Tea set markings

Can anyone please help to confirm whether this tea set is plate or solid. Everything points to it being plate (not least that it was found in an old carrier bag in a shed) but a small (0.5mm deep) nick in the base reveals only more silver. The marks on the pot and bowl are similar (JR & S S) but the jug has JR & S crown in shield. Only the pot has the 4 beneath the mark.
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It’s plated. The maker is Joseph Ridge & Co. The JR&S is identical to the mark of John Round and Son; Ridge was the manager of Round and Son. It’s probable that what you are seeing in the nick on the base is the (white) base metal.