12 Tips for Using Masking Fluid in Watercolor Painting

Masking fluid, also known as liquid frisket, is a very handy tool for fine art watercolorists to preserve white areas that would be too tiny or complex to paint around.

What is masking fluid, exactly? It’s made of a suspension of latex in water and is usually lightly tinted to make it easier to see on the paper, either a light yellow or gray. Ammonia is added as a preservative.

Glass Container with masking fluid, beside paint brushMasking fluid, I did pour a small quantity in a container so the fluid in the bottle wouldn’t dry. 

Here are some tips for using masking fluid:

1. Before using masking fluid you need to have your painting all planned so you know exactly where the highlights or areas you will want to preserve are.

Tiny areas in this painting are preserved with masking fluid.Tiny areas in this painting are preserved with masking fluid.

2. Never shake the bottle, as it will cause the product to lump and you might get tiny air bubbles in the fluid. You can stir it gently.

Rubbing a brush on a bar of soap to clean Rubbing a brush on a bar of soap before painting with masking fluid.

3. Use an old brush or a cheap plastic brush to apply masking fluid, as it would ruin a nice expensive one. The brush will be easier to wash if you rub it before on a bar of soap with a bit of water. Silicone brushes (Colour Shapers) are also very convenient for smaller areas, as you only need to wait for the masking fluid to dry and then peel it off the brush. You can also splatter masking fluid with a toothbrush or draw lines with a toothpick or a squeeze bottle with a fine tip.

applying masking fluid to watercolor paper with a silicone color shaper
Applying masking fluid with a silicone brush (Colour Shaper)

4. It is possible to add a bit of water to masking fluid to make it easier to apply, but adding too much water will make it loose its resisting properties and adhere too strongly to the paper.

5. If using a brush, clean it as soon as possible. Masking fluid dries quickly and becomes more difficult to remove.

6. It is possible to apply masking fluid on an area that has been previously painted, just know that when removed, the latex will probably pick up some of the color underneath and make that area lighter.

7. Change you water before starting to paint as the latex will make the colors appear dull.

removing masking fluid by pulling gently with fingersRemoving masking fluid by pulling gently with your fingers

8. Wait for the masking fluid to be thoroughly dry before starting to paint, otherwise it might mix with your paint. Unfortunately, you can’t save time by using a hair dryer, as the heat will make the latex adhere to the paper and it will be very difficult to take off. Exposure to full sun or high temperatures will have the same effect.

9. If left for too long on a painting, masking fluid might become almost impossible to remove. The time you can safely keep the masking fluid on the paper depends on a number of factors, including the brand, external temperature, expiration date, etc.

10. When the painting is completely dry, you can either use a soft eraser, a rubber pick up tool, or just peel it off the fluid by pulling it gently. You can pass your hand slowly on the paper to detect any small area of masking fluid you did forget to take off.

"Out of the blue" watercolor painting by Sandrine Pelissier

“Out of the Blue” by Sandrine Pelissier. The tiny white areas were preserved with masking fluid.

11. Masking fluid works very well to preserve white areas on your paper, but these areas tend to have a very hard (sharp) edge that could lend to an unnatural look on your painting, almost like a decoupage look.  A good way to prevent this is to soften the edges with a stiff brush and water.

12. You don’t need to preserve all white areas with masking fluid — sometimes it’s easier to just paint around it if the shape is quite simple.

Do you have a tip for using masking fluid that you would like to share?