Use Underpainting Transparent Base in the underlayers of a painting or as a medium in alla prima (direct) painting.
Not all painters use an underpainting, it seems that those who do want it to dry fast so they can begin coloring in the overpainting. Natural Pigments has a simple solution that does not require buying a whole new set of colors just for the underpainting. Introducing two new products: Underpainting Lead White and Transparent Base. With either or both products, you can use any of your standard oil colors and have them dry blindly fast—usually within an hour or so. Add the Underpainting Lead White or Transparent Base—from one third to one half—to your oil color and your underpainting dries quickly to a matte sheen. Add less for slower drying.
The image of the test panel shows the effects of Oleoresgel, Lead White #1, and Underpainting Transparent Base in mixtures with four oil colors: Maya Blue, Ultramarine Blue (Green Shade), Ercolano Red and Italian Green Umber.Directions
Add Underpainting Transparent Base directly to paint, mixing well on the palette. Do not apply Underpainting Transparent Base over slower drying oil paint, as this may lead to cracking or wrinkling of the layer. You can thin Underpainting Transparent Base with mineral spirits and/or linseed oil.See Also Underpainting Lead White
Underpainting Lead White (also known as flake white or Cremnitz white) is a mixed white with lead white, titanium white and calcite ground in alkyd with mineral spirits to make a brilliant, opaque white surface that is smooth and dries very quickly to a matte surface. This is the ideal white to use in your underpainting, because it dries within an hour or two. Mix with any oil color and apply as your underpainting to dry quickly to a matte surface. This is the best surface for your overpainting because the matte provides subsequent layers with ample texture for excellent adhesion. Dries to a matte finish. Underpainting Lead White does not contain driers.