A patina created during manufacture
The contrast between lighter areas and dark recesses is not the result of wear: it is created in the workshop. It will not come off with routine cleaning, but will fade on areas touched frequently after several years, as is normal for this type of finish.
Care
Use a dry cloth. Never use silver polish: it would damage the patina in the recesses.
See also
Explore old-fashioned lever handles, antique-style lever handles and retro lever handles, as well as antique silver furniture knobs to match your furniture.