This diamond review request is for Rob who is looking to buy a 0.927ct DIF Black by Brian Gavin diamond.
Rob has 3 concerns about the stone, he asks:
1) The ASET Image doesn’t quite conform to the other Black by Brian Gavin stones, as it doesn’t have the same green star-shaped line that border the star facets.
2) It has a larger table% and a smaller depth% than other Black stones he’s seen. In particular the crown angle is 34.1° whereas he has noticed that many other Black stones have 34.7° or steeper crowns. He thinks that the diamond doesn’t sparkle as much as the other Black stones he’s seen in the video.
3) He worries that this may be a Black that is barely making the cut as a super-ideal/BGD Black.
Let’s take a look to see how this diamond stacks up to what we expect from a Black by Brian Gavin.
The Black line from Brian Gavin is their top of the line range and includes criteria for color (D-G) and clarity (IF-VS2) in addition to cut. I’m going to focus on the cut criteria in this review.
What BGD says is the difference between their Signature H&A and their Black line is that there is a “fine-tuning” of the minor facets (they refer to these as ancillary angles and you can read more about this here).
The focus is on reducing the “low-intensity light zones” that show up as green on an ASET. This is understandably confusing because there are always going to be green areas in a ASET image of a diamond even in a perfect super-ideal. This is why the objective is not to completely eliminate green, but to eliminate it in the areas that are not desirable.
A better way to think about green in an ASET is that it indicates whether an area of the diamond (at least when the diamond is facing up) is displaying weak light return. What happens to a facet as a diamond is tilted is that it will change from returning obstruction/contrast (blue), to intense light return (red), to weaker light return (green), then to light leakage (background color). The areas in a diamond where we expect to see green is in the table reflection, the upper girdles, and in many cases at the edges of the crown facet.
What we want is to avoid any green under the table of the diamond because it indicates that there is weaker light return in an area where we want and expect to see intense light return. Even if you only see a little bit of green, because the ASET doesn’t do a good job telling you how intense that intense light return is, if you see some green in an ASET under the table facet then it is a good indicator that the diamond could be brighter if its angles were more ideal.
What this means is that having less green in the diamond isn’t necessarily a bad thing, and if there is green you want the green areas to be relatively small compared to the red areas and you want them to be symmetrical. The star facets are added to the diamond to create additional brilliance/contrast in the diamond. With smaller star facets the crown facet becomes larger and because the crown bends the light that you see from face up, as the crown facet gets larger it will start reflecting increasingly more green both at the base of the arrow head and at the base of the crown surrounding the star facet.
What is evident is that this diamond has a very good ASET pattern with no green between the arrow shafts.
Regarding the table percentage, a 56.9% table facet is actually almost perfectly ideal. The size of the table is a consequence of the crown angle and the crown height so basically you don’t want one that is too small so that it negatively impacts the spread but you also don’t want it to be too large so the crown height is too low. A smaller overall depth is also a good thing as it means that the diamond will likely have excellent spread and hence look the right size for its weight.
This BGD Black accomplishes excellent light return and spread because of the slightly shallow 34.1° crown that Rob has pointed out as one of his concerns. This shallower crown has produced a lower 14.5% crown height and this is low when compared to the average BGD Black but it isn’t outside my recommended range and it is also within the spec for a BGD Black. A lower crown will produce less fire when compared to a diamond with a higher crown and many BGD diamonds are cut with a higher crown to maximize fire even at a cost to the spread of the stone.
However, it would be pretty crazy to pass on a stone like this because once you factor in the color and clarity of the stone this is an extremely rare diamond and it is by no means a borderline cut as either a super-ideal or a BGD Black.