LSJ
εως, ἡ, (< ἰόω) refinement (because freq. due to oxidization of impure substances), χρυσοῦ PMagLeid. V. 6.18, cf. Olymp.Alch. p. 94 B., Zos.Alch. p. 145 B., al.
making of a tincture, ib. p. 219 B.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)