I have a Pomco slant, which is also a vintage Merkur rebrand just like the Hoffritz. I believe they are silver plated and you can get all that yucky black stuff off by using the foil and baking soda trick.
Take a glass bowl or something that can take some heat and line it with tin foil. Put some baking soda in the bottom, then put your razor on top and add more baking soda. Then pour very hot water (almost boiling) over top and let it sit until the water cools. 1-2 treatment like that should make it nice and shiny!
The white on the bottom knurling and some of the pitting on the handle are likely there to stay though.