Is ink chametz? E.g. ink on an egg – why is it not a problem?
I know that ethanol (made from wheat) is used in some inks but dissolves immediately upon touching anything.
There is no problem of chametz in ink.
The Shulchan Aruch (442:10) writes that there is no problem in using ink made from chametz, and the Mishnah Berurah (44) explains that the ink is inedible and that there is therefore no problem in using it.
The Mishnah Berurah writes that one must not intentionally eat the ink, but eggs that are stamped will not be considered “intentionally eating ink” even if they are cooked with the ink (see also Shulchan Aruch HaRav 442:34).
Therefore, there is no problem at all with using stamped eggs on Pesach.