Chapter 1
ACRYLIC MEDIUM BASICS

From the ubiquitous gloss gel, to polymer mediums that react to UV light, to custom mediums, acrylic mediums offer a world of visual and tactile possibilities to be explored. This book is your primer, your texture lexicon, your Rosetta Stone for decrypting the complexity of acrylic mediums from the ground to the final top coat.

Are acrylic mediums necessary? People who are new to acrylic painting, and even those who have been painting with acrylics for years, have asked me this question countless times. I’m never really sure how to answer, other than to say that for me and my painting process, they are absolutely essential.

It is, however, a fact that mediums will enhance and facilitate many aspects of acrylic use. For many artists, the primary barrier to incorporating mediums into their art practice is not aversion to mediums but rather ignorance of how they work. Acrylic mediums are a study in contrasts, ranging from matte to gloss, thin to thick, transparent to opaque. How they behave with each other and in conjunction with acrylic colors is dictated by their intrinsic properties. Understanding these basic properties will help you use them to their best potential.

Why use mediums? Because they augment and amplify both your paint and your process.

[ILLUSTRATION] Transparent acrylic colors mixed with mediums. From left to right, the colors are dioxazine violet, phthalo blue green shade, green gold, Indian yellow, quinacridone magenta, and transparent pyrrole red. From top to bottom, the colors are undiluted (top) and mixed with the following mediums (dilution: 5% color + 95% medium): water, liquid medium, gel medium, nepheline gel, modeling paste. The black squiggles show relative transparency/opacity.

Although the composition of acrylic mediums is not all that complex (they are simpler to produce than colors), the process of figuring out how to make them behave in a given way can certainly be fraught. That’s because it’s about chemistry. Manipulating raw materials to manufacture paint mediums that are so nuanced and varied is a delicate and exacting science. I find the science fascinating, but I understand that most people don’t really want or need to know about it. Still, it’s valuable to understand, even on a layman’s level, how some of this is accomplished.

[ILLUSTRATION] Creating samples of textures and paint treatments can be a great source of inspiration when starting a new project.

Know your stuff. Be the engineer of your artwork, the architect of your creative output.

I can’t stress enough that knowledge is power, in art-making as in all things. It’s astounding to me that people use materials without having any knowledge about what they are or how they are made. Then they react with confusion and frustration when they get less than favorable results. Most problems they encounter can be explained or solved through logic—logic based on even the most cursory understanding of how those materials are made.

KEY DESCRIPTIVE TERMS
To grasp the nuances of mediums, you must become familiar with their fundamental character, which can be expressed in five key terms: viscosity, rheology, luster, relative coverage, and texture. Each term describes a particular aspect of the material, and having a good grasp of these terms’ meanings will help you make decisions about which mediums to choose and how and when to use them.
Viscosity 
[ILLUSTRATION] Mixing high-viscosity gel medium with color.
[ILLUSTRATION] Turquoise peak.

Viscosity is the measure of a material’s resistance to flow under an applied force. We refer to thick, paste-like heavy body acrylics as high-viscosity paints. A high-viscosity paint or medium is generally thick, but to say simply that it is thick is an oversimplification. A paint can be thick, but then so can a wall or a pile of whipped cream. More precisely, the term viscosity encompasses a material’s movement as well as its density. The wall may be thick, but it is not viscous, as it is incapable of movement. The whipped cream, on the other hand, is thick but has the ability to flow and thus has a high viscosity.

Describing the viscosity of a material gives us an accurate picture of its malleability and how it will behave in a given technique or application. Viscosity is measured in units of poise (P).  The term poise is named after nineteenth-century French physicist Jean Léonard Marie Poiseuille. Although the common English word poise has nothing to do with the scientific term’s origin, it can be helpful to think of a high-viscosity medium as having “poise”—being upright and having a sense of weight. The higher the poise number, the greater the medium’s resistance to flow will be. Polymer (or liquid) mediums are thinner and have a lower poise number than gel mediums. Low-viscosity mediums are suitable for fine detail work, glazing, and creating thin, smooth layers. Higher-viscosity mediums are useful for extending color, glazing, and heavier impasto or textured applications.

[ILLUSTRATION] Here are globs of four different mediums on a flat surface; from left to right: final finish, glazing medium, polymer medium, and self-leveling gel.
[ILLUSTRATION] When the surface is tilted at a 45-degree angle, it becomes evident which of these fluid mediums have lower and which have higher viscosities.

Rheology 
[ILLUSTRATION] Mixing color into a high viscosity, short rheology gel.

Rheology is the study of the deformation and flow of matter under applied stress. When it comes to mediums, rheology describes how a medium will behave when you push it around. How a medium behaves tells us which tools to use, how it will mix with colors or other mediums, and, ultimately, how it will look when it dries.

[ILLUSTRATION] Blue gel paint peaks: high viscosity, short rheology.

A medium’s rheology is described as short or long. Some highly viscous mediums have a short rheology and will hold sharp, full-bodied textures. Others with a similar viscosity have a long rheology; heavy and honey-like, they tend to ooze into thick pools leaving no visible raised texture. So while both are highly viscous, their differences in rheology dictate their physical appearance. When you dab a palette knife into a medium with a short rheology, you pull it up and get a short, stiff peak that should retain its shape as it dries. The same action performed on a medium with a long rheology will give you a long string of material that will ooze back down onto the surface and eventually level out, leaving no discernable surface texture.

[ILLUSTRATION] Using the flat face of a plastic palette knife as the reservoir, drizzle loose strings of tinted self-leveling gel.                      

If it helps, you can think of mediums’ rheologies in less technical terms: mediums with a short rheology are pert and perky, showing off with brash and dramatic textures. Longer-rheology mediums flow and ooze, retreating into themselves; they are selfish, secretive, mysterious, and seductive.

[ILLUSTRATION] Gel mediums exhibit a short rheology.
[ILLUSTRATION] Self-leveling gel exhibits a long rheology.

Luster
[ILLUSTRATION] Masked areas of matte and gloss gel painted over a semigloss surface clearly show the subtle changes between lusters.

The surface of a painting has a significant effect on our response to it. A glossy veneer is more than just reflective—it also deepens color tones and imbues them with depth and light. A more satiny finish (what we call semigloss in the art materials world) has less flash than a glossy surface, offering a silky, luxurious sheen. A flat matte surface, which absorbs light, gives the colors and textures of a painting a softer, subtler, more nuanced appearance.

[ILLUSTRATION] From left to right: matte, semigloss, and gloss gels, lightly tinted with phthalo green yellow shade, show varying levels of transparency.

Manipulating the gloss factor of a surface is one of the primary functions of many acrylic mediums. Most families of mediums are offered in gloss, semigloss and matte formats. By using one or another of these formats—directly mixing the medium with the color or painting the medium over the color as a clear coat or layer—you can change the surface luster.

[ILLUSTRATION] From left to right: gloss, semigloss, and matte polymer medium painted on black paper. The effects are transparent, translucent, and semi-opaque.

Sheen, or reflectivity, affects our perception of depth and distance on the painted surface. A glossy surface will show every detail, divot, and irregularity in a surface, including the direction of a brushstroke or the depth of a palette knife’s gouge. Besides dulling the surface, a matte medium also gives the surface some “tooth”—a slight graininess that helps scatter the light and also allows dry materials such as graphite, charcoal, or other drawing to grip the surface. The more matte a surface is, the more it appears to recede, whereas a glossy surface gives the illusion of moving forward. Using varying lusters can add subtle contrast to a painting.

Acrylics are naturally glossy; it’s what we add to them that modifies the surface from super shiny, to soft satin, to velvety matte. Matting agent, present in semigloss and matte mediums as well as in modeling pastes and other specialty mediums, is one important component affecting the gloss factor of the paint.

Using a medium, you can modify the luster of any color, but it’s helpful to know that color pigments themselves can affect a painted surface’s luster. This is dictated by the size of the pigment particles—how fine or coarse they are. The coarser the pigment particles, the more matte the color will appear. Professional-grades acrylics, because they contain little or no filler, reveal more of the characteristic luster of the pigment. The cheaper the paint, the more uniform the colors will appear, since matting agent and other fillers have been added to the colors.
LIQUID MEDIUMS
Liquid mediums come in many forms and serve a huge variety of purposes. Whitish and opaque when wet, they all dry clear. Beyond basic liquid medium, this category of mediums includes glazing mediums, low-viscosity polymers, UV-reactive polymers, polymers with added UV protection, polymers designed to work in conjunction with digital imaging, and polymers that make paints more flexible, make paint films harder, increase adhesion during laundering, and so on. The list goes on and on, with many acrylic brands adding more liquid mediums as the demand for new materials grows.

Some brands call these polymer mediums or fluid mediums. Others call them gloss or matte mediums, which gives you no clue as to a medium’s format, only its finish. All these different names can be confusing, so I refer to this group simply as liquid mediums. Ranging in viscosity from very thin and watery to a thicker consistency similar to that of shampoo, liquid mediums all flow with ease.

Liquid mediums are available in gloss, semigloss, and matte formats, providing luster control as well as color extension and manipulation. Whether they are added directly to a color or layered on top, these mediums give the painter control over varying degrees of gloss and transparency. They can also be tinted with color in any proportion to create glazes. The more medium that’s added, the more transparent and desaturated the color will be, although the addition of the medium will bring light into the surface and create a feeling of depth. From extending drying time to providing a vehicle for glazing, liquid mediums are probably the most useful mediums to have on hand. Liquid mediums are also ideal vehicles for additives and enhancers that further modify the paint film, giving you more application possibilities. They act as adhesives, clear coats, extenders, and all-around acrylic band-aids.

[ILLUSTRATION] Hester Simpson, Pink Orange Blue Brown, 2017, acrylic on canvas mounted on wood panel, 36 × 36 inches (91.4 × 91.4 cm). Photo by Cathy Carver.

About her work, Hester Simpson says, “The use of acrylic mediums in my paintings over the last eighteen years remains simple. I use fluid acrylic colors mixed with liquid matte mediums and/or gloss medium, thinned with water to a creamy consistency. For larger paintings I add retarder for longer working time. I then run the mixture through cheesecloth into a clean container. Sometimes this mixture is ready to use immediately, but often it must sit for a day or so before air bubbles have settled. Bubbles are one of my greatest enemies, as I want my surface to be perfectly smooth.”

Working with Liquid Mediums: THE STEP-BY-STEP PROCESS

This sequence illustrates stages of Hester Simpson’s process when creating her painting Pink Orange Blue Brown, which incorporates multiple overlapping bands of color.

Step 1
After laying down the multicolored, gridded background, Simpson poured the brown band, consisting of raw umber fluid acrylic mixed with water, retarder, and polymer gloss medium.

Step 2
She then guided the flow of the brown band.

Step 3
Next, she poured the blue band—a mixture of manganese blue hue fluid acrylic, water, retarder, and polymer gloss medium.

Step 4
As before, she carefully guided the flow of the paint on the canvas.

[ILLUSTRATION] This studio shot shows the state of the painting after the fluorescent orange band had been poured.

Choosing Your First Mediums
[ILLUSTRATION] A sample kit of assorted mediums will get you started on your experimental path. These 2 ounce (60 ml) jars give you just a taste of their potential.
[ILLUSTRATION] Phthalo turquoise (liquid acrylic) loosely mixed with matte polymer.
[ILLUSTRATION] Phthalo turquoise and green gold (liquid acrylic) lightly mixed into gloss gel.
[ILLUSTRATION] A tiny drop of dioxazine violet is enough to tint this quantity of nepheline gel (coarse).
[ILLUSTRATION] Even though its palette is minimal, this composition gets some pizzazz from a combination of disparate mediums.
[ILLUSTRATION] It doesn’t take much to suggest dimension and texture. Here, granular mediums, gel medium, and strings of self-leveling gel are swept with a bit of white. A light wash of Payne’s grey bumps up the texture of the granular medium.

For your first foray into the world of acrylic mediums, I suggest starting modestly, just to get the feel of things. It is not always an easy transition to go from straight color to working with the awesome power of acrylic mediums. You might want to begin with an assorted set of mediums in small, “trial size” jars. While you may not necessarily want every medium in the set, you may be surprised to find that a medium you never thought you would use has the potential to become a favorite. If you would rather go with a larger jar or two instead, mediums from any of these four basic categories will give you a good foundation:
 
1. Polymer medium (liquid). From extending drying time to providing a vehicle for glazing, polymer mediums are probably the most useful to have on hand. They act as adhesives, clear coats, extenders, and all-around acrylic band-aids.
2. Gel medium. The consistency of gel mediums ranges from very soft to stiff (with the holding capability of modeling paste). Gels are always fun, but they can take some experimentation to really understand.
3. Self-leveling gel medium. It’s one thing to work with a viscous gel that will hold a texture but quite another to manipulate one that will not. Because self-leveling gels exhibit a consistency unlike that of acrylic colors, they encourage the use of alternative tools like palette knives and spreading tools. They’re great for stretching your experimental muscles.
4. Granular, textured, or another custom medium. You may never use it again, or it may become a staple on your art table. Either way, you should try at least one of the more unusual mediums. As when cooking with an unfamiliar spice, you can’t really know whether you’ll like it without first giving it a taste.

Of course, this list will not suit everyone, but it does provide a broad enough starting point. Most mediums currently on the shelves are variations on these four formats, ranging from gels filled with inert materials that provide texture to polymer mediums infused with UV-reactive components that glow under black light. First, acquaint yourself with the basic elements, then find the specific mediums that have the ideal properties for your process.