The best way to make black clay

Using an engobe is the best way to make a black clay surface. Left is a version of L4768E this is not the best way to make black, but the one most use (and what Plainsman Clays does with Coffee Clay). It is the darkest that it is practical to make (using the hyper-red burning C-Red clay as a base and adding umber). This method is far better than adding umber (or manganese) to a white or buff burning clay because only half as much is needed, which cuts in half issues that come with these pigments. The L4768F mug base looks black when viewed beside buff and red burning bodies, and it is black enough to host the GA6-B honey-colored glaze to produce a deep glossy jet black glazed surface. But the black body color on the right is the star! First, it is not a body, it is just a thin veneer of stained porcelain engobe, a far less expensive solution than trying to stain the whole body black. That being said, so people need a totally black body. Even in these cases it is being to make your own. Try using the L4053B recipe as a starter. Get a plaster table and a propeller mixer and you will be unstoppable!

Related Pictures

A special gummed engobe made this possible

The fired pieces appear to be made from black porcelain. But this is L3954F cone 6 black engobe over a white porcelain. Multiple factors make this work. First, a non-gummed dipping engobe will not work for this (it will not apply by brush evenly or thickly enough). This brushing version mixes 500 grams of L3954F powder (with black stain) into 280g water and 75g of Laguna Gum Solution. Second, the engobe recipe is tuned to have the same degree of vitrification as the body, in this case M370, so pieces don’t stick to the kiln shelf during firing. Of course, this procedure rewetted the bases of the leather hard mugs, extending drying time so extra precautions were needed to avoid cracking. For example, I painted wax emulsion on the handle outers and covered them all in cloth and plastic for a day to slow down drying.

L3954J black engobe on a cone 10R whiteware body

The body is Plainsman H570 (0.5-1% porosity). This piece is not glazed. The firing schedule is C10RPL. Notice the EBCT test bars in front (engobe compatibility). These sandwich the body and the L3954J engobe together in a thin strip, differences in fired shrinkage curl the bar during firing (toward the one of higher shrinkage). The straighter the bars fire the better the fit. My regular engobe for use on our buff stoneware, L3954N (Plainsman H550, 2-3% porosity), has lower fired shrinkage than this (since that body is less vitreous). This one increases that shrinkage (with 5% more nepheline syenite, 5% less silica and 3% less ball clay). This employs 10% Mason 6600 stain to produce the jet-black fired product. 6600 is their cobalt black stain but the 6666 cobalt-free one should also work, both are suitable as body stains and recommended to 2300F (1260C) - cone 10 is technically above this limit but we have not encountered issues.

Stained engobes can be applied thinly yet fire opaque

This black engobe, L3954F, is on a cone 6 buff stoneware (at leather hard stage). It contains only 7.5% Mason 6600 black stain. How is that possible? Why do people add so much more to their underglazes? Because this recipe has been tuned to have the same degree of maturity as the body - it therefore fires totally opaque. This contrasts with underglaze/engobe recipes containing significant frit, among other issues, their vitreous nature renders them translucent. Thus, up to 40% stain is needed to crowbar their opacity enough to intensify color. And a thicker application (that carries other issues).

Notice how thinly and evenly this is applied. This was possible because of another key factor: The slurry was adjusted to be thixotropic. The thinner layer enables drying more quickly. The body-compatible engobe recipe also means fewer issues with flaking during drying, better fire-fit.

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