How to Thin Acrylic Paint for an Airbrush When Painting Miniatures

I recently decided to try painting my miniatures with an airbrush instead of the old tried-and-true brush. As much as I love the control a brush gives, I needed a way to speed up the process as I have many small armies waiting for attention.

After picking out an airbrush that fits my needs, it quickly became obvious that I was going to have to figure out how to make it work with my paints.

How do you thin acrylic paint for an airbrush when painting miniatures? To thin acrylic paint for an airbrush, you need to add a thinning agent, like water or specially made thinner, to the paint, and mix until you create a paint that has the consistency of skim milk.

Airbrushes can clog if the paint isn’t thin enough for the nozzle. So, I had to figure out how to thin my paints for my airbrush. There are different paints and different ways to mix.

It is worth knowing a little about these techniques so you can have the best experience using an airbrush with your miniatures.

Why You Should Thin Your Paint for an Airbrush

Even if you don’t plan on using an airbrush, you should still be thinning your paints. Thick paint can lead to a lot of undesirable results.

If you are using a brush or airbrush, you should thin your paint, or you might have to deal with:

  • A thick base coat that hides the details of the miniature.
  • A look that is shinier or glossier than you want.
  • Cracks in the paint.
  • Either a damaged brush or a clogged airbrush.

It is important to take the time to thin out all your paints before you use them to get the best looking miniatures possible, but what should you be using to thin your paints?

Thinners to Use With Your Acrylic Paints

The substances you can use range in price from free to around $15. Which one you use basically depends on the amount you are willing to spend and the consistency you are looking for.

Substances you can use are:

Tap Water

This is the most commonly used thinner, not because it is the best, but because it is free. It is a very usable option, but if your tap water is too hard and filled with minerals, it might affect the color of your paint and how the paint behaves.

Distilled or Deionized Water

If you really want to use water but are scared of the effect hard water will have on your paints, go with distilled water. It removes all of the impurities that might mess with your paint.

Airbrush Thinner

If you are willing to spend a little more money, airbrush thinner is the best way to go. There are thinners specifically made to thin your paints for airbrushing. Airbrush thinners will give you the best consistency in your paints.

Mediums

Some paints are not meant to be thinned, like shades or contrasts. If you need to thin these, you should use a specific medium made for thinning those paints.

Types of Paint for Airbrushing

You are not going to thin all paints in the same way.

Some paints are thicker than others and you’ll need to thin them down to get the milk-like consistency you are looking for.

Some paints are specifically made for airbrushes, so they don’t need thinning at all.

Other paints are not meant to be thinned and will need specific mediums made for thinning. Here are some common paints and how to treat them.

Airbrush Paints 

Companies like Vallejo and Citadel make paints specifically for airbrushes. You don’t have to thin these paints at all, though you can thin them if they are thicker than you want or you want to dim the color.

Base Paints 

There is no set formula for thinning base paints. Different companies and even different colors will have varying thicknesses.

The rule of thumb is to start with a thinner to paint ratio of 1:1 and adjust from there if needed. It is best to err on the thin side and paint multiple coats because you cannot correct if it is too thick.

Glazes and Shades 

These paints do not need to be thinned. If you feel that you need to thin them for your airbrush, only use mediums specifically made for that paint.

How to Thin the Paint

Thinning the paint is an easy process in theory. It’s just a matter of adding the right amount of thinner to your paint until you get the consistency of skim milk.

There are a variety of things in which you can mix the paint and thinner depending on what you are comfortable with. Here are the two most common ways of thinking.

In a Cup or Bottle

Thinning your paints in a small cup, like those little, free-sample cups at the grocery store, is a common technique.

It allows you to mix a small amount of paint if you aren’t looking to use much or if you’re unsure how much thinner to add. 

For those who are more confident of the thinner to paint ratio, you can mix a large amount into a bottle, so you don’t have to thin every time you use that color.

To mix into a cup, you should:

  1. Put a few drops of paint into the cup.
  2. Add 2-3 drops of water or thinner to the paint.
  3. Use an old, cheap brush to mix the two. You don’t want to mess up an expensive brush mixing.
  4. Continue to add water or thinner a drop at a time until you get the consistency of skim milk.

In Airbrush Cup

Some people feel that using a cup is an unneeded step. Why mix and then transfer to the airbrush when you can just mix right in the brush?

The steps are a little different in order to keep the airbrush as clean as possible.

To mix into your airbrush cup, you should:

  1. Add 2-3 drops of water or thinner to the airbrush cup. If you start with paint, the paint might get into the airbrush tube which could clog the brush or make it harder to clean.
  2.  Add 2-3 drops of paint to the airbrush cup.
  3. Use an old, cheap brush to mix the two.
  4. Cover the nozzle with your finger, and move the lever back. This will cause a backflow that will further help mix the paint and thinner.

Following these simple steps should turn your acrylic paints into airbrush paints. 

Just remember, there is no set formula for thinning paint. The amount of thinner you use will change depending on brand and color.

The only thing that is going to perfect the process for you is experience.

Don’t be afraid to experiment, because the more you see what different mixtures do, the better your ability to create the right consistency for your paints will become.