Making Acrylic Paint — Grinding Pigments into Acrylic Polymer Medium

Acrylic polymer emulsion is a milky-white liquid consisting of microscopic acrylic resin particles (0.05-1 micrometre diameter) suspended in water, stabilised by surfactants. When the water evaporates, the resin particles fuse together (a process called coalescence) to form a continuous, clear, flexible, water-resistant plastic film. The acrylic polymer is typically polymethyl methacrylate (PMMA), polyethyl acrylate, or polybutyl acrylate — the same family of plastics used in Perspex/Plexiglas. Acrylic polymer emulsion cannot be made at home because emulsion polymerisation requires precise temperature control, chemical initiators (ammonium persulfate), and surfactants under controlled conditions. However, artist-grade acrylic medium is widely available and inexpensive, and it is the standard professional approach to making custom acrylic paint.

Wearing a dust mask, place a small mound of dry pigment (1-2 tablespoons) on the glass slab. Add a few drops of distilled water and mix with the palette knife to form a smooth, thick paste. This pre-wetting step is important: dry pigment powder does not disperse well directly into the thick acrylic medium — it clumps and resists mixing. The water breaks the surface tension of the pigment particles, allowing the acrylic medium to coat them more easily in the next step. Only add enough water to eliminate all dry powder — the paste should be thick, like toothpaste. Excess water dilutes the acrylic medium and weakens the final paint film.

Add acrylic polymer medium to the wetted pigment paste — start with approximately equal volumes of medium and pigment paste. Mix roughly with the palette knife, then grind with the glass muller in circular motions. The muller disperses the pigment evenly through the medium, breaking up any remaining clumps. Acrylic medium is thicker than water or gum arabic solution, so grinding requires moderate pressure. Work the mixture for 5-10 minutes until it is smooth, creamy, and uniform in colour with no visible graininess. Add more medium if the mixture is too stiff, or more wetted pigment if it is too thin. The ideal consistency depends on your intended use: thicker paint (less medium) for impasto work, thinner paint (more medium) for glazing.

Apply a brushstroke of the paint to a white surface (primed canvas or heavy paper) and let it dry — acrylic paint dries in 5-20 minutes. The dry paint should be richly coloured and opaque (for opaque pigments like titanium white, cadmium yellow, or yellow ochre) or deeply saturated and transparent (for transparent pigments like ultramarine, phthalo blue, or quinacridone red). If the dry colour appears washed out, the pigment-to-medium ratio is too low — grind more pigment. If the paint is crumbly or chalky when dry, there is too much pigment and not enough medium — add more acrylic medium and grind again. Factory-made "student grade" acrylics often contain fillers (calcium carbonate) and less pigment; your hand-ground version should have significantly higher pigment concentration and richer colour.

Acrylic paint viscosity can be modified by adding specific mediums: more clear acrylic medium thins the paint while maintaining film strength; distilled water thins the paint but weakens the film if more than ~20% water is added (too much water breaks the emulsion and the dried film becomes powdery). For fluid acrylic consistency (ink-like, for pouring or airbrush): use acrylic flow medium or thin with water up to 20% of the paint volume. For heavy body consistency (butter-like, for palette knife work): use less medium and grind with minimal water. You can also add retarder medium (glycol-based) to slow drying time — acrylic normally dries very fast, which makes blending difficult. A few drops of retarder gives you several extra minutes of working time.

Transfer the ground acrylic paint into squeeze bottles or jars with tight-fitting lids using a palette knife. Unlike oil paint, acrylic paint cannot be stored in metal tubes because the water-based emulsion corrodes aluminium over time. Plastic squeeze bottles or glass jars are ideal. Acrylic paint stored in sealed containers keeps for months to years — the key is preventing the water from evaporating, which would cause the paint to dry in the container. If a skin forms on the surface, peel it off and stir — the paint underneath should still be usable. If the paint thickens over time, add a few drops of water and stir to restore consistency. Label each container with the pigment name, date, and pigment-to-medium ratio for your records. Clean all tools with water immediately — dried acrylic is essentially plastic and is extremely difficult to remove once cured.