This article was first published in "Frequency Magazine" – November 2008.
In traditional watercolour, you paint on white paper and you save areas to serve as white areas in your paintings. This is where masking fluid helps. Masking fluid is made of liquid latex in ammonia. It forms a temporary water proof seal so that you can paint onto the paper and it will reserve the area it covers. It is generally tinted yellow or grey to make it easier to see on your white paper.
Areas protected by masking fluid will accept watercolour after the masking fluid has been removed. If the mark appears too white, you can always soften it with a wash of colour.
Masking fluid can be applied on white paper but also on a wash in order to reserve an area before you apply a subsequent wash. The main advantage of masking fluid is that you can paint uninterrupted washes without having to worry about “leaving the whites”.
It is recommended to carry out a test on the back of your paper to check that the masking fluid will come off easily. It works on most watercolour papers. The only time I had trouble with it was when I used an artisanal handmade paper. The masking fluid would not come off or would tear the paper away.
Before you start, shake the bottle of masking fluid a couple of times (after you made sure it is well sealed). This way, latex and ammonia will be well mixed together. Fluidity depends on the brand you use, but note that you can water down masking fluid in case you want to achieve certain effects that require more fluidity (like splattering).
You can use all sorts of instruments to apply masking fluid: a dip pen or a ruling pen for fine lines, an old bristle brush for looser marks or a colour shaper. You can also splatter some masking fluid onto your paper using an old toothbrush. Personally, I like to use a colour shaper with an angle chisel tip. This particular shape (rounded on one side and with a straight angle on the other side) allows for a variety of marks. The other advantage of this tool is that masking fluid comes off easily from the silicon tip.
Never use your best sable brush to apply masking fluid. Latex, once dry, is almost impossible to remove from the hair and your brush will be ruined. For the same reason, you should always make sure that the masking fluid is completely dry before you start painting over it. If you put masking fluid by accident on a good brush, remove it immediately with warm soapy water.
You should only apply masking fluid on dry paper and once you’ve applied the masking fluid, wait for it to dry. You can speed-up the drying process with a hairdryer. Masking fluid will change colour when dry. The grey one I am using at the moment takes a darker shade of grey when dry. In order to be sure it is really dry, I touch the thicker marks of masking fluid with the tip of my finger. It should not be tacky.
Another usual recommendation is to remove masking fluid as soon as possible. It may be hard to remove if you leave it for too long on your paper… in practice, it will depend on what brand you use for both your paper and masking fluid. Leaving the masking fluid on the paper for a few days should be fine, but try this first on a paper sample.
Ensure your painting is completely dry before you try to remove masking fluid or your paper will be ripped. To remove the masking fluid, rub gently the surface of the paper with your fingers or a rubber. If you use your fingers, wash your hands just before so that you won’t leave grease on the surface of the paper. Another effective way to remove masking fluid is to form a little ball of it when you clear a large area and then use this ball of latex as an improvised eraser.
In case you made a mistake, just wait for the masking fluid to dry, rub it gently and start again.
Regarding masking fluid storage: Keep the bottle upright and tightly capped. Put the bottle in a re-sealable plastic bag before you store it in your watercolour bag. Spillage may happen and dry latex won’t come off fabric for instance.
La Peniche - Watercolour by Benoit Philippe - I used masking fluid to reserve the light areas on the boat as well as the sunny areas on the path and in the bushes.
With masking fluid, you are only limited by your own imagination and you will soon find ways to use masking fluid to your advantage. This is a “must have” tool in the watercolourist’s tool box. Here are some examples of uses to get you started:
- Grass blades and flowers in a field
- Door frames and window frames
- Fence posts in a distant field
- Highlights in the eyes and hair for a portrait
- Sand on the beach or granulated texture of concrete (by splattering masking fluid with a toothbrush)