It sounds like chrome plated silver. I occasionally come across this;
the first cut with a saw or file tells me it is chrome plated. Chrome
is super hard, cracks when you bend the component, leaves steps when
you polish (the silver is rubbed away while the chrome in
unaffected), turns black or blue with heat, behaves like iron in the
acid bath and copper plates everything.
In my opinion putting chrome on silver is a waste of silver. The
articles should have been made of brass because chrome is not a
noble metal and belongs with base metals.
I tell the customer that I will do my best with the repair, but that
the article has already been damaged by the chrome plating. I treat
it as silver, use a bit more solder and leave it higher or over the
chrome, no sanding, polish just to restore the color of the chrome,
and keep it out of the acid. No hammering or stretching - the chrome
cracks and peels; cracks due to bending (as in ring sizing) are left