Question

how do you obtain the purest form of diamond

Answer 1

First off, there's a difference between carats and karats. Karat is a measurement of fineness of a metal, ie how much of the metal, by weight, is pure. When used about diamonds it is the first (carat) that is used, so it is merely a unit of weight, a 266 ct diamond is just sating it's a 53.2 gram diamond.