…at the gymnasium site in Rome. My mother mentioned to me that she liked pomegranates, that she had had one – her teeth were falling out…
One species was a liquid, which was apt to be adulterated; but when pure it had the property of blackening when added to pomegranate juice. This property seems to characterize a solution of iron sulfate in water; a solution of ordinary (potassium) alum would possess no such property. Pliny says that there is another kind of alum that the Greeks call 'schiston', and which "splits into filaments of a whitish colour",[8] From the name 'schiston' and the mode of formation, it appears that this species was the salt that forms spontaneously on certain salty minerals, as alum slate and bituminous shale, and consists chiefly of sulfates of iron and aluminium.[citation needed] In some places the iron sulfate may have been lacking, so the salt would be white and would answer, as Pliny says it did, for dyeing bright colors. Pliny describes several other species of alumen but it is not clear as to what these minerals are.
The alumen of the ancients then, was not always the same as the alum of the moderns. They knew how to produce alum from alunite, as this process is archaeologically attested on the island Lesbos.[12] This site was abandoned in the 7th century but dates back at least to the 2nd century CE. Native alumen from Melos appears to have been a mixture mainly of alunogen (Al
2(SO
4)
3·17H
2O) with alum and other minor sulfates.[13]
