When we speak of cut, we mean the proportions of the diamond. The facets of the stone reflect the light traveling through the stone. If the angles and proportions are just right, most of the light, that enters the stone, gets broken apart into the colors of the rainbow and reflects back out through the top of the stone, giving tremendous fire. If the angles and proportions of the stone are a bit off them, some of the light is allowed to escape through the bottom and sides, reducing the stone s brilliance. This lack of precision in the cut is not always an accident.
Some cutters purposely facet a stone imperfectly, to maximize the weight of the finished stone.
The cut with the greatest fire is called the brilliant cut. Its color can vary from pink to deep red. Chromium creates the beautiful red in ruby. Corundum, to which family the ruby belongs, of any other color than red is known as sapphire. Big rubis are more rare than big diamonds.