Help needed for WF stones!

[TreeScientist]

Thanks for explaining that. Makes perfect sense now. I didn't realize how much the rounding can affect performance.

You're welcome! That's why these forums are great. A good source of knowledge to make us all more informed shoppers.

Keep in mind that even AGS rounds pavilion angles. It's to the nearest .1 instead of .2 degrees, but still, discrepancies can arise because of this. Take this ACA for example:
https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-4011136.htm

On the AGS certificate the pavilion angle and depth are listed as 40.6 and 42.6%, respectively. Now, we know that an exact pavilion angle average of 40.6 would result in a depth of 42.8%, so we know that the pavilion angle on this stone is somewhere between 40.5 and 40.6. In fact, the Sarin Report lists the pavilion angle as 40.5.
https://www.whiteflash.com/jewelry/thumbnail.ashx?itemcode=sarin_ags-104100413014.jpg&type=sarin

This is probably one of those cases where the actual PA average is almost exactly 40.55, so it could go one way or the other depending on the scanning technology used. Now, I imagine that the precision cut of an ACA means that none of the individual pavilion mains falls below 40.5 degrees (maybe @Texas Leaguer could post the details from the Advanced Manufacturer's Sarin Report to confirm ), but I would still rather have a diamond with a PA of 40.6+.

That's why I like to use a combination of both the PA and pavilion depth to get a better idea of what the actual pavilion angle of the diamond, both for GIA and AGS stones, especially when diamonds are on the fringes of the Ideal PA range (around 40.6 or 40.9-41.0). It gives you a better idea of where exactly the diamond falls on the spectrum.

You can also do the same thing with CA and crown height, but the math is a bit more complicated due to the variable table size also playing a role in crown height. The PA and pavilion depth calculation is easy as long as the diamond does not have a cutlet (which would complicate the math), because PA and pavilion depth are directly correlated in MRBs without cutlets.

 

[gm89uk]

I like that diamond, but I would disagree about the potential for SuperIdeal proportions. Here's a little trick for getting around that pesky GIA-rounding for the pavilion angle. For an MRB without a cutlet, a diamond with a pavilion angle of EXACTLY 40.6 would have a pavilion depth % of 42.8%, which would be rounded up to 43.0% (GIA rounds pavilion depth to the nearest .5).

Thus, for GIA diamonds with 40.6 pavilion angle and 42.5% pavilion depth, this means that the average pavilion angle for the 8 lower half facets is somewhere between 40.5 and 40.6. For 40.6 PA and 43.0% depth, then the average PA would fall somewhere between 40.6-40.7.

The diamond you listed has a GIA pavilion depth of 42.5%, which means average PA is somewhere between 40.5-40.6. That would not be SuperIdeal territory, and may introduce some obstruction upon close viewing if one or a few of the individual pavilion mains fell below 40.45 degrees. For GIA diamonds, I try to stick with 43.0 pavilion depth for 40.6 pavilion angle stones, as the average of 40.6-40.7 is more in line with AGS Ideal specs and is very unlikely to suffer from any obstruction issues.

Hey Tree, while 40.6 42.5% stones are often <40.6 I've been caught out before and the are exceptions to the rule. With the rounding on GIA, it is theoretically possible to have a 40.65 with a 42.5% due to the number of factors there are, although you are right the likelihood is less than 40.6.

I looked into this in detail with a rounding program gmsoft.somee.com.

Through looking at lots of GoG GIA stones which had the GIA certificates and their sarin machine scans at the same time you realise a few things. A pointed culet is almost never zero, but more likely 0.1 to 0.3 and in less than 1 carat stones, it can be 0.4. Remember in smaller stones under X10 magnification a tiny culet may still look pointed.

The diameter and depth are rounded to 2dp and can be +/- 0.005. You'll see this difference in recerted diamonds with GIA and AGS for example that can have different depth percentage of up to 0.2%.

While in this diamond, I'd say most likely 40.55, I have been surprised by some sarin results before.

 

[TreeScientist]

Hey Tree, while 40.6 42.5% stones are often <40.6 I've been caught out before and the are exceptions to the rule. With the rounding on GIA, it is theoretically possible to have a 40.65 with a 42.5% due to the number of factors there are, although you are right the likelihood is less than 40.6.

I looked into this in detail with a rounding program gmsoft.somee.com.

Through looking at lots of GoG GIA stones which had the GIA certificates and their sarin machine scans at the same time you realise a few things. A pointed culet is almost never zero, but more likely 0.1 to 0.3 and in less than 1 carat stones, it can be 0.4. Remember in smaller stones under X10 magnification a tiny culet may still look pointed.

The diameter and depth are rounded to 2dp and can be +/- 0.005. You'll see this difference in recerted diamonds with GIA and AGS for example that can have different depth percentage of up to 0.2%.

While in this diamond, I'd say most likely 40.55, I have been surprised by some sarin results before.

Good to know, thanks for the info and the website! Seriously, that is one really cool program. But still, I prefer to stick with GIA depth of 43.00% unless I have access to a helium scan (Like GOG used to provide) or Advanced Sarin Report to confirm that the individual pavilion mains for a 42.5% depth diamond don't drop below 40.5. As I said, I'm guessing this would not be the case with an ACA due to their precision cut, but I think it's better to be safe than sorry. Luckily, WF has access to these scans, so I would be comfortable buying from them if they could provide the info. But for open market and/or GIA-graded diamonds it's next to impossible to get that kind of detailed info now that Jon is no longer with GOG.

 

[diamondseeker2006]

Good to know, thanks for the info and the website! Seriously, that is one really cool program. But still, I prefer to stick with GIA depth of 43.00% unless I have access to a helium scan (Like GOG used to provide) or Advanced Sarin Report to confirm that the individual pavilion mains for a 42.5% depth diamond don't drop below 40.5. As I said, I'm guessing this would not be the case with an ACA due to their precision cut, but I think it's better to be safe than sorry. Luckily, WF has access to these scans, so I would be comfortable buying from them if they could provide the info. But for open market and/or GIA-graded diamonds it's next to impossible to get that kind of detailed info now that Jon is no longer with GOG.

Thank goodness we got away from helium scans because many of us became too OCD about the numbers. I hate to see anyone giving this advice because those of us who have been around for many years here and who have seen countless ideal and superideal cut diamonds will tell you that while some people may have preferences for things like table size or lgfs, the average person coming here for advice basically can choose a superideal easily, or they can choose from the next level of stones which includes the best of GIA excellent or AGS ideal cut. We choose those more by the light return images than numbers. If I were a vendor of superideal cuts and a PS member asked for a helium scan, I'd consider that a huge red flag and absolutely refuse. I am happy to say it is just not necessary. GOG stopped doing helium scans way before Jon left. They probably figured out that OCD people would eliminate perfectly great diamonds and post negatives here on certain stones based on helium scan numbers. I wouldn't hesitate to buy a diamond from Whiteflash or High Performance Diamonds (CBI) any day with the vast and totally adequate information they provide.

The original diamonds posted we just fine for someone who doesn't care about superideal and just wants a beautiful diamond. I hope he returns to see the other posts.

 

[TreeScientist]

Thank goodness we got away from helium scans because many of us became too OCD about the numbers. I hate to see anyone giving this advice because those of us who have been around for many years here and who have seen countless ideal and superideal cut diamonds will tell you that while some people may have preferences for things like table size or lgfs, the average person coming here for advice basically can choose a superideal easily, or they can choose from the next level of stones which includes the best of GIA excellent or AGS ideal cut. We choose those more by the light return images than numbers. If I were a vendor of superideal cuts and a PS member asked for a helium scan, I'd consider that a huge red flag and absolutely refuse. I am happy to say it is just not necessary. GOG stopped doing helium scans way before Jon left. They probably figured out that OCD people would eliminate perfectly great diamonds and post negatives here on certain stones based on helium scan numbers. I wouldn't hesitate to buy a diamond from Whiteflash or High Performance Diamonds (CBI) any day with the vast and totally adequate information they provide.

The original diamonds posted we just fine for someone who doesn't care about superideal and just wants a beautiful diamond. I hope he returns to see the other posts.

Regarding the original diamond:

Acceptable for the average consumer? Sure

The best diamond for the price: Heck no.

Believe me, I'm not OCD about diamond cut, particularly when it comes to open market stones. I'm one of the people who believe that most individuals would not be able to tell the difference between a SuperIdeal and a well-cut non-branded stone.

But the original diamond in question is certainly not even what I would consider well cut for an open market stone. And it is $800 more than a stone that is much better cut, doesn't have a leaky table, and is within the parameters frequently recommended on this site.

I've made this point multiple times, but you don't address the original question. So again, why pay more for a stone with an inferior cut? Especially since the OP has made clear that they have no interest in really the only thing that would make the WF diamond superior, which is the upgrade program.

 

[Texas Leaguer]

@diamondseeker2006 You make a good point about the value of actual light performance images. That information is independent of any numbers that may appear on a lab report or be generated by a scanning device. As has been mentioned, averaging and rounding is an issue with the numbers on reports, as is instrumentation deviation of the scanners themselves. Sometimes there is a compounding effect.
LP images serve to validate the numbers, as well as sometimes indicate where the numbers may be imperfect.

@TreeScientist I am curious about the diamond you pointed out that shows 40.6 on the AGS report and 40.5 on our detail page. I will look into it.

 

[Texas Leaguer]

@TreeScientist If you look at the actual lab report, the official measurement is 40.6 average pavilion angle. There appears to have been a typo in the data spreadsheet used to populate both the spec table on the detail page and the sarine report graphic on our website. That has now been corrected, although it may take a bit of time for the website to reflect the updates.