“Bianco di San Giovanni”
This white was mentioned in an earlier post on Caravaggio as an “extender white” for oil painting. However, on a manufacturer’s website it indicates the following:
Bianco di San Giovanni is considered the white pigment par excellence for fresco painting. It is used also in tempera and grounds while it is not advised in oil and encaustic painting techniques.
Clearly there is some confusion. I will research further…
I now suspect that the “extender white” for oil is not Bianco di San Giovanni, but calcite. This is what Velazquez used with his lead white to make it thinner, as cited in the book Velazquez – The Technique of Genius.