Diamond cut - what is it?

Some polishing companies will choose to polish a diamond with less than optimal proportions to increase the carat weight or clarity of the diamond. For example, the stone can be made deeper b​y making the bottom of the stone steeper. This allows more weight to be retained in the polished diamond. However, because the angles are not correct, less light is reflected back to the eye. This is called light leakage.

In some cases, a diamond can be made too shallow. Again this means that the angles are less than optimal, so light leaks through the bottom of the stone. A round brilliant diamond is given a cut grade by the major grading labs like GIA, IGI and HRD. These grades are Poor, Fair, Good, Very Good, Excellent.

The cut grade gives you a good starting point guide but it is worth knowing that each grade involves a range of quality, so two diamonds which for example are both Excellent Cut will often have differing levels of optical performance.

Here is a comparison between a GIA "good cut" and one of our Hearts and Arrows diamonds which has been graded Excellent cut by GIA. You are looking to see which stone has more flashes of refracted colour as it moves through the light - this is what you will see when you view the diamond in direct sunlight or office lighting.

Comparing the brightness of the two diamonds, the Hearts and Arrows has a lot more white light return and so looks the brighter diamond with a better contrast pattern. The differences you are seeing are down to the quality of cut of the stone. When you are choosing a diamond, if you want it to be a beautiful as possible, it is important to choose the very best cut possible.