Kilnforming

Kilnforming, also known as fused glass, is a glassworking technique in which glass pieces are fused, slumped, or otherwise shaped by controlled firing in a kiln. It encompasses fusing (joining pieces at high temperature), slumping or draping (shaping flat glass into molds), and casting with molds. It is distinct from glassblowing or cold-working, as heat and time in a kiln determine the final form.

Materials used in kilnforming include sheet glass, fusible glass, frit, powder, and stringers. A key requirement is compatibility of thermal expansion among the ingredients to prevent cracking or warping. Designs are assembled on a kiln shelf or inside a mold, often with barrier layers such as kiln paper or kiln wash to protect surfaces and facilitate release.

The process relies on controlled firing schedules. After loading, the kiln is heated according to ramp rates, holds, and cool-down profiles. A tack fuse creates partial fusion with preserved texture; a full fuse joins edges completely into a single surface; a slump or drape shapes the piece by sinking it into a mold. Following firing, the glass is annealed, cooling slowly to relieve internal stress.

Techniques and finishes include layering multiple colors, using frits and stringers for texture, applying decals, and incorporating inclusions. Molds, fiber papers, and barrier layers influence texture and shape. After firing, pieces may undergo post-firing cold-working or polishing to refine edges.

Kilnformed glass is widely used for decorative objects, bowls, panels, jewelry, lighting, and architectural elements. Safety considerations include proper ventilation, handling hot pieces with tools, careful kiln loading, and adherence to kiln manufacturer guidelines. Kilnforming rose to prominence in the 20th century as artists explored fusing and slumping to expand the possibilities of glass art.