Tin oxide is a powerful opacifier, but the 5% in this Frit 3124 based Arbuckle Majolica cone 04 recipe on the left is not sufficient. Adding 10% zircon (e.g. Zircopax, Superpax) produces the one on the right. Would just using 15% zircon be better? No. More zircon means a stiffer melt and more issues with crawling (notice the small bare spots on the right edge). This could be managed by the addition of CMC gum or a higher clay content to get better adhesion and dry hardness). But another improvement would be worth trying first: Use 4% tin and 8% zircon. That should opacify enough and present fewer problems with crawling.

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Fusion Frit F-19 is said to be a substitute for Ferro Frit 3124, for this particular glaze that appears to be true. The Arbuckle Majolica glaze was applied on Plainsman L210 and fired at cone 04 (but not as thickly applied as would be customary on Majolica ware). On the left is the one with Ferro Frit 3124, on the right is the one with the F-19. The recipe is based on Ferro Frit 3124 and adds 20% of a feldspar neheline mix (likely to increase thermal expansion because it shivered on the original clay body). It is suspended by 10% kaolin. This may craze on your clay body, the G1916Q thermal expansion adjustable transparent base might be a better solution (it responds similarly to a zircon/tin addition to opacify).

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The body is Plainsman L215. With the 04DSDH firing schedule. The glaze is G1916Q. The body is processed at 42 mesh, so it has lots of coarse gas-generating LOI particles. But two factors can minimize them the create a more transparent glass.
The right mug: Cone 03 is working, but this in on blistering and pinholing tipping point. Cone 04 would be better.
| Glossary |
Opacifier
Glaze opacity refers to the degree to which it is opaque. Opacifiers are powders added to transparent ceramic glazes to make them opaque. |
| Glossary |
Majolica
Majolica is a tradition of Italian Renaissance white opaque glazed red earthenware having brightly colored brushwork decoration. Knowing some technical details will help you better succeed with the process. |
| Glossary |
Terra Cotta
A type of red firing pottery. Terra cotta clay is available almost everywhere, it is fired at low temperatures. But quality is deceptively difficult to achieve. |
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