The Complete 5 Minute Diamond Buying Guide:
Diamond Buying is more of a science than an art. In the first place, a diamond is a three-dimensional geometric model. That means that the pavilion angle will dictate the volume of light return. At the same time, the crown angle will determine the balance of brilliance and dispersion. The size and intensity of the sparkle are under the direct control of the proportions and facet alignment. In a similar fashion, higher degrees of optical precision will produce more virtual facets and sparkle that is more vivid and intense.
Anybody who tries to convince you otherwise is either an idiot, totally naive, or trying to pull a fast one. It’s really just that simple. With that in mind, I’m going to take 30+ years of diamond buying experience and boil it down into a five-minute tutorial.
Best Diamond Proportions a’ la Engineer:
For (maximum)2 brilliance and dispersion, the proportions of a diamond must fall within certain tolerances. Don’t fall into the trap of thinking that a diamond is “all that” simply because it has ideal proportions and a lab report. The reality is that there are certain combinations of angles and degrees that result in maximum light return and many ideal cut diamonds border on the edge of being near ideal.
Do we have your attention? We want to be sure that you absorbed that last sentence, so we’re going to phrase it another way… Just because a diamond has “ideal proportions” does not mean that it exhibits maximum light return.
Here’s the trick… The Ideal Cut Proportions Rating is based upon a range of acceptable proportions and as with most ‘ranges’ the range for ideal cut has a high and a low end. Based upon years of diamond buying experience spent sifting through literally thousands upon thousands of diamonds, we have determined that the center region of the range tends to produce diamonds with the highest degree of light return and we have dubbed this range “Super Ideal”. The term “Super Ideal” by our definition is used to describe a round brilliant ideal cut diamond within the following range of characteristics:
Total depth between 59 – 61.8%
Table diameter between 53 – 58%
Crown angle between 34.3 – 34.9 degrees*
Pavilion angle between 40.6 – 40.9 degrees
Lower girdle facets between 75 – 78%**
Star facets between 45 – 50%***
Girdle thickness between thin and slightly thick
Culet: AGS pointed or GIA none
* Crown Angle:
The preferred range of crown angle for round brilliant cut diamonds provided above is clearly quite narrow, and this is because it is likely to produce a virtual balance of brilliance (white sparkle) and dispersion (colored sparkle) when combined with a pavilion angle between 40.6 – 40.9 degrees. The idea here is to enable you to quickly and easily buy a top performing diamond by taking guesswork out of the equation.
This is not to say that other combinations of crown and pavilion depth won’t result in comparable light return, there certainly is the possibility for such diamonds to exist. We’re just trying to simplify your quest as much as possible by providing you with a tight range that almost always works. If you want to take the guess work out of buying a diamond for visual performance, then check out the options available within the Brian Gavin Signature Collection which have been hand selected for maximum visual performance. If you want to explore a broader range of proportions, then visit James Allen or check out the list of Certified Diamonds from Blue Nile.
** Lower Girdle Facet length:
The reason why I recommend keeping the Lower Girdle Facet (LGF) length between 75 – 78% is because this tends to produce “Broad Spectrum Sparkle” that is going to be larger in size, and which will look bolder, brighter, and more vivid, than the smaller pin-fire type sparkle that is created by lower girdle facets in the range of 80 – 82% for round brilliant cut diamonds with the proportions outlined above.
The problem with pin-fire type sparkle is that our human eyes tend to experience difficulty dispersing smaller flashes of white light into colored light / sparkle, and thus diamonds that exhibit pin-fire type sparkle are likely to appear to be more brilliant (white sparkle) than exhibit a virtual balance of brilliance and dispersion (colored sparkle). You might have noticed a gap between the range of 75 – 78% and 80 – 82% where 79% should be, that’s kind of the critical tipping point where the type of sparkle being created by the diamond might go either way, a good middle ground I suppose if you don’t know what type of sparkle you prefer.
However I’ll tell you that diamonds that exhibit pin-fire type sparkle tend to look best when exposed to candlelight or halogen lighting, which are both pin-fire type light sources, but they don’t look all that great, or perform very well, when viewed under diffused lighting conditions, which tends to be the type of lighting that most of us live and work under.
Note that the AGS Laboratory measures the length of the lower girdle facets by height, this is the same approach used by mathematical ray tracing software like DiamCalc by Octonus. However the GIA Gem Trade Laboratory measures the length of the lower girdle facets by radius, so that they can be measured using a table gauge, and the GIA rounds that measurement off to the nearest half a percent, whereas the AGSL provides the actual measurement without rounding it off. These differences between how the two gemological laboratories measure lower girdle facet length can create confusion, because the approach is clearly different, and thus so are the measurements!
*** Star Facet Length:
Star facets are the small triangular shaped facets that are located on the crown section (top portion) of the diamond between the kite shaped bezel facets, along the edge of the table facet, they serve to round off the shoulders or lobes of the hearts that are created in super ideal cut diamonds like Brian Gavin Signature Hearts and Arrows diamonds when the facets are polished with an extreme degree of consistency and precision.
The optimum star facet length in my opinion is between 45 – 50% however it is acceptable for the star facets to be between 40 – 58% and this is primarily dictated by the size of the table facet.
These proportions eliminate a lot of diamonds!
The first thing that you’re going to notice when you begin to use my preferred range of proportions as a guideline for picking the best diamond, is that a lot of GIA Excellent and AGS Ideal-0 cut diamonds are going to be disqualified quite quickly, leaving you with only a handful of options to choose from.
On one hand, you might realize that I adhere to this selection criteria for a reason, it enables you to quickly and easily pick an ideal cut diamond that is going to exhibit the highest level of light return, and which is going to exhibit broad spectrum sparkle that provides a virtual balance of brilliance and dispersion; it quite frankly takes the guesswork out of buying a diamond online.
But on the other hand, perhaps you want to devote hours and hours of your life, trying to figure out what other combinations of crown angle, pavilion angle, table diameter, total depth, star facet length, lower girdle facet length, girdle thickness, and culet size, might combine to create a comparable volume of light return and sparkle factor.
Because it is “possible” to find non-ideal and standard ideal cut diamonds that exhibit levels of brilliance, dispersion and scintillation equal to the visual performance of a Super Ideal Cut Diamond… However it is much easier and much more reliable to find and ideal cut diamond that exhibits a high degree of visual performance by adhering to the parameters stated above, which represent center range or “sweet spot” within the ideal cut classification for diamond proportions.
If you want to cut to the chase, you’ll discover that the diamonds contained within the Brian Gavin Signature Collection are pretty much all cut to my preferred range of proportions, and the diamond details pages provide the reflector scope images required to judge the degree of optical precision, which is a critically important piece of the puzzle which is not taken into account by gemological laboratories such as the AGS or GIA.
Note that the Pavilion Angle is the most critical of all the angles of a diamond, as it is the primary reflective surface that reflects light back out the top of the diamond. We consider the Crown Angle to be the second most critical angle on a diamond, since it dictates the balance of brilliance and dispersion. We strongly recommend keeping the pavilion angle of a round brilliant cut diamond between 40.6 – 40.9 degrees, combined with a crown angle between 34.3 – 34.9 degrees, if you’re looking for the absolute best volume of light return and sparkle factor!
Similar visual results to Super Ideal Cut Diamonds can often be found in diamonds with opposing degrees of depth for these two angles, in other words a diamond with a deeper Pavilion Angle such as 41.2 degrees with a shallow Crown Angle of 33.9 degrees. Or a shallow Pavilion Angle such as 40.4 degrees with a steeper Crown Angle such as 35.3 degrees, however it this is more of a technical “possibility” as in UFO’s could exist, people claim to have seen them, and people have told me about their experience being abducted by them, but I’ve yet to experience this phenomena personally.
If you have some time to poke around and consider all of the variables, James Allen offers plenty of options available within this broader range of proportions, as does the list of Certified Diamonds from Blue Nile, but personally I would stick to the center range of proportions outlined above, and save yourself a lot of time, frustration, and round trip shipping. Of course, you could take advantage of my free Diamond Concierge Service, and let me help you select the best option available.
While selecting a diamond with proportions that fall within the range that we have defined as “Super Ideal” tends to make the selection process easier because it narrows the field of possibilities, it is possible for other combinations of proportions to yield similar results but there is a lot more guess work involved and it is quite likely that the money which you might think you’re going to save by looking for a diamond outside of our preferred range of proportions is going to be eaten up in the form of time wasted and the cost of round trip shipping… and then there is the little matter of your princess patiently tapping her foot and waiting for her diamond to magically appear on her finger.
Back when we had our jewelry store, we made a conscious decision not to play with non-ideal cut diamonds because it seemed like we had to sift through a thousand diamonds just to to find one or two that met our expectations from a visual perspective. By focusing our efforts within the narrow scope of ideal cut diamonds, we were able to retain about 60% of the diamonds that we brought in for physical inspection and place them in our inventory. Note that this number is based upon the diamonds that we brought in for evaluation after sifting through the stacks of lab reports sent to us by the cutters for consideration. So our rejection rate was about 40% of the diamonds that we physically inspected, our cutters used to tell us that we were the strictest in the business.
Evaluating Your Ideals:
Now there are two ways for you to verify that a diamond  has ideal cut proportions and  has the right critical Crown and Pavilion angle measurements mentioned above. The first is to consider a diamond graded by the AGS Laboratory and which has been graded as having an Overall Cut Rating of AGS Ideal.
The second option is to consider a diamond graded by the GIA Laboratory as having Excellent polish, symmetry and overall cut rating [that’s the highest grade available from the GIA for these characteristics] accompanied by a Sarin DiaMension Computerized Proportions Analysis indicating that the diamond has ideal cut proportions.
The Sarin produces a report complete with all of the degrees, angles and percentages required to determine whether the measurements for all five sections of the diamond meet the criteria for the ideal cut rating. This is information that most diamond cutters have at their fingertips, but which most jewelry stores don’t ask for or don’t want to share with you… Hmmm, we wonder why?
Could it be because they prefer to sell diamonds to the masses who don’t understand the importance of proportions? Considering that the Cut of a diamond controls 98% of its brilliance, why would you want to settle for anything less?
Polish & Symmetry, the only other way that man can screw up a stone:
Back in the day when I was the primary diamond buyer for Nice Ice, I would spend a good portion of each day sifting through the diamond grading reports for literally thousands of diamonds being offered to us every day by our cutters, and I would automatically shred any diamond grading reports that had a Polish & Symmetry rating lower than GIA Excellent or AGS Ideal. That’s right, in my opinion “Very Good – Very Good” doesn’t cut it and “Good – Good” is so not acceptable. Think of it as having your mother take your very brand new, black on black, Porsche to the local gas station to be hosed down by the junior high pep squad for five bucks, “because she loves you”. That’s Polish… Now, when your mother races through the shopping center, over the speed bumps, in first gear at 43 miles per hour, that becomes a Symmetry issue.
Diamond Color – The 2nd Most Important Visible Factor:
D – E – F Colorless: Sure fire white and a phenomenal place to be if you’ve got the big bucks and don’t want to give the concept of color a second thought.
G – Near Colorless: This is a “no-brainer” white, and is still a safe color if you’re buying off paper. Most of our clients cannot determine the difference between F and G color diamonds even under the controlled grading environment provided by our GIA Gem Diamond Lite™
H – I Near Colorless: Faces up and mounts up white if the diamond has Ideal Cut Proportions as determined by either the AGS Laboratory or using Sarin, OGI, or Helium technology. A great way to get a slightly bigger bang for your buck. An H or I color diamond ill appear slightly warmer in tonal value than a G color diamond if examined closely while placed side-by-side and unmounted under a controlled light source like a GIA Gem Diamond Lite™ in a dark room, but will look the same to most people when evaluated under normal lighting conditions.
J – M & Lower: Most people are able to see color easily in diamonds that are J color and lower (L/M/N – Z) because the tonal value of the diamond will appear “warmer” than diamonds in the D to I color range. Just because a diamond is “warmer” in color does not mean that it is not beautiful. The reality is that diamond color has no effect on the actual visual performance of a diamond, the reflected white sparkle (brilliance) and colored flashes of light (dispersion) are controlled by the proportions of the diamond, not the body color. There is no right and wrong when it comes to selecting a diamond color, it is just a matter of personal preference that is probably best considered in terms of an absence of color, some people prefer diamonds which are cooler in appearance and some people prefer diamonds which are warmer in hue and thus we suggest visiting a local jewelry store to compare diamonds of different colors to determine your personal preference for color. Many people who prefer diamonds with warmer tones such as those in the J color range and lower prefer to set the diamonds in yellow gold prongs or settings because the warmth of the yellow gold metal that touches the stone will further enhance the warmer tones found within the diamond – this however is not an absolute rule since other people will prefer the look of white metal against the warmer hues of the diamond – personal preference, get it?
Fluorescence – Natures Little Whitener:
None, Inert, Negligible, Nil: A moot point… Nothing or not enough to measure. The variance in terms is merely the result of each gemological laboratory wanting to be a little different from each other.
Faint or Slight: Not enough to be concerned with even under intense black light. Faint fluorescence is really nothing more than an “identifying characteristic”.
Medium Blue: Might result in an extremely light (and very pretty) lavender blue hue under intense sunlight or black light. Enhances the natural color of most diamonds and usually makes them appear on the high side of the color grade when they fluoresce. If it is any indication of what we think about fluorescence, most of the personal diamonds that we wear exhibit medium blue fluorescence.
Strong or Moderate Blue: Beneficial in H – I color diamonds and needs to be visually considered on a stone-by-stone basis for D – F color diamonds… Diamonds with strong fluorescence often pick up an extremely light lavender blue hue in intense direct sunlight and look intense neon blue under a black light (it’s very cool actually) and if you’re interested in a diamond with blue fluorescence I highly recommend checking out the Brian Gavin Blue Collection because they are gorgeous!
No other color of fluorescence, such as yellow, orange, green, etc. is acceptable to us in our selection process with the exception of white which has no impact on the visual properties of a diamond.
Clarity – What your friends probably can’t see:
SI2 & Lower: Generally not considered to be “eye clean” by our standards. We have seen too many lab graded SI-2 clarity diamonds where we could see minute inclusions with our eyes if we allowed ourselves to relax and focus upon the stone to justify our opinion that SI-2 clarity diamonds are rarely if ever “eye clean” by our standards, thus we feel that SI-2 clarity diamonds are best suited for engagement rings only in scenarios where both parties are involved in selecting the diamond and the reality that the diamond is not going to be 100% eye clean has been taken into consideration. It is one thing for you and your fiancé to decide together to buy a diamond with an inclusion or two that might be seen with close scrutiny to pick up a little more size than you might be able to afford in a diamond that is “eye clean” and another scenario to present her with a diamond that isn’t eye clean and for her to be disappointed because she had anticipated that it was going to be eye clean… Over the years, many of our clients purchased SI-2 clarity diamonds because they found perfection in the imperfection of a diamond which exhibits inclusions that can be detected without magnification and we had other clients who would be kept up nights by a dust fragment on the surface of their diamond, the secret is knowing which end of the spectrum you and your fiancé fall into.
SI1 = Will contain minute flaws or “inclusions” that will be “readily and immediately visible” when the diamond is examined through a 10x diamond grading loupe and which are often visible without magnification once the inclusions have been identified and you know what to look for and where to find it. A great place to pick up size because we don’t live under a microscope, but only if you’re comfortable with the fact that inclusions may be visible without magnification from time to time if just the right viewing conditions present themselves or you happen to have Eagle Vision.
VS2 & VS1 = 100% Eye Clean Eye Candy that contains inclusions that are very difficult to locate under 10x magnification. A fantastic grade for engagement diamonds that will present a challenge for Mother-In-Laws who happen to carry a diamond grading loupe in their purse (we’ve seen it). Both VS-1 and VS-2 clarity diamonds will be “eye clean” and will tend to face up the same in terms of what you will see with just your eyes, the inclusions will be smaller and more difficult to locate in the VS-1 clarity grade.
VVS2 & VVS1 = Wow! Wow! Wow! Time to break in the new credit card you just got and let go of some big bucks for something you’ll never see! Get ready to burn your eyes out trying to locate the inclusions in this puppy with a 10x diamond grading loupe. Excellent for Triple A-A-Anal Engineers who just can’t sleep at night if the shirts in their closet aren’t all facing the same direction on matching cedar hangers and sorted by season, collar type and color. Extremely difficult to find the inclusion that is the “grade maker” that distinguishes the difference between VVS2 and VVS1 unless you’re examining the diamond under 40 – 50x magnification and even then in some cases it’s a challenge because the inclusions are often so minute that they look like dust particles.
IF & FL = Internally Flawless and Flawless = Why? Are you feeling masochistic today? What’s the point? If you can’t find the flipping inclusion in a VVS1 why go here? “Because something in our life needs to be perfect” is the best excuse we’ve heard thus far and hey if that works for you, it works for us.
Carat Weight – It’s a Size Thing.
The difference between men and boys is the size of their toys! You’ve been programmed to buy her a carat, every magazine and television advertisement that you’ve been subjected to since your birth says you’re supposed to. And to top it off, now some of the diamond cartels in charge of global distribution want you to spend three months of your salary on a rock… Hmmm… Uh yea, you should do it. But before you do, consider this… According to the Diamond Promotion Service (DPS) fewer than 30% of all the women in the world will own a one-carat diamond in their lifetime. Far be it from us to put you in that 30% category if you don’t want to go there, our recommendation is to focus on the quality of cut first, color second, and let the size of the diamond be dictated by your comfort level when it comes to price.