Product Article - Understanding Gouache
Gouache is both a technique and a product. The technique, dating back to before the renaissance, refers to the use of white to achieve opacity in water based colours. Originally used for illuminating manuscripts, it was Paul Sandby in the 18th century who first used the painting technique extensively and later the Pre-Raphaelites.
Opaque techniques were further popularised by the Impressionists and Post-Impressionists, in their use of pastel, lithography and wood cuts. Gouache, the product, was a result of this interest in both opaque and water based products. Poster colour appeared after the first world war and this was significantly improved upon with the introduction of Designers’ Opaque Water Colour in the 1930’s.
Technique vs. product
The technique of adding white is known as body colour. You can do this with acrylic or water colour. Although with some colours you will get the effect of brilliance with the addition of white, you will be severely limited in subsequent colour mixing as a result of the colours being tints.
The best gouache is not manufactured by adding white but by using an extremely high level of pigmentation. This leaves the artist free to add white themselves or colour mix as they’d expect in other media. Cheaper gouache colours are made opaque by the addition of white extenders and this will affect your colour mixing too.
Other types of gouache: as a result of this long history, gouache has in some cases become a general term, used for any product which is opaque and matt. This can be anything from childrens’ paints to acrylic ranges. Traditional gouache is made from gum arabic. Gum arabic produces a flow which handles better than acrylic but it is not water resistant. Acrylic gouache is water resistant but does not having the expected handling properties.
Who uses Gouache and why?
- Designers – its ease of use and brilliance make it the most popular designers colour, hence the name, Designers’ Gouache. The matt finish makes for more accurate reproduction at artwork stage.
- Fine artists – use it in conjunction with water colour or on its own. Its brilliance and opacity give it solidity, excellent for abstract work. Strong effects also result from the contrast of working on coloured backgrounds which are left partly exposed.
- Airbrushing – water based and great covering power make gouache popular with airbrush artists. It’s the high pigmentation which makes the gouache opaque and matt.
- Calligraphy – gouache is used by calligraphers because of its excellent flow, opacity and permanence.
- Marbling – the high pigmentation and gum arabic base make it a common choice with professional marblers.
What to use it on
Best results are achieved on paper. For flat artwork, use HP water colour paper or smooth cartridge paper. Use 140lb or 220g to reduce cockling, or better still stretch the paper first. Cockling is likely to be worse if you leave some of the paper unpainted. Pastel paper will give you the strongest coloured background but these papers are not generally as lightfast as artists’ colours. Try tinted water colour paper instead or colouring stretched paper yourself with gouache first.
Permanence in the main refers to lightfastness. Some of the most vivid pinks and violets are only moderately durable, more suitable for designers’ artwork than fine artists who want greater permanence. The latter should choose only the colours rated as permanent. Don’t mistake any references to permanence on lower quality products if the meaning is waterproof.
Making gouache waterproof
Gouache can be made water resistant by mixing with acrylic medium. If you want to do this because colour is dusting off, see below. The more medium you add, the deeper the tone will become and you will reduce the characteristic matt gouache finish. Some gouache colours can react, the pinks and violets may change colour on mixing with the medium whist other colours may produce lumpy or gelatinous mixtures. Both these effects occur at the point of mixing on the palette.
Preventing gouache from cracking or dusting off
The high pigmentation of gouache leaves the minimum room for binder. If painting in multiple layers the binder may be absorbed by underlayers, resulting in cracking. Dusting off can occur if the colour is diluted with too much water, leaving only pigment on the paper. This is common when airbrushing. In both cases you need gum arabic. With multiple layers, add gum arabic to the colour, keep it to a minimum or you’ll get transparency and gloss, but the amount needed will vary from colour to colour. For airbrushing, dilute all the colours with a mixture of gum arabic and water.
Gouache is likely to crack if used in thick films straight from the tube. Textured brushwork can be achieved with gouache by using Aquapasto medium. Don’t use too much or you’ll loose mattness and opacity. Added texture is possible by using acrylic texture gels, but read the section above on waterproofing as that information applies here too.
Gouache paintings are best left unvarnished because the varnish drastically affects the depth, darkness and finish of the work. It would not be removable in the future either. If you want to varnish because of dusting off, use gum arabic in the future instead. For protection, frame the work behind glass.