Retarder is a thin water-based product designed to slow down the drying time of acrylic paints. It is ideal for using with acrylic paints when plain-air painting. Mixed with acrylic colors and mediums at up to 15%, it increases open-time and allows for greater manipulation. NOTE: Using a larger proportion of Retarder to color can negatively effect the permanence and film integrity of the paint. Amber coloration may occur as the product ages in the jar. This will not effect the performance or alter the colors it is mixed with. Additives completely evaporate over time and has no effect on final finish. Always test your products and methods prior to applying to a final work.