Blocks out areas to prevent colour penetration. Easy to see and remove without damaging surface.
I'm a watercolour tutor, and this is the best masking fluid I've found. The blue allows you to see where you've put it, and it flows well so you can make fine marks. Do be sure to take it off within about 12 hrs, though, or it can tear the paper just like any other masking fluid. Elise Mann (Edgware) on 9 Nov 2008
Works really well Kim Niendorf (Wellesbourne, United Kingdom) on 29 Mar 2012
Works OK but really need applicator rather than brush. Sandra Winter (Ongar, United Kingdom) on 6 Jul 2012