I own several Merkur slant razors with all the different brandings like Hoffritz, Pomco, Coles etc.
I can say that they changed the plating on their razors over the decades. Remember that these slant razors were made for more than 70 decades! Early models had nickel plated handles, later they plated them with silver and the white silver knurling. Late Hoffritz slant razors for example had a chrome plated handle then like the current production Merkur razors. There were also gold plated razors as well.
On the silver plated handles it was the same like on the gold plated Gillette TTO's: There was a thin clear laquer that sealed the plating and when it came off the handles started to tarnish. So, if you ever get your fingers on a minty Merkur slant razor with all the different brandings avoid to clean or polish the handle with aggressive chemicals.
Once the handle shows some tarnishing the banking soda / aluminium foil method is probably the first method to get that thing shiny again. You could also try to get it shiny again with a non abrasive polish but use it carefully.
Can the white finish be replated?
