When "boutteure" is used in French, translation should be a form of boiling in the English. See related #82 "boutter" verb use
Godefroy: eau préparée dont les orfèvres se servaient pour blanchir l’argent, les monnayeurs pour blanchir les pièces de monnaie. So it could be 'pickle', the pickling solution used to whiten silver, but this should be determined in context. E.g. on 12v and 104 it is not clear that the ap uses 'boutteure' in this way.