Aesthetic, non-allergenic plating for a zinc die casting

A. There are issues with nickel allergies, as about 10% (approximately) of the population can develop "nickel itch" which is a form of dermatitis. Similarly, there are issues with electroplating nickel, for exactly the same reasons. I believe you mention using tin-nickel; this is a very much underrated alloy that is relatively easy to deposit, but it may not meet your needs as it is usually deposited in a bright state - one of the quirks of Sn-Ni! I also believe it meets the nickel regulations in that it does not release readily release nickel and cause the itch. I reckon your best option is to put down a layer of copper and then plate it with nickel and then a relatively thick layer of chromium; you may be able to get away with just copper and chromium, depending on the end use. You could also use dull tin, but that is a bit soft and white and not very brushed stainless-like. Another alternative is to use palladium - it is a bit expensive, but could do the job. My personal opinion is that cobalt could do the job, but there are issues pending with cobalt similar to those of nickel, although I reckon that sensitivity to cobalt could be due to nickel impurities in the cobalt salts used in the sensitivity tests!

I think bright tin would be a good choice. It is bright and totally nontoxic (think about tin cans). It would require for a few reasons an under plate of copper.