Glassary - H

a term for loading or unloading glass from a vehicle by hand.

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

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. See Product Data Sheet Pilkington Toughened Safety Glass.

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. See also Technical Bulletin Glass and Safety.

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 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.

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 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. See also Product Data Sheet Pilkington Toughened Glass.

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.