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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.
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!
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