Do it yourself round and fancy cut grading

[oldminer]

The new www.gemappraisers.com site is finally up and running. You can grade round and fancy cut diamonds with the AGA Cut Class system.

You can also use the shape selector tool to play with various length to width ratios, along bulge factors. Then you can submit the outline of a fancy that you like to any vendor of your choice. They, in turn, can use this same tool to send you the shape of stones they may have available. It will help everyone visualize the shape found by varying the length to width ratio and bulge factors.

The subject of diamond shape is far more complex than this new Shape Selector too, but this is a good beginning for communication. A few more parameters and the message would be lost with the complexity of the tool.

I hope it proves useful to shoppers and to vendors. There is no more reason to examine a well described diamond and have little or no idea of if it is a reasonably well cut example. Having coached hundreds or thousands of users through my Cut Class charts over the past 15 years, this automated feature should be welcomed.

Vendors: You may use the Shape Selector or automatic grading on your own site with attribution.....No problem.

 

[Lanee]

Nicely done, you're too cool.

 

[jlim]

David - I just tried using it. Just a suggestion. The format expects you to enter Length then Width. But on most GIA reports, it shows Width then Length. Also, it seem if I choose thin to medium girdle thickness, it will be graded as 2A. I read the tutorial on pricescope about girdle, it just says very thin girdles are not recommended for claw settings. So, in your opinion, what would be the ideal girdle for around 0.8ct?

Would it be possible for you to make the format of the entry form (for round brilliant) to follow the Sarin report format:

Total Dept
Crown Angle
Crown Height
Pavil Angle
Pavil Dept
Culet
Table Size

Btw, for the round brilliant, it seem strange to ask for Length and Width.

 

[Giangi]

Kewl! lol!

Very useful tool!

 

[pricescope]

Congratulations, David!

 

[oldminer]

"Btw, for the round brilliant, it seem strange to ask for Length and Width"

I suppose it does read funny, but since the maximimum and minimum are given on rounds, I'd expect those using the grader to know what to do. If they enter a smaller amount in length, it will tell them to reverse the entry. In rounds, it is the average anyway for the depth% calculation.

I appreciate the constructive advice and, in time, when I get over some of the cost involved, I will try to put the order in what seems the more standard style....

Please not that in the4 Shape Selector one may enter numerical length and width and then click on calculate for an instant view of the outline of a potential stone.

 

[Richard Sherwood]

Nice work Dave.

There you go, setting the standard again...

 

[Mara]

Nice work!

Beggars can't be choosers when using a free tool that someone set up in their rare free time.

I think it's great!

 

[job]

Brilliant, simply brilliant... all of us counsumers owe you a great deal

 

[homer_j]

Very useful tool. I used the numbers from my GIA cert and independent appraisal for my radiant and your tool calculated the numbers and grading correctly. Finally, something to help out the fancy cut freaks.

 

[Hest88]

Oh, wonderful. Thanks Dave!

 

[Bill D.]

I just noticed something:

I had printed the chart for the princess in November or so, and for the girdle the class 1 limits were Thin-Medium (1%-3%) or Medium to Thick (1.7%-5.5%).

In the new site the limits are: Thin-Medium (3% to 5%) or Medium to Thick (5%-7%).

It looks like a redefinition or a mistake. If this is a redefinition, I'd like to know what has prompted the change.

Thanks!

 

[jlim]

oldminer - I've tried entering the values from several stones which I am considering but all of them are coming up with a grade 1B for crown angle. What's the significance of it being a 1B rather than 1A? I kinda thought the stones that the vendors sell here, in general are above ideal cut. So, I assumed they would come in at 1A.

Thanks.

 

[oldminer]

Both of these issues will be addressed in the next few days. If the percentages of thickness were changed it was accidental, no changes were authorized. We will also check crown angle calculations...

THANK YOU.

 

[oldminer]

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".

I was very conservative in my interpretation. Others have been very liberal.
Somewhere in the middle is a very fair balance on "Fine and Ideal Cut"

Hope you all think that is a fair way to respond on the issue.

 

[caratgirl]

Hi David,

On the GIA cert, my diamond's girdle is listed as medium. Does that mean that it is 4% according to your chart? Thanks.

 

[oldminer]

On a GIA cert the medium girlde may not be 4% An AGA medium girdle is 1.7% to 3% in the correct AGA Chart.

I see now that the girlde thickness percentages on the new cut calculator are way off. It will be addressed promptly. I apologize for missing this obvious error....

Here are correct percentages:

Ext thin 0%-0.3%
Very thin 0.4%-0.9%
Thin 1%-1.4%
Sl. thin 1.5%-1.6%
Medium 1.7%-3.0%
Sl. thick 3.1-4.5%
Thick 4.6%-5.5%
V. Thick 5.6%-7%
Ext thick >7.0%

 

[jlim]

Dave - thanks for your prompt attention to this. I'm confused as to the girdle thickness range as well. On an unrelated note, looks like we are up pretty early. Must be the old age. I'm assuming you are *older* from your avatar.

 

[oldminer]

DOB 7/17/47

 

[caratgirl]

Thanks very much David, I had checked the Sarin and it was 2%, so I am very relieved to see your post! By the way, you are NOT that old, my hubby was born that very good year, and he is quite young to me...heehe.

 

[oldminer]

The correct girdle percentage numbers are now live on the website for DIY AGA Cut Class grading.