Recognizing phosphate coated hex nuts

How can I visually differentiate a zinc coated hex nut from phosphate coated hex nut

If a reader has photos we'd be delighted to post them here. In the meanwhile, zinc plated hex nuts are usually quite bright and look almost like chrome or nickel (as long as they are not side by side) or gold-like. Phosphate coated nuts will usually look quite dull and grayish or blackish, and rather non-metallic.

But there are several ways to zinc plate nuts, so the brightness may vary, and several ways to post-treat them, from blue through yellow through olive green; and likewise several different phosphating processes. If it's a critical application, you need the certified parts to stay with their lot identification so you know the treatment they received, rather than guessing from appearance though.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey