What is the deal with the mark?

[Firsttimecaller]

So I am certain this is costumer jewelry but I discovered the mark on the inside on the ring. It appears to read 0KP GTP. Through some digging I have found that GTP is likely the mark of a jeweler out of Long Island City, J.M. Fox, Inc (if I remember correctly) and I have learned that KP is to stand for karat plumb, to mean "exact" purity or higher. But I have never seen a ring marked with 0 karats. Why would someone do this? What is the point? Is this just a fluke in the marking process? It doesn't appear to have worn at all. I don't think it ever said 10KP GTR. I'm also not certain on the stone, best guess? Baby Sky Topaz? Not even sure if that is a proper topaz color to be honest. I really just want to know why 0KP? I cannot find anything that says a jeweler would mark a ring in such a way.

 

[VRBeauty]

Have you cleaned the stone? As it is, my first reaction is that it’s glass, probably a glass repro of an aquamarine, and that it was probably originally sold as birthstone jewelry.

I’ve never seen anything stamped “0 karats” before, though! 10kt birthstone jewelry was fairly common, though... which makes me wonder if this is just a stamping error? Far-fetched, I know.

BTW, I read the stamp as “GTR,” not “GTP.”

 

[Sibsgirl]

I see "OKP GTR." I have some older pieces that don't have hallmarks in them, but that doesn't mean they're costume. The wear on the prongs and the fact that the ring still shows gold strikes me as being an inexpensive late '80s/early '90s 10K (or maybe 14K) blue topaz/diamond ring.