The Italians called it mud!
The word “gouache” derives from the Italian word for mud – guazzo. In the Sixteenth Century, this described a process of binding oil paint with a binding agent to create a matt finish.
Today, gouache should be considered a part of the watercolour family. The pigments are the same, they’re both water-soluble, it’s just that there the ratio of binding agent is higher in gouache than with watercolour. The effect – which is why I like using it – is that you get opaque, flat colour and the same matt finish the Renaissance Italians were also looking for. Gouache was, in fact, used in Persia as far back as the Ninth Century, only arriving in Europe in the Fourteenth.
The binding agents that were traditionally used were derived from egg, a well known emulsifier and that’s why gouache is sometimes also referred to as egg tempera. Nowadays, the agent is either gum-arabic (for very expensive paints) or yellow dextrin (probably what’s in mine).
Often used by graphic designers for creating posters, gouache is sometimes also referred to as “poster paint” and can also be applied with an air brush.
I like using gouache because it’s a very forgiving medium. Unlike watercolour, which requires real skill (which I don’t have), you can add layers of paint and mix colours on the surface of the paper or board. If you make a mistake or, as I like to put it, change your mind about a line or a surface, you can easily do so. The great thing is, if you want to, you can create a watercolour effect very easily – just by thinning the paint down.
The other reason why I personally prefer gouache is that it matches my rather stylised, graphical style. My pictures are usually all about line and composition – I’m getting there with colour – and the flat treatment is just what I like.
Gouache is also very closely related to acrylic paint. While I tend not to mix the two, I don’t really perceive that much difference in the way the paint handles. For me, if I’m doing a big picture, the acrylic seems to be easier. It’s also useful if you’re creating artwork for areas which might be rather damp – kitchens for example. Once it’s dry, acrylic is more or less water resistant.