Gouache is a heavy, opaque watercolour paint which has been
used for centuries in fine art and and also in design applications.
It results in paintings that are richly and vividly coloured.
Unlike watercolour, gouache does not rely on the whiteness of
the background medium (usually archival
paper) to achieve its effect. Gouache forms an opaque reflective
layer on the surface and is not a stain like most watercolour
pigment.
Composition of Gouache
Gouache consists of pigments in a water-soluble binder (gum
arabic) with preservative and plasticiser (glycerine). Gouache
is thinned with water, the same as watercolour or acrylic paint,
and applied with brushes.
The pigments in gouache are of various types. Some are natural
products, such as earths, umbers and ochres, while others come
from metal (cadmium, cobalt, titanium) compounds and are referred
to as 'traditional' pigments. Modern pigments are also widely
used, in addition to the traditional ones, and these are generally
organic dies and compounds derived from petrochemicals.
The pigments used are the same quality as those in transparent
watercolours, but are not ground as finely because gouache is
not used in the form of a wash. It has a greater proportion
of binder to pigment than in watercolours, and so can be used
as opaque paint.
Characteristics of Gouache
Gouache is an excellent, stable and long-lasting medium for
fine art. Nevertheless, like all art materials, it is important
to understand its characteristics and to avoid circumstances
which may make the paint vulnerable to damage or deterioration.
After gouache has dried, it can be re-wetted - this is because
there is no chemical change during the drying process. While
this makes it convenient for the artist to rework a painting,
it also makes the work vulnerable to water damage. Water resistance
can be achieved by adding small amounts of acrylic matt medium.
Care needs to be taken, however, as some colours can change
or darken.
If applied too thickly (either in a single layer or successive
layers), gouache can be prone to cracking or peeling off. It
is therefore important that the paintings are moved, stored,
and displayed in secure flat containers or mounts. When painting
in layers, subsequent coats need to be applied thinly to avoid
brittleness. Gum arabic needs to be added to successive coats
to act as a binder.
Conserving Gouache Paintings
Gouache paintings on paper should be properly mounted and framed
behind glass or other protective layer. There should be a mount
or spacer between the painting and the glass and all materials
should be acid-free.
This protects the painting from damage to the surface, any
risk of water splashing or damage, prevents accumulation of
dust, and helps to reduce fading from exposure to ultraviolet
light.
Varnishing gouache paintings is not recommended because it
greatly changes the brightness and finish of the painting. Varnish
can sink into the paper, discolouring it and making it brittle.
Other points to watch out for are:
- Do not store or display paintings in places that exposes
them to high humidity or water leakage, e.g. bathroom, outside
walls, under pipes.
- Avoid areas where temperature and humidity fluctuate, or
where there is inadequate air circulation, such as an attic
or basement.
- Do not hang paintings near radiators, heating and cooling
vents, fire places, air conditioners or humidifiers.
