Each iron oxide color is not just a single oxide, but a mix of oxides or ferric oxides (rust) with manganese or colored clay. Each color tone can be altered by kiln temperatures, concentration of minerals, pH, and the size of each particle.
Synthetic iron oxides are man-made, but are actually made from natural ores and minerals, and they are widely used in the cosmetic field. They are considered to be non-toxic, moisture resistant, and colorfast.
Iron oxides graded safe for cosmetic use are produced synthetically in order to avoid the inclusion of ferrous or ferric oxides.
The synthetic iron oxides are used because they deliver light fastness and excellent dispersing properties in to the final product and being intense in color give great depth.