“I’m in the process of shopping for a diamond engagement ring online, and am trying to decide between Blue Nile Signature round diamonds and James Allen True Hearts diamonds, which seem to offer a good balance of quality and price. Neither vendor seems to have anything that matches your preferred range of selection parameters at the moment, but I’m hoping you can help me select the best option from the list provided. How important is diamond culet size? I know that you specify a preference for a culet size of either GIA “none” or AGS “pointed” and indicate that it is the same thing in concept. What difference does a very small or small culet make in the appearance of a diamond?”
The culet is the bottom point of the diamond, it is actually a facet that appears to look like a tiny point. My preference as stated in the article 15 Seconds to Diamond Buying Success is that the diamond culet size be either GIA “none” or AGS “pointed” which are different terms used to describe the same thing.
My preference for diamond culet size is that it be either GIA none or AGS pointed, because anything larger than that is likely to appear as a white or black circle or dot in the center of the table facet. It seems to me that if you’re going to spend the money to buy a super ideal cut diamond in a higher clarity so that it will be eye clean, that it doesn’t make sense to buy one with a small or very small culet, since that is going to create a white or black spot in the middle of the diamond that looks a lot like a small diamond crystal.
To be quite frank, I think that cutting a round brilliant ideal cut diamond with a small or very small culet size, reflects a lack of skill and precision by the diamond cutter. It is as if they had to cut a larger diamond culet size at the bottom of the diamond to cover up something in the alignment of the pavilion facets; or maybe they just bumped the stone a bit too hard on the diamond cutting wheel. Either option doesn’t sit well with me, and thus I personally would not purchase a round brilliant cut diamond with a small or very small diamond culet size.
The crown angle of 35.5 degrees is pretty steep, and well beyond my preferred range of 34.3 to 34.9 degrees. This is likely to make the diamond exhibit a bit more dispersion / fire (colored sparkle) than brilliance (white sparkle) however the 80% lower girdle facet length will help to offset this a bit, because lower girdle facets in the range of 80 – 82% tend to produce pin-fire type sparkle that is smaller in size, which is harder for human eyes to disperse into colored light, thus the sparkle appears to be more brilliant.
In order to produce a pattern of hearts like the one pictured above for the Brian Gavin Signature round diamond, the length of all eight lower girdle facets must be virtually identical. If the length of the lower girdle facets is not the same, then the length of the reflection that creates one half of the heart on the other side will be slightly longer or shorter than the length of the light reflected off of the other pavilion main facet. Thus the two sides of the heart will be different lengths, creating the twisting, bending effect that is visible in the Blue Nile Signature diamond referenced above.
Would you believe that it is being caused by that large gap that exists between the heart located in the relative eleven o’clock position? The one that is about half the size of the other hearts, and the arrowhead that appears beneath it? This is the type of irregularity in the distribution of light that is being reflected throughout a diamond, that could be corrected by cutting the diamond to the higher degree of optical precision required to produce a crisp and complete hearts and arrows pattern.
Now I’m wondering whether you noticed anything else in the “optical symmetry analysis” photograph provided for the 1.12 carat, G-color, VS-1 clarity, Blue Nile Signature round diamond pictured above. Like the white spot that appears right in the middle of the table facet, as a result of the small culet? I guess we now know the answer to the questions “How important is the culet size of a diamond?” and “What effect does diamond culet size have upon the appearance of a diamond?” And if you’re still not sure, check out the large white dot that appears in the middle of the light performance image provided above for this diamond by GCAL, that large white dot is because the diamond culet size is small.
With that in mind, I’m going to pass over the other Blue Nile Signature round diamonds that you referenced, which have small or very small culet sizes, since there isn’t much purpose in reviewing diamonds that I would not recommend or buy personally. The only purpose of reviewing the one Blue Nile Signature round diamond was to teach you the importance of diamond culet size and optical precision.
But only because I’m able to see that the diamond exhibits a pretty decent pattern of hearts and arrows, thus the optical precision of the diamond is very good to excellent. This will help to offset the slight variances from my preferred range of proportions.
Look closely at the hearts photograph featured above, and you’ll see that there is some variation in the size and shape of the hearts. However, it is much less than exhibited by the Blue Nile Signature diamond reviewed above, and thus I’m inclined to choose this diamond over the other.
However take note that the 80% lower girdle facet length will result in this diamond exhibiting pin-fire type sparkle that is smaller in size. It is also much more difficult for our human eyes (as opposed to a video camera) to disperse into colored light, and thus this diamond might appear to be more brilliant. However, perhaps not so much that anybody would really notice without some coaching… it’s kind of a technical thing, but my preference is for diamonds that exhibit broad spectrum sparkle, whereas some people prefer diamonds like this which exhibit pin-fire type sparkle. There is no right or wrong regarding the type of diamond sparkle you prefer, it’s kind of like Coke or Pepsi?
If you enjoyed reading this blog post and hopefully learned a little from it, and would like my help finding the diamond of your dreams, or would just like to have a little bit of professional insight about the diamonds you are considering, take advantage of my free Diamond Concierge Service.
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