Glass fusing, the art of stacking glass pieces and firing in a kiln at high temperatures, then cooling in stages, has been seen in archaeology as early as the Egyptians in 2000 B.C.E. Fusing was outdated by the invention of the glass blowpipe, but saw an artisan resurgence in the 1960s. The stacking technique used for each piece will directly affect the finished product.
Fusing Temperatures
Stacked pieces' fusing temperatures vary by project, but each desired effect has an approximate firing temperature. "Tack fusing," when glass pieces stick together but retain their shape, ranges from 1,350 degrees to 1,450 degrees F. "Full fusing," when layers of glass are heated until fully combined, occurs between 1,450 degrees and 1,550 degrees F. Always follow firing temperature and length guidelines specific for the project being created and glass being used.
Stacking "Décor on Top"
"Décor on top" involves placing smaller pieces of glass on top of a larger piece and allowing the small pieces to fuse down into the larger piece. This produces a shinier product with less defined lines of top glass and/or color. You may use plain white glue to hold glass pieces in position until firing. Glue will burn off in the kiln. Use only a small amount, as too much glue will cause black spots to appear on the finished piece where the glue was burned.
Stacking "Décor on Bottom"
"Décor on bottom," also called "reverse firing," involves placing smaller pieces of glass under a larger piece and allowing the large piece to fuse down around the smaller pieces. The smaller pieces will retain more defined lines and colors.
Nuggets
"Nuggets" are made from small stacks of glass, cut into equally-sized squares, layered and taken to full-fuse. The stacks will fuse together creating half-spheres of glass. Artisans use these for making jewelry, magnets or embellishments for other glass artworks.
Creating Horizontal Holes
To create holes, or spaces for threading within a fused piece, place a rolled piece of fiber paper across the base glass, away from the edge. Top with another piece of glass and fire. The top piece will fuse over the paper, joining to the bottom piece, leaving a hole. After firing, remove the fiber paper and discard.
