Glass fusing is the joining together of pieces of glass at high temperature, in a kiln. This is usually done roughly between 700 °C (1,292 °F) and 820 °C (1,510 °F),  and can range from tack fusing at lower temperatures, in which separate pieces of glass stick together but still retain their individual shapes, to full fusing at higher temperatures, in which separate pieces merge smoothly into one another.

Kiln-glass manufacturers will rate their glasses for compatibility with other glasses they make. To ensure compatibility, Bearriver Glassworks uses Bullseye Glass exclusively to assure quality and stable results.