While it has been good to see the colour changes that can happen when applying heat to the iron based ochres, this controlled fashion has limits for me. Without pushing things I can get the pigment samples up to about 1100 °C (roughly 2000 °F) and this gets me well into the brown range of colour.
But, if pushed further, the iron rich earths should go a dark purple, and then black. While I can’t control or measure the temperature in this process, as an artist I’ll just state that it’s, “really” hot. The pigment sample was bright yellow during the heating, if that gives any indication.
I’ll share the results when it cools down!