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OEC Ideal Cut?

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Shiny_Rock
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@prs Please do a summarized post of your findings when you’re done! I’m scrambling to follow everything
 
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ForteKitty

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I just found your thread on that absolutely gorgeous OEC WWW It's just amazing to finally get some cut details on such a beautiful diamond. Yes the AJS chart does give your stone a cut grade of 2, and if my correction factor works, it would be closer to a cut grade of 1.

I'm thrilled to be able to confirm these charts do have some relevance to OECs, and that figuring out an ideal cut is not as complicated as some would have us believe. It's that big blue area of very poor grades in the top right hand corner of the chart that has me concerned, and that I definitely want to avoid. I'm going to work on how to do that next.
I still think that going purely with numbers is more trouble than it's worth, and you could potentially leave out good contenders. I've seen some that would have fallen in the AGS 5-7 range on paper, but looked gorgeous in person, sometimes the shallow/shallow works. Not trying to sound negative or discouraging, but one decent head-on picture can tell way more about the oec's cut than any chart out there. I found it useful to look at the ones I found attractive, then look at the profile. The blue areas in the charts are pretty extreme combos and you should be able to identify them by sight if you've seen enough. They are either top heavy/flat bottom, or pancake top/heavy bottom... both of which will look leaky or dark in the center.
 

Karl_K

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So what pavilion angle would you recommend for an MRB with a T of 50%, a CA of 37°, and 80% lower halves?
Its a twitchy combo to cut that I would not recommend cutting.
But the answer is 40.5 but it would have to be super tight.
40.4 has a very high obstruction response and 40.6 has red mains in ASET.
 

prs

Brilliant_Rock
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Its a twitchy combo to cut that I would not recommend cutting.
But the answer is 40.5 but it would have to be super tight.
40.4 has a very high obstruction response and 40.6 has red mains in ASET.
Karl, thanks for the detailed reply. There's obviously something I'm missing in all this. I know AGS is a highly respected when it comes to grading cut quality because their system is much more precise. Our super ideal vendors like Whiteflash and CBI use them almost exclusively. They give the CA 37.0°,PA 40.4° combination a cut grade of 1, so on their quality range of 0-10 I thought a 1 should give me a pretty darned nice diamond.

Is it that their system does not take obstruction into account?
 

ForteKitty

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Karl, thanks for the detailed reply. There's obviously something I'm missing in all this. I know AGS is a highly respected when it comes to grading cut quality because their system is much more precise. Our super ideal vendors like Whiteflash and CBI use them almost exclusively. They give the CA 37.0°,PA 40.4° combination a cut grade of 1, so on their quality range of 0-10 I thought a 1 should give me a pretty darned nice diamond.

Is it that their system does not take obstruction into account?
Slight obstruction in MRB can look massive in OECs, which that chart doesn't account for. @Karl_K stated earlier that AGS 1 with that combo gets darker mains. In MRB, the arrows would be thin and not as noticeable. The same combo with oec will result in big dark fat arrow/petals and it can all turn "off" at the same time, creating a dark center overall. Victor Canera himself said he had to experiment a ton and play with the numbers for a long time before finding something that worked, and he had expensive software.
 

Karl_K

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The AGS system is not perfect, obstruction is its weak point.
They use ASET 40 which the blue disk is 40 degrees to try and detect obstruction issues.

In the real world obstruction issues for a mrb are:
Up close the arrows can respond to obstruction and form a pattern many find pleasing but as the diamond goes further from the viewer the mains start returning light from around the viewer.
If the mains stay dark to far away from the viewer to the point they can not easily be seen as arrows then it just makes the diamond look darker.
That distance for most people is right around 1/2 arms length but glasses and contacts can change that.
Further:
With a mbr you dont care if they all go dark at once, infact its a plus if your selling h&a but in a oec even with good angles it can be an issue. ASET is useless for designing it to not do this because people are not 30 degree blue disks.

@ForteKitty is spot on.
 

prs

Brilliant_Rock
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@prs Please do a summarized post of your findings when you’re done! I’m scrambling to follow everything
I will, this is taking far longer than I thought it would. I've had to learn a lot more about the technical aspects of diamond cut just so I could be sure I understood exactly what the experts were saying.

There's a lot of sales myth attached to old cuts, and being able to tell what is myth and what is fact has been an interesting challenge. For example it might be a myth that old cuts were designed to look good by candlelight. Presumably candle light doesn't follow the laws of physics? :eek-2:How come Henry Morse found out by trial and error how to cut diamonds for beauty and light return long before America was electrified? Al Gilbertson hardly mentions candle light in his book, but he does say loud and clear that old cuts were cut for weight out of necessity. It took hours and hours to grind down the facets of diamonds by hand.

It wasn't until the industrial revolution and automated grinding machines were invented that it was even possible to cut round diamonds. By that time the best proportions for excellent light return were well understood on both sides of the Atlantic. So it's another myth that all old cuts were being cut with steep crown angles. More to follow. :)
 

prs

Brilliant_Rock
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I still think that going purely with numbers is more trouble than it's worth, and you could potentially leave out good contenders. I've seen some that would have fallen in the AGS 5-7 range on paper, but looked gorgeous in person, sometimes the shallow/shallow works. Not trying to sound negative or discouraging, but one decent head-on picture can tell way more about the oec's cut than any chart out there. I found it useful to look at the ones I found attractive, then look at the profile. The blue areas in the charts are pretty extreme combos and you should be able to identify them by sight if you've seen enough. They are either top heavy/flat bottom, or pancake top/heavy bottom... both of which will look leaky or dark in the center.
I agree if my main goal was a beautiful facet pattern, then the numbers would not be of such a concern. However for budget reasons we are looking for a stone in the L-N color range that faces up whiter, so in order to get that I do think I'm going to need pretty good light return and that in turn requires good numbers. Also stones in our desired size range are few and far between, and the beautiful ones are often selling for a hefty premium. I may have to settle for an ugly one and re-cut it into beauty. To do that I definitely need to know the numbers!

I can now look at a face up photo and recognize a beautiful facet pattern when I see one. I'm going to have to learn how to recognize a great cut from a photo. I've found that almost all the vendors don't provide a profile picture, and even in videos they often manage to avoid showing the profile. Would appreciate some pointers on how to do that. I do know how to spot obstruction in a video, so I guess that's a start. :)

On the AGS charts the large top right area of blue "frozen spit" is actually top heavy/bottom heavy, and that's exactly where GIA puts you with their requirement for a minimum 40.0° crown angle in order to get an "Old European" cert. :eek-2: I guess that's why both Victor and Jon decided not to go there!!!
 
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prs

Brilliant_Rock
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Slight obstruction in MRB can look massive in OECs, which that chart doesn't account for. @Karl_K stated earlier that AGS 1 with that combo gets darker mains. In MRB, the arrows would be thin and not as noticeable. The same combo with oec will result in big dark fat arrow/petals and it can all turn "off" at the same time, creating a dark center overall. Victor Canera himself said he had to experiment a ton and play with the numbers for a long time before finding something that worked, and he had expensive software.
The AGS system is not perfect, obstruction is its weak point.
They use ASET 40 which the blue disk is 40 degrees to try and detect obstruction issues.

In the real world obstruction issues for a mrb are:
Up close the arrows can respond to obstruction and form a pattern many find pleasing but as the diamond goes further from the viewer the mains start returning light from around the viewer.
If the mains stay dark to far away from the viewer to the point they can not easily be seen as arrows then it just makes the diamond look darker.
That distance for most people is right around 1/2 arms length but glasses and contacts can change that.
Further:
With a mbr you dont care if they all go dark at once, infact its a plus if your selling h&a but in a oec even with good angles it can be an issue. ASET is useless for designing it to not do this because people are not 30 degree blue disks.

@ForteKitty is spot on.
Thank you both so much for your detailed replies. I'm going to need some time to absorb this before I can even think about a response!
 

Karl_K

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Don't get mad at me again.. since you want to learn this stuff im posting some pointers.

For example it might be a myth that old cuts were designed to look good by candlelight. Presumably candle light doesn't follow the laws of physics? How so? and what kind of lighting was common during this time? :eek-2:How come Henry Morse found out by trial and error how to cut diamonds for beauty and light return long before America was electrified? Morse and his contemeraries cut by oil lamp light.
 

prs

Brilliant_Rock
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Don't get mad at me again.. since you want to learn this stuff im posting some pointers.
I promise not to get mad at you again. =)2

I think I do need to point out to to you that it's much more romantic for diamond salesmen to say they were cut for candle light rather than say cut for oil lamp light. ;))I would also point out that in Al's book he does say the Europeans were forced to start cutting for beauty when rhinestones were discovered. Even by "candle light" the rhinestones sparkled a heck of a lot more than the poorly cut diamonds of the time.
 

ForteKitty

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I agree if my main goal was a beautiful facet pattern, then the numbers would not be of such a concern. However for budget reasons we are looking for a stone in the L-N color range that faces up whiter, so in order to get that I do think I'm going to need pretty good light return and that in turn requires good numbers. Also stones in our desired size range are few and far between, and the beautiful ones are often selling for a hefty premium. I may have to settle for an ugly one and re-cut it into beauty. To do that I definitely need to know the numbers!

I can now look at a face up photo and recognize a beautiful facet pattern when I see one. I'm going to have to learn how to recognize a great cut from a photo. I've found that almost all the vendors don't provide a profile picture, and even in videos they often manage to avoid showing the profile. Would appreciate some pointers on how to do that. I do know how to spot obstruction in a video, so I guess that's a start. :)

On the AGS charts the top right area of "frozen spit" is actually top heavy/bottom heavy and that's exactly where GIA puts you with their requirement for a minimum 40.0° crown angle in order to get an "Old European" cert. :eek-2: I guess that's why both Victor and Jon decided not to go there!!!
Well-cut usually equals beautiful patterns, which equals good light return. I have yet to see an ugly oec with excellent light return. Also, if you can get a video of the diamond, you don't need the profile because you can see the diamond in movement. I usually only use the profile view to gauge crown and pav angles when I buy off ebay and there's zero info + a few crappy photos.
 

Karl_K

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Candles and oil lamps were the artificial lighting of the day.
In my opinion a case can be made for both
Most people know what candle light is like where very few have personal experence with oil lamps..
 

prs

Brilliant_Rock
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@prs I looked up the Sarin for my 9.9-10mm oec. 46% table, 63.5% depth, 34 deg crown, 42 deg pavillion. It has no obstruction and is bright edge to edge, and on the AGS chart for 47% table it scores a 2, so it somewhat works for oec? Sorry the image quality isn't better, the Sarin is somewhere in the house and that's an older photo.
The articles I've read always make a point of saying that OECs are noted for their high crowns. Coupled with GIA's minimum 40.0° crown angle I've always assumed the most beautiful OECs must have at least a 40° CA. Your post has been an eye opener to me. It's tremendously valuable to know my search is not limited to stones with a steep crown angle. I was able to make the time to read through your thread this weekend, and your OEC is stunningly beautiful. I hope you don't mind that I bumped the thread to the front page of SMTB. For those of you looking to find out what a great OEC should look like, here's the LINK

Not only does your stunningly beautiful OEC not have a steep crown angle, but if it did the total depth of your stone would be increased by 4.5% to a whopping 68.2%!!! Many of the beautiful OECs here on PS have depths similar to yours, so this tells me they too don't have steep crown angles.

Earlier in this thread @Karl_K said my idea of star facets aligned with the table facets wouldn't work. I thought he was nuts because many of the most beautiful OECs here on PS have aligned crown facets. As it turns out I think he too was thinking steep crown angles, whereas I was looking at OECs with crown angles more typical of MRBs. Maybe we were both right!!! :lol-2:
 
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Karl_K

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@prs research the effect and timing of the introduction and adaptation of the diamond saw.
 

prs

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It turns out 2012 was a heck of a year for outstanding OECs on PriceScope. In addition to @ForteKitty's beauty, @dreamer_dachsie also acquired "George" the fabulously beautiful OEC she has in her avatar. Here is the LINK to her 2012 thread.

Her stone is also cut with proportions similar to an MRB, and this just confirms to me that I need to be looking at what the experts call a "transitional" cut OEC. One thing to look for in Dreamer's photos is that you can clearly see the lower half facets extending out under the table, and creating a very pronounced flower petal pattern. I think the lower half length is around 65%, just like my preferred facet patterns posted earlier in the thread.

dreamer_dachsie 8.1mm 7.jpg

I'm guessing GIA would call this diamond a "Circular Brilliant" but I'd take that any day of the week in order to get a stone as breathtakingly beautiful as this one!!! :love: :love: :love: No stats available in Dreamer's thread, but if the CA and PA are now available I would love to know them. :mrgreen2:
 
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prs

Brilliant_Rock
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@prs research the effect and timing of the introduction and adaptation of the diamond saw.
Excerpts from Al Gilbertson's book

The American Cut Pg 69.png The American Cut Pg 71.png

It appears the circular diamond saw came into general use about 1900. The fact the top portion of the rough could now be saved and turned into a second diamond made the rough much more valuable. In 1902 De Beers saw the price of rough jump 30%. Here's a great image taken from the HPD website showing exactly how this works

Circular Saw Produces 2 Diamonds.png

Karl, please correct me if I'm wrong but as I see it, mechanical bruting and the circular saw came into common use in the early 1900s. These two factors allowed for the production of round diamonds with lower crowns. In fact the lower the crown of the primary diamond, the bigger the second diamond becomes. A cutter will make more money as he lowers crown height. The early 1900s is also the time the ideal cut proportions developed by Morse start to take hold in Europe.

As I see it what we call "Old mine Cuts" were mostly produced before mechanization, and by necessity were cushion shaped and had very high crowns. However by the early 1900s when the production of round diamonds became common, the idea of cutting for light return and beauty had already taken hold.

I think what is now called a "transitional" cut with more ideal proportions could just as easily have been produced in the early 1900s as an "old european" cut with a steep crown angle and a very high crown.
 

Karl_K

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Your getting there but the timing was not overnight. It was after ww1 that the real modernization became more universal.
 
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Karl_K

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The balance between leaving the weight in the primary and size of the secondary is a delicate balance.
The price per ct is higher in the primary than the secondary.
But diamond dust is worth pennies.
 
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LLJsmom

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Just saw this thread. OP, I’m laughing but not in a bad way. Good luck. I think you’re actually having fun geeking out on all this. I didn’t see but is your wife going to be part of the process of deciding? When @missy mentioned in the first page (I admit I only got through page 2) she meant that people truly can have preferences. I have loved checkerboard-ish facets and flowery ones. It depends on the stone. I do hope you will have a chance to see more IRL. Even after you’ve picked some on paper, will you do a real life test before committing?
And to add, there some stones that we both looked at that were bright and lively and she preferred one while I preferred another. I ended up buying one of them and the other was purchased by another PSer soon after. I’m saying that you just never know what the ultimate wearer will prefer.
 
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prs

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@LLJsmom My wife was President and CFO of our manufacturing business for the 20 years we owned and ran it together. I can assure you nothing happens in our family without her OK. She will definitely be the one choosing the diamond. :)

We have been together long enough DW trusts me to do technical research, and that's what I'm doing right now! We spent considerable time visiting estate diamond dealers in LA, but unfortunately the pickings were slim in the color and size range we are looking for. Most of the stones we were shown looked nothing like the beautiful OECs seen here on PriceScope. We are likely to spend a huge amount of money on this stone, and it became obvious I needed to know a lot more about OECs before we went any further. This will almost certainly be DW's last ER upgrade, so we need to get it right.
 

LLJsmom

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@LLJsmom My wife was President and CFO of our manufacturing business for the 20 years we owned and ran it together. I can assure you nothing happens in our family without her OK. She will definitely be the one choosing the diamond. :)

We have been together long enough DW trusts me to do technical research, and that's what I'm doing right now! We spent considerable time visiting estate diamond dealers in LA, but unfortunately the pickings were slim in the color and size range we are looking for. Most of the stones we were shown looked nothing like the beautiful OECs seen here on PriceScope. We are likely to spend a huge amount of money on this stone, and it became obvious I needed to know a lot more about OECs before we went any further. This will almost certainly be DW's last ER upgrade, so we need to get it right.
In case you haven’t already perused this thread, this is where a lot of OEC posts have been collected. I’m happy for you both. Now that there is time during SIP, you can do more than your due diligence. When everything opens up you should visit Old World Diamonds in NYC. Hey have a great selection. And visit Grace or Joghani. The New York Antiques and Watch Show in October has an awesome selection of many antique stones. Keep us updated on your search. Singlestone in LA also has some stunning pieces. The first OEC I really fell in love with I saw there. But really it is hit and miss with Singlestone so I would suggest an in person viewing. And they are pricey. Lange’s in SF has some nice stones, but for NY seems to have a nice concentration of beautiful stones. A lot of the fun for me came in actually visiting various vendors and viewing and seeing how I felt about the stones. Looking forward to seeing what you decide. And one other thing. I did rely on trusted vendors. I asked the to show me the most beautiful OECs within my budget. I also examined stones with fellow OEC lovers so I had second opinions. That was fun for me.

 

dreamer_dachsie

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I never did get any kind of sarin or report for my diamond. But last time it was loose I learned that the depth is sub-60%, maybe closer to 55%, so she's a shallow girl.

And if this is the kind of cut you want, all I can say is... good luck! After the Old Miners, this is probably the most rare varietal of old cut. Probably bc it is so similar to an MRB and many were recut to fit modern tastes.
 

prs

Brilliant_Rock
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I never did get any kind of sarin or report for my diamond. But last time it was loose I learned that the depth is sub-60%, maybe closer to 55%, so she's a shallow girl.

And if this is the kind of cut you want, all I can say is... good luck! After the Old Miners, this is probably the most rare varietal of old cut. Probably bc it is so similar to an MRB and many were recut to fit modern tastes.
Yes, I love the facet pattern of your diamond. It is indeed a very rare pattern, and that's what makes your stone uniquely and extraordinarily beautiful.

I didn't realize she was so shallow, and yet the optics still seem to be terrific. The craftsman who cut it was a genius!

Does it have a very thin girdle?
 

prs

Brilliant_Rock
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The AGS system is not perfect, obstruction is its weak point.
They use ASET 40 which the blue disk is 40 degrees to try and detect obstruction issues.

In the real world obstruction issues for a mrb are:
Up close the arrows can respond to obstruction and form a pattern many find pleasing but as the diamond goes further from the viewer the mains start returning light from around the viewer.
If the mains stay dark to far away from the viewer to the point they can not easily be seen as arrows then it just makes the diamond look darker.
That distance for most people is right around 1/2 arms length but glasses and contacts can change that.
Further:
With a mbr you dont care if they all go dark at once, infact its a plus if your selling h&a but in a oec even with good angles it can be an issue. ASET is useless for designing it to not do this because people are not 30 degree blue disks.

@ForteKitty is spot on.
Sorry for the long delay in posting, life got in the way of my diamond research. :) @ForteKitty noted that obstruction can have greater impact on OECs, and indeed there are many references to it in old OEC threads. I knew I needed to become more informed on this subject. The late Bruce Harding, RIP, wrote a fascinating article describing the causes of obstruction, and detailing the PA,CA proportions required to avoid it.LINK This is a copy of the chart he produced for diamond.

BH Chart Diamond.png

I have superimposed this info onto the AGS chart I posted earlier, proportions subject to obstruction are now shaded in black.

AGS Cut Guide 10mm MRB 50% Table Rev B.png

Bruce makes no reference to lower girdle facet angles or lengths in his article, so I'm not sure how accurate the chart is.

It's all very interesting! :)
 

Karl_K

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Typically leakage under the table is off the lowers and not the mains so the lgf% is a big deal in a mrb.
An oec has typically very little to none of the lowers under the table.

However obstruction is different, mains are mains they change in size oec to mrb but....
lgfcomp.jpg
Mains are same tone but different size with everything else the same.
Question answered about the chart? ;}
 

Karl_K

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Just for fun 40c/43p lgf% just under 60%
4043..jpg
 

evergreen

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@prs I have *thoroughly* enjoyed your very thoughtful and very persistent :lol: analysis of old cut combinations. I have a transitional cut 60/60 stone in my engagement ring, and -- since you seem to be trending toward that sort of combination for DW, though I think the LGFs on mine are a little longer than Dreamer's/Arkie's -- I wondered if seeing a close-up photo of it with its numbers (EGL cert, fwiw) would be helpful for you. It certainly would be interesting for me to hear how you break down the numerical basis for what you see. Happy to post them if that isn't an unwelcome detour, otherwise, I'll just keep following along with interest! :D
 

prs

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Typically leakage under the table is off the lowers and not the mains so the lgf% is a big deal in a mrb.
An oec has typically very little to none of the lowers under the table.

However obstruction is different, mains are mains they change in size oec to mrb but....
lgfcomp.jpg
Mains are same tone but different size with everything else the same.
Question answered about the chart? ;}
Karl, let me see if I can correctly interpret what you wrote. :)

Given that Bruce was mostly interested in colored stones, and he made no mention of LGFs in the article, the odds are he did not take them into account when he made the diamond chart. For OECs shorter LGFs do not protrude under the table, and everything under the table is at the nominal PA. So for OECs the chart should be accurate. Am I right?

For MRBs the LGFs do extend under the table and will impact light reflection, so some correction factor might need to be applied to the chart. It would be interesting to know what that correction might be.
 
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