Have you ever worked with acrylic paints and wondered how they are manufactured?
Acrylic paints consist of two parts:
Because pigment is a dry powder that does not adhere to canvas all on its own, it must be stuck to the canvas with a binder. The binder also prevents the powdery pigment from clumping together.
The binder used to make acrylic paints is an acrylic polymer emulsion. Acrylic resins are a type of plastic. An emulsion occurs when droplets of one liquid are evenly dispersed and suspended (rather than dissolved) in another liquid. In this case, the emulsion is formed by tiny acrylic resin spheres suspended in water.
Acrylic paints can be considered a latex product, because latex is defined as an emulsion of polymer microparticles in water as opposed to solvent. Note, however, that the term “latex paint” is typically used to refer to house paint, which is a lower quality of paint. Unlike artist’s paints that retain their flexibility after they dry, house paints grow brittle with age and are thus not typically used to create long-lasting works of art.
The acrylic resin is largely responsible for the overall quality of the paint, while the pigment is responsible for the quality of the color. The quality of the binder will determine how the paint handles, how long it will take to dry, and how well it will resist cracking and UV-related deterioration as it ages.
Acrylic binder appears more or less white when wet. However, it becomes clear as it dries, and this is why acrylic paints often appear to darken as they dry. High-quality paints will use binders that are more clear in appearance, minimizing the darkening effect.
Once the acrylic resin emulsion is prepared, pigments are added. Pigments come in three flavors:
- Synthetic. Most acrylic paints are made with inexpensive synthetic pigments.
- Inorganic, which are mineral-based. An example is raw sienna, which is made from iron oxide.
- Organic, which are derived from plant and animal materials. These have largely been replaced by synthetic pigments, although some pigments synthesized from coal tar and petrochemicals are considered “organic.”
Before being mixed with the binder, pigments must be milled to break up any clumps. Clumps cannot be evenly wet and emulsified. Once the pigment has been milled, it is then stirred into the binder.
The quality of the pigment determines not only how the color immediately appears to the eye, but also how well it will resist fading over the years. The pigment is the determining factor in the cost of the paint, as the binder is quite inexpensive to produce. Artist-quality paints use high-quality pigments, while student-quality paints economize. Any given brand may further distinguish between grades of artist- or student-quality paints by numbering them (Series 1, Series 2, etc., or sometimes Series A, Series B, etc.) with higher numbers indicating higher quality.
While color names vary by brand, oftentimes the name of a color conveys information about the manufacturing process. For instance, the word hue after the name of the color, as in “cadmium red medium hue,” means that something similar in color to cadmium red was mixed with the cadmium red to keep the cost down. Hues are typically found in student-grade paint lines.
Why These Ingredients Matter
The combination of binder and pigment is what gives acrylic paints their unique properties. First off, acrylic paints dry by evaporation. As the water evaporates from the emulsion, the acrylic resin spheres draw closer together in a honeycomb pattern. Pigment is trapped in the open spaces between the acrylic resin spheres. The result is a flexible layer of paint, because the acrylic honeycomb can expand and contract with the canvas and thus prevent cracking and canvas tearing over time.