Art Basics: The Difference Between Watercolour And Gouache
Gouache, Not Goulash
Despite its popularity and rich history, gouache is one of the most misunderstood popular paints. It's probably the most-asked-about paint we stock (i.e., people asking about what it actually is), and probably the most-commonly-mispronounced item we stock; does anybody really paint in goulash?
Part of the Watercolour Family
In essence, gouache paints are very similar to watercolours and they both contain gum arabic as a binder. However, some key differences set them apart from their über-popular cousins. First and foremost, gouache contains an additional component which increases its opacity and reduces its dependence on the white of the paper for luminosity. This comes from powdered gypsum (calcium sulphate dihydrate), chalk (calcium carbonate) or zincite (zinc oxide), all of which occur naturally.
An array of gouache paints, including metallic and fluorescent effects colours, primaries, black, whites and higher-series colours.
Gouache contains a higher pigment load than watercolours, which partially accounts for its more-vibrant appearance. The particle size of the pigments is also larger, which increases its ‘hiding strength’, i.e., its ability to cover other pigments, pencil marks, et cetera. Too large a particle size and the gouache can feel gritty to work with. Too small, and the pigment behaves more like that of a watercolour, even if the presence of the opaque material does not.
History and Uses
The term gouache derives from ‘guazzo’, which was the term used to describe a 1500s method of applying oils over a tempera base layer. It wasn’t used to describe the watercolour variant until the 1700s, though the technique itself predates the association by several hundred years.
Gouache has a broad set of applications, and is an attractive medium because its high opacity gives it an immediacy, which saves time in commercial work, particularly ‘old school’ poster production and cel animation. I was introduced to it in the late ‘90s on a further education illustration course, and began using it in earnest, a year later, for my degree. Despite its other uses where detail is perhaps not critical, it can be used with excellent precision in illustration work where a high level of detail is paramount. It easily holds its own next to oils, traditional watercolour and acrylics, and its luminosity allows for good scanning and reproduction - so it’s ideal for briefs where the final image is to be used in print.
An example of a gouache illustration, expertly rendered by US-based Scientific & Natural History illustrator, Emily Willoughby. It shows a Changyuraptor in left lateral view. (copyright © Emily Willoughby; used with permission.)
Gouache is a relatively-forgiving medium. Depending on the quality of your chosen substrate, you can, at a push, wash off an entire image and start again, or you can soak and lift off more-specific areas. Its chalky nature allows it to be scraped off and tweaked with scalpels and sandpaper, but this is very much dependent on what you’re painting on to. I prefer Arches hot-pressed paper, usually 140lb, but 90lb works well if you’re not working too wet for too long, and canvas is supposed to be quite effective. Gouache brushes on as easily as regular watercolour, but broad, confident layers, such as skies and seascapes, can be painted speedily, without too much fuss. That's not to say it doesn't require practise, and confidence is key to mastering this rewarding paint.
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