What to Expect From Bullseye Glass

Bullseye is widely recognized for its sophisticated palette of harmonious colors. Most styles are available in two thicknesses: double-rolled 3 mm sheets and Thin 2 mm sheets. Due to the handcrafted nature of the product, all sheets have at least one rolled edge. Dimensions are approximate.

Sheet Glass Sizes
Above: Full Sheets (-FULL), Half Sheets (-HALF) and 10 x 10s (-1010) showing at least one side with a rolled edge.

Color Variation

While Bullseye strives for consistent colors, our glass is a handmade product and colors may vary between production runs (and from images in this resource). Some colors may change upon repeated firing or with extensive heatwork. We recommend that you test samples of glass using the same firing cycles and processes to be used in finished pieces. When close color matches are needed, we recommend testing new dates first to ensure the range of color between batches will meet the needs of your project. Bullseye glasses are formulated for fired color. Unfired glass color may vary.

More questions? See About Our Glass for working notes and performance characteristics of specific glasses. See also TechNotes 3: Compatibility of Glasses.

Colors That Strike

Striker Icon

Many glasses that Bullseye produces appear pale or even colorless in their cold form but “strike” or mature to a target color when fired to the right temperature. These styles are marked with the symbol above.

Kilnformers (Glass Fusers)

When choosing a style for glass fusing, focus on the fired sheet color. As with ceramic glazes, the color will emerge after sufficient heatwork.

Stained Glass & Mosaic Makers

Be aware that the color of heatworked strikers can be markedly different from the styles cold form. Therefore, we advise testing by pre-firing the glass before use, or select it in person. The unfired sheet colors for strikers vary widely.

Amount of Heatwork Matters

Illustrations in our catalog and online store identify styles that “strike” to color when exposed to heat. Keep in mind that struck color may vary depending on temperature, atmosphere and amount of heatwork. For example, heating Ruby Red Tint (001824-0030-F) too rapidly during the initial stages of a firing cycle can prevent the glass from striking correctly, resulting in a blue-brown cast (sapphirine effect) instead of a true ruby red color.


Bullseye glasses are well known for reliable compatibility. But it’s important to understand the conditions of our factory testing, especially if you intend to fire glass under unusual conditions.

At Bullseye, glasses known to be fairly stable are tested by firing to a top temperature of 1500°F (815°C) and soaking for 15 minutes before annealing. Once cooled, these tests are viewed for stress through polarized light and graded accordingly. We fire glasses known to be less stable three times to make sure they’ll perform well under multiple firing conditions, such as those used to fuse and slump a plate.

Test Your Glass

If you are using a heat process that involves an extra-high temperature or an unusually long firing time, we recommend that you test the glass yourself, under the conditions specific to your project. For example, if you want to include flameworked elements in a kilnformed project, remember that flamework takes glass to temperatures exceeding the compatibility tests we do at the factory and that some glasses are more sensitive to extensive work in the flame. Therefore, it will be important not to overwork your glass during flameworking and to test the flameworked components for compatibility using the full range of kilnforming processes planned for the finished project.

Some processes that may not appear to exceed the parameters of the compatibility test actually do. For example, holding some glasses for long times at temperatures around 1400°F (760°C), which is in the devitrification range, can cause the glass to change dramatically.

Many artists (Klaus Moje, for example) are able to push Bullseye glass to high temperatures for long times with exceptionally good results, but their success is insured by testing. No manufacturer can guarantee glass to perform as expected under all imaginable working conditions. Testing is a wise practice with whatever glass you use.

Helpful Resources

Recommended Annealing Cycle for Bullseye Glass (video lesson)
Heatwork and Frit (video lesson)
Color Reactions and Special Effects (video lesson)