Is Bullseye glass COE 90?
Glass users who ask this question usually want to know if they can successfully fuse Bullseye with another manufacturer's glasses. Unfortunately, the answer to this question is not simple. Our short response is this: Matching COEs does not ensure compatibility between glasses, in spite of what you've read or heard from other practitioners or glass manufacturers.
Our fusible glasses are factory tested for compatibility with each other. We do not test for compatibility with other manufacturers' glasses. We do not test for COE or rate our glasses with COE numbers. We do not claim to produce glasses that are rated "COE 90." The ONLY way you can insure that a Bullseye glass will be compatible with another manufacturer's glass is to conduct your own tests.
Dimensions are approximate. All colored sheets have at least one rolled edge, due to the handcrafted nature of the product. What to expect from selected Bullseye sheet glass?
COLOR VARIATION
While Bullseye strives for consistent colors, our glass is a handmade product and colors may vary slightly between production runs (and from images in the catalog). Some colors may change slightly 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.
COLORS THAT STRIKE
In order to provide the largest and most interesting palette of colors to kiln and torch workers, Bullseye produces some glasses that appear pale or colorless in the cold form but which "strike" or mature to target color upon firing. Catalog illustrations indicate which styles differ in color from cold form to struck form. Keep in mind that struck color may vary depending on temperature, atmosphere and amount of heatwork. For example, heating Ruby Red Tint Striker (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. Unstruck colors on the left. Struck (mature) colors on the right. COMPATIBILITY
Bullseye glasses are well known for reliable compatibility. But understanding the conditions of our factory testing is important, especially if you are firing glass under unusual or extreme 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. Other glasses known to be less stable are fired three times with this cycle to insure good performance under typical multiple fusing and slumping conditions, such as those used in making a simple plate.
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 again, under the conditions specific to your project. For instance, imagine that you want to include some flameworked elements in a kilnformed project. Consider that flameworking takes glass to temperatures exceeding factory compatibility tests; also, the compatibility of some glasses is more sensitive than others 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 immediately appear to exceed the parameters of the test for compatibility actually do. 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 their own testing before making large or complex pieces. Testing is a wise practice with whatever glass you use. No manufacturer can guarantee glass to perform as expected under all imaginable working conditions.
OPALESCENT Sheet Glass
For each style, the top row shows the double-rolled, unfired cold glass color. For stained glass, refer to the top row. The same glass after firing to a full fuse is shown directly below the cold glass. For kilnformed glass, refer to the bottom row.
GlassTips describe ONLY the results of standard full fuse + slumping firings, i.e.: glass 6mm thick, 10" (25cm) square, fired to 1480°F (804°C), held for 10 minutes, then fired a second time to 1250°F (677°C) for 30 minutes. To best ensure success, test glasses before use under your specific firing conditions. Use GlassTips information as a starting point only.
Glass reactivity: Not all reactions are visible. Some are too weak to be seen and others are masked by dark color. "Striking glasses" change dramatically to reach target color during firing. Colors may vary, depending on firing schedule, rate, atmosphere, and heatwork. For color-sensitive projects, test before use. Thin opal glasses (-0050) may appear more transparent in the cold sheet than their 3mm (-0030) opal counterparts. Some opal glasses may appear inconsistent in color and/or opalescence in the cold sheet. Upon firing, color and density will appear more even.
TRANSPARENT Sheet Glass
For each style, the top row shows the double-rolled, unfired cold glass color. For stained glass, refer to the top row. The same glass after firing to a full fuse is shown directly below the cold glass. For kilnformed glass, refer to the bottom row.
GlassTips describe ONLY the results of standard full fuse + slumping firings, i.e.: glass 6mm thick, 10" (25cm) square, fired to 1480°F (804°C), held for 10 minutes, then fired a second time to 1250°F (677°C) for 30 minutes. To best ensure success, test glasses before use under your specific firing conditions. Use GlassTips information as a starting point only.
Glass reactivity: Not all reactions are visible. Some are too weak to be seen and others are masked by dark color. "Striking glasses" change dramatically to reach target color during firing. Colors may vary, depending on firing schedule, rate, atmosphere, and heatwork. For color-sensitive projects, test before use.
Can I fuse or cast Bullseye with any COE 90 glass?
Matching COEs does not ensure compatibility between glasses, in spite of what you've read or heard from other practitioners or glass manufacturers. Bullseye's fusible glasses are factory tested for compatibility with each other. We do not test for compatibility with other manufacturers' glasses. We do not test for COE or rate our glasses with COE numbers. We do not claim to produce glasses that are rated "COE 90." The ONLY way you can insure that a Bullseye glass will be compatible with another manufacturer's glass is to conduct your own tests.
Do all Bullseye glasses perform the same in the kiln?
Not all of our glasses behave identically. Very slight variations can occur, depending on the viscosities of individual glasses.
How do Bullseye colors look after firing?
Many of our glasses look the same before and after firing, but a small number will mature or "strike" to target color during the firing process. The images of fusible glasses in our online store show how colors appear before and after heatwork. Note: If you plan to subject glass to repeated firing or exceptional heatwork, we recommend that you test samples of the glass to the required processes and firing cycles to most accurately predict color outcomes.
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