Specialty Glass

There are almost as many types of glass as there are possible uses for them. As you gain experience, you will become familiar with many types of specialty glass. A few of these include:
· Mirrors
· Spandrel Glass
· Laminated Glass
· Art Glass

Mirrors are made from high quality annealed float glass designated either mirror quality or mirror select. Mirrors are made by depositing a layer of silver on one surface of the glass. The surface chosen is the score side, because the tin side does not accept silver properly. The reflective quality of the miror depends upon the thickness of the silver layer, glass thickness, and glass color. High quality mirrors can have a copper backing. The copper is deposited over the layer of silver, and offers the greatest amount of protection. Mirrors deteriorate rapidly when exposed to air, so the metal films must be protected immediately by a coating. The glass is usually preheated to a range of 120 – 140 degrees Fahrenheit, before the coating is applied. This paint type coating can be applied in one coat, or consist of two coats of dissimilar, but compatible material.

If the metal backing of a mirror deteriorates, the silver turns black. This condition is known as black edge. Not much definite is known about the causes of black edge. Some experts believe black edge is caused by chloride in water. Others believe it is caused by industrial and household solutions that come into contact with the mirror. Whatever the cause, most agree that sealing the edges of mirrors helps to guard against black edge.

Spandrel glass is not specifically a type of glass. Instead, it refers to the use of obscure glass in non-vision areas of a building. One of these areas is the spandrel of a building. The spandrel is the part of the wall between the head of one window and the sill of the window above it. For aesthetic reasons, this area is often covered with glass.
Spandrel glass is made using several methods. One method is to fuse a colored ceramic material, called a frit, to one surface of the glass. The glass must be either heat strengthened or fully tempered because the frit causes the glass to absorb heat. Spandrel glass may or may not be insulated. Some codes require an open-weave glass fiber cloth or special tape to be attached to the back of the spandrel panel to ensure that the panel stays in the opening if it breaks. If reflective glass is used as the spandrel application, the back surface must be obscured in some way so that the building structure does not become visible under certain light conditions.

As mentioned above, laminated glass is used in safety glazing applications. However, it has many other applications:
· Burglar resistance
· Bullet resistance
· Sound reduction
· Sloped glazing
· Space enclosures

Laminated glass is used as the inboard lite in skylights. By varying the thickness and color of the PVB, laminated glass can be used to reduce the transmission of solar energy, control glare, and screen out ultraviolet radiation.

A new process, resin laminating, is being used to laminate curved glass and other specialized applications. In this process, two lites are spaced .030″ to .060″ apart. Three sides of the perimeter are dammed. With the assembly vertical, a liquid chemical mixture is poured into the space and allowed to cure at room temperature for two to ten hours.

Art glass goes by many names: opalescent, cathedral or stained glass. Art glass is usually produced in small batch operations. Thicknesses vary within each sheet and from sheet to sheet. Generally, colors do not match from sheet to sheet. Art glass is available in a maximum thickness of inches. It cannot be tempered.