Masking fluid is a very useful tool to a watercolour artist. It allows the artist to 'mask off' sections of a painting and allows them to leave white sections of a painting with minimum effort. These Artvids give you an idea of how it works, and masking fluid will be used in many projects you complete.
Here is a simple art activity that demonstrates the use of masking fluid. If you want to have a go at it you will need to download and print a sheet of fairy outlines. Click here to down load the sheet.