There are several different mediums available for watercolor painting. One of the mediums made by Winsor & Newton is called Granulation Medium. It gives a granulated or mottled appearance to colors that tend to dry in a smooth even wash.
For my sample, I used MaimeriBlu's Cupric Green. First I wet my brush with plain water, dabbed it into my color and created a square swash of the cupric green. Then I cleaned my brush in clear water and blotted it dry on a towel.
I poured a small amount of the Granulation Medium into a tiny little cup. I wet my brush with the medium, then picked up some of the cupric green from my palette and created the larger swash of color.
As the colors dried, the larger swash with the medium did not dry as a flat smooth color. It has slight changes in tone and a slight granulated textured appearance. It does have a splotchy, mottled, grainy look.
This can be useful in creating interesting backgrounds, stormy skies. Be creative and give watercolor mediums a try.