Editing Alum (section)

===Alumen in Pliny and Dioscorides===
A detailed description of a substance termed ''alumen'' occurs in the [[Roman Empire|Roman]] [[Pliny the Elder]]'s ''[[Natural History (Pliny)|Natural History]]''.<ref name="PlinySr-NatHist" />

By comparing Pliny's description with the account of ''stypteria'' (στυπτηρία) given by [[Dioscorides]],<ref name="Dioscor-MatMed" /> it is obvious the two are identical. Pliny informs us that a form of ''alumen'' was found naturally in the earth, and terms it ''salsugoterrae''.

Pliny wrote that different substances were distinguished by the name of ''alumen'', but they were all characterised by a certain degree of [[Astringent|astringency]], and were all employed for dyeing and medicine. Pliny wrote that there is another kind of alum that the ancient [[Ancient Greece|Greeks]] term ''schiston'', and which "splits into filaments of a whitish colour".<ref name=PlinySr-NatHist/> From the name ''schiston'' and the mode of formation, it seems that this kind was the salt that forms spontaneously on certain salty minerals, as alum [[slate]] and bituminous [[shale]], and consists mainly of sulfates of iron and aluminium.{{citation needed|date=May 2009}} One kind of ''alumen'' 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 (chemistry)|solution]] of [[Iron(II) sulfate|iron{{sup|II}} sulfate]] in water; a solution of ordinary (potassium) alum would possess no such property. Contamination with iron sulfate was greatly disliked as this darkened and dulled dye colours. In some places the iron sulfate may have been lacking, so the salt would be white and would be suitable, according to Pliny, for dyeing bright colors.

Pliny describes several other types of alumen but it is not clear as to what these minerals are. The ''alumen'' of the ancients, then, was not always potassium alum, not even an alkali aluminum sulfate.<ref name=Chisholm-1911/>{{rp|pages=&nbsp;766–767}}