I am fascinated by the amount of color in the tiny little square at the top. This urban landscape study is only 5×7 in., yet every one of those inches is packed with pure, vibrant color. You can see every stroke I put down because none of them are blended. To me, blending kills the freshness, particularly with pastels, but also with oils and acrylic. I prefer to let one color sit next or on top of another (by scumbling) to create the illusion of blending at a distance. This technique was widely used by the Impressionists, it works because our eyes blend the colors at a distance, but up close they are just little bits of vibrant, pure colors.
I’m always surprised when I hear students say “mine just looks like blobs of color up close”, ummm okay, so do mine, that’s how they are supposed to look. It’s when you get them placed in just the right spot, in the correct value and the correct temperature that they will join together to form an image at a distance. I never get tired of the magic of looking at a painting created this way up close and then at a distance.
If you have problems with your colors looking muddy, odds are that you are over blending. Over blending is a sure way to kill contrast and push everything toward a middle value range. For example, if you lay down a layer of deep red and put a transparent stroke of bright green on top, the red will show through the scumbled green and create a beautiful shadow color full of color variation. If instead you rub the two colors together with your finger, you are likely to get a muddy brown.
Optical blending also creates a much softer, less hard edged appearance. You can still get defined edges by placing contrasting values next to one another, but the overall appearance will be more painterly rather than photographic. While one style is not better than the other, they are very different in both process and end result.
If you are more interested in a photo realistic look, the way to achieve it is by working in layers and using stumps to blend more gradually. (Or working in oils or acrylics and sanding between layers, using transparent glazes to build up color gradually). The most important thing is to know what appeals to YOU as the artist–in terms of BOTH the process and the end result. Both are equally important in order to gain the most satisfaction from your efforts!