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OEC Ideal Cut?

AV_

Ideal_Rock
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Is it the low star facet and lower half facet lengths
The lower girdle facet (lgf) length seems to be the surest thing (70% is still possible among modern stones that already stand out) - star facet length seems to overlap more between old and new brilliants.

[you are reminding me of the last time I touched DiamCalc, the cut modelling software most talked about around here, ending up with some beautiful possible makes with such short facets & about 40 degree angles for both the crown & the pavilion; today I would likely know better; good fun.]​
 

LightBright

Brilliant_Rock
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This is a nice academic discussion but I recommend not looking at GIA reports to figure out your preferences. Table size below 50% and high crown over 35% is a good indicator for OEC and OMB and OMC cuts (as well as LGF under 70%, as AV says) but if you like Transitional or Early Modern you will see a larger table and shallower crown angle and higher LGF%. GIA report can tell you roughly what you might see, but you might “academically” like the stone, yet not like it in person.

You’ve got to decide if you want truly authentic untouched antique (these can be excellent to poor. Many nowadays are poor. Rare excellent cuts are usually with dealers), or repolished antique (slight tweaks to the angles and clean girdle. This tends to clean up a chipped stone but ruin the original cut), vs. recently cut antique style (these can be junk, or they can be optically excellent cuts depending on who cut them). If antique vs. modern doesn’t matter, that opens up everything. If it true untouched antique does matter, then you need to go to antique stone specialists and ask for it.

I’d recommend that you look at videos and photos on Instagram until you see the one you like, then go visit it. Or, identify what you like and ask an expert dealer like Adam at OWD or Grace at JbG to look for and find one like that. You could also take a chance and go visit a local dealer who has antique cuts. I’ve seen a lot of very nice antique looking cuts on Parks Fine Group Instagram, FWIW.

In summary, it takes a lot of time to analyze and select an antique cut diamond from just a GIA lab report, and many times the report doesn’t have all the angles anyway. And many times dealers don’t have a report for an antique stone, and sometimes the stone is set so it can’t be analyzed. So I wouldn’t use a GIA Report as a way to look for, screen and identify potential keepers.
 
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prs

Brilliant_Rock
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If you are really seeking "precision", I like the cut Victor Canera offers over the AV . But the bugger there might be finding the color, clarity and size I suspect you would be looking for.
20200308_211351.png

But it is definetly personal preference. I like a large culet, kozibe , high crown, and a flower petal center. I also found that I prefer a little wonkiness rather than perfection. Who knew?
You'll have to see a few to hone in on what speaks to you guys!
I too very much like this face up photo. However you are eerily correct about size and color! :eek2: :eek2: :eek2:
 
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Karl_K

Ideal_Rock
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[you are reminding me of the last time I touched DiamCalc, the cut modelling software most talked about around here, ending up with some beautiful possible makes with such short facets & about 40 degree angles for both the crown & the pavilion; today I would likely know better; good fun.]​
Why would you know better?
At one time 40c/40p stones were not uncommon, I have seen them in person. They were once considered the ideal in some circles.
For pendants, pins, earrings, bracelets and tiaras with candle and lamp light they are as awesome today as they were back then.
Remember back in the day a Lady's jewelry was bought in sets not just rings among the rich and royal.
There is even a very good chance that among the 25+ diamonds she was wearing none were in a ring.
 

prs

Brilliant_Rock
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This is a nice academic discussion but I recommend not looking at GIA reports to figure out your preferences. Table size below 50% and high crown over 35% is a good indicator for OEC and OMB and OMC cuts (as well as LGF under 70%, as AV says) but if you like Transitional or Early Modern you will see a larger table and shallower crown angle and higher LGF%. GIA report can tell you roughly what you might see, but you might “academically” like the stone, yet not like it in person.

You’ve got to decide if you want truly authentic untouched antique (these can be excellent to poor. Many nowadays are poor. Rare excellent cuts are usually with dealers), or repolished antique (slight tweaks to the angles and clean girdle. This tends to clean up a chipped stone but ruin the original cut), vs. recently cut antique style (these can be junk, or they can be optically excellent cuts depending on who cut them). If antique vs. modern doesn’t matter, that opens up everything. If it true untouched antique does matter, then you need to go to antique stone specialists and ask for it.

I’d recommend that you look at videos and photos on Instagram until you see the one you like, then go visit it. Or, identify what you like and ask an expert dealer like Adam at OWD or Grace at JbG to look for and find one like that. You could also take a chance and go visit a local dealer who has antique cuts. I’ve seen a lot of very nice antique looking cuts on Parks Fine Group Instagram, FWIW.

In summary, it takes a lot of time to analyze and select an antique cut diamond from just a GIA lab report, and many times the report doesn’t have all the angles anyway. And many times dealers don’t have a report for an antique stone, and sometimes the stone is set so it can’t be analyzed. So I wouldn’t use a GIA Report as a way to look for, screen and identify potential keepers.
If you read my original post you will see I point out that a GIA OEC cert is useless for determining the cut or beauty of the diamond. No offense intended, but that's the whole point of this thread! :)

The more OEC's I see, the more I feel the four criteria GIA used for determining a true OEC cut were arbitrary and likely wrong. I find it interesting that neither the August Vintage or @Victor Canera versions of the Old European would meet GIA's criteria for "Old European" and yet both receive AGS certs describing them as "Old European". I have been unable to find how AGS defines "Old European". Can anyone help?
 

prs

Brilliant_Rock
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I've been playing around with facet proportions to see if any clues can be found as to what might make the most beautiful OECs. I started with the crown facets and varied the star facet lengths to see if any particular lengths create the most pleasing "chunky" facet patterns we all look for.

OEC Facet Diagram 1A.jpg

My research indicates about 90% of OECs have tables in the 46-53% range, so I used a 50% table in all three diagrams. I was going to leave the tables empty of pavilion facets, but it just didn't look right. I put in the pavilion main facets, but I'm still thinking about the lower half facets. I'm pretty certain their optimum length will have to vary with the table%. A 60% lower half facet won't even show up in an OEC with a 40% table!!!

To me there's not a lot in it, but the 40% and 50% star facet lengths look the best, with the 50% winning by a nose. =)2

I may be doing this completely wrong so would appreciate some feedback from the experts.
 

Karl_K

Ideal_Rock
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I may be doing this completely wrong so would appreciate some feedback from the experts.
yes
it is not that easy.
The real answer is it varies combination to combination.
For example the steeper the crown the shorter the stars should be to lower the upper girdle facet angle.
They knew this back in the day which is why 45% or even 35% stars were not uncommon.
The exact number will change with table % and lower configuration.

There is also something similar with the lower girdle % relative to the table size and with the lower girdle to upper girdle relationship thrown in as something else to take into account which makes the stars relative to them also.
Every facet is relative to multiple facets.

In other words its impossible to say such and such number is the best as they are all relative to the overall combination.
 

prs

Brilliant_Rock
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For example the steeper the crown the shorter the stars should be to lower the upper girdle facet angle.
They knew this back in the day which is why 45% or even 35% stars were not uncommon.
Karl, thanks for your response. I think I understand everything you are saying except the comment above. Could you please explain this using layman's language so I can better understand the point you are making.
 

Karl_K

Ideal_Rock
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Karl, thanks for your response. I think I understand everything you are saying except the comment above. Could you please explain this using layman's language so I can better understand the point you are making.
The upper girdle facets are between the end of the stars and the girdle.
So if the stars are shorter the upper girdles are at a shallower angle because the are longer.
If the table is larger for any given star % the upper girdles are shorter and steeper.
When the upper girdles get to steep in relation to the lowers there are performance and appearance issues.
So for very steep crowns you need small tables and/or short stars or the upper girdles are to steep.
The change in the upper gidle angle is the largest impact the star% has on a diamonds performance with many crown angles.
 

prs

Brilliant_Rock
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Which , I believe, puts us right back at eyeballs, not numbers. :geek2:
20200320_012525.gif
Maybe yes, maybe no. If we had data showing multiple combinations of crown and pavilion angles with various facet lengths produced beautiful OECs then I would have to agree with you.

It's really frustrating we don't have the numbers to reach that conclusion, and I have to wonder why. We know the estate diamond dealers persuaded GIA to create the "Old European" cut category because they were unhappy their stones were being graded as MRBs and getting "poor" cut grades. We get all the cut proportion details on an MRB cert so why not on an OEC cert? I have to assume those same estate diamond dealers also persuaded GIA not to include the detailed cut numbers on the OEC certs.

Now ask yourself why the dealers would not want consumers to see the cut numbers? I don't know the answer, but they must believe they would lose money if consumers could see the numbers and make much more educated purchases. My guess is the cut combinations that produce the most beautiful OECs are quite limited, and if consumers knew what they were, the dealers' remaining diamonds would be much more difficult to sell.
 

CHRISTY-DANIELLE

Brilliant_Rock
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I guess if you were shopping for a perfectly cut oec , and the knowledge that it was perfectly cut was the thing about the stone that was most appealing to you. I do get what you are saying.
I think what some of us are trying to say is that there is something else in the appeal of these stones. If we are talking about truly antique oecs, they were not cut with modern precision and tools. They were not cut with computer aided guidelines. They were handcrafted, the rough turned in to what the cutter saw as most beautiful. Now some are frankly wonky: offset culets, dead centers, asymetrical as can be. Those are easy to spot. But by seeking only perfection in cut, you might dismiss a gorgeous stone. My stone is far from perfect, but as soon as I saw her with my eyes, I knew she was it. For ME. Someone else might say they prefer a smaller culet, a lower crown, prefer more windmill then flowery facets, a bigger table, a smaller table, etc. That's personal preference!
What's unique about these stones is that they ARE unique, each a little different. In my opinion they really can't and shouldn't be analyzed as to every ratio, degree, percentage the way some do with the modern brilliants. (There maybe you can just decide you don't like the numbers, and move on-- plenty of fish in that sea. )
I had to get some guidance when I was looking, needed some way to weed thru the options. But once I knew the basic parameters needed to find the stones with the look I wanted, I relied on my eyes after that. I wanted a sparkly, firey stone with great movement in the facets , beautiful flashes of chunky color, kozibe and a big culet. I didn't need to know all of her measurements to know she's perfect for me.
That is the point I was trying to make.
Hope that makes sense. :)
 

prs

Brilliant_Rock
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I guess if you were shopping for a perfectly cut oec , and the knowledge that it was perfectly cut was the thing about the stone that was most appealing to you. I do get what you are saying.
I think what some of us are trying to say is that there is something else in the appeal of these stones. If we are talking about truly antique oecs, they were not cut with modern precision and tools. They were not cut with computer aided guidelines. They were handcrafted, the rough turned in to what the cutter saw as most beautiful. Now some are frankly wonky: offset culets, dead centers, asymetrical as can be. Those are easy to spot. But by seeking only perfection in cut, you might dismiss a gorgeous stone. My stone is far from perfect, but as soon as I saw her with my eyes, I knew she was it. For ME. Someone else might say they prefer a smaller culet, a lower crown, prefer more windmill then flowery facets, a bigger table, a smaller table, etc. That's personal preference!
What's unique about these stones is that they ARE unique, each a little different. In my opinion they really can't and shouldn't be analyzed as to every ratio, degree, percentage the way some do with the modern brilliants. (There maybe you can just decide you don't like the numbers, and move on-- plenty of fish in that sea. )
I had to get some guidance when I was looking, needed some way to weed thru the options. But once I knew the basic parameters needed to find the stones with the look I wanted, I relied on my eyes after that. I wanted a sparkly, firey stone with great movement in the facets , beautiful flashes of chunky color, kozibe and a big culet. I didn't need to know all of her measurements to know she's perfect for me.
That is the point I was trying to make.
Hope that makes sense. :)
We upgraded DW's ER to a 2.01ct MRB on our 25th wedding anniversary back in 2006. :eek-2: We would have to wait until next year for our 40th, but this year will be 40 years since we first started dating, so that's reason enough for an upgrade, don't you think!

DW has decided this time we will upgrade to a 4-5ct, VS1 and to keep in budget a color range of K-M, and possibly N. We have seen how well cut stones in this color range can face up beautifully. The problem we are running into is that OECs in this size, color, and clarity range are few and far between, and the beautiful ones are priced at Rap+25 or more. We know we can get a very well cut MRB of similar size and quality for Rap-25, so whilst DW would much prefer an OEC, she doesn't love them enough to pay 50% more than an MRB.

I see my job as being to find her a gorgeous OEC at the right price. @CHRISTY-DANIELLE I agree with every thing you say about how unique, wonky and beautiful an old cut can be, and I'm now confident I will know one when I see it. The problem is the ones we've seen are well over budget. However there are some ugly OECs out there that are inline with our budget, and that's why I'm wondering if we could buy one of those and have it re-cut into a thing of beauty.

In order to do this I first need to know the diamond's existing cut details and then secondly I need to know how to re-cut it into beauty. Hence my frustration with GIA, and the purpose of this thread. Perhaps I should have explained all this in my OP. =)
 

AV_

Ideal_Rock
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@prs I was wondering about short star facets on a recent thread, so I have OEC on my mind still.

eg. proportions - www Numbers like this are unexpected enough to not put in writing. There are so many beautiful versions if the round brilliant, one for each piece of rough, at least.
 
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prs

Brilliant_Rock
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@prs I was wondering about short star facets on a recent thread, so I have OEC on my mind still.

eg. proportions - www Numbers like this are unexpected enough to not put in writing. There are so many beautiful versions if the round brilliant, one for each piece of rough, at least.
Yes, yes, yes! Wouldn't it be nice to know how they achieved such a beautiful OEC with a total depth of only 57.7%. I am willing to bet this stone had a crown angle less than 40°. In fact I suspect that just about every OEC with a decent spread has a crown angle less than 40°. Quite why GIA made that the minimum angle to qualify as an OEC is a mystery to me. Here's a table I put together of crown height vs crown angle for various table %.

OEC Crown Height vs Crown Angle (2).jpg

You can see that angles over 40° will start to have a very significant impact on spread as the table gets smaller.
 
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AV_

Ideal_Rock
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@prs A long time ago, I set out to draw the nicest brilliant I could do using the standard DiamCalc settings - and it was a very rounded cushion with near 40 / 40 angles (crown and pavilion); I can't recall the other numbers, sure enough. It is not difficult to construct OEC/OMC variants & look at them & pick.

I love diamonds - anything. Allot of proportions are beautiful to me for reasons impossible to reconcile in a single stone, so I'd have to have something else decide & the shape of the rough is the natural partner the cutter would & I couldn't understand how it matters.

2p


nts. I never get to do anything with the 'ETAS' thread
 

prs

Brilliant_Rock
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The upper girdle facets are between the end of the stars and the girdle.
So if the stars are shorter the upper girdles are at a shallower angle because the are longer.
If the table is larger for any given star % the upper girdles are shorter and steeper.
When the upper girdles get to steep in relation to the lowers there are performance and appearance issues.
So for very steep crowns you need small tables and/or short stars or the upper girdles are to steep.
The change in the upper gidle angle is the largest impact the star% has on a diamonds performance with many crown angles.
Karl, thank you so much for the education, I think I now know a lot more about the different facets and their relationships to each other.

In reading thru the various OEC threads, and in particular the very informative posts by @dreamer_dachsie the pavilion angle has been mentioned occasionally but not enough that I fully understand how important this angle might be. Could I impose on you again to give me your opinion on what an acceptable range might be for PA, and if the optimum PA might change with steeper CAs?
 

Karl_K

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Could I impose on you again to give me your opinion on what an acceptable range might be for PA, and if the optimum PA might change with steeper CAs?
It changes with the CA angle and lgf%.
Many oec diamonds were cut with over shallow pavilions based on current diamond cut theory. This can make them a little dark up close in rings but in pendant, earrings, pins, tiaras where the viewing distance in longer they perk up.
When you consider the ratio of diamonds used in rings and the ones not in rings but in other jewellery back in the day that starts to make sense. Diamonds in rings were far out numbered.

This might help:
 
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prs

Brilliant_Rock
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Whilst I read @Karl_K's article on PAs for the third time, =)2 I think I have a pretty good handle on the effect star length has on OEC facet "chunkiness".

OEC Facet Diagram 1B.jpg

Here are two photos that show the difference between 30% and 50% stars. The diamond in the first photo has stars that are close to 30%, and the diamond in the second photo has stars that are closer to 50%. What is your favorite flavor? :)

Star Length 30%.jpg Star Length 50%.png
 

Lessics

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Whilst I read @Karl_K's article on PAs for the third time, =)2 I think I have a pretty good handle on the effect star length has on OEC facet "chunkiness".

OEC Facet Diagram 1B.jpg

Here are two photos that show the difference between 30% and 50% stars. The diamond in the first photo has stars that are close to 30%, and the diamond in the second photo has stars that are closer to 50%. What is your favorite flavor? :)

Star Length 30%.jpg Star Length 50%.png
Where in the lab reports do you pick up on the stars specs?
 
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prs

Brilliant_Rock
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Where in the lab reports do you pick up on the stars specs?
It's not in the lab reports, that's why we have been flying blind. However there is a way to figure it out for yourself with just a ruler that has a mm scale.

First you need a good face on photo of the diamond you are interested in. The photo has to show as much facet detail as possible. I blow up the photo to screen size and print it out. I then try to outline the crown as much as possible, as shown in black in the photo below. The star facets are the eight triangles that attach to each of the eight sides of the crown, they are easy to spot once you have the crown drawn in. I try to find two well defined triangles that are opposite each other, as shown in red on the photo below. The reason I pick two opposite stars is if the photo was taken at an angle to the face it will effect the apparent length of the stars. I can then average the length of the two stars to get the correct length. In the photo below, on my printout, the distance from the crown to the tip of the star measured 21mm, and the distance to the girdle measured 45mm. So 21/45=47%. This was a great full on photo so both stars measured the same. I do hope Victor doesn't mind me using a photo of one of his OECs. To my taste his proportions are darned near perfect!


Star Length 47%.jpg

Hope this helps take some of the mystery out of buying OECs. If you know what crown facet flavor you like, you could use this method to pre-check the pattern of any diamond you are thinking of purchasing.
 
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diamondseeker2006

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I honestly think you are overanalyzing! You just need to start ordering stones to look at in person. I knew I'd have trouble finding an antique OEC that was exactly what I wanted (an outstanding cut, like you are interested in), so I ended up with an AVR which was cut by a master cutter's team. It's the one in my avatar picture. Even AVRs and CERs are different from each other. I ordered about 7 AVRs before I decided on the one I kept. It's a combination of every single spec, and that includes color and clarity, too.

I will tell you that I have a second stone in a lower color that was an OEC which Jonathan had recut bascially to similar specs to my first AVR. So your idea is a good one. I really recommend the specs of mine. It is not so deep as to lose a lot of weight and it has the beautiful floral facet pattern. However, no one is going to cover your diamond in the case of accidental damage in recutting (which is rare and I haven't heard of it happening since I have been here), and that could be costly with a 4-5 ct stone. So you might want to reconsider the idea based on that. I do think you can still find some good deals on OECs that don't have a great cut, but you are really limiting yourself if you are in the 4-5 ct range.

This pic doesn't really do them justice, but here it is just to give you an idea. Top is O color and bottom is I color.

IMG_3521(Edited).jpg
 

Lessics

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@prs Thank you for sharing your calculations. Very interesting!

@diamondseeker2006 Your I AVR is cut to perfection it really is such a special valuable diamond. Do you mean with Specs the Color/ clarity combination? Or table size, depth etc.? I would love to know your diamonds table size and depth.
 
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diamondseeker2006

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@diamondseeker2006 Your I AVR is cut to perfection it really is such a special valuable diamond. Do you mean with Specs the Color/ clarity combination? Or table size, depth etc.? I would love to know your diamonds table size and depth.
Thanks so much! I actually meant measurements in regard to the cut. Depth is 64.9. When they are deeper, they seem to lose diameter. Mine is about 2.3 cts and 8.4mm which isn't bad. The table is 45.4. Crown height is 19.7% which is higher than ideal cut rounds which are usually around 15% give or take a little.
 

Karl_K

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30 to 55 stars no other changes other than upper girdle angle that goes along with it.

55-30stars.jpg

more to come later.
I popped a rib and sitting at my desk is very painful.

edit: 45t 37cr with matching Pa and lowers.
 
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prs

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Sorry to hear about your rib Karl. Please take it easy and get well soon.
 

Lessics

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I wish you a speedy recovery @Karl_K !

I can’t really tell the difference between the pictures you generated. Inder that the stars are smaller from picture to picture but somehow it doesn’t really change the overall look for my eyes.
 

prs

Brilliant_Rock
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I honestly think you are overanalyzing! You just need to start ordering stones to look at in person. I knew I'd have trouble finding an antique OEC that was exactly what I wanted (an outstanding cut, like you are interested in), so I ended up with an AVR which was cut by a master cutter's team. It's the one in my avatar picture. Even AVRs and CERs are different from each other. I ordered about 7 AVRs before I decided on the one I kept. It's a combination of every single spec, and that includes color and clarity, too.

I will tell you that I have a second stone in a lower color that was an OEC which Jonathan had recut bascially to similar specs to my first AVR. So your idea is a good one. I really recommend the specs of mine. It is not so deep as to lose a lot of weight and it has the beautiful floral facet pattern. However, no one is going to cover your diamond in the case of accidental damage in recutting (which is rare and I haven't heard of it happening since I have been here), and that could be costly with a 4-5 ct stone. So you might want to reconsider the idea based on that. I do think you can still find some good deals on OECs that don't have a great cut, but you are really limiting yourself if you are in the 4-5 ct range.

This pic doesn't really do them justice, but here it is just to give you an idea. Top is O color and bottom is I color.

IMG_3521(Edited).jpg
Thanks for the advice @diamondseeker2006. Your August Vintage OECs are fabulous, and yes with AVC or Victor Canera one does get a beautiful stone without all the hassle. Also with both of these brands you get terrific face up size for a given carat weight.

However I'm a chemical engineer with 40 years experience solving complex technical problems, and I now regard finding out what goes into the making of a beautiful OEC as an interesting technical challenge. This is a prosumer forum with hundreds of threads debating MRB cut down to the nearest 0.1°, and yet no one seems to question why the diamond trade had chosen to keep OEC cut details hidden from the consumer. This exercise of figuring out how to measure star length has very much helped me and DW determine what flavor we prefer, so it hasn't been a waste of time at all.

I'm still trying to absorb Karl's article on PAs, so in the meantime lower half facets are next on the agenda. Please bear with me.=)2
 
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