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)
How to Use Masking Fluid and Liquid Frisket for Watercolor Painting
art-and-sterf
How to use Masking Fluid for Watercolor Painting - Watercolor Affair
Masking Fluid 101 – Etchr Lab
How to use Masking Fluid for Watercolor Painting - Watercolor Affair
Masking Fluids and Liquid Friskets
How to use Masking Fluid for Watercolor Painting - Watercolor Affair
DOODLEWASH REVIEW- Resists & Masking Fluid - Doodlewash®
A Guide to Basic Watercolor Techniques: Tips & Tricks to Upgrade Your Art - Beebly's Watercolor Painting
Comparing Masking Fluids - Jackson's Art Blog
How to use Masking Fluid for Watercolor Painting - Watercolor Affair
How to Use Masking Fluid in Watercolor Painting
Masking Fluid 101 – Etchr Lab