“A great artist can paint a great picture on a small canvas.”
Charles Dudley Warner
Your choice of what to paint on can alter the working properties of the paint and give you a different painting experience but it needn’t be a mystery, if you follow a few simple rules.
1. Acrylics straight from the tube are the most flexible medium, so can be painted on anything – paper, canvas, cardboard, metal…literally anything.
2. Oils are more tricky, so have to be painted onto a properly prepared surface (see: The Trouble with Oil) I recommend a prepared canvas or prepared board.
3. Watercolours work best on paper, I recommend Cold Pressed paper (confusingly also referred to as NOT paper meaning ‘Not’ Hot Pressed). It’s ideal for less experienced painters as it’s more forgiving. (There is a huge range of Watercolour papers see: How to choose Watercolour Paper).
Watering-Down Heavy Body Acrylics
When I’m building up an acrylic painting, I usually work from thinner diluted layers in the under-painting stages, up to more impasto thicker paint layers in the final stages of the painting.
This stems from Classical Oil Painting where you build up layers of oil paint, known as ‘fat over lean’
Fat over lean means that each succeeding layer of paint should have more ‘fat – oil’ than the preceding layer.
If you are painting in an indirect method (working in layers rather than all in one go – Alla-Prima) you need to adhere to this rule to prevent cracking and give the painting a good structure in your oil paintings.
I follow this same practice with many of my acrylic paintings.
Because the thinner watery washes at the underpainting stage create a really nice matt paint surface for the blocking-in stages. Then the subsequent layers, which are slightly thicker (less diluted) will absorb and ‘grab’ nicely into the layer below.
Don’t forget, acrylic paint is plastic based, so if you paint the first layers too thickly, you can create a hard, shiny surface completely covering the tooth of canvas (see: What are your paints made from?)
With thin layers at the beginning of a painting, you can tweak your drawing and colours and then start painting thicker layers when you’re more confident the painting is coming together.
Before we go any further, I want to draw your attention to the most important factor to consider when working with watered-down Heavy Body Acrylics.
If you applied thick acrylic paint, straight from the tube to practically any surface, it would stick.
However, when acrylics are diluted with water you need to take into account the absorbency of your support to get the best results.
When I say ‘support‘, I’m talking about your canvas, paper, canvas board or even a plastic panel you intend on using. All of these surfaces have different absorbency levels which will have a direct effect on the way the paint behaves when water is added.
The most common questions I receive on this subject are from students fearful that watered-down acrylics will harm their paintings in the long run, usually thinking the painting will ‘flake and fall off’.
To be clear, watering down acrylics with water is not a problem if the surface absorbency level you choose to paint on, is considered.
Think like a Watercolour Painter
If you think about Watercolourists, they sometimes dilute their paint 50:1 water to pigment, but they choose a rag watercolour paper that has been designed to absorb the watery paint effectively and hold the pigment when the water evaporates.
So if you think about how diluted you’re going to be applying the acrylics and then choose or prepare your surface sympathetically to that style of painting.
Below is a general guide to the absorbency level of a few common painting surfaces.
Choosing & Preparing the Right Surface
Canvas Board – Shiny surface, not very absorbent
Most beginners pick up a ready-made canvas board from their local craft/art store because they’re small and relatively inexpensive.
These can be fine for experimenting on but the drawbacks are they have an imitation canvas surface that can be really slippy to paint on.
Acrylics straight from the tube or slightly watered down (5-10%) will adhere to them fine.
But if watered down more (30-50%) the paint will tend to sit on top of the board in beads, taking ages to dry – and then when the next layer of paint goes on, it can disturb the fragile paint surface underneath.
This is because the first watery layer didn’t grab or absorb fully into the board.
Solutions for working on a less absorbent surface:
1. You can get around this by painting a couple of thin layers of Acrylic Gesso on first, to give a more absorbent base.
2. You can add a few drops of Acrylic Flow Release into your water, this will break down the surface tension of the paint and stop it beading.
Acrylic Flow Release is a surfactant. A surfactant is a concentrated surface-active liquid which reduces surface tension.
It dramatically reduces the surface tension between the stain (paint/water) and the support. Certain supports are inherently water repelling in nature and require the use of such a surface-active agent to allow the stain to wet and penetrate into the support.
Starting Dilutions – For most applications
- Mix 1 part Acrylic Flow Release to 10-20 parts water. Use this mixture whenever adding the Flow Release into a paint system.
- When painting on non-absorbent surfaces (not staining), do not exceed the level of 3% Acrylic Flow Release/water mix in the paint to minimize water sensitivity.
- For staining applications on absorbent surfaces, higher levels of Flow Release may be used as it will be absorbed by the support.
- Use Flow Release to pre-wet canvas or paper to increase the staining or spreading capabilities of the paint.
Super Smooth Pre-Primed Gesso Panels – Shiny smooth surface, not very absorbent
Some of the pre-primed gesso boards I find very hard and repel watery washes, however, if you’re painting with thicker paint they can work well. You can see a collection here. The unprimed panels can be good because you can control the surface absorbency by adding your own Gesso, just like with the canvas boards.
Stretched Pre-primed Cotton Canvas – Slightly textured surface, medium absorbency
Ready made canvas can be pretty good but the really cheap ones can be paper thin, have no texture to them and are prone to buckling on the surface if you add a lot of water.
Using a reputable brand like Winsor & Newton or Daler Rowney ensure a better quality of surface to paint on and have a bit more texture to the canvas. The texture helps pull the paint off your brush and gives a lovely dry brush effect. The best canvas is anything above 12oz in weight this helps ensure less movement in the canvas.
The thicker the canvas the more absorbent because it can hold more water.
Watercolour Paper – Slightly textured surface, high absorbency
You can paint on decent weight watercolour paper with acrylics very successfully, it can take the watery washes and the thicker impasto brushmarks too.
If you want to paint on ordinary craft paper, consider the thickness and robustness and adjust your dilution level of the acrylics accordingly.
So what do I paint on?
Usually, a Cotton Canvas that is 12oz in weight that I have primed with Acrylic Gesso making a nice absorbent base for the first layer of my painting – a Coloured Ground
Paint Film Integrity
The other concern students have when using water to dilute acrylics, is in relation to the paint film integrity.
Will using too much water to thin the paint run the risk of the paint not adhering to the canvas over time?
There are 2 answers to this question depending on whether you’re talking about the first layers of the under-painting or the very final diluted top layers known as glazes.
If the under-painting layer is diluted with water, we know it will adhere to the support if the support is absorbent enough – once it’s absorbed, it stays absorbed.
For the later stages of the painting, some artists including myself like to apply a thin layer of paint known as a glaze to optically change the paint colour underneath.
The underlying paint layer is already dry when the glaze is applied, so it will sit on top of a built up, relatively shiny surface.
To remedy the paint adhering to the canvas for these later stages of a painting, I dilute the acrylics with a medium called Acrylic Glazing Liquid Gloss rather than water. This ensures the diluted pigment will hold in a paint film, creating a layer of paint than ‘holds together’ rather than separating.
Acrylic Glazing Liquid (Gloss)
Acrylic Glazing Liquid can be blended with paints in any desired amount. Adding small amounts (approx. 25%) to paints will increase brushability. Adding 1 part paint to 10 parts Acrylic Glazing Liquid produces transparent glazes with excellent open times.
I received a reply from Golden Paints technical support team regarding the thinning of acrylic paints, I’ve posted it below as I often demonstrate with Golden Paints and hope it helps put your mind at rest.
The cautions against thinning acrylics beyond 30% (or some similar figure) is common to run across and is something we often find ourselves having to correct, at least in regards to our own paints. We cannot, of course, comment about other manufacturers’ products, where performance can differ. So the following is really only about our brand and is not a blanket statement.
The first thing to note is that our Fluids and Heavy Body acrylics can easily be thinned up to one part paint to one part water, or a 1:1 ratio, and maintain excellent adhesion onto absorbent surfaces. In fact, even when testing this on a non-absorbent material like Plexiglas, the paints still formed good films with no adhesion failures after being allowed to fully cure.
To add even a little more comfort beyond that, we can share that the adhesion onto Plexiglas remained solid even when thinning with one part paint to two parts water, or a 1:2 ratio. Which would feel like a fairly fluid wash for most people.
As you can see, the concerns around thinning with water can often be over stated, especially if using our Heavy Body or Fluid Acrylics and keeping the ratio to 1:1 or less.
And even then, one can usually get away with going even further.
However, because every application can be unique, one can always do an easy test to make sure there are no problems.
To do this create a test piece with a similar surface that you want to test, then apply a few different colors both at full strength and then at 2:1, 1:1, 1:2, and 1:3 ratios of paint to water.
Allow to fully dry.
At this point we typically test for adhesion at 24 hrs, 3 days, 1 week, and 2 weeks.
If the paint passes the adhesion test at, say, 3 days, there is rarely a need to continue testing out further.
A simpler, more down and dirty test, can be done scoring the paint with an “X” using an X-Acto blade, then apply masking tape over the center, burnish, then lift. In both cases you are seeing if the paint comes off. If not, then you have very good adhesion and no reason to believe that adhesion will lessen over time.
You can also try rubbing the film with a wet Q-Tip to see if you get color lift, which can be another sign of an underbound film.
Please note: Even though our Heavy Body and Fluid Acrylics are quite robust, when it comes to thinning, there are some products where we do recommend a lower level of water, such as our Acrylic Gesso which should not be thinned with more than 20% water, or our OPEN acrylics where we recommend a limit of two parts paint to one part water, or a 2:1 ratio. And of course we cannot comment about safe levels for thinning paints from other manufacturers.
Technical Services Supervisor
What if you want to paint really thinly with acrylics for the entire painting process?
If you want to paint really thinly with Acrylics, it’s best to use an Acrylic that has already been diluted in the paint manufacturing process.
For example, Golden paints have two further levels of paint dilution down from heavy-body acrylics:
- Fluid Acrylics
Fluid Acrylics are highly intense, permanent acrylic colors with a consistency similar to heavy cream. They offer very strong colors with a fluid consistency.
- High-Flow Acrylics
These acrylics were previously known as ‘airbrush acrylics’ and have an ink-like consistency.
Alternative Acrylic Mediums for thin applications
If you want to paint thinly with heavy body acrylics when working vertically at an easel, you can add mediums to the diluted acrylics, here are some further suggestions from Sarah Sands:
If wanting to thin the paint even further, try using GOLDEN Airbrush Transparent Extender which has a consistency close to water. Alternatively, our Polymer Medium, Fluid Matte Medium, Acrylic Glazing Liquid, or GAC 500, to name a few, could be used to thin a thicker acrylic, as well as blended with water.
For example, a 1:1 blend of GAC 100 or GAC 500 and water, then used for thinning acrylics, should allow you to safely thin the paints for application onto most canvas and panel surfaces since you will always be bringing in additional binder into the system.
If not familiar with some of these products, please see the following pages:
We hope this helps. Thinning of acrylics is an often misunderstood area, but it is always good to ask if you have doubts or concerns.And of course, if there is anything else we can do, just ask!
Technical Services Supervisor
You Might Also Like:
1. How to use acrylic gels & mediums – Video
2. Glossary of Acrylic Painting Terms – The Ultimate Guide for Beginners
3. How to paint over an Acrylic painting – What if it all goes wrong! Should you start again or rescue your work?