Very much like the gel medium used in acrylic painting, except there are tiny prisms of something like fine glitter suspended within the gel. This is the key to making your acrylic paintings come to life! Especially when painting flesh tones. Just add about a teaspoon of this substance to every four of your actual acrylic color. This also extends your workablitly time and extends your color, though be careful that it doesn't make it too opaque.