Masking Fluid 101
Masking fluid, also called masking liquid or liquid masking film, is a thick liquid that is applied to prevent paint from covering certain areas on a painting - you can keep small spots, fine lines, delicate patterns uncovered, even larger parts if you wish. Masking fluid works well with light, water-soluble paints like watercolors or ink. I have collected my top tips on how to use it - read on, or scroll to the bottom for a video version!
#1 PROTECT YOUR BRUSH
If you skip this step, you can quickly end up doing irreversible damage. Choose a brush that you will be using exclusively for applying masking fluid and nothing else.
Before dipping your brush in the fluid, put a little bit of soap onto the brush. Then you can dip it in the masking fluid, apply the fluid on your painting surface, and when you are done, go and clean your brush immediately. Thanks to the soap, you will be able to wash the fluid off of your brush easily. Don't put this step off - the fluid on your painting needs some time to dry anyway.
#2 HOW MUCH MASKING FLUID DO YOU NEED?
Be careful not to apply too little or too much fluid, especially if it's over a bigger patch. If you do a layer that is too light and thin, at the very least it will be difficult to remove. If you apply the fluid too thickly: it might tear some of the paper off when you remove it. When applying masking fluid, try to create an even but not too heavy layer.
#3 DRYING TIME If you have finished applying the masking fluid, now it's time to wait. Don't be impatient, let the fluid dry completely before you go over it with paint. It may seem like a good idea to try speeding up the drying with a blow dryer. I've tested it so I could deliver some first-hand information. The first thing that happened: as soon as the air from the blow dryer hit the liquid, it overflowed and the shape that I had created was ruined. I also have a suspicion that hot air might bake the masking fluid into the paper, making it stick too strongly, and cause problems when you try to remove it.
It's true that blow drying will help the masking fluid dry somewhat quicker, but I do not think it's worth the risk of damaging your painting. The safest way is just to wait patiently until the liquid solidifies. Be careful and avoid touching it before time, because, depending on how far along it is in the drying process, it will either smear or stick to your finger and peel off the paper completely. For the sake of the test, I checked the patch that I left to dry on its own every five minutes.
After 22 minutes, it was solid enough to be removed without a problem. Of course it will depend on the size of the area that you cover with masking fluid, but I think it's safe to say that you should calculate with a drying time of roughly 20 to 30 minutes.
When the masking fluid has dried, it's finally time for the paint! Then comes some more waiting until your paint dries. At this stage, you can use a blow dryer if you want to save some time, but I do recommend setting it at a low temperature. Make sure that the paint has completely dried, before you proceed to
#4 REMOVING THE MASKING FLUID
This is the fun part. Removing the dry mask is easy. You can simply use your fingers or fingernails, just make sure that they are clean!
Keep in mind that you might rub some of the pigments from the paint onto the parts that you wanted to keep unpainted, so be careful.
#5 FINISHING TOUCHES It's possible that you will not achieve the perfect outlines with using masking fluid alone. If that's the case, just grab a brush and perfect the edges where it's necessary.
BONUS
Here is the tutorial in video format if you prefer that:
