Such a fine ring. The hallmarks are-"AR", 750, and the third hallmark I cannot read. The top of the ring has cobalt blue enamel over the gold in a knot design. Very pretty look. The ring is size 5 1/4, and could be re-sized. Weight is 4.6 grams. Condition is very good for age. With the 10X loupe, one small chip to the blue enamel on one little curve. Not seen by my aging eyes. I would date this great ring at c1960's.