These are two cone 6 matte glazes (shown side by side in an account at Insight-live). G1214Z is a calcia matte, it has a high silica:alumina ratio. It crystallizes during cooling to make the matte effect. Melt fluidity is needed for that and this GLFL test shows that it certainly has that. The degree of matteness is adjustable by tuning the SiO2 content. The G2928C is a magnesia matte, it has high MgO and produces the classic silky micro-wrinkled the surface. Its matteness is adjustable by trimming the calcined kaolin. CaO is a standard oxide that is in almost all glazes, 0.4 is not high for it. But much less MgO is needed for it to make a matte. The G2928C also has 5% tin, if that was not there it would be darker than the other one because Ravenscrag Slip has some iron. This glaze actually has texture like a dolomite matte at cone 10R, it is great. And it has wonderful application properties. And it does not craze, on Plainsman M370 (it even survived a 300F-to-ice water IWCT test). This looks like it could be a great liner glaze.

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You will see examples of replacing unavailable materials (especially frits), fixing various issues (e.g. running, crazing, settling), making them melt more, adjusting matteness, etc. Insight-Live has an extensive help system (the round blue icon on the left) that also deals with fixing real-world problems and understanding glazes and clay bodies.
| Glossary |
Matte Glaze
Random material mixes that melt well overwhelmingly want to be glossy, creating a matte glaze that is also functional is not an easy task. |
| Glossary |
Mechanism
Identifying the mechanism of a ceramic glaze recipe is the key to moving adjusting it, fixing it, reverse engineering it, even avoiding it! |
| Glossary |
Glaze Chemistry
Glaze chemistry is the study of how the oxide chemistry of glazes relate to the way they fire. It accounts for color, surface, hardness, texture, melting temperature, thermal expansion, etc. |
| Glossary |
Digitalfire Insight-Live
A cloud-hosted ceramics-targeted LIMS (lab info management system). It does glaze chemistry and physical testing the “Digitalfire way”. For technicians, educators, potters and hobbyists. |
| Oxides | MgO - Magnesium Oxide, Magnesia |
| Oxides | CaO - Calcium Oxide, Calcia |
| Recipes |
G2928C - Ravenscrag Silky Matte for Cone 6
Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com. |
| Recipes |
G1214Z1 - Cone 6 Silky CaO matte base glaze
This glaze was born as a demonstration of how to use chemistry to convert a glossy cone 6 glaze into a matte. |
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