Acrylics dry very quickly on canvas.
Although oil paint and acrylic look similar once the paint is dry, acrylic is a little trickier to use than oil paint. Being water-based rather than oil-based means that acrylic dries faster, making mixing colors together more difficult. This can present a challenge when you're attempting to get an even skin tone or needing to blend shadows into lighter areas.
Shadows and Dark Areas
It's useful to start by using a light brown color to delineate darks areas like shadows under the eyes and on the body. This can be applied as if you were using a pencil to draw thin lines, and will provide you with the base to work from with the other colors.
Mid-Tones
The mid-tones can be painted next. To get the tones right you will need to apply several layers of paint, so don't panic if after the first few you still haven't got the skin color you design. Because acrylic paint dries fairly quickly, it's useful to use a product that will slow down its drying time, such as an acrylic retarder. By using this, the layers will blend more easily rather than simply covering each other.
Thinning Paint
If the paint has dried and you want the color you are applying to blend with an existing color; for example, to add a shadow to part of the face, you can thin the acrylic paint with water. If you apply a thin wash of paint the existing paint will still show through. You'll need to experiment with how thin you want the paint to be until you get it right.
Mistakes
If you make mistakes, the fact that acrylic paint dries very quickly becomes an advantage. You can paint over your mistakes and the previous layer of paint will not be visible.
