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OEC trade offs vs MRBs in different light settings

twang07

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So, my first diamond was an OEC. I just really fell in love with the faceting and the patterns and never even thought to compare it side to side with a MRB. In these threads I tend to see that MRBs have superior light performance and I never really understood what that translates to in terms of what you see.

After wearing the ring daily I have figured out that the only light settings I'm not a fan of is when the light is not strong, directly overhead and I'm looking at the diamond straight on. In these scenarios, my head is totally obstructing the facets underneath the table. When I put my hand up and the light is directly behind my diamond, the facets are gorgeous and reminds me why I picked this diamond. Also if I slightly tilt the stone, the center facets come right back to life

I guess to cut to the point, are MRBs less likely to suffer from this phenomena, or is this a characteristic that is in every round diamond?

I really like my stone, but I do wonder what about the cut causes this and do MRBs not suffer quite as dramatically as OECs with this regard?

Sorry if this topic has been covered before, I wouldn't mind getting some links to threads (I just couldn't quite find a thread myself after many hours spent looking). Hope some experts can chime in. Thanks!
 

Karl_K

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The pavilion is likely slightly shallow so it is gathering light from where your head is blocking it at that distance.
An oec different angles may do this less dramatically.
A well cut mrb will show arrows and the rest of the stone be bright in similar conditions.

This is very common in vintage oec cuts.
 

Karl_K

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ideal cut mrb
mrb.jpg

steeper pavilion oec (not to steep)
oecsteeper.jpg

shallow pavilion oec

oecshallow.jpg
 
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Karl_K

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mrb with to shallow pavilion
shallowmrb.jpg
 

Karl_K

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It is dependent on distance and pavilion angle how much obstruction it will show.
When your oec goes dark move it further away from you and all is good again.
 

Karl_K

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btw at the exact distance that it changes from dark to light something special will happen. Check it out.
 

twang07

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Thank you @Karl_K these are really informative!

So if I understand you correctly, the splintery facets in mrbs reflect how they gather light and mrbs just have I guess more distributed contrast zone than oecs because of the chunky facets making larger contrast zones? What happens to both diamond cuts when the pavilion angle gets too steep?

I always read that there's no ideal angles for oecs, but at least in regards to the pavilion angle, there might be a cutoff to head obstruction? I didn't get all the angles of my stone besides table % and depth. I am curious, What angles may come into play when identifying obstruction vs nail head? Are mrbs less likely to have nail heads because they don't have chunky facets?

I just love the light play in diamonds and physics was one of my worst subjects, and this is totally all optics! I just wish I could learn more about the mechanics behind these qualitative descriptions we use. So thanks for your input it's very educational for a geek like me!
 

Karl_K

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Who ever said there were no ideal angles for an oec is 100% wrong.
Both Morse and Tolkowsky had "ideal" angles for an oec over a 100 years ago.
There are new cut branded oec being cut to AGS0 ideal specs.
The correct angle depends on the crown angle and table size to min. obstruction but below ~40.5 degrees there is guaranteed to be issues.

These might be of interest:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

https://www.pricescope.com/communit...irst-100-years-al-gilbertson-free-pdf.228643/
 
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Victor Canera

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Obstruction is actually a very common issue with OECs. Some people don't know the term and just mention the diamond being dark in the center which is basically the same symptom. I don’t think though that a blanket statement can be made that it applies to all OECs because they were polished with so many different and varying proportions. Some antique OECs don’t have obstruction issues.

The reason why you don’t see obstruction with MRBs these days is because the industry has established Ideal proportions and most MRBs follow these guidelines. When you have complimentary proportions in a MRB, obstruction isn’t an issue.

At the same token though, if you can apply this understanding into the OEC design, you will not get obstruction or leakage issues.


Good luck.
 
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Maggiemeans

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Karl, any chance for a diagram of the transitional cut?
I realized I can't tell the OEC''s from the transitionals.
 

Karl_K

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Karl, any chance for a diagram of the transitional cut?
I realized I can't tell the OEC''s from the transitionals.
transitional means different things to different people.
There is not universal accepted perimeters for them, many experts dont like the term at all.
 

Karl_K

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To some people tansitional means a closed culet, larger table and lower crown.
To others the stone the computer generated image I posted above labeled oec would be a transitional because it has a closed culet.
It really isn't that cut and dried because they were cut along side each other for decades.
A so called transitional could be much older than an antigue stone called an oec.
For example, the rough could have been broken, or have a huge inclusion so the table was cut larger and the crown shallower.
While open cults were considered better they were not entirely universal.
When the diamond saw come into common usage which took a long time for the entire industry to adopt it the switch over started gaining more universal acceptance.
 

Maggiemeans

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Thanks Karl!
that explains it.. as well as why i was having trouble figuring it out on my own.
 

Karl_K

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Spell check got me, that should be open culets not open cults
 

foxinsox

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btw at the exact distance that it changes from dark to light something special will happen. Check it out.
What happens?? I can’t work it out and I’ve tried! (Sorry for the thread dredge!)
 

Karl_K

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What happens?? I can’t work it out and I’ve tried! (Sorry for the thread dredge!)
Huge amounts of scintillation as its moved in and out.
Slight differences in the pavilion angles means they wont all go at once some times but its a pretty big light show.
Often there will be big fire also as it switches depending on lighting.
In a modern RB with the smaller mains its often impossible to get the right distance but with an oec and the huge mains its much more dramatic.
 

foxinsox

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Huge amounts of scintillation as its moved in and out.
Slight differences in the pavilion angles means they wont all go at once some times but its a pretty big light show.
Often there will be big fire also as it switches depending on lighting.
In a modern RB with the smaller mains its often impossible to get the right distance but with an oec and the huge mains its much more dramatic.
definitely something I’ll keep trying to see then - thanks @Karl_K!
 

Karl_K

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definitely something I’ll keep trying to see then - thanks @Karl_K!
Depending on the pavilion angle it is more subtle and harder to find the right distance with some diamonds than others.
 

Octo2005

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Thank you Karl!
 

twang07

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btw at the exact distance that it changes from dark to light something special will happen. Check it out.

It took me a while to figure out if what I was seeing is what you were talking about. It helped having a MRB to compare to. Definitely not as big for sure. I see fire from the stone! Is that it??
 

Karl_K

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It took me a while to figure out if what I was seeing is what you were talking about. It helped having a MRB to compare to. Definitely not as big for sure. I see fire from the stone! Is that it??
Fire is part of it, find the distance then move the stone so it goes nearer and further away than that point.
It should not take a lot of movement to give a massive scintillation show.
 

LLJsmom

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I see obstruction on my OEC at certain angles. However when I look at the specific facets that are obstructed I see flower petals, not skinny dark shards as from my old MRB. So the obstruction in an OEC doesn’t bother me because it looks like part of the patterning. When I twirl the OEC, the obstructed facet doesn’t rotate unless I change the angle at which i am viewing the stone. It looks like a kaleidoscope to me so it’s actually very pleasing. I am only bothered when certain facets remain obstructed, regardless of how I twirl the stone. I hope what I am saying makes sense.
 

twang07

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I see obstruction on my OEC at certain angles. However when I look at the specific facets that are obstructed I see flower petals, not skinny dark shards as from my old MRB. So the obstruction in an OEC doesn’t bother me because it looks like part of the patterning. When I twirl the OEC, the obstructed facet doesn’t rotate unless I change the angle at which i am viewing the stone. It looks like a kaleidoscope to me so it’s actually very pleasing. I am only bothered when certain facets remain obstructed, regardless of how I twirl the stone. I hope what I am saying makes sense.

It makes perfect sense and you have put into words exactly how I feel about my stone. This is more exacerbated in certain lights. In certain lights I can't get it to obstruct at all, and in some lights all I see is the darkness and it goes away as I twirl. Now that I have a MRB it's been much easier to qualify.. now if only this MRB was as big as my OEC... hahah a girl can dream!

Fire is part of it, find the distance then move the stone so it goes nearer and further away than that point.
It should not take a lot of movement to give a massive scintillation show.

Haha OK, I see it better now, great tips. I might be crazy, but kind of looks like my facets are quivering in the changes of light.
 

Karl_K

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[QUOTE="twang07, post: 4383049, kind of looks like my facets are quivering in the changes of light.[/QUOTE]
*grin*
 

Lovesparklesparle

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I see obstruction on my OEC at certain angles. However when I look at the specific facets that are obstructed I see flower petals, not skinny dark shards as from my old MRB. So the obstruction in an OEC doesn’t bother me because it looks like part of the patterning. When I twirl the OEC, the obstructed facet doesn’t rotate unless I change the angle at which i am viewing the stone. It looks like a kaleidoscope to me so it’s actually very pleasing. I am only bothered when certain facets remain obstructed, regardless of how I twirl the stone. I hope what I am saying makes sense.


You have an amazing stone, maybe you could post some videos to demonstrate the effects you are describing and we can ogle ;-)
 

Lovesparklesparle

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ideal cut mrb
mrb.jpg

steeper pavilion oec (not to steep)
oecsteeper.jpg

shallow pavilion oec

oecshallow.jpg


Really interesting information! What effect would a steep/shallow crown have on the optics? Does that mean it is a combination of either steep Pavillion + shallow crown or shallow Pavillion + steep crown?
 

Karl_K

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Really interesting information! What effect would a steep/shallow crown have on the optics? Does that mean it is a combination of either steep Pavillion + shallow crown or shallow Pavillion + steep crown?
obstruction is mostly controlled by the pavilion main angles and how wide the arrows are is controlled by the lower girdle/half facets..
How visible it is can be modified somewhat by table size and crown angle.
For example a smaller table will show less of the pavilion mains when they are obstructed, but to small and it can look like a donut.
 

Mina-Lo

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Who ever said there were no ideal angles for an oec is 100% wrong.
Both Morse and Tolkowsky had "ideal" angles for an oec over a 100 years ago.
There are new cut branded oec being cut to AGS0 ideal specs.
The correct angle depends on the crown angle and table size to min. obstruction but below ~40.5 degrees there is guaranteed to be issues.

These might be of interest:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

https://www.pricescope.com/communit...irst-100-years-al-gilbertson-free-pdf.228643/

Hi @Karl_K
you mention there are "ideal angles" for an OEC, do you mind sharing them please? I'm trying to buy an OEC online but I'm in Australia and want to know what stats I should be looking for.
Many thanks.
 

Karl_K

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Hi @Karl_K
you mention there are "ideal angles" for an OEC, do you mind sharing them please? I'm trying to buy an OEC online but I'm in Australia and want to know what stats I should be looking for.
Many thanks.
The long answer takes a book the good news is the book is written.
Review here: https://www.pricescope.com/articles/american_cut_first_100_years_al_gilbertson_gg
Book for free here:
https://archive.org/details/AmericanCut--theFirst100YearsTheEvolutionOfTheAmericanCutDiamond

The angle information is not as easy to get on old cuts as new production.
The biggest question is how do they react to obstruction in close viewing to mid range viewing.
Many of them were cut with what today is considered to much obstruction for a ring.(to dark up close and not going bright over the mains soon enough with distance.)
Considering the use case of the day its understandable.
 
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