Pumice Gel enables oil painters to texture their painting surface before painting. (It is also used by acrylic painters.) It is an acrylic medium, so you cannot mix oil paint into it. The pumice gel must be completely dry before applying oil paint over it. If the gel is too stiff and grainy straight out of the jar, you can use acrylic medium or molding paste too thin it.
This is a painting of door in Venice that I did, and used a lot of Pumice Gel. The gel comes in fine, course, and extra-course. In this 3 ft x 5 ft painting, I used the course gel. The extra course would have been way too grainy.
Here is a close up of the grainy surface of my painting.
This is what the gel looks like straight out of the jar.
Pumice Gel is made by Golden.