To me, getting the best value for money means getting the most out of whatever you’re trying to optimise for. This tutorial is designed to help you take what you’ve learned in level 2 to choose specific sets of proportions to maximise the characteristic that you’re going for, whether it’s size, light return, fire, or scintillation.

When optimising a diamond, it’s important to remember to find a diamond with tight tolerances so you want to find a diamond with high optical symmetry, preferably an H&A or near-H&A.

Optimising for Size

Optimising for size is fun! It involves thinking about what are the reasonable hits we can take on other aspects in order to increase the diameter of the diamond.

The difference between a thin and a medium girdle is around 1% girdle thickness. A medium girdle will look like a thin line and a thin girdle will just look like an edge. Because the girdle is the widest part of the diamond, a 1% increase in the thickness leads to a more than 1% increase in its weight.

However, a thicker girdle does not increase the diameter of the diamond at all so it is always bad for spread. In my opinion, the weight going into the girdle is less valuable than the weight going into the diameter so you take this into account when valuing a diamond.

The reason we want thin-to-medium, or medium girdles is because these are a good balance between a girdle being too thin and therefore prone to chipping and a girdle that is unnecessarily thick.

The next thing is the pavilion angle. Remember, the only reason you would ever want a 41 degree pavilion angle is that it compensates for shallow crown angles. But we know that at around 41-degree is where the pavilion angle begins to leak light.

The reason why a cutter will want to cut as steep a pavilion angle as possible without leakage is that this maximises their rough yield. But you have to think that as a consumer, what is good for the cutter may not necessarily be good for you.

We also know that a 40.4 degree pavilion angle will have obstruction problems. Therefore the shallowest pavilion angle on the certificate is 40.6 degrees if you want to ensure that the actual pavilion angle is over 40.5 degrees. The exact pavilion angles that are optimum will depend on what the crown angles are.

Another way we can increase spread is to look for the lowest crown height possible. The easiest way to do this is to find a diamond with a large table percentage, something like 62% which is the largest table within the GIA excellent cut grade. Let’s pair this with a 31.5-degree crown angle, which is the shallowest crown angle that will stay within a very good cut grade when coupled with a 40.5 pavilion angle. Because a shallow crown also means a shallow upper girdle, you may want to consider shorter lower girdles (75%) so that they don’t leak before the pavilion mains .

You get shallower upper girdles when you choose shorter stars. Just make sure you avoid painting of the girdles, which add unnecessary weight. That means you should aim for 50% stars, which may be difficult to acheive when the crowns are this shallow. Since the crowns are shallow, you also don’t want a girdle that is too thin.

Lets sum it all up now:

The specs would be:

• Thin to medium girdle
• 62% table
• 31.5 degree crown angle
• 40.5 degree pavilion angle
• 75% lower girdles
• 50% stars
• 40-43 degree upper girdles
• No painting or digging!

Optimising for Light Return

Optimising for light return means minimising unwanted light leakage. The first thing is therefore choosing a pavilion angle between 40.5 and 40.8 for maximum light return. The next thing you can consider is a large table to let a lot of light in, something around 60%. With the large table, we are actually trying to reduce dispersion by making the crown facets smaller.

We should choose a pavilion angle that is toward the steeper end of the range mentioned above. This will increase the amount of tilt required before you see a fish-eye and to some extent manage the size of the table reflection. As you already know, the choice of crown angle in this range depends on the pavilion angle so we would pair a 40.8-degree pavilion angle with a 34.5-degree crown angle.

If you go for a painted girdle, the diamond will be brighter around the edges. But if you do this, the diamond will be noticeably darker in the bottom half of the diamond when you look at it from the face-up view. A painted girdle is usually accompanied by shorter stars, and this will mean less obstruction and an overall brighter diamond albeit with less contrast.

I would stick to 50% stars to keep the upper girdles relatively shallow. For the lower girdles, it’s more of a matter of preference whether you choose 75% or 80% lower girdles. But for my personal tastes, I wouldn’t go with too long of a lower girdle because I personally don’t think thin arrows look good with a large table/table reflection. 75% lower girdles will also ensure there’s less head shadow/body obstruction and maximise light return from the minor facets.

Therefore the specs for a brilliance optimised diamond without painting is:

• Thin-to-medium girdle
• 60% table
• 34.5 degree crown angle
• 40.8 degree pavilion angle
• 75% lower girdles
• 50% stars
• 40-43 degree upper girdles
• no painting

The specs for a brilliance optimised diamond with painting is:

• Thin-to-medium girdle
• 60% table
• 34.5 degree crown angle
• 40.8 degree pavilion angle
• 75 – 80% lower girdles
• 45% stars
• <40 degree upper girdles
• crown-only painting

Optimising for Fire

Although we can make choices to optimise a diamond for fire, you should know that a diamond’s fire is affected by lighting more than any other factor. Also, if you’re a fire aficionado, you may want to consider diamond simulants because they usually have more fire than diamond. Finally, if you’re settled on a diamond but want a similar type of fire to simulants, then there is a type of surface treatment known as ‘fire polish’ that you can apply to the diamond to increase fire in a diamond.

The first thing to do when optimising for fire is to maximise the size of the crown facets. You do this by having a really high crown, and you get that by having a small table coupled with a steep crown. I would recommend a 53% table coupled with a 36-degree crown angle, which keeps you within GIA excellent cut. You want a 40.5-degree pavilion angle to compensate for the steeper crown angle.

Now we get into preference for either pin-fire flash or bolder flashes. If you prefer pin-fire flash and to maximise scintillation, then you will want at least 80% lower girdles and perhaps even closer to 85%. With such thin arrows, you may want more of them and that’s when I would refer you to the Solasfera cut. Since you have long lower girdles, you want to pair this with long stars which will also increase the size of the hotspots increasing the pin-fire flash even more.

For a fire-optimised diamond, you don’t want any painting of the diamond as that reduces contrast. The leakage in the upper girdles from an unpainted diamond that you see in the face-up view will return flashes of light adding to scintillation when the diamond is rocked.

If instead you like bold flashes, you will want shorter lower girdles (75% or less). Even if you have decided on bold flashes, you can still make a decision about whether you want to only have bold flash or mix it in with some pin flash as well for a more balanced appearance. If you want a balance of pin and bold flash, you will still want stars around 55%. Just make sure the upper girdles are not so steep that they begin to leak when they are over 43-degrees. If you want to focus only on bold flash, you can stick to 50% stars and also consider painted girdles. This will reduce the prevalence of hotspots and also the contrast in the edges of the diamond so that your attention will be focused on the larger events of flashes coming from the arrows.

To summarise, the specs for a pin-fire flash/scintillation optimised diamond are:

• Thin-to-medium girdle
• 53% table
• 36 degree crown angle
• 40.5 degree pavilion angle
• 80-85% lower girdles with 55% stars
• 40-43 degree upper girdles
• no painting

The specs for a balanced-fire flash optimised diamond are:

• Thin-to-medium girdle
• 53% table
• 36 degree crown angle
• 40.5 degree pavilion angle
• <75% lower girdles
• 55% stars
• 40-43 degree upper girdles
• no painting

The specs for a bold-fire flash only optimised diamond are:

• Thin-to-medium girdle
• 53% table
• 36 degree crown angle
• 40.5 degree pavilion angle
• <75% lower girdles
• 50% stars
• <40 degree upper girdles
• crown-only painting

Optimising a Balanced Diamond

To complete this tutorial, these are the full specs for what I consider to be an overall balanced diamond.

• Thin-to-medium girdle
• 57% table
• 34.5 degree crown angle
• 40.8 degree pavilion angle
• 75% lower girdles
• 55% stars
• 40-43 degree upper girdles
• no painting

A 57% table gives a good balance between allowing light in, making the diamond appear big, and allow good sized crown facets so that there’s good fire as well. The 34.5/40.8 CA/PA combination is a tried and true balance between brightness and fire. Having 75% lower girdles and 55% stars gives that mixture of bold flashes from thicker arrows and pin-fire flash coming from hotspots. The classic girdle is also a better balance between brightness, fire, and spread.

The balanced diamond achieves a nice balance between spread, brightness, contrast, pin and bold fire flash, and scintillation. It should therefore come as no surprise that it is this combination that I selected for my wife’s engagement diamond.

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