Passivation

[Voicecoil]

Had a little look into this and it seems that Citric Acid can be used instead of Nitric Acid(link) but you would still have to put a protective coat over that so it looks like the etch primer would be a better solution,Just had a check in the shed, the Manor Paints is the Chromate(yellow base) that i prefer but Chromadex do a none Chromate etch if you prefer that.I got this for refurbishment of Spilka H type window hardware as they are made from mild steel then passivated and clear coated but this deteriorated after about 10 years, just out of interest where are you located, i am near Ulverston.
Hope that helps.
Regards
Mike
https://www.amazon.co.uk/Citric-acid.../dp/B00GOT02C2

Thanks for that Mike, but I really wanted a simple chemical passivation process (i.e. just dip it) rather than some kind of painting. BTW, I'm just over the hill from you in Broughton, nice to find someone else up this way - one often feels a bit out on a limb living up here!