Antique Hardstone Cameo Earrings

by KH
(USA)

I have a wonderful antique pair of hardstone cameo earrings. On the backs they have a V carved into the agate or onyx stone. Do you know what that is for? Also I am not sure if these are agate or maybe onyx, how do you tell?

They have a goldish bright brassy finish, however I have tested them for gold content and they tested as 14K. (the ear post and screw back part are not gold)

I did it several times to be sure it was down into the metal underneath. They clearly pass the 10K and fail the 18K so I am sure these are 14K gold. Why would the gold be covered in this finish? Not sure when these were made ?

but was this something they did back then? Thanks so much. Any other information about these earrings would be much appreciated : )