Cut quality on diamonds vs CZ

[erislynn]

I've been shopping around for colored lab diamonds lately, and have noticed extremely poor cut quality on some lab diamonds, including colorless, and even natural diamonds, for that matter. Crown angles of 38, no arrows in sight, wide open tables. I know to avoid those but I have a collection of 6A CZ for designing purposes that are consistently acceptable. Not super ideal, but nice symmetry, clear arrows, no wide variations from Tolkowsky ideals. At least nowhere as bad as some diamonds with central black holes. With natural diamonds, every carat cut off is a huge difference in price so I get it. But with lab grown rough, why aren't cuts more consistent? If they can bother to cut something worth $10 to ideal proportions, why not something worth hundreds more?

 

[monipod]

A CZ would be softer to cut and therefore take less time and would be easier to get right (or discard if you get it really wrong).

It's not a proven fact but I have heard that lab roughs are harder to cut than natural roughs. About 1.5 times the time taken? I would suggest to you therefore that there are less experienced cutters having an awful time getting a lab rough right. It doesn't excuse the bad cuts of diamonds out there but I guess that's why there's the super ideal grade for the discerning consumer.

 

[Garry H (Cut Nut)]

I've been shopping around for colored lab diamonds lately, and have noticed extremely poor cut quality on some lab diamonds, including colorless, and even natural diamonds, for that matter. Crown angles of 38, no arrows in sight, wide open tables. I know to avoid those but I have a collection of 6A CZ for designing purposes that are consistently acceptable. Not super ideal, but nice symmetry, clear arrows, no wide variations from Tolkowsky ideals. At least nowhere as bad as some diamonds with central black holes. With natural diamonds, every carat cut off is a huge difference in price so I get it. But with lab grown rough, why aren't cuts more consistent? If they can bother to cut something worth $10 to ideal proportions, why not something worth hundreds more?

Good question - the size would be important.
Very large sizes are more likely to be grown with CVD and most CVD are not cut too deep.
HPHT are grown as cubo-octahedra and by and large cut too deeply like natural diamonds.

 

[Karl_K]

For a long time 1ct equivalent size cz's that where cut to super ideal levels could be had for well under a buck each.
It looks like they were bought by Swarovski but a bunch of china sites are using the name illegally.

 

[Garry H (Cut Nut)]

For a long time 1ct equivalent size cz's that where cut to super ideal levels could be had for well under a buck each.
It looks like they were bought by Swarovski but a bunch of china sites are using the name illegally.

https://www.preciosa.com/en/home velly nice

 

[Karl_K]

https://www.preciosa.com/en/home velly nice

kewl going to have to look at it more later when i wake up.

 

[erislynn]

kewl going to have to look at it more later when i wake up.

Checking pricescope in your sleep? That’s dedication.

 

[erislynn]

Ok, so CZ being softer and maybe easier to cut makes sense. But with lab rough there should be enough margins to warrant better cut quality, right? Or is cutting lab rough a challenge even for experienced cutters?

Sorry Gary, the technical stuff went over my head.

 

[Rockdiamond]

Crown angles of 38, no arrows in sight, wide open tables.

HI erislynn!
Based on these aspects: We're talking about Round Brilliant Cut Fancy Colored Diamonds. I've seen some unconventionally cut FCD rounds that actually looked nice because the goals of the cut are different when cutting colorless, versus trying to project color out of the table.
With Lab Grown Rough, your assumption about the cost being so low makes sense....but again, if they're trying to get a stone that looks pink, blue, yellow, etc....it might make sense to cut a deep stone with a 64 %table.
I was just looking at an amazingly vivid, vivid yellow round Natural diamond the other day about a carat and a quarter.....66.6% depth, 62% table.
D R O P dead gorgeous........
SO it might not be the cost or lack of skill...it might indicate an abundance of knowledge of cut.

Or not

 

[Garry H (Cut Nut)]

Ok, so CZ being softer and maybe easier to cut makes sense. But with lab rough there should be enough margins to warrant better cut quality, right? Or is cutting lab rough a challenge even for experienced cutters?

Sorry Gary, the technical stuff went over my head.

Yes - but if you google images of HPHT and CVD rough - you will see the different shapes dictate cutting rules

 

[Karl_K]

cutting style also changes over time, the early cvd stones were super shallow to the point of being blah in rings.
Now they run steep deep, what changed?
The rough, at first they had trouble making thicker rough gem grade and now they can to the point they can make them steep deep.

David is also 100% correct in that fancy colored diamond cutting parameters are way different than colorless and other none fancy colors.

 

[Karl_K]

Checking pricescope in your sleep? That’s dedication.

I check PS right before I go to bed and often get notification of people liking/quoting posts that I dont even remember making when I wake up.
Does that count as posting in my sleep lol?

 

[erislynn]

I check PS right before I go to bed and often get notification of people liking/quoting posts that I dont even remember making when I wake up.
Does that count as posting in my sleep lol?

Yes. Yes it does. #sleepposting

 

[holyrock]

A CZ would be softer to cut and therefore take less time and would be easier to get right (or discard if you get it really wrong).

Id assume the softness of CZs wouldn't actually matter that much, since moissanites from my supplier are almost always identical in terms of cut quality. Always H&A worthy and they don't offer any other cut quality. Moissanite is 9-9.5 Mohs so the same tools diamonds are cut with are used id assume. Though i have no idea about moissanite production, in terms of what is the overhead loss if a stone isn't satisfactory. If a CZ cut isn't satisfactory its literal cents if that, and yet there are some really ugly CZs sold out there.

 

[Garry H (Cut Nut)]

Id assume the softness of CZs wouldn't actually matter that much, since moissanites from my supplier are almost always identical in terms of cut quality. Always H&A worthy and they don't offer any other cut quality. Moissanite is 9-9.5 Mohs so the same tools diamonds are cut with are used id assume. Though i have no idea about moissanite production, in terms of what is the overhead loss if a stone isn't satisfactory. If a CZ cut isn't satisfactory its literal cents if that, and yet there are some really ugly CZs sold out there.

They cut these stones on large barrel polishing machines - they are proprietary so never seen photos.
Essentially maybe 100 stones are polished at once on one abrasive wheel with each facet taking a few seconds.