Red Clays

"Red earthenware clay. The potter's name for brown clay. When fired to about 1000°C (1832°F) these clays burn to a deep orange colour, sometimes called flowerpot red. The red colour is due to 5% to 8% of red iron oxide which is often heightened in its brightness as a red by the natural presence of some titanium oxide. The titanium oxide may only be a trace amount below 1% but it has an effect upon iron oxide during firing. Red clays vitrify below 1200°C (2192°F)."
-The Potter's Dictionary of Materials and Techniques