Glassary - R

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.

R1:
see bullet resistance.

R2:
see bullet resistance.

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™ range of acid etched decorative glass. See consumer leaflet Pilkington Texture Glass™ for further details.

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. See also Technical Bulletin Glass and Fire Resistance.

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 (see Product Data Sheet). 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, i.e. Pilkington Suncool™ Classic, Pilkington Eclipse™.

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.

Rm:
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.

RTRA:
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 ft2hrºF/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).

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