Thinning miniature paint properly means adding enough water or medium that the paint flows off the brush without dragging, while still holding enough pigment to build coverage in two or three thin coats rather than one thick one. For most Citadel Base and Vallejo Model Color acrylics straight from the pot, that lands around a one to one ratio with water, adjusted by feel until the paint moves like milk rather than cream.
Why thinning matters more than the paint itself
Acrylic miniature paint out of the bottle is formulated to be thinned. It is deliberately thick so it does not dry out in the pot, which means painting it straight from the bottle almost always produces a chalky, texture-hiding coat that pools in recesses and drags across raised detail. Thinning is not an optional technique for advanced painters, it is the difference between paint that looks like paint and paint that looks like a wash of color over the sculpt. Getting the ratio right by finish type matters more than which brand you are using.
Thinning ratios by finish type
There is no single correct ratio, because base coats, layer paints, washes, and metallics all need different amounts of medium to behave correctly. Use these as a starting point and adjust by how the paint actually moves once loaded on the brush.
| Finish type | Starting ratio (paint to water) | What you're aiming for |
|---|---|---|
| Base coat | 1:1 | Flows evenly, needs two coats for full opacity |
| Layer / highlight | 1:1 to 1:2 | Thinner than base, so edges stay crisp |
| Wash / shade | Usually pre-thinned, do not add more | Settles into recesses without pooling on flat surfaces |
| Metallic | 1:1, mix gently rather than shaking | Keeps the metal flake evenly suspended |
| Contrast / one-coat | Do not thin, or a light 4:1 at most | Depends on the pigment settling into recesses as-is |
Washes and contrast-style paints are formulated pre-thinned for their job, so adding water to them usually weakens the effect they are built for rather than improving flow. Base, layer, and metallic paints are the categories where thinning technique makes the biggest visible difference.
What to thin with
Plain water works for most acrylic miniature paints and is the default most painters use day to day. A dedicated thinning medium, sold by most of the major ranges, extends drying time slightly and can improve flow on paints that get gummy when thinned with water alone, which matters more for airbrush work than for brush painting. For airbrush use specifically, a purpose-built acrylic thinner like Vallejo Airbrush Thinner(affiliate link) keeps the paint from clogging the nozzle in a way plain water sometimes does not.
A wet palette changes this equation somewhat, since paint sitting on a hydration membrane stays workable and gradually self-thins as it draws moisture from the membrane below it. Painters who work off a Redgrass Games Everlasting Wet Palette(affiliate link) often add less water upfront and let the palette do part of the thinning work over the course of a session. The wet palette guide covers whether the setup is worth it if you are not using one yet.
The two thin coats rule
"Two thin coats" is the standard advice in the hobby for a reason: a single thick coat of base color almost always looks worse than two properly thinned coats of the same paint, even though it takes longer. The first coat goes down patchy and slightly transparent, showing primer through in places. The second coat, applied once the first is fully dry, closes those gaps without burying the detail underneath. Trying to get full opacity in one pass usually means the paint was too thick, which is the exact problem thinning solves in the first place. The Citadel to Vallejo conversion guide touches on how this same two thin coats habit carries over once you switch a base coat between brands.
FAQ
How do I know if my paint is too thin?
If the color barely shows after two coats and looks watery on the brush, you have gone past the point of usable coverage. Add a small amount of full-strength paint back in rather than starting over.
Can I thin Citadel Contrast or Army Painter Speedpaint?
These are formulated to be used close to bottle consistency, since their pigment is designed to settle into recesses on its own. Thinning them weakens the shading effect they are built around, so use them sparingly if at all.
Does thinning ratio change between brands?
The general finish-type ratios hold across brands, since they are about acrylic paint behavior, not brand formulation. Some ranges run slightly thicker out of the bottle than others, so expect to adjust the exact ratio by a little even if the starting point is the same.
Is water as good as a dedicated thinning medium?
For brush painting, plain water is fine for most base and layer work. For airbrushing, a dedicated acrylic thinner reduces clogging and improves flow more reliably than water alone, especially through a fine nozzle.