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Two transparent glazes applied thickly and fired to cone 03 on a terra cotta body. Right: A commercial bottled clear, I had to paint it on in layers, I ended up getting it on pretty thick. Left: G1916S, a mix of Ferro frits, nepheline syenite and kaolin - one dip for 2 seconds and it was glazed. And it went on more evenly. Bubbles are, of course, generated by and clay body during firing, but terra cottas are the worst. And when fired toward vitrification the gas volume can really increase. Complicating this is the fact that low temperature glazes melt early, while body gassing may still be happening. Improvements? Both of these could have been applied thinner. And I could have fired them using a drop-and-hold and a slow-cool schedule. But the biggest improvement would likely be firing lower, to cone 04.
Glossary |
Glaze Bubbles
Suspended micro-bubbles in ceramic glazes affect their transparency and depth. Sometimes they add to to aesthetics. Often not. What causes them and what to do to remove them. |
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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. |
Glossary |
Glaze thickness
Many ceramic glaze benefits and issues are closely related to the thickness with which the glaze is applied. Many glazes are very sensitive to thickness, so control is needed. |
Materials |
Kaolin
The purest of all clays in nature. Kaolins are used in porcelains and stonewares to impart whiteness, in glazes to supply Al2O3 and to suspend slurries. |
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