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Perception of Diamond Carat Weight

By Todd Gray

November 7, 2012

“I have some questions about the perception of diamond carat weight. I am looking to purchase a round brilliant diamond engagement ring. I want to get the Ferrari of Cut – either Brian Gavin Signature or Crafted by Infinity (is one better than the other – i like the Infinity “story” but is it just a sales gimmick ). I am also open to James Allen True Hearts or Blue Nile Signature Ideal.”

“My g/f wants size – as your article on size states – size matters. I want quality in cut (don’t mind SI-1 to VS-2 if it is eye clean and color of J/H/I if necessary). Is it possible to get a stone not deemed true hearts and arrows but very close in cut dimensions so that it is almost a top grade cut but pick up some size.”

“I’d love to be in at around $12k for just the stone but could push it to $15k if necessary. Also at what point in Carat size do you start noticing size optically – i.e. is a 1.35 noticeably different from 1.5 when they are not right next to each other? (If a 55″ TV is in your home and not next to the 60″ TV in a showroom would you notice the difference).”

“I also like fluorescence so would like to drop down in color if I can pick up size w/ the fluorescence to boost face up white (Brian Gavin Blue?) Please attempt to find an eye-clean diamond and provide insight into hearts and arrows vs almost hearts and arrows and when carat difference becomes noticeable. Thank you.” — Timothy B.

Diamond Carat Weight & Visible Diameter:

This project provides us with an opportunity to learn a little bit about the visual perception of diamond carat weight which is something that I usually address when working with clients face-to-face, but rarely get an opportunity to discuss online so I thought it would make an interesting blog post.

Since Timothy specifically asked about the visible difference between a 1.35 carat diamond and a 1.50 carat diamond, I thought we’d begin by comparing this 1.338 carat , H color, VS-1 clarity, Brian Gavin Hearts & Arrows round brilliant ideal cut diamond with this 1.524 carat, H color, VS-1 clarity, Brian Gavin Hearts & Arrows round brilliant ideal cut diamond.

The reason why I selected these two diamonds, in particular, is because they are close to the specific carat weights mentioned by Timothy in his initial inquiry, but they are also identical in terms of diamond color, diamond clarity and diamond cut quality. So we’re actually comparing “apples to apples” and more specifically True Hearts & Arrows to True Hearts & Arrows.

With that in mind, it’s important to realize that minor differences in cut quality of diamonds within the same brand can affect light performance and price. Of course, some brands are more prone to variance than others. Generally speaking, I find the cut quality of Brian Gavin Signature diamonds to be the most consistent.

So the 1.338 carat, H color, VS-1 clarity diamond from Brian Gavin Diamonds is selling for $13,705.00 and the 1.524 carat, H color, VS-1 is selling for $19,425.00 which is a pretty substantial increase in price for a difference of only 0.186 carats of diamond!  If we consider the Price Per Carat (PPC) of the two diamonds, the 1.338 carat is selling for $10,242.00 per carat and the 1.524 carat is selling for $12,746.00 which might seem a bit absurd at first glance… So what the heck is going on?

Is the 1.524 carat, H color, VS-1 clarity diamond really that much more impressive than the 1.338 carat?  Is it going to look $5,720.00 larger?  Is it going to visually outperform the 1.338 carat enough to justify the difference in price?  Let’s start with the understanding that both diamonds are cut practically identical in terms of proportions and were produced by the same cutting house using the exact same precise standards of production.

As a matter of fact, both diamonds were graded by the American Gem Society Laboratory (AGS or AGSL) as having the top overall cut grade of AGS Ideal 0 which is the highest cut grade available from the AGSL and both diamonds were graded as having the same clarity and color… so the only real difference is the carat weight.

The outside diameter of the 1.338 carat diamond is 7.05 – 7.09 millimeters and the outside diameter of the 1.524 carat diamond is 7.38 – 7.40 mm so it’s highly unlikely that you’d be able to visually distinguish between the two diamonds if they were set in rings and you were looking at them from across the dinner table.

Of course, you might be able to tell the two diamonds apart if you were comparing the diamonds side-by-side on a diamond sorting tray where they are separated by a distance of about half an inch, but that’s not the real world.

So what’s up with the difference in price?  Did Brian Gavin just decide to charge $5,720.00 more for the slightly larger diamond because he thinks that it’s a prettier diamond?  Absolutely not… the fact of the matter is that diamond prices are calculated using price per carat formulas which increase in price at specific increments of carat weight and in this particular instance there is a substantial increase which occurs between the 1.49 – 1.50 carat marks.

There is also one which occurs between the 0.99 – 1.00 carat marks and the 1.99 – 2.00 carat marks and across most of the breaks between the “magic numbers” pertaining to carat weight, i.e. quarter carat, half carat, three-quarters of a carat and so on… The increases in the price per carat of diamonds is dictated by the diamond cartels and not the individual dealers…

So when does it make sense to spend the extra money to jump up into the next tier of carat weight?  Well certainly if your more comfortable telling people that your diamond is a carat and a half than saying it’s one and one-third carats… or if the designer mounting you are looking at requires a specific size diamond and many of them are designed for very specific sizes.

Of course, you could just have a custom jeweler like Brian Gavin make a similar ring for you to accommodate whatever diamond you decide to purchase.  Now if you’re thinking that you’re going to beat the system by buying a diamond just under the magic mark of the new carat weight pricing tier or that it makes more sense to buy something like a 1.70 or 1.80 carat if you decide to jump up into the 1.50 – 1.99 carat pricing tier, I’m afraid that I’m going to burst that little bubble by explaining the next part of the equation…

You see while there are the obvious price increases that occur between the tier carat marks, there are additional less obvious increases that occur about every tenth of a carat as the scale increases, so the fact of the matter is that you either need to decide to purchase something in one weight category or the other and accept whatever the price is going to be because just like the house has the advantage when you’re gambling in a casino, the diamond industry has had the upper hand in this case for the last two hundred years or so.

All right, so now that we have some idea on how the carat weight of a diamond affects the price behind the scenes, I think that this option is pretty interesting: 1.533 carat, J color, VS-2 clarity, Hearts & Arrows diamond from Brian Gavin which is selling for $12,202.00 which falls well within the price range that Timothy indicated in his initial inquiry.

Dropping down one clarity grade and two color grades allow us to pick up a little size while saving a little money and maintaining the diamond cut quality!  One of the benefits of buying a super ideal cut diamond that has been cut to a high level of precision is that the increased brilliance, dispersion, and scintillation make it more difficult to discern the actual body color of the diamond when it is being worn, so people are more likely to see the liveliness of the diamond and not the body color…

But this is where it gets interesting… if we’re going to consider diamonds with slightly warmer body color, we should really look at diamonds with blue fluorescence like the diamonds featured in the Brian Gavin Blue collection which was previously referenced by Timothy in his original inquiry because the blue fluorescence is kind of like nature’s whitewash for diamonds and it will serve to lift the body color of the diamond just a bit.

So this 1.698 carat, VS-2 clarity, J color diamond with Strong Blue Fluorescence from Brian Gavin is definitely calling to me. It brings the outside diameter of the diamond up to 7.66 – 7.68 mm and is currently selling for $13,018.00 which is $687.00 less than the 1.338 carat, H, VS-2 that we discussed at the beginning of this thread.

So we’ve picked up considerable size which is easily discernible from across the dinner table and maintained the diamond cut quality, the eye clean appearance of the diamond and it’s still going to look nice and white because of the little boost that the strong blue fluorescence provides.

But wait… we’re not finished yet. Because Timothy wanted to know about the difference between the diamonds produced by Crafted by Infinity and how they compare to the diamonds produced by Brian Gavin.  To be clear, I have a history with both companies. I’m friends with both Brian Gavin & Paul Slegers and think that both companies produce some pretty impressive diamonds.

So really I don’t have a preference between BGD and Infinity, it just comes down to which company has the particular diamond that I’m looking for at the moment.  With that in mind, let’s wander over to High Performance Diamonds which is operated by my buddy Wink Jones who is an authorized dealer for the Crafted by Infinity brand of diamonds and see what they have available.

There are two options which look interesting to me, one is this 1.34 carat, I color, VS-1 clarity, Crafted by Infinity super ideal cut diamond which is selling for $14,159.00 and the other is this 1.73 carat, I color, VS-2 clarity, Crafted by Infinity super ideal cut diamond which is selling for $19,122.00 and has very strong blue fluorescence.

Both diamonds exhibit crisp and complete patterns of Hearts & Arrows and are graded by the AGSL as having an overall cut rating of AGS Ideal 0.  If we were to set these diamonds on a diamond sorting tray side-by-side with the options mentioned earlier from Brian Gavin Diamonds it is unlikely that we would be able to detect any distinguishable difference and this is why my decision to go with a BGD Signature or a Crafted by Infinity diamond usually comes down to a matter of availability and the characteristics of the inclusions (type, location and extent).  Both companies offer comparable inspection periods, satisfaction guarantees and upgrade policies.

Okay so up to this point, we’ve been considering options which represent the top 1/10th of 1% of the annual production for round brilliant ideal cut diamonds… the creme de la creme so to speak, the best of the best, the ultimate in optical precision and visual performance… but not everybody wants or needs this type of precision and not everybody wants to pay for it.

The first thing to understand is that the definition for what constitutes a “Hearts & Arrows Diamond” varies from dealer to dealer, some diamond dealers conform to the grading standards for Hearts & Arrows diamonds as originally defined by the Zenhokyo and Central Gemological Laboratories of Japan and other dealers look through a scope and see some sort of pattern of hearts and arrows or rabbit ears and wands and say “close enough / hearts and arrows” and somewhere in between lies my opinion of the James Allen True Hearts line of “Hearts & Arrows” diamonds. The patterns of hearts and arrows are pretty good, but don’t seem to be as precise as the patterns which appear within the Brian Gavin Signature collection of Hearts & Arrows diamonds, nor the Crafted by Infinity production…

That said, the visual performance of the diamonds found within the James Allen True Hearts collection can be quite nice and they are worthy of consideration on a stone-by-stone basis.  Generally I find that the proportions of the James Allen True Hearts production is a little looser than the range relied on by BGD or Infinity, but if you’re willing to sift through a myriad of options for awhile, there’s a reasonable chance you might find something worthy of comparison and consideration… so I went for a walk about through the inventory of James Allen and this is what I found interesting:

1.35 carat, J color, VS-2 clarity, James Allen True Hearts diamond which is selling for $7,610.00 and graded by the GIA as having an overall cut rating of GIA Excellent which is the highest rating available from the GIA.  Obviously, the price of the diamond is pretty good, but the proportions of the diamond are not quite as tight as the options mentioned previously from BGD and Infinity… not too far out, but enough so that the diamond wouldn’t have made it through the evaluation process which I relied on when I was the diamond buyer for Nice Ice because the crown angle is a little shallow at 34.0 degrees and the pavilion depth is a little deep at 41.0 degrees, but it’s not too far off of my preferred range of 34.3 – 34.9 degrees for the crown angle and 40.6 – 40.9 degrees for the pavilion angle.

The diamond is most likely quite lively and therefore is worthy of consideration.  Now the one thing that I really don’t like about the diamond is the inclusions, I’m personally not a big fan of twinning wisps which are a striation in the growth pattern of the diamond crystal, but it should be noted that I’m in the minority in my opinion here among other dealers.

More interesting to me is this 1.67 carat, H color, SI-1 clarity, James Allen True Hearts diamond which is selling for $15,670.00 because it is cut tighter and therefore should exhibit slightly better visual performance… the diamond is graded by the AGSL as having an overall cut rating of AGS Ideal 0 and the inclusions appear to be reasonable for an SI-1 clarity diamond.  A quick call to James Allen would determine the extent to which the inclusions are visible with and without magnification.  The diamond appears to exhibit a nice pattern of Hearts, so it’s one of those options from James Allen that I like to see and I’m happy to promote.

There are likely quite a few options to be found within the list of certified diamonds from Blue Nile however I really prefer to work with Brian Gavin, Infinity and James Allen because these dealers actually take the time to personally evaluate the diamonds that they sell and Blue Nile usually drop ships the diamonds to their customers from their suppliers without seeing them first and I’m not terribly fond of that business model.

I hope that this response to your inquiry Timothy is helpful and that I’ve answered your questions… feel free to ask any other questions that pop into your head as you proceed through the buying process and by all means, post a comment below if you’d like to provide me with some feedback on your experience with Nice Ice and any of the vendors discussed herein.

About the author

A mad scientist with a passion for improving diamond cut quality to maximize light performance and sparkle factor. I speak geek in degrees of optical precision between bouts of freediving. My ghostwritten ramblings haunt the rabbit holes of information found on many diamond vendor sites. Diamond buyer, author, consultant, errant seeker of deep blue water.

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  1. I have up to $195,000 and I would like your opinion of what you would suggest to be the diamond you would choose if it was you choosing a stone for myself. I have been many weeks reading and researching the various options; now I just need to find the right one that meets budget along with the best of the c’s. I am getting buried in the process of finding the right stone and need your help in narrowing it down.

    Patricia from Canada

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