Schmincke College Retarder is a heavy body additive which delays the drying of acrylic colours and gels to render them workable for a longer period. Ideal for prolonged wet-on-wet painting. Adding around 20% retarder to an acrylic colour extends the colour's drying time by approx. 50%. A maximum of 30% retarder can be added. Not to be used in pure form. Available in a 200ml tube. Price per tube.