Just out of curiosity - why nickel? Shouldn't be chrome the original finishing?
Nickel is also a known, proven cause of possible allergic reactions, whose severity may vary depending on an individual's sensibility; for this reason, here in the EU, its maximum content in items destined to skin contact -i.e. costume jewelry- is limited by law (btw, didn't you have issues in sourcing the nickel plating solution? Use of that product is restricted to professionals only here, and sale to private customers is not allowed).
I wonder, if items as small as earrings can already cause problems, what about a large watch case, heavily custom-plated?