I have seen a lot of discussions around mixing watercolor and acrylics, going on over internet as well as with my artist friends. I am not an artist, but I am a member of an Art Promotion platform, www.artflaunt.com, and know a lot of artists from that network. Here are my findings from a discussion with them over mixing of Acrylics and Watercolor.
In general, oil paint and acrylics cannot be mixed because of their properties. Acrylics are water based colors, and oil paint has oil as a base, which cannot mix chemically.
Though, I have seen one of my artist friends mixing dry acrylic with oil paint. Many a times, it may not have mixed well though, but it has given a nice blotty effect to the painting.
Also, you can use both the paints in one single painting, which really gives a great effect to the painting, but it is subject to certain things to be kept in mind.
The acrylics must be used on the canvas first, and then oil paint can be used over acrylics.
The acrylic paint on canvas must be completely dry before painting with oil paint, else the oil paint will not stick to the acrylics.
Always try to mix same kind of base colors with different shades to provide a classy look to the painting (kind of gradients). If you use different colors, they may not appear clean when you see the work from near. Same colors with different shades look good even from nearer. Though, it also depends on the artist’s imagination and skill to a larger extent.
Using colors is totally a way which is specific to every artist, and you cannot say who can do what kind of wonders with the same colors.
The world of colors is beautiful, sweet and crazy which has enormous possibilities beyond our imagination (in an artists mind), and when taken up on a canvas, can drive us crazy.