Masking fluid is a water-soluble liquid used to preserve white areas in your paintings… areas of paper you wish to leave white… or subsequently paint over, for example, with bright, lightly pigmented highlights of thallo green, bright yellow, orange or opera. Whatever masking fluid you use, make sure it’s not plain white, but that it has a tint to it so you can distinguish it from the adjacent white paper you don’t cover with masking fluid.
I use masking fluid liberally because it allows me to return to areas I’ve already painted and expose the white paper for further work. You have to do this. You can’t just leave masking fluid on the paper, even though you’ve painted over it, because the masking fluid will eventually come off. It’s not a permanent fix.
I nearly always apply masking fluid somewhere on a painting, but only after I’ve completed the drawing of the composition… and certainly before I begin to start painting with watercolors. For me, it’s a separate step in the watercolor painting process. It’s the first bit of so-called “painting” I do, since I actually use a brush to apply the masking fluid. Thus, when you lay down masking fluid, the way you manipulate your brush (size, shape, hairs) influences what happens with the masking fluid as it lands on the paper. These effects actually become an integral component of your painting, once the masking fluid is removed. The edges of areas where you apply the masking fluid are particularly affected by the type of brush you use and the amount of masking fluid on it.
Masking fluid dries rather fast, particularly when you’re painting outside in the sun and if you don’t apply it in big globs. It dries not only on your paper but also on your brush. So you have to work rapidly so the fluid wont dry on your brush before it gets on the painting! If you need to lay down more masking fluid, you’ll need another brush, because the one you’ve already used will have dried up. You’ll also have to clean it if you ever want to use it again.
If you end up with some areas that have a bit too much masking fluid, you can use a paper towel to remove it. I will also touch these areas subsequently with my fingers to make sure the wet masking fluid won’t get on my good brush during the follow-up painting effort. If you paint indoors, it’s best to have a hair-dryer on hand to speed up this drying process… and, for that matter, the entire watercolor painting process!
I use turpenoid or isopropyl alcohol to remove masking fluid from my brushes. Don’t use the normal turpentine you’d get at a hardware store. Soak your brush(es) in it overnight. The next day, take a paper towel and squeeze as much of the gooey stuff as you can from the brush, then work the brush hairs around on a bar of soap. Next, rinse the brush with hot water and repeat this process several times ’til the brush is good and clean. It also helps at the end to rub a bit of the soap back into the brush with your fingers, since this will make it easier to clean your brush the next time around.
Working with masking fluid is virtual painting. I apply the masking fluid with a brush, that is not one of my best ones, since the masking fluid may sometimes be difficult to remove from the hairs, once it has dried. I lay it down with broad sweeps to define the lightest parts of a cloud. Or I may do much the same thing with a smaller rigger brush to simulate blades of grass or sun striking the branch of a tree. And I may also sprinkle masking fluid over an area to create a series of little round white dots that simulate flowers, leaves or rocks.
I do these things to introduce bright areas or highlights which contrast sharply with darker painted areas around them, once the masking fluid has been removed. The degree of contrast and brightness will depend, of course, on how dark the areas around the masking fluid actually turn out to be.
The application of masking fluid can be viewed as “reverse” painting, since the process is opposite to how you do conventional watercolor painting. Whereas when painting, you lay down darker values over paper that’s light… or paint over lighter values of areas that have been previously painted, the application of masking fluid allows you to reveal the original paper or preserve lighter areas of your painting that would otherwise have been darker.
Once the masking fluid has dried, it’s easier to see where you’ve applied the tinted masking fluid, since these areas are shiny. You can paint over them with your watercolors, but after you’ve removed the dried masking fluid, any such over-painting disappears along with the masking fluid. Though I myself rarely do this (because I apply masking fluid before I do any watercolor painting), successive layers of masking fluid can be applied. Since I’m a transparent watercolor artist, I tend to do limited amounts of over-painting. But in a real sense, the use of subsequent layers of masking fluid supports the true objective of transparent watercolors… by namely removing and thus minimizing over-painting.
As already indicated, the placement of masking fluid is something you have to plan for, since you’ll be removing it and exposing the paper beneath. If you don’t want to expose the paper in a particular area, you shouldn’t place masking fluid there. Though I lay down masking fluid on the paper before I do the actual watercolor painting, as indicated, you can also lay down masking fluid on areas you’ve already painted. But if you were to do this, it makes sense to only lay it down over lighter value areas, so areas surrounding them will subsequently appear darker. If you don’t lay the masking fluid over lighter value areas, it’s a wasted effort. There will be no value contrast.
Over-painting with masking fluid allows you to preserve whatever you’ve painted over… plain paper or previously painted areas. It’s the removal of the masking fluid that provides the subsequent contrast in values, once the lighter value of the bare paper or the lighter-value painted areas beneath are exposed. Over-painting with masking fluid provides more contrast once the darker value over-painting with watercolors has been accomplished and the masking fluid removed.
But after all is said and done, too much over-painting of any type (watercolors and/or masking fluid) tends to muddy up things and take away the freshness you’ll always wish to achieve with a transparent watercolor painting.
Since masking fluid is water-soluble at the time you apply it to the paper and before it dries, realize you can drop watercolor media into it or wipe watercolor media around it, letting either one or the other bleed into one another. I suggest you experiment with this a bit. Interesting effects can take place as these two media flow into one another. But you won’t realize the final results until both have dried and you’ve rubbed off the masking fluid. Allow plenty of time for things to dry or you’ll have a real mess!
I apply thin, long sweeping lines of masking fluid over the paper with a rigger brush that appears as if the painted paper has been scratched… which, of course, is another way to draw white paper through a painted area… scratching it after the paint has dried with the point of a razor blade or knife. (Don’t scratch paper before it dries ’cause you’ll only create a mess.) The amount of masking fluid in your brush and the manner in which you apply it can create the same kinds of effects as you’re able to do with conventional watercolor painting. Using a very modest amount of masking fluid allows for partial or rough coverage rather than the neat little round area that would result from a drop of masking fluid. Similarly, texture and true brushstrokes can be replicated by the manner in which you apply the masking fluid.
If you want anything you’ve created with the masking fluid to read, you must provide the necessary contrast by laying down darker values of adjacent paint. Otherwise the application of the masking fluid is a wasted effort because it’s white-on-white!
To highlight something that appears brightly lit… like the peak of a roof which you wish to contrast with the darker sky beyond… consider laying down a thin line of masking fluid with your rigger brush. Similarly, in much the same manner you can simulate a tree branch or the rigging of a boat.
Something you should avoid is covering large areas of watercolor paper with masking fluid. If you do this and subsequently over-paint, the removal of the masking fluid takes all the over-painting with it, exposing paper, and thus wasting time because you’ll probably have to paint over the same area again. So it’s best to restrain yourself from laying down any more masking fluid than necessary. Be stingy with the stuff!