18th C tea set marked "R.Swan"

[hbrenrut]

I am attempted to discover the maker of an 18th century 4-piece silver tea service inherited through the Key family of colonial Maryland. Each piece is marked with the letters "R.SWAN". Though I have found references to a Robert Swanson in London in the mid-18th century, I have been unable to reference this mark. Any help would be greatly appreciated.
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[Neruda]

I believe there was a R Swan working from Andover, Mass, Philadelphia - he may be your man!
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