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I found six secrets. 1. A lot of Zircopax, in this case 20%. 2. The whitest burning materials. New Zealand Halloysite as the kaolin, Veegum as the plasticizer and Nepheline syenite as the feldspar. 3. A terra cotta body the engobe fits (has the same fired shrinkage). I found a mixture of these materials that fits the terra cotta bodies I am using at cone 04: L4170B (20% nepheline syenite, 55% New Zealand kaolin and 25% silica), L215 and L210. 4. 55% kaolin will certainly produce drying cracks, to stop it the secret is 3% Veegum (to gel the slurry) and 1% CMC gum (to glue it and slow drying). These make it paintable and work for dipping on bisque. It works so well that pour-glazing the insides of these two slip-cast pieces produced an absolutely even, yet very thin paper-white layer. This is an excellent base for clear-glazing and brushwork decorating. 5. A clear glaze and 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, preserving the color of the engobe. 6. The right firing curve: The 04DSDH drop-and-hold schedule.