Using brushes with art masking fluid
Using a brush repeatedly for art masking fluid will certainly damage the brush over time.
Although some artists swear by vaseline, soap or petrol, our tests do not show any of these methods to be 100% reliable or safe. We suggest that if you are using a brush, make sure that the art masking fluid used is as fresh as possible and that you wash it from your brush with soap within a split second of use.
However, it is better to use low priced brushes or old ones if possible. If fine lines are required, a goose quill is ideal and for larger areas try a colour shaper (a colour shaper is like a brush, but instead of hair it holds a rubber shape). Both of these are excellent as due to their plastic-type nature and lack of hair, ensure that the fluid can be rubbed off easily.