There is no universal water-to-paint ratio, and anyone who gives you one is guessing. The right consistency depends on the paint, the colour, the brush, what you are trying to do with it and what is underneath. This guide teaches you to judge paint behaviour rather than measure drops.
That sounds vaguer than a number, but it is far more useful. Once you can read what paint is doing on the palette, you stop guessing on every colour.
Why one ratio cannot work
The variables that change how much thinning a paint needs:
- Formulation. Ranges differ enormously in how much medium and pigment they contain. Some arrive close to ready; others are thick out of the pot by design.
- Pigment. Different pigments have different particle sizes and densities. This is a property of the colour itself, not the brand.
- Colour. Yellows, oranges and many reds are naturally less opaque. Blacks and some earth tones cover in a single pass.
- Age. An older pot has lost water to evaporation and needs more thinning than a new one, sometimes dramatically more.
- Palette type. A wet palette adds moisture continuously, so paint that started correct gets thinner over ten minutes. A dry palette does the opposite.
- Brush. A large brush carries more paint and more water. A tiny detail brush dries out mid-stroke.
- Technique. Basecoating, layering and glazing want three different consistencies from the same pot.
- The colour underneath. Painting light over dark demands more opacity, which means less thinning and more coats.
Signs paint is too thick
- Visible brush marks that stay after the paint dries, as ridges rather than colour variation.
- Texture on the surface. The model feels or looks slightly rough where it should be smooth.
- Obscured detail. Rivets soften, panel lines fill, fabric folds lose definition. This is the serious one, because it is permanent.
- Poor flow. The paint drags rather than laying down, and the brush stutters across the surface.
- A visible edge where a stroke ends, rather than a smooth transition.
Signs paint is too thin
- Uncontrolled pooling. The paint runs off raised areas and gathers in recesses when you wanted flat coverage.
- Pigment separating. You can see the pigment settling out from the water, often as a grainy ring at the edge of a stroke.
- Weak, uneven coverage that looks streaky no matter how many coats you add.
- Flooding recesses when you were trying to paint a surface, which effectively turns your base coat into a wash.
- Tide marks. A darker ring where a thin layer dried at its edge.
A practical palette test
This takes five seconds and tells you more than any ratio.
- Load the brush and wipe the excess on the palette edge.
- Drag a single stroke across a clean area of the palette.
- Look at what the stroke did.
If the stroke is opaque, has clean edges and did not spread beyond where you dragged it, the consistency is right for basecoating. If you can see the palette through it, it is thinner than a base coat wants, which may be exactly right for a glaze. If it sat as a raised bead and did not flow at all, it needs water.
Doing this on a white or light palette makes opacity much easier to judge than on a dark one.
Water versus acrylic medium
Water thins paint by diluting everything in it, including the binder that makes the paint stick and film properly. A small amount is fine. A lot of water produces weak, chalky, poorly adhering paint, which is why heavily watered-down paint often looks dusty when dry.
Acrylic medium thins the paint while replacing the binder, so the film stays sound. Flow improvers reduce surface tension so paint spreads more readily without diluting as much.
In practice: water is fine for ordinary thinning of base coats and layers. Reach for medium when you are going very thin, particularly for glazing, or when thinned paint keeps drying chalky.
Why different colours behave differently
Opacity is a property of the pigment, not a measure of quality. Some pigments are naturally transparent and no amount of formulation fixes that. This is why a yellow that needs four coats and a black that covers in one can sit in the same range at the same price.
The practical consequence is that transparent colours want less thinning and more coats, and they benefit enormously from a helpful colour underneath. Yellow over a light grey or bone base is a completely different experience from yellow over black. Our guide to priming properly covers matching primer colour to your scheme.
Is "milk consistency" useful?
Partly. It communicates the right general idea, that paint should flow, and it is better than painting straight from the pot.
But it fails in three ways. Milk is not one thing, so the analogy is imprecise from the start. It gives a single target when the correct consistency changes by task. And it describes viscosity while ignoring opacity, which is what actually determines whether you get coverage. Paint can be exactly milk-like and still be useless for the job in hand.
Use it as a rough starting point and then judge the stroke on the palette.
Basecoating, layering and glazing
| Task | Consistency | What matters |
|---|---|---|
| Basecoating | Thin enough to flow smoothly, thick enough to build opacity in two or three coats | Even coverage without losing detail |
| Layering | Slightly thinner than a base coat, applied to a smaller area | Control over placement and a soft edge |
| Edge highlighting | Slightly thicker than layering | Paint stays exactly where the brush puts it |
| Glazing | Very thin, closer to tinted water, ideally with medium | Shifting colour gradually without hiding what is underneath |
| Shading into recesses | Thin and free-flowing | Paint travels into recesses on its own |
The same pot of paint serves all five. Only the water changes.
How much paint should be on the brush?
This matters as much as consistency and gets discussed far less.
Paint should sit on the tip and first third of the bristles, never up in the ferrule. An overloaded brush deposits a blob at the start of the stroke, floods recesses you were trying to avoid, and dries paint inside the ferrule, which splays the bristles and ruins the point within a few sessions.
The routine that fixes it:
- Load the brush from the palette.
- Wipe one side against the palette edge or a piece of paper towel.
- Check the point has reformed and the bristles are not saturated to the metal.
- Reload after every few strokes rather than trying to make one load last.
For fine work, less paint and more frequent reloading gives far better control than one heavy load.
Frequently asked questions
How many drops of water per drop of paint?
There is no reliable answer, which is why this guide teaches the palette test instead. If you want a starting point for a mid-range paint on a wet palette, begin at roughly one part water to three or four parts paint and adjust from what the stroke does.
Why does my thinned paint look chalky when dry?
Usually too much water relative to binder. Try thinning with medium instead, or thin less and add another coat. Some pigments also dry lighter than they appear wet, which is a different effect and not a fault.
Should I thin paint in the pot?
No. It commits the whole pot to one consistency, and water added to a pot encourages the paint to spoil over time. Thin on the palette, a small amount at a time.
Does a wet palette change how much I thin?
Yes. A wet palette adds moisture continuously, so paint gets thinner the longer it sits. Start slightly thicker than you want and let the palette do part of the work, then check the consistency again after a few minutes.
My old pot has gone thick. Can I save it?
Often. Add a little water or medium, close it and shake or stir thoroughly, then leave it to reintegrate before judging. Paint that has separated into lumps and liquid rather than simply thickened is usually past saving.
Once your consistency is under control, our guides to drybrushing and edge highlighting cover two techniques that depend heavily on getting it right. If something has already gone wrong, our guide to fixing painting mistakes covers the repair options.
Independent guide published by Blubbercove Ltd/WarSplay. This article is not affiliated with, sponsored by, endorsed by, authorised by or licensed by Games Workshop Limited. Warhammer 40,000 is a trade mark of Games Workshop Limited.