Next is silver platter one.

[meekamag2]

It was an antique given as a wedding present. It hasn't been cleaned and has no markings. 

It's very heavy. Weighs almost 1 kg. (930g) 

It's diameter is about 30.8 cm and height it about 2 cm at highest points. 

I suspect that it's silver plated only, by looking at the marks on the bottom

Again, thank you for your time. 

[siddieswans]

Seems to me that there are traces of copper underneath the pattern on the front - which could mean EPBM. Rather than EPNS. Look very carefully around the edges, front and back, very often there is a small maker's mark, which may be quite faint.

[twyngwyn]

have a look here for similar 'edges':

Antique US Sterling Silver Platters & Trays for sale | eBay

[meekamag2]

Thanks, twyn. Will give it a go.