Acrylic Painting Mediums for Thickening Paint

A variety of gel mediums
Photo by Lisa Marder

There are many mediums available to mix with acrylic paints, adding to their versatility. There are mediums for thinning and glazing, as well as those for thickening and building body and texture into your paintings. The latter are "gel mediums," "texture gels," and "molding (or modeling) pastes." These mediums can all be added to the paint without affecting its longevity, durability, or drying time since they are all made with the same acrylic polymer that is the binder for the paints themselves. The various mediums influence the body, gloss, and texture of the paint.

Gel Medium 

Gel Medium is a white creamy medium (not pourable, for the most part) that comes in different viscosities and different finishes - gloss, matte, and semi-gloss - giving painters a wide range of ways to add body and texture to paintings, from impasto techniques to textured glazes. They are equivalent to a colorless paint since they are made of an acrylic polymer without the pigment. They come in various degrees of viscosity and transparency. They are translucent when wet and transparent when dry, becoming more translucent with more layers. 

Gel mediums are very useful as a paint extender, maintaining or increasing the thickness of the paint without losing the intensity of the color. Since the paint and binder are the same composition you can mix any amount of medium with the paint that you want and the paint will continue to hold together without beading. It is similar to making your own student-grade paint, which has a higher binder to pigment ratio. Mixing a gel medium with paint allows you to save money by using less quantity of an expensive pigment in an underpainting or when building texture.

To use, mix the paint and medium thoroughly together and apply with a palette knife or brush. You can quickly cover a large area by spreading the mixture on with a palette knife as though you were frosting a cake, or you can paint on with a large brush if you want the effect of visible brush strokes.

Gel medium can be used as a ground, building up the texture and letting it dry before paint is applied. It can even be added to acrylic gesso to extend the gesso and build up the ground before painting on it.

You can also make your own paint by adding powdered pigments to gel medium in whatever concentration and mixture you choose.

Gel mediums can also be used for collage and mixed-media work as they also have adhesive properties.

Texture Gel 

Although you can add your own textural elements, such as sand or sawdust, to any acrylic medium, some manufactured gel mediums come with textural elements as part of their composition. These products have been tested so you can be assured that they will be durable and long-lasting. Some of the ingredients that have been added to textured gels include sand, pumice, glass beads, and fibers. Liquitex makes a variety of texture gels, including Black Lava, Ceramic Stucco, and Natural Sand Fine, among others. Golden also has an extensive array of texture gels. 

Molding Paste (Also Called Modeling Paste)

Molding pastes are extra thick opaque pastes made with actual marble dust and acrylic polymer emulsion. They are very viscous and hard to manipulate without a good palette or putty knife. Molding pastes are meant to be used sculpturally, for creating heavy textures and three-dimensional surfaces. 

Unlike gel mediums, which dry clear, molding paste dries to a hard opaque white finish. Molding paste can be sculpted, sanded, carved, chiseled, and painted on when dry. You can also mix paint with it when wet, although because it is white rather than clear it will tint the color with which it is mixed.

Molding paste is also good for mixed media collage and for embedding objects into the surface. 

Also watch this acrylic heavy gel medium texture demonstration by Millie Gift Smith to see how she uses gel medium for embedding natural objects, creating texture, and for painting on to create a beautiful finished work.