Thinning your paints.

1 July 2017


For most painters the first advice they get is to “thin your paints”. In a lot of cases this is correct, but to be clear – there is a whole lot stuff to know about thinning paints. The second suggestion they get is that the paint should have milk-like consistency. Again this does not provide a lot of insight and actually can be incorrect.

So, what to do?
At first, consider the paint you use. Most of us use acrylics, because of their easy use, fast drying and are very easy to acquire. Some use oil (they DO look gorgeous, but damn they are troublesome…). I know people who use other stuff like watercolors (sic!).

Let’s assume, that you, like me, prefer acrylics.
Acrylic paint is a mixture of pigments and water that is combined with a binding agent (polymer emulsion) which becomes quite resilient as the water eventually evaporates from the paint mix.
Firstly, there is a lot of paints on the market, which have different properties (think GW Base, Layer, Glaze) and consistency, some will have less pigment, or more biding agent.

But there are few rules of the thumb that you can apply:

1. Water is a good solvent for acrylic paints, but loses this property if you add more than 50% of it to the mix.
2. It is better to paint a number of thin layers than a single thick layer.
3. Paints richer in pigment need more solvent – and ideally – such, that dissolves the pigment.
4. Far better solvents for acrylic paints are thinners (which are pigment dissolvers).
5. Thin your washes with an acrylic medium, not water (Lahmian Medium works great here).
6. There are specific mediums like flow improvers and retarders than can help you work with your paints.

Products I recommend:
* Tamiya Acrylic thinner (it includes flow improver, retarder and isopropyl)
* Valleyo glaze medium (it includes flow improver and retarder)
* Lahmian Medium (it includes flow improver and retarder, but also some thinner)
* A pipette from a pharmacy (to apply that thinner)

As to more in depths explanation:

In general, when added, water does not dissolve pigment – it just spreads it on a bigger surface. Moreover in vast amount it can make the bidding agent not work correctly. Hence it is better to use a thinner when you want to apply smaller semi transparent layers.
The smoothness of blending is achieved by working with a smooth surface, hence, always try to apply a number of thin layers rather than a single thick one.
Aside from the fact that fact that small number of paints look better, it also helps applying glazes – as a smooth surface greatly improves the flow of the paints and its distribution.

Richer in pigment paints need more solvent & far better solvents for acrylic paints are acrylic thinners.

The difference with water and acrylic thinner is thrice: firstly, water doesn’t dissolve pigment – thinner does, secondly, too much water weakens the binder, thinner doesn’t, and lastly thinner helps improving the flow of the paint – as it breaks surface tension, water doesn’t.
You can thin your paints with a thinner, water, windshield fluid or isopropyl alcohol. All of those have their merits, but to be honest I would only focus on water and thinner. Use water when you want to apply base layers and thinner for transitions between them.

Thin your washes with an acrylic medium, not water (Lahmian Medium works great here).

Adding to washes water kind of breaks the whole point. Washes don’t have surface tension and are able to flow smoothly into recesses. Water breaks that effect. If possible add Lahmian Medium or acrylic medium if you don’t want to have those really intense washes.

There are specific mediums like flow improvers and retarders than can help you work with your paints.
Acrylic Retarder: a retarder is a substance, usually added to water, used to slow the drying time of acrylic paints, giving more time for blending or layering highlights.
Flow improver: This is an additive that loosens the surface tension of water within the acrylic film. It increases flow, helping with applying glazes, working on transitions or making wet blending fairly easy.
Glaze mediums: are mix of pigments dissolvers, retarder and flow improvers.

I touched here some basics around paint thickness. Notice, that there is a lot around the topic and I could expand it further, not mentioning milk once : P

That’s all folks!