Kevin Scully
Gouache is a medium that is often overlooked, particularly when it comes to painting landscapes, even though many artists, notably John Singer Sargent and Turner, have used it. White gouache is often used for highlights in watercolour painting in preference to white watercolour or Chinese white, because of its far superior covering power.
A water-based paint with a matt finish, and a first cousin of watercolour, gouache can be used in a variety of ways, and in many respects falls halfway between watercolour and oils as a painting medium. It can be used in both transparent and delicate washes, as well as in semi-opaque and opaque layers, one on top of the other. Some of the techniques used in both watercolour and oil paint can be applied to gouache, but it differs greatly from acrylics in that once dry it can be rewetted. Mistakes in watercolour can be corrected, albeit with great difficulty, whereas gouache colour can be adjusted and rectified without too much drama.