I don't remember where I read about using rock salt rather than table salt to create texture on paper or fabric, but I'm thrilled that I had the good sense to purchase some. I'm working on backgrounds for a swap and they were looking very boring until I sprinkled some rock salt onto the wet fabric. I never got an effect this great with table salt and yes, the salt has been brushed off so the pattern is permanent. The only problem is that some of the texture will be covered up once I start adding elements; right now I'm enjoying the rawness of painted canvas fabric. I used Golden Fluid Acrylic paint, three shades of green, that were randomly brushed onto very wet fabric. The purplish gray is just some cheap deep purple acrylic paint. When the pieces were dry I heat set them with an iron.