This week we are looking at diamond cut grades and shapes. Why is diamond cut grade, symmetry and polish important and how does this affect prices. This in itself is a deep dive subject but I will cover the basics as best possible to give more insights as to a standard explanation that you will normally get. As per the following 2 images of a diamond certificate  Round Brilliant cut diamonds get graded for it's cut quality in 3 areas namely: Cut, Symmetry and Polish. You will note that fancy cuts (any diamond shape other than a round brilliant cut ) only has Symmetry and Polish.


Now how do they judge each variable? Well a lot of factors get taken into consideration with certain tolerances for every grade this is mostly the relation in % of every facet to one another , the depth ratio the top table ratio to the overall diameter, angles of the facets, thickness of the "centre line" of the diamond ( girdle) between the top( crown) and the bottom (Pavillion) in ratio. So diamond cut grade is determined by ratios, angle degrees in percentages to one another. The Laboratories have certain angle variance tolerances to consider on the overall combination of all these % angles and ratios. The closer the angles all are in the ideal ratios and angles the higher the cut grade or scale ranging from Ideal/Excellent to Very Good , Good, Fair and Poor. See the diagram below:

Now the laboratories all have their own scales and slight variances in their respective threshold exist e.g. as per above AGS lab has 6 levels , GIA has 5 and HRD has 4. In all the main levels are very similar with Ideal/Excellent in very tight scales to Very Good that is close in it's tolerance, then Good with a much wider tolerance and Fair and Poor with even wider tolerances. The scale below in my experience shows the spread pretty well in terms of strictness of the tolerances. The cut grade shows the diamond cutter degree of accuracy and craftmanship on the particular diamond hence the skill level and time spend on cutting a particular diamond in a sense. Also the amount of rough diamond lost also plays a part in this that we will touch on later. All these individual factors influences the pricing.

Symmetry is the second factor and that is basically the alignment of all the facets with one another and accuracy in sizes to one another. Extra facets as small as they are, girdle thickness variation or diamonds not 100% round usually not even noticeable with the eye impacts the symmetry grade. With round brilliant cut diamond the cut grade and symmetry usually runs close to each other as overall cut grade takes into account the symmetry and polish grades. With fancy shapes the ratios of the facets, overall alignment of facets , proportion and ratio of the diamond in length , width and depth all goes into the assessment of the symmetry grade by the diamond grader, this allows for some subjectivity as the overall appearance is taken into account in fancy shapes. Below is a round brilliant diamond facet breakdown that is considered and compared with one another in their alignments and how well the compare to one another:


Polish is the 3rd factor and that is part of the finishing process of a diamond. Here polishing basically grades how clear the diamond is polished i.e. how many and how obvious is polish marks left on diamonds. Yes diamonds can have polish marks see the following example:

So basically the better and cleaner the polish the sharper and better the reflection through the diamond and that promotes more sparkle and fire.

Right so what does this have to do with the appearance? Well as you can guess a lot. A Diamond will only look like a proper diamond if all the facets, angles and ratios work together once light enters through the top of a diamond and "bounce" around inside the diamond and reflects back out through the top of the diamond. The better the reflection the more striking the diamond appears and less "deadspots" as light does not escape through the side or bottom of a diamond as it enters called light leakage. Note all diamond and gems will have a degree of leakage but the better the cut the less. Below diagrams illustrates this concept:

So this is why cut grades are important because the cut grade is what the eye sees in terms of brilliance and sparkle. Note for fancy cuts I would look at the symmetry as an indication of the "cut grade". Now everybody would say well go only for excellent grade right? Well not so fast- Remember I highlighted the tolerances that they use to judge, to a degree subjectively, the grade? Now the higher up the scale the more technical the differences become. Now looking at the above pictures the big swings are between excellent , good and poor. So as with the factors in colour, clarity , weight look for the in betweens if you want to get more out of your money. I know a diamond that has excellent cut, symmetry and polish referred in our trade as EX EX EX demands a premium as it should, but little sweet spots can exist where you get a Very Good (VG) cut grade and still excellent or very good symmetry and polish depicted as VG EX EX, here you can find a good price drop for technical reasons. The level between Ideal, Excellent and Very Good is very tight and small minute technicalities can throw a diamond one down the scale. Here you can win. Also for experts we can see compared with one another a change but for most people they probably won't notice a difference between the top 20% percentile of grades ( Excellent and Very Good range). Now one can go even further and I am also happy to look into Good cut, it has a much wider tolerance so you can get not so nice Good cuts but know what too look for. Below diagram show the differences in these major scale grades:

Now next to each other and magnified you see parts missing or not aligned etc. In real life they look way closer to eachother never mind seperate from one another. I would like to always try when looking for a good (not perfect) quality diamond to find a top side Good cut graded diamond as they trade as bigger discounts but can still off the eye to public look excellent! Main issues to look and compare is the depth as a lot of these are cut deep so the diameter of the top vs a better cut stone noticably smaller when comparing , sparkle is usually there I might look for a Good cut grade with Very good symmetry and good polish to give an idea. These one's I will definitely want to see beforehand and make sure they are close to top view diameter to a better cut grade. If ordering online make sure you can return as a lot of online stock can be the lesser preferred Good cuts that are being sold off cheaply. I would for engagement rings etc. stay away from fair to poor cut especially Round Brilliant. It is not worth the drop in price and more so drop in the look.

Fancy cuts would be even more subjective in their assessments and they tend to have more Very Good and Good symmetry grading. Here these grades should serve on well and again don't jump under those grades as they will be noticeably worse in appearance. Here are all the fancy shapes: 

These are the major fancy shapes there are lots more but for a center stone I would say these are by far the most popular. Big trick with fancy shapes(and round brilliant to an extent) is to not buy diamond where all the weight is in the middle( stomach line) or buldging diamonds with fat rounded out bottom pavillion, basically a lot of the "carat" weight is caught in the depth of the stone or thickness and the face (viewable) size is smaller or not in ratio. This causes wasted money as there is no real appearance value in having the fat diamond. Rather then go for a lesser carat weight but better spread of the top view, it will give you the same look as the bigger one but will cost less. Hey if you want a carat weight and save a bit then use this to negotiate a better price. In the end it's about what you see and like, factors like this can be build into a cheaper price and should just make sure it is by comparing the correct diamond variables to one another.

Last part on this brief overview is why does excellent or very good grades cost more? See the following image to show how cutters cut diamonds from rough diamonds:

So without over complicating the better the cut the more of the original diamond rough is lost. This is one reason why better grades are more expensive and why all diamonds are not cut excellent because in a way all diamond could be cut excellent. So this is why people cut diamond fatter, shallower, deeper etc. is to get the most out of the rough or a lot of times hit weight thresholds as explained in my previous blogs to get higher prices. A cutter would most likely rather want a 1ct diamond good cut that is is little deeper than a 0.95ct excellent cut. A lot of factors like colour and inclusions play a role but basically they will cut to get the most out of the rough dollar wise. Round Brilliant diamonds are approximately 20% more in price vs a comparative fancy cut. Reasons are the loss as seen above from rough is much higher, more facets and stricter symmetry is needed to get the look and higher skill is needed. Fancy cuts can also be cut out of all types of diamond rough crystals whereas round brilliant cut need certain quality rough to cut from. Round diamonds are also more stable in demand of over 80% of diamond demand where fancy cuts are more subject to fashion trends. This all plays a role to demand a premium on round brilliant cut diamonds.

So why is this important and what is better?

The facts about why this is important says it all - the better the angles and ratio in a diamond the more fire, sparkle/brilliance and life it has- this is obvious. The send question- What is better, depends on how you approach cut grade. Better in terms of technical , overall appearance or budget vs value add? Technical if factual Ideal/Excellent cut will (in most parts) based on this one variable give you the perfect/ near perfect appearance.

Appearance can be a combination of lots of factors but what looks good? A lot of times your eye catches other factors that you like and stand out more e.g. the florescence, luster , clarity or colour aspects combined with the cut grade. Appearance is subjective and in the eye of the beholder and different sparkle based on angles and even jewellery setting can play it's part. Antique style jewelry you would want to look at off "perfect" ideal proportions that will give the look so a good/fair cut can work well to fit the motif. Remember the cut grade is based on perfect alignment and specific defined ratios from the grading institute so what is excellent to you in your eye? A-symmetrical or perfect symmetry?

As far as budget vs value add goes you can see, depending on your end goal in jewellery what will work best. The best cut isn't necessarily the best option. However most modern style rings the go to is the better symmetry. Here I would from a value vs budget perspective go for the combinations and mix of grades that serves my personal tolerance from a viewing perspective. If the diamond look visually off to you it's obviously a no go. When weighing up a EX EX EX diamond to another grade I usually, assuming a noticeable price difference, would aim for a Very Good(VG) cut grade in all three areas or mix of EX VG- there is usually >10% price difference and then the difference in the grade is technical reasons as the tolerance is so tight. Any gems in the good (GD) range I would entertain if they just missed the VG cut , I noticed these will usually have either cut grade or symmetry VG and other one GD that is a great indication. The GD range also trades at more discount than the VG en EX grades so worth comparing. Just again , it depends on your preferences and tolerance, so always physically look at diamonds in this category (assuming you want more symmetrical diamond) and compare with one grade up. If the difference is really noticeable then go higher or look further but if it looks great on it's own or holds itself against the higher grade then go for it as the lower price is worth more than the difference you see. As I always say use the money movers where it is visual - rather then go for a bigger diamond in look with the slightly lower cut grade because the bigger face you will notice.

So deciding what is better is a personal choice, know what the jewellery piece end goal is or communicate it with your seller so they know. If you want the picture perfect diamond go EX and VG they all are in terms of cut in the top 20% so that's an A grade with the premium vs GD grade! If you want more value consider VG and GD with a combination, I would first visually look before committing if all areas are GD due to the wide tolerance in this scale grade. There are great deal to be had here so worth entertaining with doing more due diligence work.    

I hope this gave some insights into the cutting world of diamonds and how it all plays a role to get to the money value of a diamond; simple end price yet very complex variables playing into it. Next week I will dig into who grades diamonds and differences in them so my focus will be on certification.