Sts 14kw


I’ve been asked to repair a ring which has this stamp inside it: STS

I did repairs for many years in a custom goldsmithing shop but have
been doing my own work, along with a bit of repair work, in my own
shop at home for the last few years. I have not run into this
marking before and I want to know what it is because the ring feels
very light-weight to me. Is this stamp an indication of sterling
that is plated or…?

I am replacing a missing 2.0 tanzanite and may need to do some
re-tipping but I do not want to get a torch anywhere near this thing
until I know what I am dealing with.

Thanks for your help.
Highland Goldsmiths