One of the final levels of sophistication in painting is the character of the marks you make on your canvas. Growing artists often overlook this attribute in painting, choosing to blend everything instead. Over-blending is a contrived approach to painting surfaces and removes the power and character of the painting process that marks bring to the work.
I suppose this over-blending tendency comes from seeing the paintings of the Renaissance masters, who’s surfaces appear blended. Those surfaces were the result of the painting mediums and required application techniques available at the time. Most artists of the fifteenth century were painting with egg tempera, a very transparent painting medium. The application required elaborate underpainting and glazing techniques, where a complete, dark, monochromic underpainting base was created, before layer after layer of semi-transparent egg tempera color was glazed, painstakingly, over the top. The slow building up of these many semi-transparent levels gave the edges in the final surfaces of the painting a very smooth and blended appearance.
If you examine the paintings of later oil painting masters, you’ll find the character of THEIR surfaces to be more active. Take a close look at a painting by John Singer Sargent, for example. In your memory you see his surfaces as smooth and blended, but through a more precise examination you’ll realize they’re made up of precisely placed individual marks. Areas of less focus, like her lace blouse and jacket are painted with even more energetic strokes.
Other painting giants were even more expressive. Each with a character to their marks that were all their own.
While most subjects present both hard and soft edges, you don’t have to blend an edge to make it appear soft. A more interesting approach is to retain your marks and simply apply a series of close values to turn an edge, like Vincent did on the leading edge of his face and the back of his head in the above, “Self Portrait.”
One of the best ways I know of for breaking the habit of blending everything is to do what you should be doing anyway and work the entire painting at the same time, working from rough to tight. When you’ve adjusted everything else to your satisfaction, then and only then ask yourself if any of the edges need to be blended. I think you’ll find that they do not!