Melting ten-gram GBMF test balls like this is a great way to compare the melting of glazes and materials (e.g. frits, feldspars). This is a good example. The differences in the degree and character of the melting are better explained by the chemistry than by the recipes. Compare the yellow and blue numbers in the unity formulas. The obvious is that glazes 2 and 3 have much more B2O3 (boron, the key flux for cone 6 glazes) and lower SiO2 (silica; it is refractory). But knowing the recipe is also valuable. Notice that glazes 2 and 3 have the same chemistry, but 3 melts better because of the mineralogy of Gerstley Borate. It releases its boron earlier in the firing, getting the melting started sooner. Notice it also stains the glaze amber; it is not as clean as the frit. Not to be ignored is how the calculated thermal expansions are impacted: The greater melting of #2 and #3 comes at a cost: More likelihood of crazing. Which of these is likely best for functional ware? #1, G2926B (left). Its high SiO2 and more modest B2O3 content likely make it more durable. And does not craze.

This picture has its own page with more detail, click here to see it.
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.

This picture has its own page with more detail, click here to see it.
Boron (B2O3) is like silica, but it is also a flux. Frits and Gerstley Borate supply it to glazes. In this test, I increased the amount of boron from 0.33 to 0.40 (using the chemistry tools in my insight-live.com account). I was sure that this would make the glaze melt more and have less of a tendency to craze. But as these GBMF test balls for melt flow show, that did not happen. Why? I am guessing that, to get the effect, B2O3 has to be substituted, mole for mole, for SiO2 (not just added to the glaze).
| Glossary |
Mineralogy
Raw ceramic materials are minerals or mixtures of minerals. By taking the characteristics of these into account technicians can rationalize the application of glaze chemistry. |
| Glossary |
Calculated Thermal Expansion
Calculation of the thermal expansion of glazes is a very useful comparative glaze-fit tool. But it’s not a laboratory measurement. |
| Glossary |
Fluid Melt Glazes
Fluid melt glazes and over-melting, over fired, to the point that they run down off ware. This feature enables the development of super-floss and cyrstallization. |
| Glossary |
Melt Fluidity
Ceramic glazes melt and flow according to their chemistry, particle size and mineralogy. Observing and measuring the nature and amount of flow is important in understanding them. |
| 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. |
| Tests |
Glaze Melt Fluidity - Ball Test
A test where a 10-gram ball of dried glaze is fired on a porcelain tile to study its melt flow, surface character, bubble retention and surface tension. |
| Materials |
Gerstley Borate
Gerstley Borate was a natural source of boron for ceramic glazes. It was plastic and melted clear at 1750F. Now we need to replace it. How? |
![]() PayPal | No tracking, No ads, No paywall, No transient content! Just organized, concise information constantly updated and improved. Was this helpful? Consider supporting me. |
Buy me a coffee and we can talk