Thermal tempering with fused glass: Opportunities for fused glass designs in kitchens, baths expand

Artists have long decorated the surface of annealed glass with thin pieces of colored substrate and used heat to fuse them to the surface. The thermal tempering of such fused glass panes has been of great interest to users of this material—particularly glass artists—and has been extremely difficult to achieve.

The challenge
Researchers at Schott AG in Germany conducted tests with specialists at professional tempering companies. Initially, these efforts did not meet with success. The panes burst as soon as they were placed into the tempering furnace. In cases where they were able to withstand this initial shock without experiencing damage, many fell prey to the conditions inside the cooling station. Finally, the sheets that had withstood the tempering process exploded when they were placed on glass racks.

Every possible theory on how fused glass designs could be altered to help withstand tempering were later refuted during actual practice.

Success at last
A breakthrough was finally made during a series of tests on applications that involved Artista glass frits and thin glasses about 1.9 millimeters thick. The stability that was achieved with the panes and the breakage results were convincing.

The extremely thin layer of colored glass on top of the substrate glass closely matches the thermal characteristics of the clear glass substrate.

As a result, several Artista thin glasses that would be suitable for this type of processing were produced. The assumption that the key to success lies in the thickness of the colored glass layer was thus confirmed.

Recommendations
As described above, certain rules must be adhered to in order to successfully achieve tempering of fused Artista panes:

• The thickness of the colored layer should not exceed 1.9 millimeters, about 5⁄64 inch. This means that the overlapping of the thin colored glasses is not possible.
• The surface of the area should be fully fused. The surface of fully fused glass must be perfectly flat. With so-called “tack fusing,” the different glasses just keep their individual shapes, creating a hard relief structure on the base glass. Either way, after fusing, all pieces join to become one piece.

When using thin glasses, the total surface area of each piece of colored thin glass should be selected in such a way that the formation of larger bubbles can be ruled out completely. In our initial tests, no bubbles were observed under squares with edges of 5 centimeters, about 2 inches in length.

Bubbles may result, even when the frits are used. We recommend that “medium” and “coarse” grain sizes be used in one single layer.
The temperatures inside the tempering furnace should be set 68-to-77 degrees Fahrenheit lower than for float glass.

Materials included in the Artista product line, used to make thermally tempered glass panes, are: clear sheet glass (color No. 0189) in 6-, 8-, 10- or 12-millimeter, about 1⁄4-, 5⁄16-, 3⁄8 or 1⁄2-inch thicknesses.

Schott’s Artista thin glass, available in 10 colors, is about 1.9 millimeters thick. Glass frits in 28 colors and four textured grain sizes are available.

For more information, visit www.us.schott.com/architecture.