The raw and burnt pigments in traditional palettes record a practical discovery: heat can change colour. Makers could obtain a different red or brown from an existing earth by processing it, rather than locating a completely new deposit.
Heating can drive off bound water or alter mineral phases. In suitable yellow ochres, this can shift hydrated iron-bearing material towards red . and also change when heated, although the details depend on composition.
This is an explanation of industrial and historic processing, not a home experiment. Heating unknown powders can create dust and fumes; do not use a domestic oven or attempt to make pigment from unidentified material.
These articles explain pigment and mineral families, not the sourcing or complete formulation of any Cameron Colours paint. Historical names can cover different materials. Follow the product guidance and safety data for the paint you use; do not handle or heat raw pigment powders at home.
