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This is a white engobe (L3954B) drying on two dark burning cone 6 stoneware leather-hard mugs (Plainsman M390). Those lumps are on the left cannot be screened out, they are agglomerates. That slip has excessive flocculant (powdered Epsom salts are added to gel it so that it stays put on the piece after dipping). About 4 drops of Darvan were added to one gallon of the slurry, this immediately made it smooth and a perfect consistency for application. It remains stable on ware (without runs). Engobes require tight control to have the right viscosity and thixotropy (which can be achieved over a range of specific gravities (about 1.45-1.6). When they are right they are a joy to use, when they are not ware is ruined.
Left is Plainsman M340. Right is M390. Each mug has been white-engobed inside (by pouring), using L3954B, and halfway down the outside (by dipping). The insides have been glazed using G2926B clear. The inside surface has more depth and a richer appearance than could be achieved using a white glaze (especially over the dark burning body). The outside of the left one is Alberta Slip base GA6-B. The outside glaze on the right is the clear plus 4% iron oxide. This technique of using the engobe enables porcelain-like functional surfaces on the insides and the visual contrasts and character on the outsides of the stoneware mugs.
Recipes |
L3954B - Cone 6 Engobe (for M340)
Dry and firing shrinkage fitted to Plainsman M390, M340 |
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URLs |
https://insight-live.com/insight/share.php?z=uiqNgtxwws
White Cone 6 Engobe, New Alberta Slip glazes, Firing Schedule |
Glossary |
Engobe
Engobes are high-clay slurries that are applied to leather hard or dry ceramics. They fire opaque and are used for functional or decorative purposes. They are formulated to match the firing shrinkage and thermal expansion of the body. |
Glossary |
Thixotropy
Thixotropy is a property of ceramic slurries of high water content. Thixotropic suspensions flow when moving but gel after sitting (for a few moments more depending on application). This phenomenon is helpful in getting even, drip-free glaze coverage. |
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