Diamond Cut

This style of diamond is often referred to as an Asscher cut diamond. In this light, we are looking to see which diamond has the brighter, whiter areas on the diamond and so which shows the best light return.

The stone on the left is a typical square emerald. It is suffering from light leakage in the table of the diamond, making it a little glassy, which you can see by the lack of light return. The stone on the right is absolutely gorgeous with excellent light return. This is what you should be aiming for in Asscher cut diamond.

It is apparent is the lack of fire in the table of the diamond on the left. This is caused by the facets not being correctly positioned causing light leakage in the stone. In comparison, the diamond on the right is looking absolutely stunning. This is also the amount of fire you should be aiming for stone cut to give the best optics.

In terms of their proportions, both diamonds have a depth percentage of 68%. The table on the size right stone is 62% whilst the left hand stone is 58%. You might expect the stone with the smaller table to generate more fire from the crown, but as you can see this is not the case.

This is why when we select our Asscher cut diamonds, we find it is essential to hand pick each one for perfect optics to ensure right level of brightness and fire in the diamond. This way we can weed out diamonds like the stone on the left, which sound rather good based on the information in the GIA lab report, but in practice disappoint when you inspect them with your eyes.

When choosing a princess cut diamond, it is important to first assess the brilliance of the stone - this is the level of white light return and pattern of contrast generated by the diamond. Here is a comparison between one of our hand-picked, princess cut diamonds certified by GIA on the left, versus a typical GIA certified princess cut diamond on the right which didn’t pass our optical tests.

The stone on the left has a very strong amount of white light return coupled with very nice pattern of contrast. The stone on the right has patches of good light return, but also has areas of light leakage which tend to give to give the diamond a grey overtone which looks less attractive to the naked eye.

If you are researching buying a princess cut diamond, you will usually find suggestions on-line for the ideal table and depth percentages that the diamond should have. Both of these stones have a depth of 71% and a table of between a 71% and 72%. This is considered to be in a premium range and so accordingly you might expect both diamonds to be similar in terms of the amount of fire they create. However, they have very different levels of fire/refraction. This shows that it isn’t possible to reliably predict the optical performance of the diamond just from a GIA grading report or by comparing table and depth percentages.

Another interesting observation is the size of the flashes of fire. Even though the stone on the right has less refraction, you will notice that the flashes of fire are a little larger in size than the diamond on the left. This is because it is a three chevron princess cut and hence has fewer facets on the pavilion. This doesn’t make the diamond more or less beautiful; it just changes the character of the stone a little.

Next you can compare the sparkles of the diamond. The diamond on the left has a very good level of sparkle which is very attractive to the eye. In comparison, the diamond on the right has some areas of the stone which are really underperforming.

Using the common dimensions of table and depth % as a guide to predict the optics of a princess cut diamond is very unreliable. The comparison shows that two stones which, according to the GIA report might suggest they are very similar, are in fact poles apart in terms of the appearance of the fire, scintillation and brilliance. This is why we hand pick every princess cut diamond.

Description

It surprises many people that only a small fraction of diamonds are cut with the intention of making the diamond as beautiful as possible. Most are cut to maximise the carat weight or the clarity of the diamond. Why is this the case?

Video Summary

The angles and proportions of the diamond are often called the 'cut' proportions, not to be confused with the shape of the diamond. A diamond which has better angles and proportions will have noticeably superior amounts of brilliance, fire, and scintillation.

The brilliance of the diamond is the proportion of light which is reflected back to the eye. The scintillation is how the light reflects off the top facets of the diamond and gives the diamond its sparkle. The fire of the stone is how the facets refract the light into the colours of the rainbow. So as you move the diamond through the light, you see flashes of blues and reds within the diamond.

If the cut it so important, why are all diamonds not perfectly cut so they look as beautiful as possible? The answer is all about yield. It is more tempting for a polishing company to cut a diamond to retain more carat weight, as this is more easily explained to a customer, than to cut the diamond with more fire and scintillation.

At Samara James, we would recommend choosing the diamond with the best cut, even it means reducing the colour and the clarity, to keep within budget. This is because the perfectly cut diamond will have visibly more brilliance, fire and scintillation and look more beautiful to the eye.

When a lab like GIA assess the 'cut grade' of a diamond, they measure an average of the main facets on the crown and pavilion of the diamond. This method means that, whilst many facets on the diamond might not be correctly positioned, as long as the averages fall within certain ranges, the diamond can still be Excellent Cut.

Hearts and Arrows looks at the optical symmetry of a diamond, i.e. making sure that every group of facets is at the same angle on a round brilliant cut diamond. The term Hearts and Arrows comes from the pattern displayed on a perfectly cut stone, with perfect internal optical symmetry, when viewed under a special viewer.

When you look at the stone from above through the viewer, you will see a series of 8 perfectly formed arrows on a standard 57 facet round brilliant diamond. When you view the stone from the bottom, you will see 8 perfectly formed hearts. There is no difference in terms of the number of facets - it means though that every facet is cut to the same angle creating perfect optical symmetry.

A common misconception is that a diamond that is known as a ‘Triple Excellent’, which means it has Excellent Cut, Excellent Polish and Excellent Symmetry, will also display a Hearts and Arrows pattern. Unfortunately, this is not the case. Because the cut grade is based on an average of the main angles, the position of the facets can vary quite significantly.

You can see the differences in the optical performance of a diamond which is perfectly cut with Hearts and Arrows versus an Excellent Cut without Hearts and Arrows. In this comparison, the Hearts and Arrows diamond on the left has more sparkle evenly distributed when compared to the Excellent Cut stone without Hearts and Arrows.

Comparing the light return of the same two diamonds, you can see that the Hearts and Arrows diamond is noticeably brighter. It also has a better contrast pattern.

Comparing the levels of 'fire', or light refraction, of the two diamonds, the Hearts and Arrows stone has more fire that is evenly distributed across the stone.

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.

Description

Whether you are looking to learn a bit more about diamonds or you would like to become more of an expert, our diamond videos and diamond guides are made just for you. In this video, we explain 'diamond cut' and why it is so important to how beautiful the diamond looks.

Video Transcript

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 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 cut possible.