One of the great advantages of watercolour is its simplicity. All you need to start painting is water, a brush, and some pans or tubes of colour. But what if you want to take watercolour a little further? Watercolour mediums can help you control how watercolour paint behaves – including its texture, how it flows, how it lifts from the paper, and how fast it dries. In this article I look at some of the many watercolour mediums available, and explore how they could be used in watercolour painting.
I have used two blue watercolours- Phthalo Blue and Cerulean Blue. I chose these because they represent two very different pigment characteristics. Phthalo Blue (PB15) is staining and doesn’t granulate, while Cerulean Blue (PB35) doesn’t stain is highly granulating. The paper used throughout is Jackson’s Watercolour Paper, cold pressed.
Naturally granulating watercolours, like Ultramarine Blue, Viridian Green, and certain earth pigments, have large pigment particles which separate and settle into the paper, creating a textural effect. Texture mediums are designed to add or enhance the texture of watercolour, and I wanted to see if they could be used to mimic the effect of granulation in pigments which are not naturally granulating. Here I tried them with Phthalo Blue:
Sprinkling salt onto wet watercolour and brushing it off when the paint is dry is a popular way to add texture to watercolour, and with the Phthalo Blue it seemed to be the most effective in mimicking granulation. The other mediums created some textural effects that could be interesting and useful in their own right. Schmincke Aqua Granulation spray is particularly dramatic.
I found that the texture mediums works nicely with Cerulean Blue, a pigment that already granulates. It enhances the natural textural quality of the paint:
Creating Impasto Effects
Impasto (or the technique of applying paint thickly) is not usually associated with watercolour. Neat watercolour is brittle and prone to cracking if it is applied undiluted in a thick layer, but modelling paste can add another textural dimension to watercolour painting. Modelling paste can be applied under the paint to prepare an impasto ground, or mixed directly with the paint. When mixed with watercolour, it tints it white and increases its opacity, creating a gouache-like effect.
For working on top of an impasto ground, I’d also recommend trying textured watercolour grounds – take a look at this post to find out more.
As watercolour remains soluble in water even after it’s dry, it can be reactivated with a wet brush and lifted from the surface with a rag. It is a great way to bring out highlights or rectify mistakes. Staining pigments, like Phthalo and Quinacridone pigments, penetrate the paper fibres and are difficult to lift, but this can be made easier by applying a lifting preparation to the paper before painting. Non-staining pigments like Cerulean Blue (below right) don’t need a lifting preparation to lift away cleanly. I found that it didn’t work well with Phthalo Blue (left), but it felt unfair to judge it with such an extremely staining pigment.
It worked better with Hookers Green and Ultramarine Blue – two pigments with an average staining ability.
Lifting with Gum Arabic Solution
A wash of diluted gum Arabic on paper before painting on it forms a barrier between the pigment and the paper reducing the staining effect of pigment, making them easier to lift.
While gum Arabic solution makes an excellent lifting preparation, it is a brittle medium that is prone to cracking if applied thickly. You can see in the swatch above that it changes the colour of the paper slightly, and it also adds a slight sheen:
Increasing Flow with Ox Gall Medium
Ox gall is an additive rather than a medium, because it is added to the painting water rather than the paint itself. It is a surfactant that breaks the surface tension of the water, allowing pigments to disperse more easily.
The difference might look subtle, but it was much easier to achieve a smooth graduation of colour with the ox gall medium, while without it the Cerulean Blue clumped together. Synthetic versions of ox gall are available, and work just as well.
An impasto medium like Winsor and Newton’s Aquapasto adds body to the colour without adding opacity, retaining brushstrokes and making the watercolour behave more like oil or acrylic. It does, however, add a slight yellowish tint to certain colours, like the Cerulean Blue below:
Increasing Drying Time
Watercolour is a fast-drying medium, but there are ways that this can be slowed down. One way is choosing a hard-sized watercolour paper that is relatively unabsorbent, increasing the time that the paint sits on the surface before being absorbed. Another way is to add gum Arabic. Gum Arabic is the binder in watercolours, so by adding it to the paint you are extending it without diluting the binder, increasing transparency and slowing the drying of the paint. You could also use watercolour blending medium, designed to give more time for reworking the paint before it dries. To find out how they slow drying, I painted out three swatches of watercolour diluted with water, gum Arabic solution, and Winsor and Newton Blending Medium. I ran a dry brush over each swatch after one, five, and ten minutes to see how fast they dried. The swatch without any medium dried completely within five minutes. Gum Arabic solution extended the drying time by a few more minutes. At the ten minute mark, only the Blending Medium remained wet enough to rework.