Watercolor mediums and additives are liquids or gels that you can add to watercolor paint to make it glossy, more transparent, textured, pearlescent and more. Their use in watercolor painting isn't as common as other media like acrylics and oils, but they can be useful for certain techniques.
If you're new to watercolor painting, it's best to focus on mastering the fundamentals of watercolors before experimenting with mediums and additives. By just mixing water with watercolor paint you'll be able to create a wide range of effects.
Some of these mediums and additives can wreck your painting if overused. When using a new product for the first time, always scrutinize the packaging and conduct a few tests before using it on a painting.
Some watercolor mediums and additives just need to be added to your mixing water, and can be used with both pan and tube watercolor paint. Others, like impasto gel, need to be mixed with the paint directly and are therefore more suited to watercolor paint from tubes.
This page will introduce the following common mediums and additives for watercolors:
Gum arabic is manufactuered into watercolor paint as a binder, but you can also buy it separately. It's a solution or paste that can be added to mixing water or directly into the paint to make it glossier and more transparent. It will also heighten the intensity of the colors and make the paint more soluble, which aids the correction of mistakes. Gum arabic should be used in proper proportions, usually just a few drops at a time, or else the gloss effect may be too strong and the dried paint may crack.
Ox gall comes from the gallbladders of cattle and acts as a paint flow improver when added to mixing water. It does this by lessening the surface tension of the water, which makes it more fluid, and inhances the flow of washes, especially when working on smooth, heavily sized paper which can repel washes and cause puddling. Increased flow also helps when it comes to mixing paint and using blending techniques.
Overuse can result in a dull finish, so it should be used sparingly.
It can also be diluted and applied to paper before painting to make it more receptive to watercolor paint.
The phrase "watercolor medium" has come to refer specifically to a product that is similar to both gum arabic and ox gall. It has similar properties and produces similar effects to gum arabic but also enhances the flow of washes like ox gall. It can really add a brilliant vibrancy to your paintings, but be mindful that you don't use too much.
Watercolor medium, like ox gall, can also be used to enhance your ability to mix and blend paints by increasing flow and prolonging paint drying time. Artists used to use glycerine to extend drying time (which was very useful when painting in hot, windy conditions) but it's hard to get these days.
If you want to speed up the drying time of watercolor paint you can add some alcohol to your mixing water. Watercolors already dry quite rapidly on their own, but alcohol can be handy when you're painting in very damp conditions.
These are clear products that are mixed with tube paints to give it body and dimension. It is then painted on as normal and contrasts with the usually flat appearance of watercolor paint.
Aquapasto and impasto gel is very hard to remove once dried, so keep it away from your watercolor pans and wash your brushes immediately after they've been used.
Texture medium is basically a type of modeling paste or liquid that contains many tiny particles.
When you mix it with paint (or apply it directly) it creates interesting textural effects on the support and can be built up to create sculptural effects.
Another cool way to add some textural effects to your painting is to apply rock salt to wet paint on the support. After the salt has dried, you can remove the salt and you're left with interesting crystalline shapes.
Granulation will occur naturally when certain blue and earth pigments separate from the wash and settle on the support to create an interesting granular texture.
The effect can be artificially triggered in any color with the use of granulation medium.
You can vary the level of granulation and tailor it to your subject, usually skies and landscapes.
Iridescent Medium is a decorative watercolor medium that doesn't get much use by purists. When mixed with paint or applied on top, it creates a pearlescent effect. This can be fun to experiment with, but be careful you don't contaminate your watercolor pans.