i was hoping to get some information on this platter. Its marked Sheffield. under that It has a man, a crown and an “S”. Lastly it says S.Co. 1220.
there is an ingraved monogram and it has copper showing through.
It must be plated but i thought the mark meant it was sterling. So im a lttle confused about this piece. Ive searched for it and cant find anything useful. Any information would be appreciated. Thanks 
Hi there and thanks for joining us. Your platter was made by the Sheffield Silver Co. of Brooklyn, NY. The company was incorporated in 1908 and made silver plated holloware, not sterling. It became part of Reed & Barton in 1974 and moved to Norton, MA.
A general rule of thumb is that American sterling silver made after about 1860 has the word “sterling” on it or the number “925”. Your platter is electroplated - a thin layer of silver over the copper base.
Regards,
Uncle Vic
Thank you for taking the time to answer. I was going on info from the 925-1000 website . it listed the mark in the sterling section and said they made a small amount of sterling… thats why I was confused. I knew it couldn’t be sterling with copper showing but still…i was puzzled. Thanks again. 
The sterling silver they produced was in the form of rims and bases for glass pieces.