D. Atlas DIY ideal cut definition and the better than "ideal" cut diamonds sold here

Not open for further replies. Please create a new topic or request for this thread to be opened.


Apr 29, 2003
Perhaps D. Atlas, vendors and individuals alike can shed some light on this question.

Looking at the chart for "American Ideal Cut" 1A on D. Atlas ( site, the crown angle is listed as 34.3'-34.7'. As explain by D. Atlas in another thread, this is a narrow range according to him and I quote


I have just checked the crown angle calculation and it seems to be working. I have a very narrow range of 34.3 to 34.7 degrees for 1A. That is likely why many "ideal CUts" being sold are 1B in crown angle.. It is not the end of the world if the crown is 35 degrees or 34 degrees. A 1B can be a wonderful stone.... It just depends on how one defines the words "Ideal Cut".


Now, I got to ask the obvious question. When I came to this site, I was drilled that cut cut cut is what it's all about and I'm better off buying from the vendors here because they sell merchandise that are in the top 2% of the diamonds sold.

I don't doubt this may be true, and as D. Atlas pointed out, it is not the end of the world if a diamond is off by a degree or two from being "ideal" but I got to say I didn't expect this. I was happy chugging away at HCA but now, I'm paying closer attention to the "ideal" crown angle.

I use crown angle because the diamonds that I've been looking at here often time gets a 1B rating on the crown angle. As a comparison, the diamonds which interest me on bluenile (signature ideal) have gotten 1A in each category. But to be fair, I did find one that came in 1B this morning. So, even bluenile Signature Ideal is not really the holy grail "ideal" either.

Another question is about the girdle thickness. But looks like D. Atlas found it after it was brought up by caratgirl.

caratgirl also observed the same thing.

I have also discovered that most of what I thought were the better stones from the really good vendors don't make the 1A cut grade!

Also, the polish/symmetry selection is "Excellent/Very Good". BlueNile Signature Collection has "Ideal/Ideal" as well as "Excellent/Excellent".

I suspect they are the same but can someone shed some light on this? What is the *official* rating terminology that is suppose to be used when describing polish/symmetry?

Colored Gemstone Nut

Nov 21, 2002
Jlim-Your post is intersesting but the Charts Dave Atlas set up are guidelines to follow just like the HCA is. Read GOG's website on how he explains how the minor facets play a role in how a stone will perform visually. Bases on certain crown/Pav. Angles some stones are going to perform better than others visually, but there is a lot more involved than just using those 2 tools for your search criteria.

Here is a qoute from Richard Hughes from the palagem website:

If the gem is beautifully cut, things such as depth percentage or length-to-width ratio matter not one bit. What works, works. The eye, the mind and the heart are the final arbitrators, not numbers.

Maybe Dave can comment and clear up some of your concerns..

-Josh Rioux
Sitka, Alaska



Mar 21, 2001
Don't take these chart number guidelines as
ABSOLUTES. They're not. You can have ideal-diamonds with
Crown angles of 34.2 or 34.8 that are visual
knockouts. Maximizing light output and minimizing light leakage is the result of the interaction between Table, Crown, and Pavillions. Of critical importance in
addition to the facet angle, is facet size and facet placement; these latter two are not addressed by these



Sep 3, 2000
The AGA charts, the AGS 0 the GIA grading system, all fall short of the authority of the Ten Commandments. The grading of diamonds has been greatly refined over the past few years, but it is a work in progress and still very subjective sometimes.

Beauty is to be seen and not described by charts, graphs, tools and vendors or appraisers. Having tools can help consumers shopping for diamonds, but the way to appreciate their beauty is by looking at them with the most wonderful tool of all, your own eyes.

I am going to make every effort to perfect these AGA charts and computations so that people can shop with a degree of security that they have not had before. However, the mind and the eyes are the true tools to use in finding the diamond that pleases you and your budget.

We have not lost sight of our original goal, which was to help people buy a diamond. The technicalities are useful, but are certainly open to further revision and subjective disagreement. A 1B grade of a parameter generally would not make or break a diamond's overall "quality"..


Jan 1, 2003
I actually really like the strict parameters, because you can definitely make sure that if a stone is a bit pricier, the vendor has a legitimate reason for it, such as a 1A cut. It makes for better apples to apples comparisons when you can't view both stones together.

Having said this, I have seen lesser quality cuts look just as beautiful. It took me a very long time lurking on this forum to finally have everything percolate. I must have changed my mind about which of the 4 C's took precedence about 20 times!

I finally just decided that cut would win, so I ended up with a 1A cut (even though my crown % is just over at 34.8%, the other parameters are right on). I had always wanted that 2 carat, but I also wanted an F color or better, in a VS2 or better. So I compromised. I saved the cash for two years, then was very surprised to see that there were very few stones available in my price range that I was willing to settle for.

I then decided that 8 mm would be my target - that would look close enough to a 2 carat. Surprise! Even fewer stones to look for that were also very well cut. I just 'happened' upon the right stone while on vacation in Florida.

I took a chance and called DBOF to see if they had anything in the range I was looking for. Amazingly enough, they did. Long story short, we drove to look at it, it looked great, and was less than the 18K high water mark that I had set for myself. Everyone has one of those! I could afford to spend more, but just didn't want to.

I have been very happy with my purchase since then (about 4 months), and attribute that to all the exposure I had to Pricespoce and all of the helpful experts and consumers. I am almost embarassed when my diamond sparkles, since everyone stares so much (yeah, like that's a bad thing).

The bottom line is - choose what makes you happy, or you will always wonder 'what if', whether it is clarity color or size or even cut (as long as it is still a good sparkly cut).


Feb 22, 2003
When I was learning, someone posted a link in a PS thread to an article at GIA, or AGS (or somewhere, I forget now) about crown angles and cuts. Gist of the article was the Tolkowsky Ideal Cut is not the "perfect" model. When researchers were comparing diamonds of similar color/clarity/carat weight in blind studies, observers preferred the slightly shallower cut diamond over the TIC cut diamond by a significant percentage. Slightly shallower crowns tend to yield very brilliant/firey diamonds.

Wish I had book marked the site to post here now. Maybe one of the PS folks remembers the article I'm speaking of and can reference it for Jlim.

This is why sooooo many experts and other posters in the Price Scope forum say, "All the Certs, HCA, reports, and pics are tools to weed out poor performers. Ultimately, diamond choice comes down the eye of the beholder."
Not open for further replies. Please create a new topic or request for this thread to be opened.
Be a part of the community Get 3 HCA Results