Many painters use this watercolor technique to preserve white areas on the painting. There's much more you can do with masking fluid (aka liquid frisket)
Using the different art masking fluids
A Guide to Basic Watercolor Techniques: Tips & Tricks to Upgrade Your Art - Beebly's Watercolor Painting
Masking Fluid (Liquid Frisket) Watercolor Technique - Beebly's Watercolor Painting
Trending This Week - Course - Beebly's Watercolor Painting
Masking Fluid for Watercolours - The Paint Spot - Art Supplies and Art Classes, Edmonton
Comparing Masking Fluids - Jackson's Art Blog
J.M.W. Turner, Chateau de Rinkenberg, on the Lac de Brienz, Switzerland,†1809, watercolor.
Best Masking Fluids and Liquid Friskets for Watercolors –
How to Use Masking Fluid and Liquid Frisket! (for Watercolor Painting)
Dr. Ph. Martin's Frisket Liquid (Level 2) Masking Flud, 1.0 oz, Clear : Tools & Home Improvement
Annie Strack news: Tips for using watercolor masking fluid
Trending This Week - Course - Beebly's Watercolor Painting