Would any of the more experienced restoration folk offer up an opinion here?

This is an all original Blue Diamond razor. The tang has an amazing sapphire blue coloration to it, that blends to a purple as it approaches the heal of the blade. it has a translucent semi iridescence that reminds me of case hardening. But judging from the wear marks, it is little more than an thin coating of some sort.

Would anybody know how this was achieved? A form of anodizing perhaps? I have never seen gun bluing of this coloration before, but perhaps a similar method?
Pic is not the best, but it should give you a good enough idea what I am talking about. I will try and get a better one in daylight if you think it will help.
I want to restore an older blue diamond, and have no clue what to do.
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