Preserving lighter shapes in your watercolor painting is tricky. Sometimes you can simply paint, with care, around them. As an alternative, however, you can preserve the light areas or develop special effects by taking advantage of one of several masking or resist materials available. These include candle wax or wax crayons, dripped wax, rubber cement, packing or masking tape or Scotch Magic tape #810, masking Frisket film, and liquid latex fluids. The two types of masking materials that watercolorists use most often are liquid latex masking fluid and tape. Apply the masking, paint around it, then when the paint is dry, remove the masking (wax resists cannot be totally removed) to reveal the lighter shapes. Rubber cement pickup erasers are easy to find and use to remove masking, or you can rub with your finger if the mask-covered area is not overly large.

Not every light area should be masked, as masking can inhibit spontaneity or alter your painting process. Consider your purpose in masking. Masking can allow you to save delicate white areas in a picture and protect intricate lighter areas temporarily from nearby dark paint. I have also used masking fluid to make sense of very complex areas in a painting. For example, in this White Primroses painting, I masked many but not all the flower petals in order to distinguish and simplify the painting of leaves and negative spaces.

Masking can also create interesting special effects. Splattering masking fluid before painting can create the impression of snow falling. Use an old toothbrush dipped in mask by gently dragging your thumb over the bristles to get spots of mask. Splatter from a variety of directions to suggest snow swirling. Or try dropping masking fluid into wet paint and allowing it to dry before removing mask. This technique is said to create the effects of moss or lichen on a wall. You can also create textures to suggest tree bark or rocks. Apply masking fluid, let it dry, then gently rub the mask with your finger to partially remove some of the mask, leaving uneven blotches. Paint the area, and when it is dry, remove the rest of the mask. 

It’s possible also to paint color first, let the paint dry, then mask to protect the first color, and later add more paint. Or you could mask multiple times, between several applications of color. Multiple masking, however, requires good quality paper! Transparent or semi-transparent colors, which layer well, work best for multiple masking layers. 

MASKING WITH LIQUID MASKING FLUID.

Masking fluid is an emulsion of natural latex, water, and ammonia (used as preservative). Many brands of masking fluid are available, although quality varies. I find Pebeo, Grumbacher, and Winsor Newton to be the highest quality, but you can also search for other brands that suit your needs. My favorite is Pebeo Drawing Gum, which covers smoothly and is easy to see because of its gray-blue color. I find Grumbacher’s bright orange to be very distracting, and Winsor Newton’s clear and lightly tinted options difficult to see on white watercolor paper.

TIPS:

1. Make sure to test your choice of masking fluid on your watercolor paper before using it on your painting. Some masking fluids can damage softer, poorer quality, or student-grade types of watercolor paper when they are removed. 
2. DON’T shake masking fluid; it’s better to stir it gently. Shaking adds air bubbles, and too much agitation can cause the fluid to clump or start to solidify.
3. Let masking fluid on the paper air dry naturally. Adding any heat, from the sun, a heater, or a hair dryer, makes it extremely difficult to remove without damaging the watercolor paper. Similarly, I don’t apply masking fluid to wet or damp paper because it seems to be absorbed into the paper and become permanently attached. I have read that you can wet the paper and float in the masking fluid to create a soft-edged shape; however, that technique doesn’t work well for me.
4. Don’t leave masking fluid on the paper too long. It becomes more difficult to remove as time goes by. The time limit for removing the masking fluid may vary by brand, yet I would try never to leave mask on the paper longer than a week or two. I have seen masking fluid carelessly left so long that it becomes permanently bonded to the paper.
5. Let the masking fluid completely dry before painting over it. Keep the cap closed tightly when the container is not in use, as masking fluid dries when in contact with air, and the contents of the masking fluid bottle can deteriorate quickly.
6. Remove your masking fluid only when you have finished painting around it AND the paint is completely dry. 
7. While hard edges result when masking fluid is removed, the edges can easily be softened by wetting and tickling the edge with a somewhat stiff brush after removing masking fluid.
8. Apply masking fluid with careful attention to detail. If you are sloppy or careless, your preserved light areas will also appear messy and unattractive when the masking fluid is removed. Practice your application technique on scrap paper until you are able to apply masking fluid carefully and neatly.

There are many tools available to use in applying masking fluid. Use one or many, depending on the effects you want to create. Possible tools include inexpensive synthetic cellulose brushes, sponges, sticks and toothpicks, a dip pen, a palette knife, found objects like pencil erasers, leaves, the handle of a paint brush, or bottle caps, a cheap synthetic brush, a toothbrush to create spatter, and my favorite, a ruling pen. (Be extremely careful to protect any brush you use by first applying soap to the brush and wiping any excess soap off prior to dipping the brush in masking fluid. Immediately after applying the mask, rinse and soap your brush again, then rinse, to remove masking fluid before it dries and adheres to the brush. Also, keep masking fluid away from clothing!)

MASKING WITH TAPE.

Tape can be used to mask larger or straight areas (e.g. parts of a building or the horizon line) in a picture. Masking film (which is available in sheets) can be used to cover and cut to fit larger areas of a picture, as well. Brown packing tape (lightweight economy grade) or Scotch Magic tape (#810 only) work better than masking tape on ‘Rough’ watercolor paper. Masking tape can be too thick to bend and adhere well to the numerous depressions in rough paper, allowing watercolor paint the chance to sneak under the edge. Experiment with different brands of tape and paper. Again, test the tape on the watercolor paper you intend to use to make sure tape removal does not cause damage. Good quality paper, such as Arches or Saunders Waterford, is preferable to poorer quality or student-grade papers. 

To mask objects with tape, cover the shape with tape (overlapping edges if more than one strip is needed), then use a very sharp  X-acto or craft knife with slight pressure to carefully cut around the saved shape, and remove excess tape. Don’t use too much pressure when cutting the shape with the knife as you can apply so much pressure that you cut into your paper. Experiment first on a test sheet. After cutting the tape, press the tape down firmly. Paint.

Tape can also be precut prior before application to your paper. For example, to mask a window frame or a picket fence, you could attach a strip of packing tape to a self-healing cutting mat, cut narrow strips in the tape with your X-acto knife and a ruler, and then apply the strips to mask out a window or fence on your watercolor paper.

Personally, unless the area to be masked is large or straight, I prefer applying masking fluid with a quality, vintage German ruling pen (purchased on Ebay), as I have better control. I seem to struggle with tape, finding it difficult to apply, cut accurately, and also to remove. You should try it, however, as it has some advantages.

MASKING WITH BOTH FLUID AND TAPE.

If desired, masking fluid and tape can be combined to make it easier to mask larger areas, or a combination of a hard-edged area with nearby uneven areas. Both masking fluid and tape might be helpful if you wish to protect: 1.) blotchy, partially snow-covered ground (masking fluid) and a large, hard-edged snow-covered roof (tape), or 2.) a grove of tree trunks (tape) and a few leaves (masking fluid) that will be painted in contrasting colors or values, or 3.) lots of sky reflections on a lake (tape for straighter reflections and masking fluid for more erratic ripples).                                                   

First, apply overlapping pieces of tape over the chosen masking area. Press down lightly and carefully cut tape with an X-acto knife. Remove unwanted tape pieces, then press the remaining tape down firmly on the paper. Add masking fluid and let dry. Proceed with painting.

AVOID OVER-DEPENDENCE.

Try not to become overly dependent on masking materials. Instead, practice and improve your brush handling skills so you don’t need to use masks as often. Think about whether you can easily paint around an area and whether you need masking at all. Not every painting benefits from the use of masking. Sometimes painting is more spontaneous and quicker without masking. Choose the times when applying masking fluid or another type of mask material makes sense for you.

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