subjected to accidental human impact, or
• the reduction of hazard from breakage of glass in overhead glazing, or
• fire protection.

Safety backing:
an alternative term for safety film usually used in connection with mirrors.

Safety film:
a plastics film adhered to one surface of the glass with the intention of holding it together after fracture, so that the glass can be classified as a safety glass.

Safety glass:
a glass or glazing product, which conforms to BS 6206, which classifies the product as giving no break or safe breakage when the glass is tested. The glass is classified as Class C, Class B, or Class A (or Class Co, Class Bo or Class Ao, if the test is from one side only of an asymmetric product) according to the drop height achieved in the test.

Safety rating:
the classification achieved for a safety glass to BS 6206.

Sag bending:
technique for bending glass. Glass is heated over a mould till it becomes soft and sags into the shape of the mould. It is then allowed to cool slowly for annealed glass or can be cooled rapidly to make toughened glass. See also curved glass.

Sand blasting:
a process whereby the polished surface of glass is etched by exposure to high-pressure air blown sand or grit. The process is done primarily for decorative effect.

SAP:
stands for Standard Assessment Procedure. It is the Government approved method of determining the energy efficiency of a dwelling. It is measured on a scale of 0–100 with 100 being the most efficient. From 1st January 2001 it is a legal requirement that house builders display the SAP rating in all new dwellings.

Satin:
Pilkington Optifloat™ Satin is the old brand name for a translucent decorative rolled glass that has been specially processed to give it the appearance of having been grinded. It has been replaced by Pilkington Optifloat™ Opal - translucent acid etched glass.

Screen printed glass:
glass which has been given a specific decorative surface finish of either ceramic ink (a type of enamel) which is subsequently fired onto the glass, or epoxy based ink. This product can be used for decorative effect or as a means of glare reduction or solar control.

Sealant:
a glazing compound, which sets after application into a rubbery consistency.

Sealed unit/s:
another name for insulating glass units.

Secondary glazing:
see secondary sash glazing.

Secondary processing:
subsequent processing of glass after initial manufacture, e.g. manufacture into laminated glass, toughened glass, insulating glass units or decorative processing.

Secondary sash glazing:
a double window.

Secondary seal:
see dual seal system.

Security:
depending on the context this means either:

• the ability of glass to withstand manual attack or armed attack, or
• blast resistance, or
• electromagnetic shielding, or
• one-way vision.

Security glass:
a glass, which assists in giving security.

Security glazing:
a glazing system including security glass, which assists in giving security.

Secur-VU™:
The old brand name for Pilkington Glass System for Observation. This product consists of a polyurethane frame available in six standard colours containing two panes of Pilkington Toughened Safety Glass with applied stripes and one internal louvered glass. By moving one pane relative to the others, vision through the panel can be allowed or prevented.

Seed:
a small bubble trapped within a piece of glass.

Setting blocks:
small packers, usually of hardwood, hard rubber or plastics, placed under the bottom edge of the glass to support it off the glazing platform and allow clearance for drainage and ventilation.

Shading coefficients:
the total shading coefficient is a measure of the total amount of heat passing through the glazing (known as the total solar heat transmittance) compared with that through a single clear glass. Glass lets heat through in two ways; a proportion of the short wavelength radiation is transmitted straight through, while some is absorbed by the glass and re-radiated as long wavelength radiation.

The total shading coefficient is split into two parts relating to the proportions of the total solar heat transmittance, which are:

• the short wavelength - the short wave shading coefficient, and
• the long wavelength - the long wave shading coefficient.

Shadowlite:
old brand name for 9% light transmission tinted interlayer.

Shopbond™:
an old brand name for Pilkington Glass System for Shopfronts. This system involves bonding laminated glass into a special reinforced frame, to prevent the glass being removed from the frame.

Shopshield:
an old brand name used by Pilkington Leeds to describe laminated glass manufacture in a range of thicknesses between 7.5 mm – 13.5 mm in sizes of 3210 x 2000 and larger.

Short wavelength energy:
an alternative term for short wavelength radiation.

Short wavelength radiation:
that part of electromagnetic radiation (i.e. from 280 to 2500 nm wavelength), which is radiated by the sun. The main components of glass are transparent to the majority of this short wave radiation.

Short wave shading coefficient:
see shading coefficients.

Side frail:
see frail.

Silica gel:
a chemical often used as a desiccant or molecular sieve.

Silicone sealant:
a type of glazing compound made from silicone material which is gunned into position and cures into an elastic solid. The product is more resistant to UV light and so is used in roof glazing and structural glazing situations where the sealant could be degraded due to exposure to UV light.

Silkscreen:
see screen printed glass.

Silver:
see silvering.

Silvered:
see silvering.

Silvering:
depositing silver on glass to form a mirror. The layer of silver is then protected by a copper backing, which is then protected by a lead based backing paint.

Single glazed:
fitted with only one pane of glass, neither an insulating glass unit nor a double window.

Single sealed:
usually used to describe an insulating glass unit that only has one seal. All Pilkington Insulight™ units are dual sealed.

Sloping glazing:
an alternative name for inclined glazing.

Soda lime silicate glass:
ordinary window glass, including float glass, patterned glass and wired glass and any products made of these.

Solar Control:
the effectiveness of glass is limiting solar heat gain. Solar control can be described in terms of the total shading coefficient of the glass, as being low (shading coefficient > 50%), medium (35% < shading coefficient < = 50%), or high (shading coefficient < = 35%).

Solar direct transmittance:
the proportion of incidence solar radiation, which passes straight through the glass, expressed as a fraction. (See solar properties).

Solar energy:
an alternative term for solar radiation.

Solar gain factors:
numbers related to and derived from shading coefficients, which also describe the ability of the glazing to reduce solar heat gain.

Solar heat gain:
the amount of heat from the sun, which passes through the glass into a building.

Solar Panels:
These fall into two main types, Photovoltaic which convert sunlight to electricity and panels designed to use the sun's solar radiant heat properties to warm water.

Solar properties:
these properties of glass related to solar radiation, i.e. reflectance, absorptance, solar direct transmittance, total solar heat transmittance, shading coefficients and solar gain factors. The term is also used occasionally to include emissivities and optical properties.

Solar radiant heat properties:
see solar properties.

Solar radiation:
the heat, light and UV light emitted by the sun as received at the surface of the earth.

Solar spectrum:
the electromagnetic radiation emitted by the sun and its variation with the wavelength of the radiation. The solar spectrum effectively has a range of wavelengths from 280 to 2500 nm, with the largest proportion present as visible light.

Sound insulation:
see acoustic properties.

Spacer/s:
depending on context can be:

• an alternative term for spacer bar, or
• a glazing spacer.

Spacer bar/s:
the preformed section, usually aluminium or steel, which spaces apart the panes of an insulating glass unit in order to form the cavity. The spacer bar also usually acts as a container for the desiccant in the insulating unit. They are available in a variety of widths usually acts as a container for the desiccant in the insulating unit. They are available in a variety of widths usually 6, 12, 16 and 20 mm. They are also available in a variety of colours, silver, black, white, bronze and gold.

Spall:
the pieces of glass ejected from one face of a pane of glass when it is impacted from the opposite face. This term is commonly used in connection with bullet resistance, where a requirement fro reduced spall may be part of the classification system.

Spandrel panel/s:
a glass panel, commonly used in a curtain wall, which is made of an enamelled glass or an opacified glass in order to hide parts of a building structure, such as the edge of floor slabs. This product is known as Pilkington Spandrel Glass.

Spectral distribution:
the proportion of different wavelengths of a spectrum.

Spectrum:
the wavelengths contained within a particular type of electromagnetic radiation, such as the solar spectrum.

Speech hole/s:
holes drilled or sand blasted into a cashier screen to allow cashier and public to hear each other.

Spontaneous breakage:
an alternative term for spontaneous fracture.

Spontaneous fracture:
the breakage of glass for no immediately obvious reason. The term is more often associated with fracture of toughened glass than any other type, because the mode of fracture of toughened glass tends to disguise the cause. See also nickel sulphide inclusion.

Spread of flame:
See reaction to fire.

S.R.H.T.:
solar radiant heat transmission another name for total solar heat transmittance.

S.S.S.:
Standard stock size, our range of smaller glass sizes. Usually refers to 2500 x 1605 and smaller.

Stained glass:
depending on the context, this may mean:

• a traditional leaded light made with glass of different colours to form a picture or decorative pattern, or
• a pane of glass with coloured applied film and applied leading which looks like a traditional leaded light,
• a piece of glass of the type used in the leaded light.

Steady state:
under constant conditions. This is usually associated with environmental properties. Since the environment (temperature, wind and sun) is in a constant state of flux, this makes calculations of the glass performance very difficult. The solar properties and U_g value of the glass are therefore calculated with a steady state set of conditions.

Stepped unit:
an insulating glass unit with one pane larger than the other. The unit may be stepped on only one edge (often used on the bottom edge of roof glazing) or it may be stepped on more than one edge.

Stillage:
a packaging method for transporting and sorting glass. See also rack and pallet.

Stippolyte™:
Pilkington Stippolyte™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Stippolyte™ has an obscuration level of 5.

Stock plate:
an alternative term for stock sizes.

Stock sizes:
the glass as manufactured and stored ready for cutting down to cut sizes.

Stone:
a foreign body in the surface of a piece of glass.

Stress pattern:
the effect seen on toughened glass when it is viewed under polarized light or through a polarizing filter, which shows a patterning of spots or bars due to slight non-uniformity of the surface compressive stress in the glass.

Structural glass:
glass used in a manner where it may be supporting other building components (e.g. glass mullions) or where it performs a semi-structural role (e.g. free standing glass protective barriers). The term may also be used for glass fixed using bolted connections (frameless glazing), even if it performs no structural function.

Suncool™:
Pilkington Suncool™ is the global product name for a range of off-line coated, high performance solar control glass. The products combine both solar control and Low Emissivity into one product.

Surface 1:
the surface of the glass exposed to the weather.

Surface 2:
the room side surface of single glazing, or the cavity surface of the outer glass in an insulating glass unit.

Surface 3:
the cavity surface of the inner glass in an insulating glass unit.

Surface 4:
the room side surface of double-glazing.

Surface coated glass:
see coated glass.

Surface comprehensive stress:
see toughened glass.

Surface resistances:
the inverse of the heat transfer coefficients at a surface.

Surface spread of flame:
see reaction to fire.

Surveillance Mirror™:
an old brand name for Pilkington Mirropane™ our one way vision mirror.

SWSC:
short wave shading coefficient.

Sycamore™:
Pilkington Sycamore™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Sycamore™ has an obscuration level of 3.

Taffeta™:
Pilkington Taffeta™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Taffeta™ has an obscuration level of 3.

TEC™:
NSG TEC™ is an on-line coated glass (formerly called Pilkington TEC Glass™) for the Refrigeration and white goods industries. The product is designed to reflect heat back into ovens and to reduce frosting on refrigerated display cabinets.

Tempered glass:
another name for toughened glass.

Template:
an exact size physical model of the shape of the glass to be manufactured.

Textured glass:
depending on context this can either be:

• a patterned glass, one of Pilkington Texture Glass range or
• Pilkington Pyroshield™ 2 Textured.

Thermal break:
a gap or a portion of low thermal conductivity in a metal frame, separating the inner and outer parts of the frame, designed to increase the thermal insulation of the frame.

Thermal comfort:
the physical feeling of comfort in relation to the absence of cold radiation and down draughts from window surfaces of insulating glass units with low U_g value.

Thermal fracture:
a phenomenon where glass is broken by the heat of the sun. See thermal stress and thermal safety.

Thermal insulation:
the ability to restrict the flow of heat. The lower the U_g value, the better the insulation.

Thermal properties:
depending on the context this could mean either:

• the U_g value, or
• the solar properties, or
• both of the above.

Thermal safety:
the determination of whether annealed glass is thermally safe, given that it has good quality edges. If a glass is not thermally safe it is necessary to use toughened glass instead.

Thermal Stress:
stress developed in glass due to difference in temperature across its surface. In buildings, this is commonly related to glass exposed to the sun, where the central part is heated, but the edges, in the frame, remain relatively cool. Too high a temperature difference can result in thermal fracture of the glass.

Thermal transmittance:
an alternative term for U_g value.

Thermally safe:
has a risk of thermal fracture sufficiently low to be acceptable.

Thirdoctaveband:
a range of sound frequencies that is 1/3 of an octaveband. (Note that this is not a numerical 1/3. For example, the octaveband from 200 to 400 Hz is split at 250 and 320 Hz.) See Technical Bulletin "Glass and Noise Control".

Thirdoctaveband centre frequency:
the frequency commonly used by sound engineers to ascribe the average loudness or sound insulation over that thirdoctaveband. See Technical Bulletin "Glass and Noise Control".

Tight size:
the size of the opening in frame into which glass is to be glazed. The glass should be smaller than the tight size, to allow a suitable edge clearance.

Time/temperature curve:
the prescribed temperature rise in a fire test furnace as a function of the duration of the BS 476 test.

Tinted float:
float glass that has small amounts of metal oxides added during the melting process to colour it and give it solar control properties. Sometimes called body-tinted float, the product was called Pilkington Antisun™ but is now known as Pilkington Optifloat™ Tint or High Performance Tint.

Tinted interlayer:
a coloured interlayer in laminated glass, which is tinted to give the glass solar control properties. The tints for PVB laminated glass are described by 4-figure code; the first two digits refer to the colour, the second pair, the amount of light transmission through the vinyl (the light transmission will fall the amount will depend on thickness of glass). The code numbers for the tinted interlayers produced by our sites as at 11/00 are listed below. As there are different vinyl manufacturers it is recommended that glass be supplied from one source to ensure tint matching.

It is possible to tint the resin used in cast-in-place laminated. However this is extremely susceptible to colour inconsistencies from sheet to sheet and batch to batch. The cast-in-place method is not recommended where any consistency of colour is required

Total shading coefficient:
see shading coefficients.

Total solar energy transmittance:
an alternative term for total solar heat transmittance.

Total solar heat transmittance:
the proportion of incident solar radiation transmitted by the glass, including both the solar direct transmittance and a portion of the absorbed radiation which is re-radiated, expressed as a fraction. (See solar properties).

Total transmittance:
an alternative term for total solar heat transmittance.

Toughened glass:
glass which has been heated past its softening point and chilled rapidly to build in a surface compressive stress which gives it greatly increased strength and makes it break into small fragments if broken.

Traffic noise reduction index (R_tra):
is derived by taking into account a typical spectrum of road traffic noise (see acoustic properties). Also Technical Bulletin "Glass and Noise Control".

Translucent:
letting light through, but obscuring clear vision.

Transmission:
an alternative word for transmittance, expressed as a percentage.

Transmittance:
the proportion of incident light or solar radiation transmitted by the glass, expressed as a fraction. (See optical properties and solar properties).

Transom:
a horizontal bar across an opening. Often used to refer to a window that is attached to the bar. Derived from Latin "transtrum" meaning a crossbar.

Transparent:
allowing through vision.

Triple glazing:
an alternative name for insulating glass units comprising three panes of glass.

T.S.C.:
total shading coefficient.

T.S.H.T.:
total solar heat transmittance.

Ultraviolet transmittance:
the proportion of incident UV radiation transmitted by the glass, expressed as a fraction.

Unit:
an abbreviation of insulating glass unit.

U value:
a measure of the rate of heat loss through the wall of a building material. Also described as thermal transmittance. U values depend on several different variable factors, such as wind speed and temperature, so they are usually quoted in relation to a specific set of steady state environmental conditions.

U_g value:
a measure of the rate of heat loss through the glass.

UV curing resin:
a resin that has to be exposed to UV light in order to cure. This sort of resin is used in the manufacture of cast-in-place laminated and for sticking decorative features such as applied bevels to glass.

UV filter interlayer:
an interlayer in a laminated glass, which blocks the majority of the UV radiation. 

UV Filter Layer:
an alternative term for UV filter interlayer.

UV light:
an alternative term for UV radiation.

UV protection:
an alternative term for UV reduction.

UV radiation:
the part of the electromagnetic spectrum with a slightly shorter wavelength than visible light, within the UV range, known as ultraviolet light or UV light.

UV range:
the wavelengths of the electromagnetic spectrum usually described as being UV radiation. There are two common descriptions, the ISO range (280-380 nanometers nm) and the Parry Moon range (from 300-400 nanometers nm).

UV reduction:
the proportion of UV radiation, which is blocked by the glass.

UV Screen™:
This is the old brand name for Pilkington Anti-Fade™ our old range of Cast-in-place, laminated glass.

These products incorporate a special UV filter interlayer that depending on the product selected can greatly reduce or eliminate altogether UV transmittance.

UV transmission:
an alternative expression for UV transmittance, expressed as a percentage.

UV transmittance:
the proportion of incident UV radiation transmitted by the glass, expressed as a fraction.

Vandal resistance:
the ability to resist damage, as opposed to the ability to resist penetration. We do not have an "unbreakable glass".

Vent hole:
usually a round hole cut into an insulating glass unit for a fan or ventilator.

Venetian striped mirror:
This product is now known as Pilkington Mirropane™ Venetian Stripe. It consists of a mirror where the backing paint has been sand blasted in parallel lines. This creates alternate clear stripes and silvered stripes. These can create a one-way vision effect to allow discrete observation.

Vertical glazing:
glazing which is either true vertical or within 15 degrees of true vertical.

Visible spectrum:
that part of the electromagnetic spectrum, which is visible to the human eye, i.e. at wavelengths between 380 and 780 nm.

Vision area:
depending on the context, either:

• an oval with axis equal to the height and width of the pane, or
• the parts of a building façade or curtain wall which are intended for the passage of light.

Vision panel:
depending on context, either:

• a term used to distinguish a part of curtain walling as being distinct from the spandrel panel, or
• a small pane of glass in a door to alow people to look through without necessarily opening the door.

Visual distortion:
the warping of images when seen through the glass, due to the surfaces of the glass being not exactly flat and parallel. The term also sometimes applied to reflected images.

Visual quality:
an alternative term for optical quality.

Warwick™:
Pilkington Warwick™ is the brand name for one of the Pilkington Texture Glass range of patterned glass. Pilkington Warwick™ has an obscuration level of 1.

Wavelength:
a characteristic of electromagnetic radiation, by which it can be described. Usually used to discriminate between different types of electromagnetic radiation, such as visible, UV and infrared (heat).

Weight:
the area density of a pane glass, expressed in kg/m². Glass weighs 2.5 kg/m² per mm of thickness (i.e. 4 mm = 10 kg/m², 6 mm = 15 kg/m², 10 mm = 25 kg/m²).

Weighted sound reduction index (R_w):
incorporates a correction for the ear's response and has been derived in accordance with BS 5821:1984 (see acoustic properties).

Whisperply™:
an old brand name for Pilkington Acoustic Laminated Glass Pilkington Optiphon™.

Wind resistance:
the ability of the glass to withstand wind loads.

Wired glass:
generic name which covers polished wired glass and wired cast glass. Our product range is called Pilkington Pyroshield™.

Wired cast glass:
the old generic name for Pilkington Pyroshield™ Textured. Glass with a welded steel mesh incorporated within the body of the semi-molten glass and formed by passing between two rollers, one of which forms an impression or pattern into the glass.