Madder roots has been used since ancient times as a vegetable red dye for leather, wool, cotton and silk. For dye production, the roots are harvested after two years. The outer brown layer gives the common variety of the dye, the lower yellow layer the refined variety. The dye is fixed to the cloth with help of a mordant, most commonly alum. Madder can be fermented for dyeing as well (Fleurs de garance). In France, the remains were used to produce a spirit as well. The roots contain the acid ruberthyrin. By drying, fermenting, or a treatment with acids, this is changed to sugar, alizarin and purpurin, Purpurin is normally not colored, but is red when dissolved in alkaline solutions. Mixed with clay and treated with alum and ammonia, it gives a brilliant red colorant (madder lake).