Masking fluid is a great tool for your watercolor paintings. Most of the time when using it, I have a few old brushes that I save just for that purpose. The photo shows one of them. However, you can use your good brushes and still keep them in good shape by doing just one simple thing; putting your brush in some liquid soap. Here’s what I do…
I just use whatever liquid hand soap I have at home. BEFORE dipping my brush in the masking fluid, I dip the brush in the liquid soap and work it into the bristles all the way up to the metal, then I just wipe it off with a clean dry paper towel. No water.
After that, I just dip the brush in the masking fluid and apply to my paper like normal. When I’m finished, I clean the brush with soap and water and the masking fluid comes right out.
I had been painting with watercolors for years before attending art school and had never heard of that before college. Now I can use my old brushes like normal, but I can also use my good brushes for more refined detail work and don't have to worry about ruining them.
I used masking fluid on the below painting to keep the lightest parts of the birds feathers.