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Artists started using gouache to make their work more lifelike. The technique enhances the image by adding shades of light and dark that better depict the subject of a painting.

They would wet their brush, generally with pure water, and spread some of the colors used in the painting. Sometimes they also accentuated the effect by running the wet brush over certain parts of the work,� either wet or dry. In this way, and in most cases it was done with drawings done with a quill, the gouache strokes would give the drawing new effects of light and color.

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History
Miniaturist painters were the pioneers in using this technique. It showed all its potential during the Renaissance, thanks to Italian masters led by Guercino.

But it was Rembrandt who perfected the method. No artist since then has been able to match his talent for applying the technique in just the right place or applying it in seemingly infinite gradations.

The only artist to come close was Claude Lorrain who, like Rembrandt, first used a quill to sketch the outlines of the painting, then filled it in with gouache.

Later, in the 17th and 18th centuries, the technique was still popular because of the effects it could render with light. In the 19th century it was still used but faded in popularity. It was used more to represent a subject than as a means of expression.

Key elements
Using the technique correctly requires accurate analysis of how light is distributed in the painting. An initial stroke must be followed up by another, diluted gouache touch. This means that you must think for a few seconds increasing the intensity of� a tone in a given part of the painting.

A wide variety of opaque colors can be used, although the most common ones are walnut, bister, indigo, kaolin green, neutral ink and charcoal black.

It can be applied with problems to drawings done in pencil or with a fountain pen, but you have to be careful when using pastel, chalk or charcoal.

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Application
Gouache is a cumulative technique, which means you start using it with pale and transparent layers, then add coat after coat until you attain darker tones. It is very important not to use too much color because it is very hard to reduce the intensity of a tone once it is on the painting.

The goal of applying successive coats, generally darker and darker, is to produce an effect of velvety shadows. You must have loads of patience because you must wait for one layer to dry before you put the next one on top of it.

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The paper
The kind of paper you use is very important because it is has to withstand water: the greater the weight of the paper, the more water it can take. The other point to keep in mind is the surface, which can be rough or smooth. It is a question of choice.

Before using the paper you must stretch it so it can take wet strokes without deforming. The most common procedure is to wet both sides of the paper with a spray gun. Let it absorb the water for a few minutes. Then stick the sheet on a board without stretching. Place it horizontally, and let it dry slowly so it occurs evenly on both sides. Otherwise tension can be stored in the paper and it might tear.

When it is completely dry, use a blade to cut through the center of the adhesive tape used to attach the paper to the board. Then soak the paper in water for 15 minutes, and stretch it on a board with clips on the edge.