My first layer of paint is a monochromatic underpainting. This serves many purposes. It gets me started painting in a stress-free way (It’ll be covered up later!). Also, it’s easier to judge final colors and values painted onto this underpainting than onto a stark white canvas. Finally, the underpainting shows through here and there between the top layers and also through subsequent glazes, providing a consistent color harmony to the finished work. This provides a feeling of unity and reality in the finished work.
I choose to paint the underpainting in lead white and burnt sienna. I like the warm color of the burnt sienna, and both colors are low in oil, important for an under-layer. (An important rule of oil painting is to always have the oilier layers on the top, and the leaner mixtures underneath.) I mix up 9 values from lightest to darkest.
All of the values in the underpainting will be in a lighter key than the finished painting. This lighter tone will allow subsequent layers to appear brighter. I keep this paint layer very thin so that it will dry quickly, because I can’t paint over it until it is dry to the touch. I blend out any obvious brush marks, so they won’t show through and interfere with my more considered brush strokes in the finished painting. I paint only the general shapes, not any details. Since this layer will be mostly covered up with more paint, it would be a waste of time to spend any time working on details. I keep edges clear and visible to preserve my drawing for the over-painting.
It’s hard to judge values correctly when mixing paint on the palette. I find it useful to use my black-and-white study as a value guide. If I’m unsure about the value I mixed for a part of the painting, I paint a dab of it right onto the corresponding area of the black-and-white study, which I have tacked to the wall nearby). I can tell immediately if the value I mixed is darker or lighter. Since I’m painting my underpainting a few values lighter than the final result (which are the values represented in the black-and-white study), I might think, “So this dab is the same value as the black-and-white, so I’ll paint it two steps lighter in the underpainting.”
It takes me two sessions to complete the underpainting. Now, it’ll take about a week to dry completely.