Mediums for Watercolour and Gouache

Watercolour and gouache mediums are used sparingly alongside standard paint and water. They produce different effects; some increase transparency and luster, some slow drying time, and others are humectants designed to reduce surface tension. Frisket (reserve gum) is a liquid that, once dry, becomes a flexible film that is used to mask areas of the painting surface to block any paint from setting in those areas, given that, in watercolor, white is achieved by leaving the paper blank rather than by applying white paint.