More Window and Glass Tips

by Tobe Walter
(New Jersey)

When you buy replacement glass for one of your average-sized windows, it is almost certain to be a type called "sheet glass" or "window glass." It comes in several thicknesses and quality grades. In addition, you may run into any of several other types Of glass.

Sheet glass Formed when molten glass is drawn vertically. The faster the speed, the thinner the glass. Finished product has some wave or distortion. Sheet glass from about 3/32 inch to 1/8 inch thick is used to glaze most residential windows and doors. The term single strength refers to glass 3/32 inch thick, weighing about 19 ounces per square foot; double strength glass is 1/8 inch thick, weighs 26 ounces. Quality grades are AA (special order), A (superior), B (standard), and greenhouse. Thicker sheet glass (3/16, 7/32, and 1/4 inch thick) is called heavy sheet or crystal sheet and is used in large windows.

Float glass. A relatively recent method of manufacture, float glass is formed on molten tin, then cooled and conveyed through an annealing oven. It is exception-ally flat and free of distortion. Available in 1/4-inch thickness.


Plate glass. Molten glass is rolled into large. continuous flat sheets, then ground and polished on both sides to a uniform thickness.There is little wave or distortion. Regular polished plate usually refers to clear 1/4-inch plate, widely used in building construction. Heavy polished plate is 3/8 inch, 1/2 inch, and thicker. It is used for large uninterrupted window areas. Rough plate has not been ground and polished on both surfaces, so it is not clear.

It is available regular or tempered, tinted or not, with both sides rough or one side polished. In addition, there are several specialty glasses manufactured from the basic types.

Heat-strengthened glass. Partly tempered to increase its strength, which is about double that of the glass from which it is made. It is not a safety glass.
Insulating glass.Two pieces of glass with a dry air space between and all edges sealed.
Laminated glass. Two pieces of clear or patterned glass with a clear or tinted plastic between, sealed together into a single unit. If broken, glass fragments are held together by the plastic interlayer.
Light-diffusing glass.

Patterned, normally in a prism-like design, or coated so light rays passing through are diffused.

Patterned glass. Made like regular plate, except passed through patterned rollers. Designs range from finely pebbled to deeply fluted.

Reflective glass. A transparent metallic oxide is fired to the surface of a 1/4 -inch plate glass, providing a light and heat. reflecting mirror-like coating.

Tempered glass. Controlled heating and cooling produces a compression layer on the glass surfaces, and a tension layer inside. This glass is as many as five times stronger and more impact-resistant than unprocessed glass of the same type.

Tinted glass. Formed by the introduction of coloring agents into molten glass. Trans-mission of visible light is lowered. Various shades of green, gray, bronze are available.

Wired glass. Glass with wire mesh incorporated within the body of the glass during manufacture. When glass breaks, the wire holds it together.

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