Ceramics and shellac
With the first coat you should dissolve the  crushed shellac flakes in denatured alcohol with a bit more shellac than usual, and stir in an emulsion of premixed marble dust, a touch of linseed oil and fresh egg yolk until you get the right consistency for painting. If it doesn’t dry fast enough for you, consider adding a few drops of saponifying ‘japan drier’.

I can’t give you mixture ratios because shellac comes in lots of grades, but as an explanation, the marble dust gives hardness, the linseed oil suspends the marble, the egg yolk binds the shellac with the oil.