One of the most common questions I get is how to avoid this common painting pitfall. Painting wet into wet paint in oils and acrylics can yield beautiful fluid paint effects, evocative lost edges and those elusive 'happy mistakes' but it's also just as easy to make mud.
Think of mud like weeds in your garden. It's a perfectly fine colour/plant on it's own, but it's just growing in a place you don't want it.
Generally 'mud' is a very greyed down colour where you wanted a more vibrant colour. The easiest way to make this is to mix colours that are opposite on the colour wheel (complements).
Another way to think of it is mixing warms and cools together = grey/mud.
So, if you're in a spot in the painting where you want vibrant colour, you don't want to mix warms and cools together. Mixing warms and cools together often occurs accidentally when you're painting over a wet layer of paint. Here's how to avoid that...
1. Make the layer of paint quite thin, just thick enough to cover the canvas and, this is a trick I learned from John Crump, scumble (rub) it on with your brush, so that it’s a really thin layer that doesn’t have much painting medium in it.
2. Use thicker paint with more painting medium in it to brush lightly over the top.
3. Lighter colour over dark works better than dark over light. That’s because a lighter colour will tend to have white in it which is opaque and covers the paint below it.
4. Use larger brushes with long flexible bristles that can lay the paint on the surface rather than scratching paint off.
5. Try to use fewer brushstrokes to say what you want to say. (Larger brushes help). Every time you make a brush stroke you are mixing with the layer beneath. Fewer brushstrokes means more vibrant colour.
6. Be aware of the paint that your brush has picked up off the surface of the canvas. If you want vibrant colour instead of mud, wipe your brush often and reload with fresh paint often.
I hope that helps you with your next painting.
PS. Learn more about colour in Mastering Color 2