Talk:Diamond cut

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Delisted version: October 23, 2006


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.
  • 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.
    • 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] 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-BIASED vendor-Beware

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

I agree with you, thus I removed it. Twice. We'll see if it stays off. I have been going through various diamond articles attempting to "clean house" and wipe out all of the commercial and promotional links to online sellers. We need more links to articles from the GIA, AGS, and other credible gemological institutions. Malachite84 05:40, 26 August 2007 (UTC)

Pricescope is a biased vendor. Their advertisers are the ones usually blogging and leading you to buy from them. Please remove the title pricescope

[edit] Fancy cuts

I propose that Fancy cut be merged into the Diamond cut#Fancy cuts section, as they are essentially duplicates. Diamond cut is much better written, while Fancy cut would take a great deal of editing to make it encyclopedic. It would be a more profitable use of editing time to move any information from Fancy cut which can be cited to Diamond cut, and then change Fancy cut back to a redirect. AndyBQ 01:06, 1 May 2007 (UTC)

As a person who is full time engaged in diamonds and jewelry business I can agree with the view expressed above. Prakash Lakhi Plakhi 22:46, 16 May 2007 (UTC)

Diamond Shape and Cut are frequently confused!

Shape is the model or form of the diamond, such as round, oval, pear and more. Classic shapes The classic diamond shapes following are set standards: round brilliant, princess, radiant, cushion, oval, pear, marquise, emerald, heart, trilliant also named trillion, taper and baguette. The most popular diamond shape is round brilliant. View standard shapes: www.ajediam.com/diamond_shapes.html

Fancy shapes A diamond cutter can cut a rough diamond into any fancy shape such as a flower, horse… View a horse shaped diamond: www.ajediam.com/free-printable-greeting-cards-horse.html There are no standards for fancy shapes. Jan Huts janhuts —Preceding comment was added at 13:34, 17 October 2007 (UTC)

[edit] Contested article links

I restored the links to:

  • The HCA's graph of the tradeoff between crown angle and pavillion angle.
  • Bruce Harding's article on Faceting Limits
  • Peter Yantzer's article on Indexing the Upper Girdle Facets.

These links are to articles that cover important theoretical issues with diamond cut, in a scholarly manner.

I did not restore the link to the Pricescope discussion of a GIA article about indexing the upper girdle facets. It seemed to me that most of the value of this link seemed to be covered by Yantzer's more scholarly article on the subject.

-- Jasper 02:44, 24 August 2007 (UTC)

These articles link to or are hosted by a non-scholarly website. I have deleted them. See what I wrote on this page under "Pricescope". I would not object to the articles if they were hosted on a scholarly website (GIA for example), or simply a website that was not commercial and biased. As they are not neutral, they are not credible and should not be in an encyclopedia article. Malachite84 05:44, 26 August 2007 (UTC)

Malachite,

Are you seriously claiming that an article by Peter Yantzer (the director of the AGS Laboratory) is not credible?

Are you seriously claiming that Bruce Harding's article on "Faceting Limits" is not credible? This article originally appeared in the Fall 1975 edition of the GIA's journal Gems and Gemology, according to Mr. Harding's post at http://www.diamondring.com/forums/showthread.php?t=7101 .

-- Jasper 17:53, 26 August 2007 (UTC)


The articles themselves are not the issue (as they are well-written), but it is because they are hosted by a biased website. It's the same exact thing as posting a link to "all about diamonds" written by the head of the GIA but posted on Blue Nile, Zales, or any other jewelery store website (not that the GIA would ever allow that). Credible scholarly sources keep their distances from retail sources. That is why the most credible source for University papers is still scholarly journals.

Even that website link you just posted is on a website that deals with buying and selling diamonds online.

I would even reccomend hosting the articles (or rather, asking to host the articles) on a free server yourself if you still feel these articles are worthy of being included in an encylopedia, and being sure to not link to sites that deal with online sales. I have no problem with an article allegedly written by the director of the AGS laboratory as long as the AGS hosts, endorses, or at least stands by the article, and ditto for GIA. Feel free to ask a Moderator here for their opinion.

Notice that this article was removed (not by me) from the Good Article list because it does not meet WP:WIAGA criteria 2b, which deals with using sources that are factually accurate and verifiable. Quoting: "(b) cites reliable sources for quotations and for material that is challenged or likely to be challenged, preferably using inline citations for longer articles"

Malachite84 02:48, 27 August 2007 (UTC)

Malachite,

I am glad that you stipulate that the "articles themselves are not the issue (as they are well-written)".

Thank you for asking for an administrator's insight into this topic. I have asked User:Hadal if he can participate.

I think that you are worrying too much about whether the articles are in sources that accept advertising aimed at retail purchasers. By your logic, a biography in Bill Gaines' Mad Magazine (which accepted no advertisements while he was alive) would be more credible than a feature biography in the American Society of Mechanical Engineers' magazine (which accepts copious advertisements and press releases). (I used the latter magazine as a source for the articles on Thomas and Emily Davenport.) Whereas, there are circumstances in which I would accept a sufficiently well-written, significant white paper by a manufacturer or retailer of a product. Typically, the circumstances would involve the paper being the best and most reliable article (on the narrow topic that justified linking to the article) that a typical wikipedia reader could reasonably be expected to have access to. For example, most wikipedia readers can readily access Mr. Harding's article at the link I provided; most wikipedia readers do not have access to the Fall 1975 edition of Gems and Gemology.

Sincerely yours,

Jasper 03:54, 28 August 2007 (UTC)


I will await an administrator's presence before commenting further. Malachite84 00:24, 29 August 2007 (UTC)