Thinning paint is one of the first skills every miniature painter needs to learn — and one of the most common areas where beginners go wrong. Paint straight from the pot is often too thick for smooth application, causing obscured details, streaky coverage, and brush drag. This guide covers when and how to thin paint correctly for miniature painting.
Why Thin Your Paints?
Miniature detail is measured in fractions of a millimetre. A paint layer that is too thick fills in panel lines, obliterates fine textures, and leaves a lumpy surface. Thin paint — applied in multiple coats — builds up colour gradually while preserving the sculpt underneath. This is why experienced painters often say “two thin coats” is better than one thick one.
- Thin paint flows off the brush more smoothly and covers evenly without brush marks
- Thin paint dries faster and can be layered more quickly
- Thin paint preserves sculpted detail rather than filling it in
- Thin paint blends more easily and allows wet blending techniques
- Thick paint can obscure fine edge details, block panel lines, and crack as it dries
What Can You Use to Thin Miniature Paint?
Water
Plain water is the simplest and most accessible thinning medium. Add 1–3 drops to your palette for most painting tasks. Distilled or filtered water is recommended over tap water — tap water contains minerals that can cause paint to separate or dry with a slightly chalky finish over time. For most hobby use, tap water works fine; distilled water is a minor upgrade worth considering if you paint frequently.
Acrylic Thinning Medium
Purpose-made thinning mediums (such as Citadel Lahmian Medium, Vallejo Thinner Medium, or Army Painter Wash Medium) thin paint without weakening its adhesion or affecting its drying properties. Unlike water alone, thinning mediums maintain paint consistency and reduce the risk of the paint “breaking” (separating into pigment and binder). They are particularly useful for glazing — applying very thin, translucent colour washes over completed highlights to unify shading.
Wet Palette
A wet palette keeps paint wet while you work, slowing drying time and making thin paint easier to manage. Paint on a wet palette stays workable far longer than on a standard dry palette — this is essential for blending techniques but helpful for any painting session. The constant light moisture also naturally keeps paint at a workable consistency without requiring constant thinning adjustment.
Flow Aid
Flow aid (also called flow improver) reduces surface tension in the paint, making it flow more freely and reducing brush drag. A few drops mixed with your thinning water can improve coverage significantly, particularly for large flat areas. Liquitex Flow Aid and Vallejo Flow Improver are the most common products. Flow aid should be used sparingly — too much makes paint waterlogged and reduces adhesion.
How Much to Thin: Consistency Guide
Different painting tasks require different consistencies. Think of it in terms of milk:
- Base coating: Consistency of full-fat milk. Should cover well in two coats without being thick. Add 1–2 drops of water per palette pool.
- Layering and highlighting: Consistency of semi-skimmed milk. More transparent, builds up gradually. Add 2–3 drops per pool.
- Glazing: Very thin, almost like tinted water. Translucent colour that tints without obscuring. Add 5–8 drops per pool — you may need to apply 3–5 glazes to build colour.
- Washing (with wash medium): Very thin and runny. Flows freely into recesses. Pre-made washes (Nuln Oil, Agrax) are already at the right consistency — do not thin them further.
- Dry paint for drybrushing: Never thin. The thick, near-dry consistency is required for the technique to work.
How to Thin Paint: Step by Step
- Put a small amount of paint on your palette. Never thin paint in the pot — this can ruin the rest of the paint. Use a dedicated palette (wet or dry).
- Add water one drop at a time. Add a single drop of water next to the paint on the palette, then mix them together with your brush. Test consistency by picking up a small amount and observing how it flows.
- Test on the back of your hand or a piece of card. Drag a thin line across the surface. Correctly thinned paint should flow smoothly with no visible brush marks and cover evenly. Thick paint will look uneven and drag. Over-thinned paint will appear translucent and bead up.
- Adjust until correct. Add more water if too thick; add a fresh drop of paint if too thin.
- Apply in thin coats and allow to dry before the next coat. Two thin coats give better results than one thick one.
Thinning Different Paint Types
Base Paints (Citadel) / Foundation (Vallejo)
These are high-pigment paints designed for coverage. They can be used at near-pot consistency for coverage, or thinned 1:1 with water for smoother application. Two coats at medium consistency is usually the right approach.
Layer Paints
Already formulated for highlighting — thinner than base paints. Add 1–2 drops of water to improve flow. These are designed to be applied over a base coat and shade, not to achieve full coverage in a single pass.
Contrast Paints / Speed Paints
Do not thin Contrast paints with water — this destroys the formula that makes them flow into recesses. If you want to thin Contrast, use Contrast Medium (Citadel) or Speed Paint Medium (Army Painter) exclusively. These maintain the paint’s unique properties while adjusting opacity.
Metallic Paints
Metallic paints contain metal flake particles — thinning them too much causes the particles to separate from the binder. A few drops of water is fine; heavy thinning will produce a streaky, washed-out metallic effect. Thin sparingly and use a smooth-bristled brush to minimise brush marks.
Texture Paints
Never thin texture paints (Astrogranite, Stirland Mud, etc.) — they require their thick consistency to create the texture effect. If the pot dries out, add a single drop of water and stir well to rehydrate, but do not thin during application.
Thinning FAQs
Can I thin paint with isopropyl alcohol?
IPA (isopropyl alcohol) at 70–90% concentration can be used to thin paint but is primarily used for cleaning brushes and equipment. IPA dries very fast, which makes it less practical than water for painting. Some painters use a tiny amount mixed with water for specific techniques (smooth blending on large flat areas), but for general painting, water or medium is preferable.
My paint is drying on the brush mid-stroke. How do I fix it?
This is usually caused by painting in a dry environment or using a brush with too little paint loaded. Try working on a wet palette, add a single drop of flow aid to your thinning water, and ensure your brush is properly loaded before each stroke. Painting in direct sunlight or near a heater will dramatically accelerate drying.
My Nuln Oil is leaving tide marks. What went wrong?
Tide marks occur when a wash pool dries at the edge before the rest of the wash has dried, leaving a ring. To avoid this: apply wash only to recesses rather than over entire surfaces, use a clean almost-dry brush to wick up excess pools before they dry, or add a single drop of drying retarder or flow aid to the wash to allow it to self-level. You can fix existing tide marks by re-applying a layer of your original base colour over the affected area.
How thin is too thin?
Paint is too thin if: it beads up and refuses to adhere to the surface, it dries completely translucent with no visible pigment, or it flows uncontrollably across the model regardless of brush placement. At this point you have broken the paint — add a fresh drop of paint from the pot to restore the balance.
Do Contrast paints need thinning?
Contrast paints come pre-formulated at the correct consistency for single-coat coverage — you do not need to thin them for standard use. If you want to use Contrast as a glaze (more transparent application over existing highlights), use Contrast Medium to thin rather than water. Using water to thin Contrast destroys the formula.