Product Reviewed: Gamblin FastMatte
Supplier: https://gamblincolors.com/gamblin/
Summary: Ideal for underpainting and suitable for all artists working in oil. Not solvent free.
Most experienced oil painters are aware that the "fat over lean" rule is one of the few true rules in oil painting: paint used for laying out, massing in, or blocking-in on a canvas should contain little oil (or other medium). Each subsequent layer should be thicker and contain more medium than the layers underneath.
The "fat over lean" rule is important for the integrity (and thus the longevity) of oil paint layers.
What I like about Gamblin FastMatte is that it is specially formulated for use in underpainting. You can put it on in thin washes, or even lay it down in heavy amounts, and be able to safely paint over it.
My favorite Gamblin FastMatte colors
Texture-wise, it is a stiff and gritty paint, like a thick gesso. I use it thinned with solvent for laying out and for the first layers that I put on the canvas.
Most notably it 1) dries overnight (at least, most of the colors do), 2) sticks to the canvas, and 3) dries to a flat matte finish which the subsequent layers of paint can grab onto.
A monochrome underpainting done with Gamblin Fast Matte
There is a range of colors available, although I tend to stick to raw umber, yellow ochre, and transparent red oxide.
I will cover all the areas of FastMatte with regular oil paint, except where I choose to let some of the underpainting show through for effect. However, there's no reason you couldn't execute a painting entirely in FastMatte—you would just have to accept that the finished piece will have a more unfinished look that something done in the traditional way.
Unless you work on large paintings, I'd recommend staying with the small 37 ml tubes. Like most alkyd paints, these tend to stiffen after being open for 12 months or so and a large tube is likely to end up going to waste. You'll want to replace them with a fresh tube of paint every so often.
In summary, this has become an important part of my painting process. I strongly recommend it for all oil painters, even for those who like to work alla prima.
Update November 2022: My attempts to boost this product have obviously failed. I learned that Gamblin has discontinued this line of paint. It's disappointing, as there is nothing quite like it available. The closest related products are the CAS Alkyds and Winsor and Newton Griffin Alkyds, neither of which I have yet tried.