Dates to the Art Deco era, circa 1925.
Crafted in solid 18K white gold, and bears a maker's mark (the letter K within a diamond) I am not able to positively identify.
Beautiful openwork design, which detailing extending into the shoulders, as well as on top and bottom. Almost a Greek key like design. The ring is set with a 3.5 mm diamond (between 0.16 and 0.18 carats), which is an Old European cut. It's a good clean stone with loads of sparkle.
The front of the ring measures 0.34" from top to bottom, with a band that narrows down to 0.04" at the very back. The ring is presently a size 4.75 and weighs 2.1 grams.
Condition is very good, with no damages.