Properties of Hot Glass
When heating glass to a full fuse (1450° F) it wants to become ¼" thick and round. A standard sheet of glass is approximately 1/8" thick.
When firing a single layer of glass the edges will contract to become ¼" thick.
If fusing three layers of glass your glass will expand to become ¼" thick.
Unless you are damming the glass, two layers are ideal to maintain your projects original size and general shape.
In the picture below, notice how the following stacks of glass appear before and after firing.
In the next picture, notice how each cabochon is approximately the same thickness
In the next picture, notice how each cabochon is approximately the same thickness
Viewing the cabochons from the top you can see how the stacks spread when they were fired.
Keeping the ¼" rule in mind with help you achieve the desired effect without growing or shrinking your project.
Watch this video on the difference between tack , contour and full fuse pieces: https://www.youtube.com/watch?v=6OXLusw8g54
and this one https://www.youtube.com/watch?v=6OXLusw8g54
Its important to start with glass that has the same COE. The Coefficient of Expansion (COE) refers to the rate at which glass expands and contracts when heated and cooled. It's important that all of the glass you are fusing together expands and contracts at the same rate or stress and cracking can occur. Glass manufactured specifically for fusing is tested for compatibility. Always fuse glass with the same COE or tested compatible glass. We are using a glass with CEO of 96.
Heating and Cooling Glass
Glass cannot be heated or cooled too slowly. Heating and cooling too fast can result in cracked glass or thermal shock. Ideally you want your glass to stay approximately the same temperature as the kiln. Because the glass heats more slowly than the kiln, you should consider your project size and how long it will take the piece to "catch up" to the kiln temperature.
The larger your project the slower you should go 200°– 300° F an hour is a safe speed.
Smaller projects, like jewelry, can be heated more quickly – 500° F per hour is a safe speed.
Be sure to keep track of the schedules you try so you'll know what works best.
Slow, controlled cooling, commonly referred to as annealing, is the process in which you allow the glass to gradually cool down in order to remove internal stresses that may have occurred during the firing process.
Annealing allows the glass to stabilize and adds strength to your finished project.
Ideal annealing temperatures are 900° F for 90 COE and 950° F for 96 COE glass.
30 minutes is usually sufficient for small projects but you may choose longer annealing times for larger pieces.
GLASS TIPS
Tack colorful bits of glass to your base with TINY PINPOINTS OF GLUE. CAREFUL! “Too much” glue can ruin your piece!
Place design bits UP TO THE EDGE of your base, but DON’T let them hang over.
When SEE-THROUGH COLORS overlap, it creates a new color, i.e., YELLOW + BLUE = GREEN. 6. When OPAQUE COLORS overlap, the colors lay on top of each other and don’t combine. DON’T use see-through colors over BLACK glass. They will become INVISIBLE when fired. Use only OPAQUE colors over black glass.
Opaque frit says OPAL on the label. If the label does not specifically say OPAL, the frit is a SEE-THROUGH color. Don’t use it over black.
The first firing – THE FUSE FIRING – will meld your glass together into a FLAT, FUSED PIECE.
The second firing – THE TACK/ CONTOUR FIRING - wiLl meld your glass together with pieces raised and slightly contoured.
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