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Cut Proportions Cheat Sheet?

Junc80

Rough_Rock
Joined
May 6, 2018
Messages
46
Hello,
I have seen recommended cut proportions by Todd Gray and AGS ideal cut range. I was wondering if anyone or site had the most comprehensive explanation of ideal cut proportions and combos for round brilliant. This is pretty much the talk of the trade here i imagine someone put something extensive for us to use?
 

crbl999

Shiny_Rock
Joined
Jan 21, 2010
Messages
447
Table: 54-57
Depth: 60-62.3
CA: 34-35
PA: 40.6-41.0
Girdle: thin to medium, thin to slightly thick; avoid extremes like very thin , thick, or very thick

A crown angle of 34.0, 34.5 or 35.0 is usually safe with a 40.8 pavilion angle. If pavilion angle = 40.6 lean toward a 34.5-35.0 crown. If pavilion angle = 41 lean toward a 34.0-34.5 crown.
 

OoohShiny

Ideal_Rock
Premium
Joined
Apr 25, 2014
Messages
7,062
Table: 54-57
Depth: 60-62.3
CA: 34-35
PA: 40.6-41.0
Girdle: thin to medium, thin to slightly thick; avoid extremes like very thin , thick, or very thick

A crown angle of 34.0, 34.5 or 35.0 is usually safe with a 40.8 pavilion angle. If pavilion angle = 40.6 lean toward a 34.5-35.0 crown. If pavilion angle = 41 lean toward a 34.0-34.5 crown.
For reasons I can't remember, I have in my head that a 53% table is also acceptable in a MRB, and a crown angle of 35.5 degrees in some cases - is that correct??

I guess the best method for sifting stones is to remove all stones outside of the parameters, then run the HCA tool on the remaining list!
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
4,441
Although outdated, this may also be helpful. It's the AGS proportions chart and should give you a good idea where a stone may land based on table size, crown and pavilion.

A good rule of thumb is that if a particular combo lands on ideal, then go 1 box in each direction and consider that a range of what you may see with actual measurements. You will end up with a total of 9 boxes.

The goal is to get an ideal cut diamond. If 6+ boxes out of 9 are ideal you have about 67% chance it will be ideal. Obviously 1 out of 9 boxes is considerably less likely to be ideal.

Again, these are just good guesses. Actual images tell us hard truths.

Have fun!

https://agslab.com/docs/pbcg/AGSLProportionCharts.pdf
 

Junc80

Rough_Rock
Joined
May 6, 2018
Messages
46
Wow thank you! Did you guys go to school for this or been on PS long enough? ^^
 

oldminer

Ideal_Rock
Trade
Joined
Sep 3, 2000
Messages
6,360

bmfang

Brilliant_Rock
Premium
Joined
Jan 2, 2017
Messages
1,852
Wow thank you! Did you guys go to school for this or been on PS long enough? ^^
Most of us have been on PS a while. But I want a copy of @sledge’s spreadsheet!!!
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
4,441
Most of us have been on PS a while. But I want a copy of @sledge’s spreadsheet!!!
I am happy to share. Right now I am out of town dealing with a family death, but will upload into Google Sheets and share so others can can enjoy it!

If you don't see me post within a few days please hot tag me as I've got a few things on my mind that might distract me before I get back.

Also, @Ella, any forum violations sharing such information?
 

Junc80

Rough_Rock
Joined
May 6, 2018
Messages
46
I like this a lot. Thank you for sharing.

Right on Pricescope you will find this assistance tool as well as the HCA tool. Choosing from individual parameters is not a good idea, but combining meaningful parameters in a balanced way can be a helpful screening tool. https://www.pricescope.com/tools/AGA_NAJA_Cut_Class_Grader
Right on Pricescope you will find this assistance tool as well as the HCA tool. Choosing from individual parameters is not a good idea, but combining meaningful parameters in a balanced way can be a helpful screening tool. https://www.pricescope.com/tools/AGA_NAJA_Cut_Class_Grader
 

Junc80

Rough_Rock
Joined
May 6, 2018
Messages
46
Hi Sledge, I am sorry to hear about a death in the family. I dont think that's ever easy to navigate through. I hope you and your family is doing okay my man

I am happy to share. Right now I am out of town dealing with a family death, but will upload into Google Sheets and share so others can can enjoy it!

If you don't see me post within a few days please hot tag me as I've got a few things on my mind that might distract me before I get back.

Also, @Ella, any forum violations sharing such information?
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
4,441
Hi Sledge, I am sorry to hear about a death in the family. I dont think that's ever easy to navigate through. I hope you and your family is doing okay my man
Thank you, I appreciate that very much. :cool2:

And for @bmfang and others that was interested in an a copy of my spreadsheet, I have a version in Google Sheets and Excel that is available. Prior to providing links, I have sent a request to the moderators to ensure there are no issues with me doing so.

FYI, the sheet was originally designed in Excel so I believe that is the best version. However, the Google Sheets version is incredibly powerful in the fact you don't need special software or a physical computer to run it. You just need an internet connection and phone, tablet, etc.

As soon as I hear back I will further update this thread.
 

bmfang

Brilliant_Rock
Premium
Joined
Jan 2, 2017
Messages
1,852
@sledge , hope that your family members are doing ok at this time of grief and profound sadness.

As for the spreadsheet, I wait with bated breath for it.
 

oldminer

Ideal_Rock
Trade
Joined
Sep 3, 2000
Messages
6,360
https://www.pricescope.com/wiki/diamonds/diamond-grading-chart-round

The above link is the round diamond "cheat sheet" that has been hiding away right on Pricescope for many years. It is the basis for the automated AGA/NAJA Automated Cut Class grading tool that is somewhat easer to locate on Pricescope. I think it best to use the automated process, but the sheet is no secret, just not well publicized. All the major shapes except Cushion cut are covered by one of 4 Cut Class sheets and the automated system that I had a programmer generate from them over a decode ago. The built in rules of the automated operation left subjectivity out of the process. Also, using one or two individual parameters is very subject to misunderstanding or even abuse by unethical sellers. You must look at how everything works together to best understand how well a diamond works with light.

The sheets and their configurations were started back in the mid-1980's by me and by the mid-1990's were slowly making their way into daily use in many places. Garry Holloway's concept of the HCA occurred nearly at the same time on the other side of the world and the end results are very similar. We independently saw a set of problems with cut grading and worked independently of one another to make the diamond world better for consumers. That's how the two of us met one another, with our similar interests and our creative powers. 10,000+ miles apart and on virtually the same wavelength.
 

Diamond_Hawk

Brilliant_Rock
Trade
Joined
Apr 8, 2014
Messages
1,214
https://www.pricescope.com/wiki/diamonds/diamond-grading-chart-round

The above link is the round diamond "cheat sheet" that has been hiding away right on Pricescope for many years. It is the basis for the automated AGA/NAJA Automated Cut Class grading tool that is somewhat easer to locate on Pricescope. I think it best to use the automated process, but the sheet is no secret, just not well publicized. All the major shapes except Cushion cut are covered by one of 4 Cut Class sheets and the automated system that I had a programmer generate from them over a decode ago. The built in rules of the automated operation left subjectivity out of the process. Also, using one or two individual parameters is very subject to misunderstanding or even abuse by unethical sellers. You must look at how everything works together to best understand how well a diamond works with light.

The sheets and their configurations were started back in the mid-1980's by me and by the mid-1990's were slowly making their way into daily use in many places. Garry Holloway's concept of the HCA occurred nearly at the same time on the other side of the world and the end results are very similar. We independently saw a set of problems with cut grading and worked independently of one another to make the diamond world better for consumers. That's how the two of us met one another, with our similar interests and our creative powers. 10,000+ miles apart and on virtually the same wavelength.
It is always great to learn the many paths one may follow on their journey to find the right diamond for them, and who cut those paths through the wilderness for them.
 
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