Q: I recently painted a watercolor that contained a larger, dark-brownish area where I combined Van Dyke brown, burnt umber, and green earth. In that spot, the paint took nearly two weeks to dry. What do you think occurred?

A: In general, the ingredients in watercolor (particularly the amount of glycerin in the paint) rather than pigments themselves that most affect drying time. Specifically, the colors you mentioned can be problematic. Green earth tends to behave like a clay in that it absorbs a good deal of water, particularly when applied heavily. And Van Dyke brown is not considered a permanent pigment: it tends to be unstable, whether used alone or in mixtures.

Another possibility that comes to mind is the opacity of your paint. If you applied the paint too thickly, the binding action of the paper on the pigment particles would lessen, causing the paint to dry more slowly and inviting the possibility of cracking.