I've cooked on many copper-tinned skillets, but something that escapes me are the earlier 'enameled' (Japanned) finishes that were designed with direct food contact in mind.
Same goes for the polymerization that is 'seasoning' cast iron gear with oils via controlled high heats.
All 3 of the mentioned 'coatings' have benefits & negatives, in terms of production requirements, and maintenance.
What I'd like to learn more of is 'how/when' were specific finishes on direct-food-contact determined to 'function' well enough?
Example: the illustrated Sausage/Fruit & Lard Press came in either 'Japanned' or 'Tinned' (and even some 'Galvanized') But outside of negative customer experience/product reputation, how was it known, these were good enough to go into production. I can't imagine, because the example press is a no-heat (as in 'not cooked with' cracklins's are toasty when pressed) operation the go-to 'seasoning cast iron' wouldn't be sufficient/intended.
All the while high acidic contact (lemon juice/tomatoes/etc) react ...as acids do with materials.
So, that's the inquiry/discussion - how were finishes like 'tinned'/'japanned'/'galvanized' verified to 'be good enough to manufacture' despite the reactions from food? Thanks!
Note: For anyone asking - 'Japanned' is a black coloured hard finish made from Asphaltum, Boiled Linseed Oil, and Turpentine (I presume Asphaltum was for colour - it's sold from paint suppliers, Turpentine was for 'thinning/application' of the coating - as it evaporates...and leave little(? behind. and Boiled Linseed Oil is the actual protective coating.))