Silver oxidizes very slowly, going from that desirable pure white to a pale brown to blue to black.
However, there are different "recipes" for the alloys used to make the sterling silver used in jewelry. Some alloys contain platinum-series metals- platinum, palladium, osmium, rhodium or iridium- and tarnish extremely slowly. I have a ring I designed in 1999 that needs to be polished every month.
OTOH, a ring I designed in 2005 needs polishing only a couple times a year, and my mom owns a necklace bought back in the 1970s she's only polished a few times.