Every paint is the same two things: pigment, and something to stick it down with. The pigment is often identical across mediums — the same cadmium red can appear in oil, acrylic and watercolor. What changes is the binder, and the binder decides everything about how the paint handles, what it sticks to, how you clean it, and how long you have to work.
Acrylic
Binder: acrylic polymer emulsion. Thin and clean with: water.
Dries by evaporation, which is why it is fast — touch-dry in minutes, fully cured over weeks. Once dry it is a flexible plastic film and it does not re-wet, so layers stay put and you can paint over anything.
Opaque enough to correct mistakes, adheres to nearly any primed surface, needs no ventilation. It dries slightly darker than it looks wet, which takes some getting used to. Its one real weakness is blending: the working window is minutes, not days.
Oil
Binder: a drying oil, usually linseed, sometimes walnut, safflower or poppy. Thin and clean with: solvent, or purpose-made low-odor alternatives.
Dries by oxidation rather than evaporation, which is a chemical reaction with air and takes days at the surface and months underneath. That slowness is the point. Oil is unmatched for soft transitions and subtle color, and the color you mix is the color you get, with no shift on drying.
The costs are practical. Solvents need ventilation. Rags soaked in oil and solvent generate heat as they dry and are a genuine fire risk, so they need spreading out flat or storing in water rather than balled in a bin. And there is the fat over lean rule: each successive layer needs more oil in it than the one below, or the upper layers dry faster, become brittle, and crack.
Water-mixable oils are real oil paint modified so it thins and cleans with water. They handle very close to traditional oil and remove the solvent problem, which makes them the sensible choice for anyone painting in a room they also live in.
Watercolor
Binder: gum arabic. Thin and clean with: water.
Transparent by design. The white in a watercolor is the paper showing through, not paint, which is why the medium has to be planned in advance — you cannot put light back once it is gone. It re-wets indefinitely, so a dried pan is simply used again years later.
It needs paper made for it. Anything lighter than about 300gsm buckles once it is properly wet.
Gouache
Binder: gum arabic, with added white pigment or chalk to make it opaque.
Essentially opaque watercolor. It gives flat, matte, even color, which is why it was the standard for illustration and design work for most of the twentieth century. Like watercolor it re-wets, so an underlying layer will lift if you overwork it. It also shifts as it dries — darks dry lighter, lights dry darker.
Acrylic gouache is a different thing: acrylic binder, matte finish, and it does not re-wet once dry. It behaves like acrylic and looks like gouache.
Egg tempera
Binder: egg yolk.
The dominant panel painting medium in Europe before oil took over in the fifteenth century. It dries almost instantly, cannot be blended, and builds tone through fine hatched strokes laid one over another. It is durable to an extraordinary degree — surviving panels are six hundred years old and still bright. Almost nobody uses it now, and it is worth knowing about because it explains why early paintings look the way they do.
Encaustic
Binder: hot beeswax, usually with a resin added.
Applied molten and fused with heat. It gives a thick, translucent, physically layered surface unlike anything else, and it is even more durable than tempera — the Fayum mummy portraits are encaustic and are around two thousand years old. It requires heated tools and constant ventilation, which keeps it a specialist medium.
Casein and alkyd, briefly
Casein uses milk protein as a binder and gives a matte, slightly chalky surface. Alkyd is a modified oil resin that behaves like oil paint but dries in a day rather than a week, which makes it useful for underpainting.
Three rules that cross all of them
- Acrylic will not hold on oil. Oil over fully dry acrylic is fine and common. Acrylic over oil will eventually lift, because the oily surface gives it nothing to grip.
- Prime the surface. Raw canvas and paper absorb the binder and leave the pigment dull and unbound. That is what gesso prevents, and it is also what protects the fibers from the oil in oil paint.
- Check lightfastness, not price. Reputable ranges publish a rating, commonly ASTM I for excellent and II for very good. A cheap paint with a good rating outlasts an expensive one with a poor one, and there is no way to tell by looking.
Which to choose
For a first medium, acrylic. It is forgiving, cheap, and works on a kitchen table. For soft blending and portraits, oil or water-mixable oil. For working in a sketchbook or away from home, watercolor or gouache.
And if what appeals is the painting rather than the deciding, our numbered canvases use ordinary acrylics on pre-primed cotton, with the drawing and the color choices already made. The beginner guide covers how one goes, and understanding how colors relate on the color wheel makes any of the above easier to mix in.
