|Canvas toned a mid-value, warmish grey with oil paint. The paint|
used was leftover paint on my palette, mixed together to get this flavor.
I used a small brush and intentionally left the strokes showing.
A reader asks: "Please discuss painting on a colored ground, both pastel and oils. For oils, do you feel comfortable using acrylic as an underpaint for oils? What colors would you choose and why?"
I'll answer the second question first. I think acrylics work just fine for toning the canvas - if they are applied thinly and as a wash. Too thick, and the oil paint you apply next may not adhere well enough to last the ages. "Too thick" is if you can see an obvious glossy appearance to the acrylic. If you want to use thicker acrylic, consider using an acrylic gesso (also called "acrylic dispersion ground") that has been toned. Acrylic gesso has been formulated to provide the right tooth and absorbency to serve as a substrate for oil paint; regular acrylic paint has not. The safest bet, however, is to tone your canvas with oil paint. I like to use a paint that dries relatively quickly, such as raw umber. By the way, for pastel surfaces, acrylic is a great medium to use for toning.
Before answering the other question, I should note that the point of toning the canvas (or paper, in the case of pastel), is threefold. First, it gives the whole process of painting a jumpstart. If you have trouble beginning a painting , throwing some paint on the canvas and scrubbing it in with a paper towel is a great way to get going. Second, it kills the white and establishes a darker value. This not only makes the canvas easier on the eyes, but it also gives you a value to judge your mixtures (or pastel choices) against. It's almost impossible to judge the value of any given color against white; every mixture just looks dark! Third, your color choice will affect the overall color harmony of the finished painting and will help to unify the piece.
I generally try to choose a color that will enhance the mood I'm shooting for. As a landscape painter, on a sunny day I may choose a warm color to give the painting an overall warm feeling; on an overcast or foggy day, I may choose a cool color. Or, I may choose a complementary color to liven up the color scheme. It's a common trick among plein air painters to start with a red tone to make a scene that is predominantly green more interesting. If you don't completely cover up and obliterate the initial tone - and you shouldn't - some of the red will pop through the greens, adding sparkle. Sometimes, I'll start a painting with a mid-value, neutral grey, as pictured at the top of this post. This is the most helpful in making accurate color and value choices.
Finally, you should have fun with the toning! You don't have to stick with one color or value. You can have warm passages mixed in with cool passages, light areas mixed in with darker ones. Sometimes a "randomized" underpainting will give you fascinating results.