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Black-burning bodies are popular with many potters. This one is stained by adding 10% raw umber to a buff-burning stoneware. Umbers are powerful natural clay colorants, they have high iron and also contain some manganese oxide. Could a white engobe produce a porcelain-like surface on such a clay body? Yes. L3954B engobe was applied during leather-hard stage to this Plainsman Coffee Clay mug (on the inside and partway down the outside). After bisque, transparent G2926B glaze was applied inside and GA6-B outside. Notice the GA6-B over the engobe fires amber but over the black it produces a deep glossy brown. The engobe was mixed into a thixotropic slurry, as explained on the page at PlainsmanClays.com (see link below), and applied in a relatively thin layer. This porcelain-like result is a testament to the covering power of a true engobe. It is no wonder they are so popular in the ceramic tile industry - a red-burning body can be turned white as a porcelain, which enables all the marvellous glazing and decorating they can do.
Yes. If it is a true engobe. This is L3954B fired at cone 6 on Plainsman M340S, it is fire-shrinkage-fitted to this clay body and opacified with Zircopax. The cover glaze is G2926B transparent. The opacity that this engobe is able to achieve here is because it is vitrifying to the same degree as the body, no melting is occurring and that is why it is completely opaque (even though it is applied as a very thin layer at the leather hard stage). This same performance could be expected in reduction firings to block the iron speckle (using the L3954N and variations recipes).
Materials |
Burnt Umber
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Materials |
Raw Umber
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Hazards |
Manganese Inorganic Compounds Toxicology
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Hazards |
Manganese in Clay Bodies
Manganese is used to stain clays (using black) and to impart fired speckling (as a decorative effect). It is dangerous? |
Recipes |
L3954B - Cone 6 Engobe (for M340)
Dry and firing shrinkage fitted to Plainsman M390, M340 |
URLs |
https://plainsmanclays.com/l3954b
The L3954B engobe page at PlainsmanClays.com explains how to mix and use it on Plainsman clays bodies at cone 6. |
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