drk14
Brilliant_Rock
- Joined
- Jun 25, 2014
- Messages
- 1,061
As part of the appraisal of a marquise diamond I recently purchased from JA, Dave Atlas provided me with an ASET generated from Sarin scan data in DiamCalc. Given the notorious difficulty of photographing ASETs in general, and JA's past tribulations with their AGS ASET setup in particular, as well as periodically recurring discussions on PS about the usefulness of ASETs in evaluating fancies, I thought it would be interesting to compare the JA-supplied ASET photograph against the DiamCalc version and my own amateur observations of the diamond IRL.
JA ASET Photograph:
Sarin/DiamCalc ASET:
JA High-Definition Photograph:
Overall, I think the agreement between the JA and DiamCalc ASETs is remarkable, which is a testament both to JA's efforts to fix their past ASET issues, and to the accuracy of the ray tracing software. Here are the differences that I see:
So, which gives a more accurate representation of my IRL impressions? I think the DiamCalc version is in slightly better agreement with my observations.
In particular, to check for leakage, I placed the diamond on a colored background and examined under a loupe in diffuse lighting. Under these conditions, I could see only a few small spots of the background color under the table, so this observation matched the DiamCalc prediction better than JA's ASET. In separate tests, I also placed a small dot of color against the girdle (i.e., near 0°), and noticed that a faint hue of that color would appear throughout large swaths of the table. To me, this suggests that maybe the JA ASET setup has the girdle (and maybe even a sliver of the crown adjacent to the girdle) below the horizon (thus black), and/or that DiamCalc places all or part of the girdle above the horizon (thus green).
Also, in my (heavily biased) opinion, the uniformity of brightness throughout the MQ body and the sharpness of the virtual facets in the DiamCalc ASET is more representative of the IRL behavior of this particular diamond than is the JA ASET.
I offer this post primarily as a data point to assist those of us who use JA ASETs make purchasing decisions (or help others make purchasing decisions) about fancy cut diamonds. Nonetheless, I would welcome corrections, comments, expert explanations, or discussion!
ETA: I know that the accuracy of ASET photography can depend on diamond size. In case it helps anybody interpret the images above, this particular marquise is 1.05ct, has a total depth 3.34mm, crown height 0.90mm, girdle 0.22mm, and pavilion depth 2.27mm, length 11.08mm, and width 5.00mm (Sarin scan data).
JA ASET Photograph:
Sarin/DiamCalc ASET:
JA High-Definition Photograph:
Overall, I think the agreement between the JA and DiamCalc ASETs is remarkable, which is a testament both to JA's efforts to fix their past ASET issues, and to the accuracy of the ray tracing software. Here are the differences that I see:
- Some regions that are blue in the DiamCalc ASET are black in the JA ASET (most notably, the virtual facets reflected in the vertically oriented pavilion mains, at the inside edge of the table -- i.e., just above and below the red 'mini-bowtie' shape in the center).
- There is more red in the DiamCalc ASET, whereas the some of these facets are green in the JA version.
- The JA ASET suggests a fair amount of leakage under the table, whereas the DiamCalc version only shows a handful of small black (leakage) spots under the table.
- The overall light return (red+green) is fairly uniform in the DiamCalc ASET, but in the JA ASET, the belly region seems much brighter than the points of the MQ.
- The calculated ASET image has crisp virtual facets throughout, whereas the JA ASET has more blur in the facet edges, especially away from the MQ belly.
So, which gives a more accurate representation of my IRL impressions? I think the DiamCalc version is in slightly better agreement with my observations.
In particular, to check for leakage, I placed the diamond on a colored background and examined under a loupe in diffuse lighting. Under these conditions, I could see only a few small spots of the background color under the table, so this observation matched the DiamCalc prediction better than JA's ASET. In separate tests, I also placed a small dot of color against the girdle (i.e., near 0°), and noticed that a faint hue of that color would appear throughout large swaths of the table. To me, this suggests that maybe the JA ASET setup has the girdle (and maybe even a sliver of the crown adjacent to the girdle) below the horizon (thus black), and/or that DiamCalc places all or part of the girdle above the horizon (thus green).
Also, in my (heavily biased) opinion, the uniformity of brightness throughout the MQ body and the sharpness of the virtual facets in the DiamCalc ASET is more representative of the IRL behavior of this particular diamond than is the JA ASET.
I offer this post primarily as a data point to assist those of us who use JA ASETs make purchasing decisions (or help others make purchasing decisions) about fancy cut diamonds. Nonetheless, I would welcome corrections, comments, expert explanations, or discussion!
ETA: I know that the accuracy of ASET photography can depend on diamond size. In case it helps anybody interpret the images above, this particular marquise is 1.05ct, has a total depth 3.34mm, crown height 0.90mm, girdle 0.22mm, and pavilion depth 2.27mm, length 11.08mm, and width 5.00mm (Sarin scan data).