Retarder is a medium used to delay the fast drying time of Acrylic Colors. Acrylic Colors mixed with this medium allows to create watercolor effects such as gradation and also reduces brush marks. It may also be used with Watercolors. Two to three drops should be used for about 1cm of painting colors in a 200cc jar. Mixing too much of Retarder should be avoided as this may delay the drying time too much and may turn sticky.