There seems to be a myth that you aren’t supposed to use water with acrylic, and then there’s another one that you should always use water. This issue about water was something that really intriqued me when I first starting using acrylic paints.
I address this issue in the video above, as well as in my book, Acrylic Revolution. The book has lots of recipes and techniques and the idea of when to use water and when not to use water becomes more clear. But here I’ll write about it more specifically and in depth.
Basically water is not a bad thing to add to acrylic. However, there are some basic issues that when understood will help you decide when to use it and when not to use it – when it helps your work and when it works against the effects you are trying to achieve.
First, lets look at what makes paint. Generally, all paint is made of 2 basic components: pigment (for color) and binder (to make the pigment usable as a paint). The binder is what identifies the paint. For instance, take some pigment and add oil – now you have oil paint. That same pigment mixed with milk makes casein, with gum Arabic makes watercolor, and with polymer (or plastic or acrylic) you get acrylic paint.
So there’s pigment and binder, and then there’s the solvent. Each medium has a solvent that will break it down. For acrylic the solvent is water. Acrylic without water (just pigment and polymer binder only) will produce a paint film layer that looks juicy, glossy and substantial when applied over any surface. The surface could be absorbent or non-absorbent, colored or white. It doesn’t matter, because once you apply the undiluted acrylic on top the paint film will all look the same. You can add up to 20% water to acrylic paint and it will still have that glossy paint film, it will just get a bit thinner.
However, it’s a very different story when you add A LOT of water to the paint. When you make a 1:1 ratio (equal parts of paint and water) or even more water that that (I like 80% water to 20% paint color), we can call this “overdiluted” paint. Once acrylic paint gets overdiluted with water it will look totally different depending on the surface absorbency that it is applied to. For instance, a diluted acrylic paint applied on an absorbent surface like watercolor paper will have a matte, soft, muted evenly applied layer of color. This same diluted paint on a non-absorbent surface will look very crazy, puddling up in places with some interesting effects. (All this is in my book). So it’s TWO things that work together to create the interesting water effects – overdiluting the paint with water along with changing the absorbency of your surface. To change the surface you first apply some type of paste, gel or ground that makes it more or less absorbent than just the plain old gesso primer usually found on store-bought panels and canvases.
So, here are some key ideas: (1) use acrylic without any water at all for a rich, glossy, plastic, high coverage layer. (2) Use up to 20% water in acrylic paint to slightly loosen the paint, make it a bit more fluid to get evenly applied linear effects and decrease texture (3) Combine 80% water to 20% paint to get an “overdiluted wash” – and now use this on a selected surface (absorbent, non-absorbent, textural or smooth, colored or uncolored) to get a specific effect. (4) Use retarders and glazing liquid or the new “Open” slow drying acrylic to keep the acrylic from drying fast. Do not use water all over your palette to slow the drying or you won’t be able to control how much water is going into your paint.
I do think the whole water issue with acrylic is a bit confusing. Adding water is not bad. Its just that when water is used haphazardly and uncontrollably (spraying palettes with water to keep it wet, or not blotting the brush after washing it) this reduces the range of possible effects you could otherwise obtain. Again, the most important thing to remember is determining how much water you want in your paint depending on the type of effect you are looking for. The more water you add, the more important your choice of surface is to get certain effects.
Article from Golden: How Much Water Can you Safely Add to Acrylic Paint?