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About your cup. This is not an easy case so I'm just providing a wild guess. To me the badly punched maker's mark looks like ПД----maybe (Latin PD). A master that comes close is Pavel Dimitrijev 1883-1887. But as you can see the cup is assayed in 1889 so there is a gap of 2 years. Of course the cup might have been assayed later but....? Another possibility would be Pierre Lusyen Dupen but he was more known as a jeweler.
Unfortunately there are still many unidentified masters in Russia.
Of course the mark could be something else. This is my opinion only.....as I said, a wild guess. Let's see if somebody else has better suggestions.