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These two mugs are the same dark burning stoneware (Plainsman M390). They have the same clear glaze, G2926B. They are fired to the same temperature in the same C6DHSC firing schedule. But the glaze on the left has 4% added iron oxide. On a light-burning body the iron changes the otherwise transparent glass to honey colored (with light speckle because of agglomerates). But on this dark burning clay it appears transparent. And, amazingly, the bubble clouds are gone! We have not tested further to find the minimum amount of iron needed for this effect but with other glazes 2% is working.
These two mugs are made from a dark red burning stoneware and fired in a cool-and-soak firing schedule. A white engobe (L3954A) has been applied on the inside and half way down the outside. Both are glazed inside with G2926B whiteware transparent glaze. The outside glaze on the left is the same transparent with 4% added iron oxide. It has been sieved to 80 mesh. Notice the iron agglomerates and still produces specking (an effect that may be desired, but difficult to keep consistent). Interestingly, that iron is producing a clear amber-colored glass about equal in color to the Alberta Slip GA6A base glaze (80% Alberta Slip, 20% Frit 3195) on the mug on the right. Neither has the micro bubbles that mar a typical clear glaze on bodies like this.
Recipes |
G2926B - Cone 6 Whiteware/Porcelain transparent glaze
A base transparent glaze recipe created by Tony Hansen for Plainsman Clays, it fires high gloss and ultra clear with low melt mobility. |
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Materials |
Iron Oxide Red
Red iron oxide is the most common colorant used in ceramic bodies and glazes. As a powder, it is available in red, yellow, black and other colors. |
Troubles |
Clouding in Ceramic Glazes
There a many factors to deal with in your ceramic process to achieve transparent glazes that actually fire to a crystal-clear glass |
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