NEED HELP WHEN DATING 925 MARK

Hi, ive got a ring with a black stone looks like a victorian mourning ring it opens up to put a locket of hair or a photo its only stamped 925 could someone tell me when they started stamping 925 on silver, this ring looks very much scottish to me bought it here in glasgow and the woman who was about 65 said it was her mothers, thanks kieran

PHOTO OF RING

RING OPEN