Porosity of Greek Pottery
Pollux, Onomasticon, VII, 161 ff.
162. Aristophanes says that a clay vinegar jar has leprosy, instead of saying that it is moist (sweats?).
Λεπρᾶν δὲ κεράμειον ὀξηρόν, ἀντὶ τοῦ μυδᾶν, Ἀριστοφάνης λέγει.
This appears to refer to the fact that unglazed ware (and even painted Athenian pottery is unglazed in parts) becomes moist when filled with liquid, on account of its porosity.