A Guide to Masking Fluid
Masking fluid is a liquid latex-based product that is very effective at keeping small areas and thin lines 'masked' and therefore free of paint when painting on watercolour paper. The rubber prevents the paint from reaching the paper and is peeled off to expose the white paper left untouched.
The masking fluid can be applied in many ways, almost any tool will work. You may use a brush, a ruling pen, a dental pick, a Colourshaper applicator or a special Masquepen or Super Nib which is a needle that gives extremely fine lines. (The Super Nib comes with an empty bottle that is for filling with water, attaching the needle to the end and squirting the water through the needle tip to clean it when finished. Do this straight away or the needle will be very difficult to clean.) If you need splattered white dots you can flick the masking fluid from an old toothbrush.
If using a brush you might want to keep one inexpensive brush to use exclusively for masking fluid because the latex might not come out completely when you are finished. One trick to make it easier to clean your brush is to wet the brush thoroughly and wipe the hairs over a bar of soap or dip it into washing up liquid, making sure that the hairs are thoroughly coated right up to the ferrule and then use it to apply the masking fluid. Wash the brush thoroughly immediately after use.
Masking fluids come in different tints so you can see where you have painted it. The places where masking fluid is most useful are small white areas or lines within a large even wash of colour, like sailboat rigging against the sky, where you don’t want to paint around areas and interrupt a smooth wash.
The paper must be dry when you apply the masking fluid. If it is wet the masking fluid will soak deeply into the paper rather than sitting on the surface. The paper will usually tear off with the masking fluid when you attempt to remove it when you are finished. The same problem occurs if you dilute the masking fluid when you use it. Shaking the bottle will introduce air bubbles and if applied the bubbles will pop during drying and leave unprotected spotty areas.
Wait until the masking fluid is completely dry, at least five minutes, before you paint the watercolour. After you have finished your painting and it is completely dry you can then remove the masking fluid. Some artists rub with their finger or a putty rubber to get it started. The artist Kory Fluckiger shows in his book Watercolour for the First Time how he paints a patch of masking fluid the size of a penny on a corner of his palette when he starts painting and later when it is dry he rubs it into a little stump and uses this, as the masking fluid sticks best to itself. Get a corner to pull away and then lift this away from the paper and it should pull away in thin stretchy strips or sheets.
Remove the masking fluid as soon as possible after the painting is dry. The longer the mask is left on the paper the more likely it will be to adhere and be harder to remove. Also, the colouring in the tinted fluids can stain the paper if left on for a long time.
After you have mastered using masking fluid you will be rewarded with those lovely sparkling whites in your watercolour paintings.