Is it safe to eat off of partially tarnished silver?
If it's pure silver, it's fine. Silver isn't toxic. Well...if you get some colloidial silver, and you dose yourself with it every day, you'll have some disturbing symptoms. The same is true of almost all metals. Iron pills, for example, are worse, but we commonly cook with cast iron. Metallic silver is sometimes used as a chelating agent, so it can purge your body of other metals you may have absorbed.

If its heirloom electroplated silver, it's probably still fine. If it's heirloom pewter, coated in copper, then electroplated with silver, its still fine (because pewter doesn't tarnish, so the tarnish is either silver or copper) but I wouldn't eat anything acidic with it, because it'll leech lead into your food.

Note : There is no way you have pewter. That was a joke.