I calculated a frit-based recipe to match the original G1947U Cone 10R clear feldspar-based one. Only after seeing the fired results did I fully realize how much better it melts and how much more transparent it fires. It costs more money to make, but in some situations it is worth it.
My original approach was just theoretical: Shift KNaO-sourcing from feldspar to frit to get a better melt. As calculations took shape, it became clear that I could increase KNaO because it enabled increasing SiO2 also. When the kiln opened, I got a surprise with the original G1947U: It never looked white on the ware, but when seeing it thick like on this GBMF test (bottom), it looks really cloudy. Likely the melt is not completely dissolving the particles of quartz! The surface brilliance of the new G3910 blew me away at first; it really is better (top right is G1947U left, G3910 right on buff and brown bodies). This glaze develops a better interface with the body and on porcelains, it is more crystal clear and much brighter.

This picture has its own page with more detail, click here to see it.
To get a better, more brilliant transparency than G1947U, at cone 10R, I tried sourcing KNaO from a frit. The inside surface on this mug is the result (v2), it is so glossy it looks like a low-fire leaded glaze. This screenshot of side-by-side panels shows the frit-enhanced version(s), G3910 and G3910A. Frit 3110 has a much higher concentration of KNaO than the feldspar, a key to making a brilliant glass. While this increases the COE, the fact that it comes from this frit brings multiple benefits:
-A brings a little B2O3, a better melter than zinc (which volatilizes anyway at cone 10).
-It dissolves more low-expansion glass-forming SiO2 (in v2 I switched to 400 mesh silica to enhance that even more).
-The glaze can then tolerate some low-expansion MgO (introduced by another frit, 3249 or its equivalent F-69).
More details about this project can be found by clicking/tapping the Insight-live recipe code numbers G1947U, G3910 or G3910A. The red outside glaze is G2571D1.
| Recipes |
G1947U - Cone 10 Glossy transparent glaze
Reliable widely used glaze for cone 10 porcelains and whitewares. The original recipe was developed from a glaze used for porcelain insulators. |
| Glossary |
Transparent Glazes
Every glossy ceramic glaze is actually a base transparent with added opacifiers and colorants. So understand how to make a good transparent, then build other glazes on it. |
| Typecodes |
Glaze Chemistry
Case studies where glaze chemistry was used to solve a problem. |
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