There seems to be a universal acceptance that if a cuprian/paraiba tourmaline has a purplish cast/overtone it is unheated. This not true. At least early on the exploitation of the Mozambique deposit,, large highly toned red/purple nodules were found. They were so dark that they were heated to make lavender colored gems. The change in color/tone level took hours of heating and could be halted at any stage in the change. This was before anyone realized that they contained copper and might be of more value if heated to their ultimate very pale blue color.. There was some variability in the end product produced by the prolong heating, with at least one superior green gem being produced that I know of.
Whether a cuprian tourmaline is heated or not is not critical to its value/beauty, but sellers like to make a point about knowing if the gemstone was heated or not. Sort of like the big deal made out of heated or unheated corundum. No lab will certify that a tourmaline has or has not been heated yet. They are working on it.
Bruce
