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Well, actually they are not exactly the same. This is 80% Alberta Slip and 20% frit. But the frit on the left is Ferro 3195 and on the right is 3134. By comparing the calculated chemistry for these two we can say that the likely reason for the difference is the Al2O3 content. Frit 3134 has almost none whereas 3195 has 12%. Al2O3 stiffens the glaze melt, that impedes crystal growth. And it stabilizes the melt against running during firing. Frit 3195 is thus much more "like a glaze" than is 3134, it is what Alberta Slip needs to melt as a transparent glass under normally cooling in the kiln.
This is GA6-A Alberta Slip base glaze (80 Alberta Slip:20 Frit 3134) fired using the C6DHSC firing schedule (on Plainsman M390 iron red clay). If this is cooled rapidly or 1% tin oxide inhibitor is added, it fires to a glossy clear amber glass with no crystals. This base is needed to make GA6-C rutile blue, otherwise we recommend the GA6-B base (which uses frit 3195 instead), it has a lower thermal expansion and guarantees gloss regardless of cooling speed. If, on the other hand, you want to enhance this effect, just add a little more frit (to gloss it more) and more iron oxide (that should enable matting even at faster cooling speeds.
Oxides | Al2O3 - Aluminum Oxide, Alumina |
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Materials |
Ferro Frit 3134
A frit with 23% B2O3. The most common of frits used in pottery in North America. Around the world, other companies make frits of equivalent chemistry. |
Materials |
Ferro Frit 3195
A commonly used boron frit, it is a balanced glaze all along at cone 06-02 (with the addition of 10-15% kaolin). Not fully glossy. |
Glossary |
Crystallization
Ceramic glazes form crystals on cooling if the chemistry is right and the rate of cool is slow enough to permit molecular movement to the preferred orientation. |
Recipes |
GA6-A - Alberta Slip Cone 6 transparent honey glaze
An amber-colored glaze that produces a clean, micro bubble free transparent glass on brown and red burning stonewares. |
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