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I found seven secrets with recipe, process, glaze and firing. 1. A lot of Zircopax, in this case 20% (for whiteness, opacity). 2. The whitest burning materials: New Zealand Halloysite as the kaolin and nepheline syenite as the feldspar. 3. 3% Veegum to gel the slurry (enabling low specific gravity for thin and even coating). 4. The recipe, L3685Z2, has 55% kaolin, that will certainly produce drying cracks. But 1% CMC gum stops that and makes it brushable. It even works on on bisque, I pour-applied it to the insides of these two slip-cast pieces, it drained to perfectly even coverage (in a very thin layer). 5. A terra cotta casting/throwing body to fit the engobe to (has the same fired shrinkage at a target temperature, e.g. cone 04): Initially I am using L4170B. 6. A clear glaze that fits and is transparent: Notice how much whiter the left one is, G3879. At the same thickness as the G1916Q on the right, it is more transparent, better transmitting the white of the engobe. 7. The right firing curve: The 04DSDH drop-and-hold schedule for defect free surfaces.