Minor Facets = Minor Effect

[elmo]

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On 9/1/2003 8:54:37 PM Cut Nut wrote:

In other words Brad, just trust you and consumers should never bother to use their owns nouse or efforts.


HCA is most dependant on the pavilion angle, the most accurate of the measured proportions - because it is the longest facet.


If you really can not add any evidence to support your "trust me" rocket guidance system Brad, why bother typing the words?


And are you still selling lots of those really beautiful diamonds with the 41.6 degree pavilioon angles? The ones you get a great margin on?
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Hey Garry, you're using a bit of a double standard here aren't you? On a thread two weeks ago when someone asked about Aurias/Ekati stones from Canada you said they mostly had 41 degree pavilions and 35 degree crowns, but that you used the idealscope (your eyes) to pick the nice ones for your store. However, if you were using the cut advisor alone, none of those would see the light of day.

So I wonder in general which stone folks would prefer, one with the great numbers that looks great at 10 over, or one with deviant numbers that looks great at 30 back?

 

[Richard Sherwood]

Brad, you've got a point in that the profile the DiamCalc program produces is only as good as the data input.

However, if the data is correct, the DiamCalc will produce an extremely close Light Return Analysis and simulated IdealScope image.

Usually if a Sarin is functioning within their stated limits of variation the resulting simulated profile will be very close if not dead-on to the actual profile.

The times that it is not close (5% or less?) because of faulty data or extreme ranges of minor facets doesn't seem to justify tossing the system.

You have the luxury of examining all your diamonds visually. The internet customer doesn't have this luxury while in the process of narrowing their search.

The DiamCalc and the HCA are both good guides in navigating through the jungle of poor performing diamonds. They both will help speed the customer through to a decision making point.

I believe if you worked closely with the DiamCalc program for six months your opinion would change. I learned more about the factors which affect the performance of a diamond in six months with DiamCalc than in the six years prior.

 

[Garry H (Cut Nut)]

well said Rich

Elmo what is the problem with my Aurias comment? The stones are so close to the No Go Zone that scanning them with Sarin and reading the results is just too slow - we use the Ideal-Scope to pick the eyes.
But from a data sheet even if it was not scanned as accurately as we would like, we still know which stones to call in as likely prospects and which to not bother them wasting theirs and our time.
If Brad has never used HCA for the same purpose I would be quite surprised.

 

[mike04456]

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On 9/2/2003 9:49:55 AM Richard Sherwood wrote:
The DiamCalc and the HCA are both good guides in navigating through the jungle of poor performing diamonds. They both will help speed the customer through to a decision making point.

I believe if you worked closely with the DiamCalc program for six months your opinion would change. I learned more about the factors which affect the performance of a diamond in six months with DiamCalc than in the six years prior.----------------

As Garry said, good point. Brad started out attacking the science but his objection is one of application, not science. Sticking with the rocket metaphor, the science behind the space shuttle is not faulty just because a couple of them have blown up. And the science behind cut grading is not faulty because some people have trouble getting accurate Sarin readings.

I also have a serious problem with Brad's continued exaltation of the human eyeball as a foolproof instrument, which is far from the case. Too many consumers have been fooled by jewelry store lighting into buying poorly cut stones that look great until they get them outside.

 

[aljdewey]

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On 9/1/2003 8:35

3 PM DBOF wrote:

Then there are the other 2/3rd`s of the diamond that started this thread.

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You know, I've read over and over throughout the last few weeks your continued focus on the "other 2/3s" of the facets, which are "the majority" (sheerly by virtue of their number).

I'm no diamond expert....I'm just an average consumer......but I'd like to point something out. Not every element has equal weight; that is to say, if there are 58 facets, that doesn't mean each facet affects the performance by exactly 1/58.

Think of a cake....there is the flour, the sugar, the eggs, the oil.....which are all MAJOR elements. If you forget any one of them, the cake doesn't come out even resembling cake. Other ingredients in the cake might be a tsp of vanilla or a tsp of grated lemon zest or a 1/2 of cinnamon.......all of which certainly affect the nuance of a cake, but hey......leave any one of them out and you still have CAKE. Leave out the flour, though......NO cake!

Yes, the cake has 7 ingredients, but not every ingredient carries equal importance to the finished product.

Same with a house....there might be 24 walls in a house, but 8 of them are load-bearing walls. You can knock down 2/3 of the walls....the 16 non-load-bearing walls......and the house will still stand. Knock down one of the 8 load bearing walls, though, and the integrity of the house is compromised.

On this premise, I'd have to put more stock the arguments Richard/Garry/etc. make regarding probability of reasonably.....not exactly, but reasonably.....predicting a diamond's performance.

Just my opinion.

 

[Rhino]

Just catching up on this thread here while I have a little time. Rich I would agree with your assessment. We can get a good "general idea" by the major facets. Minor facets (primarily the lower girdles) can tweak the stone one way or the other.

One reason why the hairs on the back of my neck stand up a little when I see DiamCalc pics posted is because the default measurements in the program for stars and lower girdles are 46.1% stars and 82% lower girdle height. These are NOT the norm from my experience. There is only 1 or 2 factories I know of that consistently cut star facets to 43-46% and NONE I know of that cut lower girdle heights to 82% (though I do know one that consistently cuts em around 80-81%).

One other small dilemma ... there are 2 machines currently measuring lower girdles. The most expensive Sarin and the most expensive OGI. The Sarin measures lower girdle length (along the slope of the pavilion) while the OGI measures lower girdle height (much the same way pavilion depth is measured). The measurements are not the same. The DiamCalc uses the "height" measurement (OGI) so if you're using a Sarin and punching in THOSE lower girdle numbers you'll get a wrong representation.

Best bet is to just do a 3d scan of the stone and import it into the DiamCalc.

Ok... enough rambling. You see Rich ... I see so many stones from so many different sources. I DO look for consistency among the cutting houses, primarily in their optical outputs but I've seen plenty that fall outside of the norm and all over the spectrum regarding minor facet cutting. That's the only reason why I would never attempt to predict the scintillation of someones diamond without knowing the facts. Unfortunately most dealers AND CUTTING FACTORIES FOR THAT MATTER do not provide that info to their clients. I have a hard enough time getting basic Sarin info from most dealers.

My .02c

Rhino



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On 8/30/2003 7

7:32 AM Richard Sherwood wrote:
It is my experience that diamonds with the same major facet proportions will generally produce the same general light return performance with minor facets that fall within the average range of proportions usually encountered.

It is only when you encounter minor facets which fall significantly outside of this "average range" that you see noticeably differently light performances. This is usually the exception rather than the norm.

The minor facets seem to "tweak" the performance of the diamond rather than dictate it. Extremes aside, of course. In my opinion, if you looked at a 100 stones, maybe 5 would fall in the "extreme" range as far as minor facets were concerned.

The major aspects of a stone- light return, light leakage, contrast, fisheye effect, steep & deep syndrome with the "ring of death" are all mostly influenced by the major facet proportions and crown/pavilion angle relationships.

It is my contention that you can get a pretty good "overall" idea of the light performance of a stone from the proportions of the major facets and crown/angle relationship, while the "exact" idea of the light performance is obtained when you tweak the profile of the stone with the minor facet proportions.

The minor facets are the "accessories" which rev up it's performance, while the major facets and crown/angle relationship is the "engine".
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