How Glass Reacts to Heat

Lisa Vogt

1 year ago

You have choices when it comes to how to fire your projects. Different temperatures will result in different project characteristics. My goal here is to give you the tools to make educated decisions when selecting your firing method so you have greater control and more satisfying results.

Fusing Defined

Fuse: To heat glass pieces in a kiln until they melt together into one piece.

Glass Fusing Process Temperatures

Full Fuse

Full Fuse 96 COE 1465°F (796°C) 90 COE 1480°F (804°C). Full fuse is the most common firing method. At this temperature the assembled glass project pieces melt together to form one smooth piece with visible, but not tactile, seams. The project has a smooth surface and round, shiny edges. I choose this temperature when I’m making decorative and functional artwork where I want a smooth, uniform surface.

Contour Fuse

Contour Fuse: 96 COE 1425°F (774°C), 90 COE 1400°F (760°C). A contour fuse is a fired look between full fuse and tack fuse. At this temperature the glass layers are fused, and the edges are soft and rounded. The project surface has both visible and physical texture. I use this temperature when I want to create a decorative project with physical texture that increases the surface area to reflect more light.

Tack Fuse

Tack Fuse 96 & 90 COE 1365°F (742°C). At this temperature, the glass pieces stick together. The project edges will be square and shiny. Design elements will retain their texture but are generally not sharp to touch. This is a great temperature for suncatchers and other ornaments where you want a light firing that really sparkles.

Combine Techniques

You can fire a project to a full fuse for the smooth rounded edge quality. Then refire it to a contour or tack fuse temperature with additional design elements on top for a unique and dazzling look.

My Building Process

Most of my work is assembled with the two layers, plus accent method. I refer to the bottom layer as the base and the second as the design layer. The base layer and design layer are the same shape and size. The base layer is often a single piece of clear, but not always; sometimes it’s made up of cut pieces. The second design layer can be a single piece of glass, but often, its pieces fit together to make a specific pattern or design. The third accent layer is minimal, and it usually consists of small fusible elements that enhance the design theme. I choose to build this way because I get consistent results time after time. The finished size and shape of the artwork is predictable. The pieces come out of the kiln with beautiful, rounded edges and a consistent thickness that is both attractive and durable.

It’s All Good

Keep in mind, there’s no single right or wrong way to make any project. Personal preference, design style and function should all play a role in helping you decide which approach is best. The objective is to consciously choose your firing temperature based on a solid understanding of the results.