Monthly Tech-Tip | No tracking! No ads! |
Fired at cone 6. The samples on the bottom tiles are from ten-gram balls that have melted down (in our GBMF test). These glazes have the same chemistry, but the one of the left sources its B2O3 from Gerstley Borate (which has a high LOI). The one on the right gets it from a frit. Because the fritted version has less gases of decomposition to expel, the glass is much smoother. Curiously, the fritted version is flowing less and the red color has been lost. Why? This could be because the Al2O3, which stabilizes glazes against excessive fluidity, is being dissolved into the melt better and thus is more available for glass building.
The words "blister" and "Gerstley Borate" are very often used in the same sentence. This recipe is 60% Gerstley Borate, 20% Silica, and 20% OM4 ball clay. The piece was fired a second time to try to heal the blisters but they only got worse. While it is possible to fire this without blisters beginners often end up with this result.
Glossary |
LOI
Loss on Ignition is a number that appears on the data sheets of ceramic materials. It refers to the amount of weight the material loses as it decomposes to release water vapor and various gases during firing. |
---|---|
Glossary |
Limit Recipe
This term refers to sanity-checking ceramic glaze recipes by noting whether materials present or their relative percentages fall outside typical norms for functional ware. |
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? |
Buy me a coffee and we can talk