Well, I remembered to ask Colin and Sophie, who make the jewellery
for the Downton Abbey productions and I am told that the producers
decided not to use the ring he had made and bought a plated copper
one from Marks and Spencers, a well known chain store that is better
known for its clothing and food. The plating rubbed off in no time at
all and they got him to replate it which made negated any saving they
had made by buying a lookalike instead of precious metal.
it is common for decent jewellery to go missing on set and is often
written into major actor’s contracts they can keep the clothes,
jewels etc that they wear, never mind who actually owns them.