Mica

Mica is a naturally occurring mineral that is ground into a very fine powder and coated with pigment to create a wide range of shimmering colors for soap and cosmetics. Because the base mineral itself is not very reactive, mica works in both melt and pour and cold process soap, though its color can shift slightly in a high-pH cold process batter.

Micas are typically mixed into a small amount of oil before being blended into soap, which helps prevent clumping and speckling. The amount used is small, generally measured in fractions of a teaspoon per pound of oils, and more is not always better since overloading can dull rather than deepen a color.

When buying mica, look for cosmetic-grade powder rated for use on skin rather than craft or nail-art mica, since formulations differ. A common mistake is stirring mica in at trace without first dispersing it in oil, which leaves gritty specks or uneven color streaks in the finished bar.