Salt can add a pretty cool effect to your watercolor painting. There is a trick to using salt and it's all about timing.
1. Paint a test swash of color on your watercolor paper.
2. Wait until the shine begins to disappear from the wet paint.
3. Spring some kosher salt just as the shine is going away.
4. Wait. Let the salt do it's thing, there is no way to rush this step.
5. When the salt, paint and paper is completely dry you can then brush away the salt. Make sure you remove all of the salt.
6. Voila, the effect of salt.
If you sprinkle the salt down too early, it will melt and stick to the paper. If you wait too long, nothing happens. It's all about timing!