The One Minute Diamond Buying Guide:

Everything you need to know to succeed when buying a round ideal cut diamond online.

Ready. Set. Go.

This is the minimum selection criteria that we recommend for round brilliant cut diamonds:

  1. 1
    Overall Cut Grade of AGS Ideal or GIA Excellent.
  2. 2
    AGS Ideal  Proportions (see below).
  3. 3
    AGS Ideal or GIA Excellent Polish.
  4. 4
    AGS Ideal or GIA Excellent Symmetry.

The Proportions Range for the AGS Ideal and GIA Excellent Cut Grade Is Too Broad.

The following range of proportions will produce a high volume of light return and a virtual balance of brilliance (white sparkle) and dispersion (colored sparkle/fire):

  • Total depth between 59 – 61.8%
  • Table diameter between 53 – 58%
  • Crown angle between 34.3 – 35.0 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.

 Diamond Color Grades:

The spectrum between D-color and G-color will face-up  bright white.

Diamonds in the H-color and I-color range will look white to most people. Which is why I selected and I-color diamond for my own wedding ring. 

Most people begin to detect a hint of color more easily in diamonds that are J-color and lower (L/M/N and so on) because the tonal value of the diamond will appear “warmer” than diamonds in the D to I color range.

K-color Brian Gavin diamond.

The diamond will still face up white when set in white gold or platinum prongs because the color of the white metal touching the edge of the diamond will reflect throughout the stone.

Which is why this K-color Brian Gavin signature diamond faces up white in this Anita Halo setting by Brian Gavin in 18 K white gold.   The accent diamonds set in the ring are F-G-color. The larger surface area of the center stone draws our eyes to it naturally and makes it harder to see the difference in body color.

Some people prefer diamonds which are cooler in appearance. While other people might prefer diamonds which are warmer in hue and saturation.

Diamond color has virtually no effect on the light performance of a diamond. Which means that diamond color is strictly a matter of personal preference.

One diamond color does not look better than another. However, the perception of diamond color might contribute to your preference for one diamond color over another.

Diamonds With Blue Fluorescence:

Lots of people love blue florescent diamonds because they face up whiter and brighter than non-fluorescent diamonds.

Brian Gavin. Blue Florescent Diamond

Practically every diamond which I've selected for myself has exhibited medium to strong blue fluorescence.  The center stone in Brian Gavin's wife's wedding set is a Brian Gavin Blue florescent diamond.

It goes without saying that our trade status provides us with access to everything. The reason why we choose diamonds with blue fluorescence is because it tends to make diamonds look even whiter and brighter.

Blue fluorescence is like nature's whitewash for diamonds. It's like a blue filter for photography. Plus, I just love the way that blue florescent diamonds glow neon blue when exposed to blacklight. 

Diamond Clarity Grades:

The VS-2 diamond clarity grade delivers the biggest bang for the buck.  Diamonds which are VS-2  in clarity face-up eye clean and will look the same as higher clarity diamonds without magnification.

VS-1 clarity diamonds are a good option if you want the inclusions to be more difficult to locate using 10x and higher magnification.

SI-1 clarity diamonds may be deemed to be eye clean. However, the industry standard for making this determination is to simply glance at the diamond from a distance. of 9-12 inches.The diamond is considered to be eye clean if the inclusions are not readily and immediately visible to trained diamond grader from that distance. However, this is not how people tend to scrutinize their diamonds upon receipt.

Consider diamonds in the SI-1 clarity range if you’re trying to get the biggest bang for your buck and don’t mind being able to see an inclusion or two without magnification.

VVS-2 and higher clarity diamonds contain inclusions which will be difficult to locate using 10x diamond grading magnification. Higher clarity diamonds are good if you can’t sleep at night unless all the shoes in your closet are facing the same direction and your shirts are arranged by type on matching hangers that are all facing the same direction.

Don’t accept a diamond graded by any other laboratory other than the AGS, GIA, or HRD. The latter of which is the diamond grading laboratory for the Belgium High Diamond Council.

Now you know all the details necessary to buy a stunning looking diamond. However, I'm willing to bet that you want to know more. Which is why the following section expands on the reasons behind our recommendations.

 Why Adhere To Such A Strict Range of Diamond Proportions?

The range of proportions outlined above will produce the highest volume of light return and a virtual balance of brilliance and dispersion. It represents the center range or "Target Zone" of the AGS Ideal and GIA Excellent Grade.

They like to say that there's an ideal cut diamond for every preference. Which might explain why the range of proportions for the AGS Ideal and GIA Excellent cut grades are so broad.

I suppose that one could argue that high levels of light return and performance are possible within a broad-spectrum of proportions.  However, I find that the proportions outlined above are more likely to produce the look that I prefer in a diamond.

Diamonds with proportions outside my preferred range are more likely to exhibit:

* Crown Angle:

A crown angle between 34.3 to 35.0° tends to produce a virtual balance of. brilliance (white sparkle) and dispersion (colored sparkle/fire). Any variance from this range is likely to affect the balance of brilliance and dispersion.

For example, a crown angle less than 34° is likely to produce more brilliance. However, it will probably be at the expense of dispersion.  Diamonds with shallow crown angles are also more likely to exhibit obstruction under the table facet.

A crown angle steeper than 35.5° is likely to produce more dispersion in a round brilliant cut diamond. However, it will be at the expense of brilliance. In addition, a crown angle steeper than 35.5° is likely to make round brilliant cut diamonds look dark in the middle.

Pavilion Angle:

My preferred range of pavilion angle is quite narrow. This is because it's most likely to produce the highest volume of light return. A pavilion angle lower than 40.5° in a round brilliant cut diamond produces a reflection which looks flat. Just think of the way that light reflects off a shallow fishpond and you've got the picture.

A pavilion angle steeper than 41.0° is not likely to produce good light return. Especially if the pavilion depth is 43.5% which happens to be "the critical tipping point" where light begins not to reflect fully off the pavilion facets.

** Lower Girdle Facet length:

I recommend a Lower Girdle Facet (LGF) length between 75 – 78% because that tends to produce broad-spectrum sparkle. Which means that the sparkle should be larger in size and be bolder, brighter, and more vivid​.

Round brilliant cut diamonds with lower girdle facets in the range of 80-82% tend to produce pin-fire sparkle which is smaller and less intense. 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. 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).

Be advised that 78% lower girdle facets will be rounded off to 80% by the GIA Laboratory. Which means that some visual estimation is necessary to determine whether the lower girl facets are closer to 78% or 80%.

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. Which might make it seem like a good middle ground. I suppose that it is if you don’t know what type of sparkle you prefer.

However, I can tell you that diamonds that exhibit pin-fire type sparkle tend to look best when exposed to candlelight or jewelry store 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 in this modern age.

*** Star Facet Length:

Star facets are the small triangular shaped facets located on the crown section of the diamond. They appear between the kite shaped bezel facets and border the edge of the table facet.

Star facets serve to round off the shoulders or lobes of the hearts in super ideal round brilliant cut diamonds.

The optimum star facet length is between 45 – 55% which will create nice rounded shoulders on the hearts. However, it is acceptable for the star facets to be between 40 – 58%. The length of the star facets is affected by the size of the table facet and the crown angle.

It's important to understand that the star facets are considered to be a minor facet group. While people tend to get caught up on specific measurements, I suggest simply focusing on the images.

If the hearts pattern is formed consistently, the exact star facet measurements are not important. If the hearts are irregular and there is heavy obstruction, then I’d suggest a different diamond.

Remember that a more in-depth explanation of the concepts touched on here can be found in the 5 Minute Version of Diamond Buying Success if you're looking for more information.

Ultimate Diamond Buying Cheatsheet free download

Download the Ultimate Diamond Buying Cheat Sheet!

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