Recently I was experimenting with iron oxides for colouring soap. In case you are wondering, whenever you see letters and numbers at the end of an ingredient list for a cosmetic product, that normally denotes the colours that have been used. Most commonly you will see iron oxides in colour cosmetics or in soap. But are they natural? This is what Wiki has to say;
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.
Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely used by humans, e.g., as iron ores,pigments, catalysts, in thermite (see the diagram) and hemoglobin. Common rust is a form of iron(III) oxide. Iron oxides are widely used as inexpensive, durable pigments in paints, coatings and colored concretes. Colors commonly available are in the “earthy” end of the yellow/orange/red/brown/black range.
The ones I experimented with were ultramarine blue ( C.I. 77007), chromium oxide green ( C.l. 77288) and Yellow Iron oxide ( C.l. 77 492). I mixed them with a small amount of water and added them to the soap is at light trace and mix thoroughly.