How to Thin Miniature Paint

Why this is the most important technique on the site

Paint out of the pot is formulated to survive shipping and shelf life, not to go onto a 28 mm model. It is thicker than you want it. Applied unthinned it does three things, all bad: it fills the fine detail the sculptor put there, it dries with visible ridges where brush strokes overlap, and it goes on in one opaque slab so you cannot build color gradually.

Almost every “why does my painting look worse than the tutorial” question has this at the bottom of it. Not brush quality, not paint brand, not talent. Consistency.

What consistency to aim for

The usual description is “like milk”, and it is a good one because it is a thing you have seen. More precisely, for the three main jobs:

• Basecoating: like milk. Flows off the brush in a smooth line, still opaque enough to cover in two coats.
• Layering and highlighting: slightly thinner, like skimmed milk. Semi-transparent, so the color underneath influences it.
• Glazing: much thinner, like tinted water. Almost invisible per coat; you build the effect over many passes.

The test is on the palette, not on the model. Drag the loaded brush across the palette surface. A smooth continuous line that still shows color is right. A line that beads up or breaks into dots is too thin. A line with a visible ridge along it is too thick.

What to thin with

Water, usually. For most brush work, plain water is fine and free. Use clean water, and for glazing use distilled or filtered water — hard tap water leaves mineral deposits that show up in very thin layers.

Flow improver, when paint misbehaves. If paint beads up, retreats from a raised edge, or refuses to sit where you put it, the problem is surface tension and water will make it worse. A few drops of flow improver in your water cup breaks that tension. This is the single most useful additive to own and it costs very little.

Acrylic medium, when adhesion suffers. Water thins pigment and binder equally, so heavily watered paint has proportionally less glue in it and can wipe off. For anything thinner than a layer coat, replacing some of the water with a thin acrylic medium keeps the binder concentration up.

Proper airbrush thinner, for an airbrush. Not optional there — see thinning for an airbrush, which is a different problem with a different answer.

Never thin in the pot

It is worth stating on its own because it is irreversible. Water added to the pot cannot be removed, it thins the whole pot to one consistency when you need several, and over time it promotes mold in the bottle.

Thin on a palette. Preferably a wet palette, because thinned paint on a dry palette dries in about ninety seconds — which is the other reason beginners end up painting with unthinned paint. They thin it, it dries, they add more from the pot.

“Two thin coats”

The most-repeated advice in the hobby, and it is repeated because it is right. Two thin coats:

• Cover better than one thick coat, because each layer fills the gaps the last one left rather than pulling into a thick film that cracks or beads.
• Preserve the detail underneath, because thin films follow the surface instead of bridging it.
• Dry flat, because there is no thick edge to leave a ridge.
• Are recoverable. A thin coat that goes wrong can be painted over. A thick one has to be stripped.

The cost is patience, and it is less than it sounds: a thin coat dries in a minute or two, and on a squad you work round the models in rotation so there is no waiting at all. That batching habit is also the core of painting faster.

Troubleshooting