It’s more than likely a PVD coating (physical vapour disposition) as it is suitable for steel. There are a few companies in the U.K. that specialise with this process and it’s not ‘too’ pricey.
Oh wow! Player you genius! Wasn’t expecting to have the mystery solved so rapidly. That was a great show. I met Keith Bontrager and Ross Schafer (who offered me some jelly beans) there is a video on YouTube of the show and Sir Clive Sinclair was there too peddling his Zike