The unexplained violet
Nobody has published a complete account of why nine-times-roasted salt turns purple. The explanations on offer — trapped carbon from incomplete bamboo combustion, iron and manganese state changes, colour centres in the crystal lattice — each explain part of it and none explain all of it.
We have stopped trying to settle the question and started measuring it instead. Here is what we see across our own batches, including the two where the colour did not arrive at all.
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