Looks like people have already covered the casemaking aspect, so I'll stick to the gizzards:

Had they plated their own tuning pins, there would be copper plating residue and Nickel plating residue to get rid of-some kind of acidic solution.

Had they blued their own pins there would be some chemical bluing agents in use, probably with some sulphur content.

If they cut their own tuning pins and music wire, they would have gone through quantities of cutting oil and the like.

It is likely they had their own physical plant and may have used oil or gas to run it.

In making their actions there were many wood cutting steps and gluing processes, but none of the old animal based glue that I encounter is hazardous.

If they made any player actions, they may have used lead for hoses and seals and the like. Also they may have hade some process in place for the manufacture of macanaw cloth for the striker and exhausting pnumatics, likewise a place for the leather used in pouches, couplers (as nuts because they were noisless) and gaskets (except Schultz, who used a nasty little paper-covered pnumatic in leu of a pouch.) Some older player actions were painted with a lead based flat paint, but not many. There aren't many player actions with lead tubing either but there are a few around-Norris and Hyde made one that I know of, as did Simplex, and the Cable-Euphona had lead elbows up to the point just above the top tier of pnumatics, where they changed to black rubber. The hoses were just black rubber, as a rule, and the great hoses between the upper and lower stacks were cloth covered rubber.

Good luck

Chaz