Raw materials used in perfumery include natural products, of plant or animal origin, and synthetic materials. Essential oils are most often obtained from plant materials by steam distillation. Certain delicate oils may be obtained by solvent extraction, a process also employed to extract waxes and perfume oil, yielding—by removal of the solvent—a solid substance called a concrete. Treatment of the concrete with a second substance, usually alcohol, leaves the waxes undissolved and provides the concentrated flower oil called an ***absolute***.