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Arrange and stack them however you want them to look once they're fused. Place the largest piece of glass on the bottom and stack the smaller pieces on top. Use a thin glue to keep your pieces in place if you're having a hard time. Place the shelf in one of the central slots in the kiln so it's not too close to the top and not too close to the bottom. Try to leave a inch (6.35mm) between your glass design on the kiln shelf and the side of the kiln itself so your glass has room to expand. The temperature you use to fire your glass in the kiln depends on the look you're going for. Decide which kind of fuse -- tack or full -- you want to do. Consult your kiln manual for specific instructions on how to set a firing schedule. With a tack fuse, the edges of the glass will melt and round slightly, but any pieces stacked on top of one another will remain stacked. Fire your kiln to between 1350-1370 degrees Fahrenheit (around 738 degrees Celsius) for this fuse to form. Full-fused pieces have a smooth, flat surface. Program your kiln to reach around 1460-1470 degrees Fahrenheit (around 796 degrees Celsius) to achieve a full fuse. Don't open the kiln until it's cooled off below 100 degrees Fahrenheit (38 degrees Celsius). Opening the kiln prematurely can cause your glass to break, and you might burn yourself. Examine your piece and check for any cracks. If you find cracks, the types of glasses you fused might not have been compatible. If you want to fire your fused glass for a second time to make a piece with dimension, place it over one of your molds. Set your glass and the mold on the kiln shelf and place it back in the kiln. Consult your kiln manual and program the kiln to reach around 1225 degrees Fahrenheit (663 degrees Celsius). Let the kiln cool completely before you remove your glass.
Place the glass pieces you've cut on the kiln shelf. Place the kiln shelf in the kiln. Turn on the kiln. Do a tack fuse if you want the glass to retain its features. Do a full fuse if you want the glass to melt into a single layer. Wait for the kiln program to finish and let your glass cool. Remove the kiln shelf and your glass from the kiln. Slump your fused glass over a mold to create a three-dimensional piece.