I have done the technique before where you sprinkle either rock salt or plain table salt over wet watercolour where the salt soaks up some of the liquid to leave you with lighter areas where the salt was. This is a variation on that theme but you mix table salt with water in a spritz bottle and spray onto the wet watercolour instead. After reading several articles about properties of watercolours including the difference between student quality and artist quality, it became obvious that certain colours granulated more than others.
This is another of those techniques that you need to just play with to see what works and what doesn't. Even the ones that don't work as well as you'd like, you will still end up with a useable watercoloured background. My ratio of mix was 1tspn salt to 6tspns of water, but you can certainly play around with those quantities to see what works for you. Besides my atc samples below I have posted my unadorned samples so you can see the granulation better. You can also buy granulating liquid for watercolours but I wanted to try the cheaper (and at hand!) alternative of salt and water spritz.
(this started out with a layer of gold first,
the added a layer of black over it before
spritzing with the salt spray. The little
black & white skulls are nail art!)
(this is burgundy and black with gold over
the top section and dripped down)
(only one colour, pale blue)
This is the "edgy chic" before adding the rest.
Pink, Purple and Gold.
Purple and pale blue.
This is the "be quiet" pale blue before adding anything.
Love the striations and granulation in this one!
Blue, rust and a bit of black.
Blue and teal.
Olive and navy.
Green and black.