The body is Plainsman H570 (0.5-1% porosity). Notice the EBCT (engobe compatibility) test bars in front. These sandwich the body and the engobe together in a thin strip, differences in fired shrinkage curl the bar during firing (toward the higher shrinker). 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 the 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.
L3954N - Cone 10R Base White Engobe
Cone 10 reduction black engobe for stonewares (not porcelains).