No, I meant etchant, cartridges filled with strong corrosive. I don't know any particular brand and that's just word-on-mouth knowledge, but that wasn't your average etchant like ferric chloride sollution, I think these were pretty special cartridges too. Since the etchant doesn't land anywhere outside the etching area, it may be as strong as it can get, no risk of dissolving the (nonexistent) etch-resistant layer. Just so it won't dissolve the cartridge itself. (and since it's sprayed as hot vapor on the copper, the efficiency is quite high...)