Red iron oxide is the main coloring agent in red ochers like Indian red, Terra Pozzuoli, and Venetian red. These pigments are primarily made up of the mineral hematite with varying amounts of other minerals such as clay, chalk, and quartz. They are distinguished from yellow and brown ochers by the absence of water in their chemical structure. In other words, the iron responsible for their color is iron oxide rather than iron oxide hydroxide.
Natural red oxides, such as hematite, are opaque, permanent, and have a high coverage power. They are excellent ultraviolet light absorbers.
