I often take a traditional approach to oil painting that begins with a monochramatic underpainting, followed by successive layers of color. This approach requires me to follow the "fat over lean" rule: an under layer should be leaner (have less oil) than its over layer.

This procedure not only allows the first layer to dry faster (so you don't have to wait as long to apply the second layer); more importantly, it results in a stronger bond between paint and painting surface – while the reverse creates a weak bond resulting in much, much quicker deterioration of the work.

In deference to the "fat over lean" rule (a law of chemistry, actually), traditionalists usually dilute the paint used for the first layer (the monochromatic underpainting) with thinner. In the past, this was invariably turpentine – the very smell of which so intoxicated Vincent van Gogh and other artists of history that they reportedly wound up drinking it.

Acrylic Underpainting

Thus, I prefer to avoid even low-toxicity thinners, and begin each oil work with an acrylic underpainting followed by oil glazes and impastos (which adhere well to an acrylic base). Acrylic paint not only dries much more rapidly than the thinnest standard oil paint – it goes beyond lean to FAT FREE, since it contains no oil in the first place.

I used this oil-over-acrylic approach to paint Dreamcatcher, the still life shown above. Click through the gallery to follow this work from acrylic underpainting to finished oil.

To clean my brushes during the oil-painting part of this process, I just use clean rags or thick white paper toweling (such as, VIVA). I never park my brushes in thinner, and use only soap and water to clean them when I'm done for the day. Even when I was using thinner, I washed my brushes this way. You don't want to leave any thinner in a brush; it will eat away at it.

BTW: Never use acrylic paint OVER a layer of oil paint. This flies in the face of "fat over lean," and could lead to rapid deterioration.