Don’t Use Water to Thin Your Acrylics

Don’t Use Water to Thin Your Acrylics: A Review of Acrylic Mediums

By Rick Jones

If you’re using water to thin your acrylics while creating that masterpiece, it could flake off your canvas before it reaches thousands of dollars in value. In fact, if you happen to be in your 30’s, it could begin to flake off before you reach 50! If you’re wondering why you shouldn’t use water to thin a water-based paint, let’s take a look at why.

Not enough artists—and especially up and coming artists—realize that adding too much water to acrylic paints breaks down the binder (some refer to it as the vehicle) that holds the pigment together. In acrylic paint, that binder is polymer. Polymer is essentially a liquid plastic compound that is comprised of millions of small molecules that are arranged in repeating patterns. These repeating patterns of smaller molecules form larger molecules. It’s this structure that acts to bind the pigment into paint form. When water is used to thin acrylic paint, these molecules get widely dispersed suspending the pigment molecules in water and detaching them from the polymer molecules. Losing this attachment to the polymer molecules, the pigment becomes what is known as “unbound” since the water holds virtually no ability to bind the pigment molecules. Think of the polymer molecules as forming a sort of glue that holds the pigment onto the surface. When this glue, known as polymer, gets thinned by water, it loses its strength to bond. When the paint pigment is left unbound, over time it will release from the surface on which it was applied (usually canvas) and begin to flake off. How well the surface was prepared can also play a role in how well paint binds to it, but even the best prepared surface cannot overcome the damage too much water mixed with the acrylics causes to its adhesion properties.

Thinning your acrylic paint with any of several polymer mediums allows the pigment to bond with the surface as the medium dries forming a very solid structure to hold the pigment. If you prefer more of a wash effect, similar to watercolor, say, to tone down your white canvas, then airbrush medium works very well. It can have the consistency of skim milk and works like water as a thinning agent, but enhancing rather than decreasing the binding of the paint to the surface. Other polymer mediums can perform any number of tasks to change the application and body of your acrylics producing very interesting effects. For example, you can extend the drying time of your paint to be able to work it from hours to days; you can extend the colors; increase the flexibility of the dried paint skin; increase the translucency or even shape the surface or crackle it when it dries. Your paint can also become better for glazing techniques by using the appropriate polymer medium, which can add a matte, satin, or gloss finish depending on which medium you choose. Another important attribute over water is that the UV resistance of your paint can also be enhanced by mixing with polymers.

So, give the multitude of polymer mediums on the market a try to improve the workability, flexibility, and longevity of your acrylics. Use less water. And have fun exploring the creative potential of the many gels, pastes, and other polymer mediums that you can find at better quality art supply stores—a place where you can find a live person to answer your questions and help you solve technical challenges with your art supplies.