Antique ring in 18K yellow gold composed of three old cut diamonds

Yellow gold : Yellow 18K gold is an alloy contianing 75% of pure gold, whereas 14K gold contains only 58,5% of pure gold.
Old cut : Refers to a cut not following the cutting rules described by "Marcel Tolkowsky" in his book "Diamond Design". Any cut made before 1919.
Carat : The carat (ct) is a unit of mass equal to 2 g. Carat is used for measuring the weight of gemstones.
Diamond : In mineralogy, diamond is an extremely rare, precious and hard (named after the ancient Greek "unbreakable") metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice.