>sangiovani. Lime white changes the colors after
>a few days, and bianco sangiovani doesn't
>'calcinate' completely, but leaves a little
>white powder after drying.

let me know what did you do exactly to end up with this result - this thing happens with all pigments if they are applied after the plaster locks (run out of painting time)... Also at the beginning it is better to use pure lime putty for white, since it is more active the refined bianco san giovany, after all it is the same thing, but "bianco is more of a chalk" due to the process of prep

I want to be able to use some
>whitened tints, and not just paint
>transparently, like watercolor.

You do it at the end of the day, and you have to ajust for "whitening when dry", always since the plaster itself changes to prure white and shifts all colors lighter - this is a spesifics of fresco - you need to paint 2-3 shades darker then you want the final result to be.

The one will paint in "watercolor like" just because it is faster then using tempera-like (mixed with white) tones also in fresco you are "building up" the pigment layer - not applying paint coats (paint over medium)...

in short you need to build the color before you can put white on top and work out the lighter value, it does not make much sense to put white ontop of already white plaster, does it?

this is very important to define, at the end of the day plaster fills up and you work-refine the primary plain with the use of white.