So I called up Robert Doak over the Summer to order some paint. As he does, he asked me about how I paint and started suggesting additional things for me to buy (he’s a very good salesman). One of the things he pushed was his new medium, “cristallo.” At $12 USD for a 40 ml tube I decided to splurge and pick some up.
Mr. Doak says that the primary ingredients in cristallo are leaded glass powder and sun-thickened walnut oil. It also contains small amounts of cold-pressed walnut oil, beeswax, and lead drier. It is based on recent research indicating that 16th century Venetian painters added more powdered glass to their paint than was previously thought, although he makes no claim that this is the “rediscovered” medium of Titian, Giorgione, and Tintoretto. He suggests that it is best used by spreading it thinly onto the surface and painting into it. He also suggests that it is a good replacement for varnish on a dried painting, but I am dubious about that application and have not tried it.
I’ve now painted with it, off and on, for a few months. It is a sort of thick, colorless fluid, about the consistency of ketchup. It is not sticky the way mediums containing resins, balsams, or stand oil tend to be. It is easy to spread very thinly onto the painting surface with a finger (you can feel a slight granularity from the glass powder, but it is barely perceptible) and it becomes more fluid as you move it around (i.e., it is somewhat thixotropic). It is nice to paint on, providing a pleasant, slippery quality to the painting surface. Mixed into paint, it dilutes it slightly and gives it extra brushability. It doesn’t hold brush marks. It does not seem to markedly increase or decrease the drying time of oil paint. So far, I like it. It does not make the paint magically transparent or luminous, but I didn’t expect it to.
If you do use cristallo or any other painting medium, add only very small amounts to your paint—never more than 20% of paint volume and preferably much less than that.