How to Temper Glass

Stacks of tempered glass.
What You'll Need
Kiln or oven
Safety glasses
Safety gloves
Industrial tongs
Drilling machine
Concrete countertop
Polarized glasses

Home accents such as temper glass cuttings help to augment the style quotient of a home’s interiors. Tempered glass is actually a kind of safety glass. It is recommended for areas wherein chances of the glass being damaged are high. In household use, home accent items are being increasingly made from tempered glass to ensure that they don’t pose a threat to the occupants. Unlike conventional glass, tempered glass does not shatter into sharp-edged bits when damaged. In the retail market, tempered glass is available as treated glass which essentially means that it has been tempered through an industrial process. You can temper glass at your home too.

Temper Glass Basics

The basic principle of tempering involves sudden heating and immediate cooling of the heated glass. These sudden temperatures changes change the intrinsic molecular configuration of the glass item. Tempered glass is slightly more susceptible to breaking than normal glass, being more brittle. However, its greater safety-of-use makes it an ideal option for household usage. Tempered glass is also more heat resistant. This means that painted, tempered glass items retain the surface paint for a longer time.

Step 1 - Prepare Glass for Tempering

Tempered glass.

Using a fine-bit drilling machine and glass-cutter, shape your glass sheet in the required design. Once the glass is tempered, you cannot drill or cut it. Using some sandpaper, polish-off the edges of the glass sheet. This is done to ensure that the powder-like debris doesn’t stick around the edges. Such debris can melt and take an unshapely form upon heating the glass, called bending or warping of glass.

Step 2 - Temper the Glass

Wear your safety gear, including the gloves and safety glasses before approaching the kiln. Light the kiln and maintain the temperature around the 600 degrees Fahrenheit mark. Using the tongs, place the glass sheet within the kiln. Try to keep the glass away from the inner edges of the kiln. Heat the glass until it develops a distinct shiny, film-like coating.

Step 3 - Cool Heated Glass

Tempered glass on a black background.

Using the tongs, remove the heated glass from the kiln. Place the heated glass sheet on the cement countertop. If a countertop is not available, you can use a makeshift countertop made from bricks. Ensure the countertop is at room temperature and dry. Using the spatula, slightly press upon the edges of the heated glass sheet. Edges are often under-cooled which creates an imperfectly-tempered glass sheet. Allow the glass sheet to cool for a few hours.

Step 4 - Check Cooled Glass

Remove your safety glasses and put on the polarized glasses. When light from a nearby source shines through the cooled glass, certain markings emerge on the glass. These patterns are visible clearly through a polarized lens. These markings should be pronounced and appear in a uniform pattern upon the glass sheet. These markings are also called quench marks. A uniform and dense spread of these markings means that the tempering is successful. The edges of the glass sheet should be straight. If there are signs of warping, scrape off the small bends with the glass-cutter.