It has been quite a while since I’ve made one of these Pricescope Rockytalky reviews. There is good and bad to this. The good thing is that I’ve noticed in general better responses to people’s questions. The bad thing is that it is also because it seems like less people are asking interesting questions.
Here is a post I came across that I found interesting because it is typical of the responses that are given to those seeking expert advice, yet they are being turned away by telling the original poster that they cannot nitpick without more detailed information. When reading this the first time, I felt that I could give the original poster the kind of advice he was seeking and that is why I chose his question for a review.
Here is how the thread went:
Posted by Icycherry on July 31st, 2013, 10:03 pm
“Hi guys,
I’ve got a diamond produced in Canada, which has very good figures (at least to the eyes of a newbie): 61.9%depth; 55%table; 34.5crown angle and 40.8pavilion. What bothered me was the star and lower half, which was 45% and 75%. Would this combo affect the fire (which I highly care) and brilliance of the stone? I have heard that if the star is smaller, it should go with a steeper crown. It seems that 34.5 is not steep enough. Appreciate any opinions!” (Emphasis Added)
Posted by Icycherry on August 1st, 2013, 10:20 am
“Here are the more detailed figures of this stone:
1.72carat; measurements: 7.69-7.71*4.76; Depth: 61.9%; Table: 55%; Crown Angle: 34.5°; Crown Height: 15.5%; Pavilion Angle: 40.8; Pavilion Depth: 43.0%; Star Length: 45%; Lower Half: 75%; Girdle: Medium, Faceted (3.5%); Culet: None
The report is issued by GIA.(That might be a great problem ’cause the figures are rounded ones, not accurate enough) I understand that it would be uneasy to tell exactly how this would affect the performance of the stone just by figures, but I really have no way to see the stone before I pay for it. So….still want to hear some opinions, even conjecture would be greatly appreciated.”
<h2>Best Pricescope Rockytalky Responses:</h2>
Posted by John Pollard on August 1st, 2013, 9:52 am
“On its face 55-40.8-34.5-45-75 is not an issue. But it depends on how specific you want to get.
Impossible to say more because, aside from table, the data points are averages of 8-16 separate measurements apiece. Those averages are further rounded up-or-down if it’s a GIA report. From this data there’s no way to know how consistent the cutting is facet-by-facet, if that is important to you.”
Posted by Yssie on August 1st, 2013, 10:56 am
“Here’s a tutorial from Good Old Gold that introduces LGF and star (link removed)
The numbers are what the PS community would call “safe” – worth further investingation. But what you’re asking… well, garbage in, garbage out! GIA rounds star and lgf to 5%, crown to 0.5deg, pav up to 0.2deg, and the numbers printed on the report are averaged around several sections of the stone as Mr. Pollard said…
And to add to those uncertainties are other errors: the Sarin scanners GIA uses in the labs are listed (on the Sarin webpage) as accurate to +/- 0.1deg, the GIA report tells us nothing about optical symmetry (the symmetry of the reflections of facets you see when you look into the stone – it’s a function of facet meet symmetry but there are other parameters)…
IMO your best friend in this situation is an idiot-proof return policy. Or buying from a boutique vendor who specialises in exactly this sort of nitpicking – GOG, WF, BGD, Infinity (sold by HPD) are the first PS favourites who come to mind.”
<h3>My Comments:</h3>
Now John Pollard is a trade member who works at Crafted by Infinity. He knows a lot about diamonds and I have personally learnt a lot from his previous posts. Although his post was accurate, it doesn’t help the original poster by telling him there is insufficient information. In fact, his response led to Icycherry to believe that a diamond certified by the GIA may be a great problem when the GIA is the most respected lab in the world. This, of course, was not John Pollard’s intention, but that is what happens when trade members post without addressing all of the key concerns of the original poster.
Yssie, who is a diamond prosumer with 16116 posts to date responded by saying that the numbers were ‘safe’ – I find this generalisation dangerous for a newbie. There is further scaring of the newbie with more rounding and measurement errors without indicating what kinds of risks are safe and what are not. Is the best advice here an ‘idiot-proof’ return policy? Yssie’s second piece of advice is to purchase from basically any one of several PS vendors…
<h3>My Response to Icycherry’s question:</h3>
Icycherry first lists the proportions of the major facets of his chosen diamond and states that these are “good figures”. He has obviously done his base research on proportions. The problem he has is mainly with the lower girdle percentage and the star percentage, which are 45% and 75% and he wants to know whether these numbers raise any red flags because he has a preference for fire.
Although in most cases when referring to the star and lower girdle facets, I would bring up measurement errors, in this case I actually think that it may not be necessary. Yes there may be some slight variation in the proportions, but the question asked is not about optical symmetry and the variances are not likely to be so large as to invalidate any reasonable advice.
The diamond Icycherry has chosen has an excellent length and width 7.69-7.71mm and has a CA/PA of 34.5/40.8 with a 55% table, it sounds like a fairly promising stone. What she needs to be aware of is that the shorter the stars, in general the shallower the stars are. Also, with shallower stars, the upper girdle facets are also shallower. With 45% stars, there is a likely chance that the upper girdle angle is less than 40 degrees. The effect that this will have on the diamond is that there will be less contrast in the upper girdles. Also with 45% stars, the bottom half of the diamond will appear noticeably darker than one with 50-55% stars. The point is that these are diamonds with different contrast pattern character.
The edge of this diamond would probably look a bit like a diamond with a painted upper girdle:
smallstars
If Icycherry prefers the contrast pattern of the 45% stars, then the risk that Icycherry needs to know is that if the stars tend to the shorter side, say 42.5%, there will be quite a bit of unnecessary weight lost.
Also, with 45% stars and a 75% lower girdle length, we would not expect many hotspots around the base of the arrow shafts. If these facets are even shorter than stated, then you may lose the triangular hotspots under the stars as well. All this means a detriment to a further detriment to ‘pin’ fire in the diamond. With 75% stars, the diamond is already not optimised for pin-fire but rather for more bold flashes. If that’s the only thing Icycherry cares about, then the lack of pin-fire flash could make the bold flashes stand out more.
If it is the case that these facets tend to 47.4% and 77.4%, then the diamond becomes more typical of a TIC and there is not many concerns. In fact, coupled with the proportions of the major facets, I would expect this potential possibility to have excellent light return.
As for whether the crown facets should be steeper? Well the crown facets do not work that closely with the star facets except for perhaps physical constraints. The advice Icycherry probably heard was that because shorter stars generally reduce fire, then going for a steeper crown could make up for some of that. The thing that is misleading in this sort of advice is that although a steeper crown produces more dispersion from the crown, it has no bearing on the potential fire that could have been produced by the star facet. These are two different things.
My advice to Icycherry is to first figure out which kind of fire she prefers (bold or pin flash fire), and then to optimise for it throughout the diamond. If it is the case that she likes pin-fire flash, then perhaps going for 45% stars and 75% lower girdles may not be the best choice. If Icycherry happens to read this, I hope you have found my conjecture to be a bit more helpful than the responses you’ve received from the other Pricescope experts.
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