Talk:Diamond cut

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Contents

[edit] Viewing distance

The current debate about cut-grading standards involves explicit assumptions about lighting and the distance at which a diamond is viewed. The choice of 10 inches versus 14 inches explains some significant differences between two proposed grading standards, according to this PriceScope thread.

[edit] Cut

Cut (table, pavilion depth, crown angle)

Diamonds take a high polish which enhances its scintillation.

You can also test a diamond's light responsiveness

Round brilliants are the most resistant to breakage, but a princess cut will give more caret weight per rough. A modified princess cut called the Arctic Empress (by Sirius) clips the vulnerable corners. Girdles on brilliants may be cut too thin as well. Pear cut and Marquise cut diamonds have sharp points which are vulnerable to damage.

Statements where reasonable people may disagree

  • (Various cuts with points or very thin girdles) may be uninsurable, or require much higher payments. [These cuts] should have issues with insurance due to inherent vice (legal term).
    • This depends on the insurance company, legal jurisdiction, and the fine print of the policy.
  • AGS Diamond Quality Report (different from the AGS Diamond Quality Document) is considered the most complete and desirable report, contains all the information in the GIA report. It also includes information from the Sarin report, like the crown angle and pavilion depth, which are missing from the GIA report.
    • Unfortunately, the AGS' overall cut grade (e.g., AGS 0, AGS 1, etc) is still in its first draft, and is the subject of considerable controversy.
    • A number of discussions on PriceScope, DiamondTalk, and the first international cut conference are about possible improvements to the AGS cut grade.
    • The AGS has announced major changes to its cut grading. Many (perhaps most) stones that currently grade as AGS 0 will not grade as AGS 0 under the new standards. Many other stones that currently get lower cut grades will grade as AGS 0 under the new standards.
    • The new standards more closely align with computer simulations of cut quality, and with Tolkowsky's model of the crown. Unfortunately, the new standards have not been described in detail yet.
    • The AGS' new cut grading standards for round brilliants take effect in the summer of 2005.
    • The AGS also plans to issue cut grades for some fancy-cut diamonds.

~ender 2004-09-04 MST 19:22

[edit] Old Mine cut

what is?

Pud 09:17, 5 Sep 2004 (UTC) My fiance has a ring from her Great Grandmother that contains Old Miner Cut diamonds in it. When it was cleaned recently it shined up beautifly. They apear to be round with less facets than a round brilliant diamond. I asked a jeweler what a ballpark insurance value of the ring would be and she guestimated it at around $400.00 (the ring has a 18 ct platinum head with yellow gold on the bottom aproximately .30 ct's of diamonds in all). We are actually considering using it for her wedding band or at least she can wear it as a right hand ring. It is actually very pretty and sort of antique looking. (The ring not my fiance.) 70.232.141.53 06:55, 23 March 2006 (UTC)

[edit] Theory

I think the theory section should both:

  • Mention that a crown angle of 34.5°, a pavilion angle of 40.75°, and table ratio of about 56% is a common reference point for the round brilliant cut.
  • Discuss the tradeoff between crown angle and pavilion angle.

Doing this clearly, succinctly, and accurately will be a neat trick. Should we reorganize the material in the "Theory" and "Cut Grading" sections?

Should this section describe the various approaches to modelling a diamond's light return?

  • 2-D modelling (a la Tolkowsky) that emphasizes average rays and the crown and pavilion facets
  • 2-D modelling (a la Harding) that emphasizes "head blockage" and other lighting effects
  • 3-D modelling (a la Octonus, GIA, and Adamas Gem Labs) that shows the effects of the other facets

-- Jasper 23:50, 7 May 2005 (UTC)

Well, I see you've edited out the quoted crown and pavilion angles, presumably because they refer to the round brilliant only (which I neglected to make explicit). I agree that there could be more discussion with regards to tradeoffs, but it seems sleep deprivation is making me slow, because I can't begin to formulate a way of expressing it clearly, succinctly, and accurately. However, the section already mentions how crown angle/height affects fire/brilliance, and how pavilion angle doesn't budge much because it's so important to TIR. All the while I realise there's an inherent POV in explaining the subject, because after all, who's to say how much fire a diamond should have? ;) One aspect of fudging the proportions is weight retention, but I already mentioned that under "Choice of cut".
As for the modelling approaches, if the subject can be done justice with 1-2 paragraphs, it should fit into the Theory section. Alternatively a new section could be created. I originally meant the theory section to be something of a jumping off point for the rest of the article, so complex concepts were already explained and "out of the way", which would make discussing the later topics easier and would mitigate repetition.
Anyway, I'm wide open to corrections and proposals. You do seem to be well-studied in diamond cut theory, and you've certainly kept a closer eye on recent (i.e., over the past 2-3 years) developments than I have. I had planned to expand the "Cut grading" section during my initial expansion, but I couldn't decide how I'd tackle it. To be honest, I was/am also uncomfortable describing AGS's and HCA's techniques because I don't feel I understand them enough to do so. I was trained to grade diamonds in the conventional manner, so the new methods that incorporate stone-viewer distance maximums and proprietary software are still a bit new to me. (Gah, I suppose it's back to school for me. It doesn't help that AGS is guarding all meaningful details from outsiders like a bunch of scrapyard hounds.) Should we even bother describing the conventional method, since it seems even GIA has joined the ray-tracing bandwagon? Sigh. Sorry for rambling. -- Hadal 05:44, 8 May 2005 (UTC)
Hadal,
Thank you for your kind reply. I have similar concerns, but from a different point of view: I am much more familiar with the last 4 years of the theory than with traditional gemology. I should read up on how the mid-twentieth century "ideal" cut models were derived.
I edited out the quoted crown and pavilion angles because their context was about finding a single combination of proportions. The context did not consider the trade-offs of crown angle vs. pavilion angle, brilliance vs. fire, et cetera. And like you did, I had trouble coming up with suitable replacement text.
I think I understand the HCA. Holloway has explained it in detail, and I could probably summarize it. The AGS, GIA, and Adamas Gem Labs models are much more complicated, and much harder to explain.
-- Jasper 00:42, 9 May 2005 (UTC)

[edit] Minor spelling difference on the graphics

Pavilion is pavillion in at least one place.

This graphic is taken from a document that consistently uses "pavillion". "Pavillion" is a legitimate alternate spelling. -- Jasper 20:04, 9 December 2006 (UTC)

[edit] Delisted GA

This article has been removed from the Ga list as it has failed WP:WIAGA criteria 2b. Feel free to renominate the article once these issues have been addressed. Tarret 23:42, 23 October 2006 (UTC)

[edit] Pricescope

I disagree with the validity of the Pricescope link on this article. While it is a valid topic of discussion, Pricescope is a biased forum owned by someone who is in favor of certain diamond cutters... and in some cases "paid off" by them to show favoritism, thus degrading the value of information found within. The population of the forum is a blunt mix of curious consumers, old hat diamond fans, and employees of the diamond cutting companys which pay the forum... the employees exist to provide carefully disguised sales pitches as if they are unbaised valid information. -- Jess 208.179.106.90

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