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Diamond Weight Lost During the Cutting Process

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niceice

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From time to time we are asked to explain why diamonds cost what they do... Most people have a cursory knowledge of the Basic 4C''s but they don''t realize how much diamond rough is actually lost during the cutting process nor do they make the correlation between the diamond weight lost during the cutting process and the cost of the finished polished stone... One of the diamond cutters who we work with provided us with a breakdown today that we thought some of you might find interesting, it is for a parcel of Canadian sourced diamonds which we just purchased and as part of the Canada Mark program the diamond rough is tracked from the source Ekati Mine by a number assigned to the parcel and tracked through the cutting process where upon completion it is assigned a specific registry number through the Canada Mark program... As diamond dealers, we know that the loss of diamond rough during the cutting process is substantial, but this is an excellent example of exactly how much diamond rough is lost during the cutting process:

A 0.97 carat diamond started out as a piece of diamond rough weighing 3.24 carats and after being sawn the rough weight was 2.58 carats.
A 1.10 carat diamond started out as a piece of diamond rough weighing 3.32 carats and after being sawn the rough weight was 2.55 carats.
A 1.60 carat diamond started out as a piece of diamond rough weighing 4.25 carats and after being sawn the rough weight was 3.84 carats.

Note that we are not mentioning specific clarity and color grades because it has nothing to do with the subject at hand, nor are we posting the statistics for other diamonds which are similar in weight...

Industry statistics indicate that approximately one ton of earth has to be moved for every one carat of diamond that is mined, so in the case of the 1.60 carat diamond about 4.25 tons of earth were moved... That''s a lot of dirt for a tiny rock
 

YoungPapa

Shiny_Rock
Trade
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Jun 18, 2002
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Robin & Todd,

It is amazing, even to me after all these years how much is lost. I was talking to a manufacturer in Israel about business and told him that we sell quite a few diamonds in the 3/4ct range. He replied by saying that he just increased his allocation of two carat rough and would have more diamonds to sell in that range in several weeks. It shouldn''t have surprised me, but I had just forgotten about how much material is lost during the process!

Years ago I thought about trying to sell rough diamonds, sorta like how they used to sell the "crystals" back in the mid to late eighties - remember those tied around your neck with a leather cord? I figured I could sell two carat + stones for the price of 1/2ct finished diamonds. Problem is I don''t think 15 year old kids can afford $2000 crystals, nor do most thirty-somethings want that style of jewelry.

Oh well - looks like we''ll stick to the polished stuff...
 

Kaili

Brilliant_Rock
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Sep 13, 2004
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Wow! How amazing!

You guys always have the greatest information to share.

Thanks
 

strmrdr

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How many smaller sister stones were cut from the rough?
If Im remembering Paul''s lessons right usually 2 are cut from a well formed rough.
Even an odd shaped rough might yield enough for a couple melee left over.
If it wont its discounted to the cutters.

The 1 ton number sure does get thrown around a lot but Iv not been able to find any evidence that its accurate.
I spose it might be for some mines and for some it might be more but having seen a ton of pictures/tv shows on the Canadian mines there is no way they are moving that much earth for each 1ct of diamond rough.
 

Garry H (Cut Nut)

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These yileds are 30-40% - which given that a lot of Ekati rough has a dark coating - is about what you expect for a nice round stone. The smaller size sawn from the top of an octahedra will generally have a slightly higher yield - An average of 40% would be good.

Nice octahedra can yeild 70% for princess - that is why they are cheaper per carat
 

Wink

Ideal_Rock
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May 3, 2001
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Todd,

I just got my first Canada mark diamind from Paul Sleggers, I was delighted to have that starting and finishing weight stated on the card. It is fascinating even to those of us in the trade.

Wink
 

valeria101

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Date: 3/8/2005 8:35:57 PM
Author: Garry H (Cut Nut)
These yileds are 30-40% - is about what you expect for a nice round stone.
... Nice octahedra can yeild 70% for princess - that is why they are cheaper per carat
Since rounds produce so much diamond dust, how on Earth did they become so popular ???
 

Garry H (Cut Nut)

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Date: 3/8/2005 11:22:41 PM
Author: valeria101

Date: 3/8/2005 8:35:57 PM
Author: Garry H (Cut Nut)
These yileds are 30-40% - is about what you expect for a nice round stone.
... Nice octahedra can yeild 70% for princess - that is why they are cheaper per carat
Since rounds produce so much diamond dust, how on Earth did they become so popular ???
Iit is just like women Ana -the most costly ones to maintain trnd to be the most desirable. Or is that the other way round?

But - It iwas a good message to post and a a good topic Robin & Todd
 

valeria101

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Date: 3/8/2005 11:48:27 PM
Author: Garry H (Cut Nut)

Iit is just like women Ana -the most costly ones to maintain trnd to be the most desirable. Or is that the other way round?
There''s hardly open bidding for desirable women... so the first version must be the right one
 

Colored Gemstone Nut

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Date: 3/8/2005 11:48:27 PM
Author: Garry H (Cut Nut)

Date: 3/8/2005 11:22:41 PM
Author: valeria101


Date: 3/8/2005 8:35:57 PM
Author: Garry H (Cut Nut)
These yileds are 30-40% - is about what you expect for a nice round stone.
... Nice octahedra can yeild 70% for princess - that is why they are cheaper per carat
Since rounds produce so much diamond dust, how on Earth did they become so popular ???
Iit is just like women Ana -the most costly ones to maintain trnd to be the most desirable. Or is that the other way round?

But - It iwas a good message to post and a a good topic Robin & Todd
Hi Garry:

How would you assess the yield of diamond rough compared to ten years ago.

With current ray-tracing & sarin technology and the development of instuments used to evaluate diamond rough and internal inclusion charateristics should be helping yield larger, cleaner more valuable diamonds from an existing rough which in the past might have yielded a poorer quality smaller diamond.


I understand and think what R&T post is great, but shouldn''t yields on rough be getting much better with technology?
 

Antwerpman

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I think the diamond producers would be jumping for joy if they got 1ct/tonne or earth moved.

See this link for details of diamond yield from the Letseng mine in Lesotho (3rd from last paragraph). Other mines yield even less (down to 1ct/100tonnes), although some do yield more

I explained more here if anyone is interested about ratios of extraction to diamond yield if anyone is interested
 

Colored Gemstone Nut

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Date: 3/9/2005 4:48:18 AM
Author: Antwerpman
I think the diamond producers would be jumping for joy if they got 1ct/tonne or earth moved.

See this link for details of diamond yield from the Letseng mine in Lesotho (3rd from last paragraph). Other mines yield even less (down to 1ct/100tonnes), although some do yield more

I explained more here if anyone is interested about ratios of extraction to diamond yield if anyone is interested
Hi Antwerpman:

I understand the point your getting across concerning the economics of yield per tonne of earth moved.

I am speaking in terms of from this yield of existing rough and the advances being made in fashioning higher quality larger diamonds with advanced cut technology. Machines which evaluate diamond rough ( for example..plotting inclusions ) and computer based models generating the best possible outcome of diamond rough before the cutter fashions the rough into cut-diamonds. Yielding bigger cleaner stones from existing rough which might have been fashioned differently without this technology.


Garry I would like to hear what your thoughts are on this and how many major cutting houses are using this type of technology?
 

Antwerpman

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You are of course correct in thinking that technology has brought about advances in the evaluation and cutting of diamonds and that as a result diamantaires are better able to control the outcome of a particular stone more closely.

However I am not sure that an increase in yield has resulted from this, as what has actually happened is that the technology has been used to drive up the quality of the product in terms of the make(cut) that is expected from a polished diamond. So where as on the one hand the technology has armed the diamantaire with information which would have allowed him/her to increase yield, it has simultaneously become a tool to check that many of the weight saving measures that were used before (thick girldles, playing with proportions, etc) are NOT used as they will detract from the (now easily measureable) beauty of a well proportioned stone.

So if anything I would say that probably this technology has probably resulted in an overall decrease in the yield from the diamonds polished, but has led to an increase in the quality of the end product
 

Garry H (Cut Nut)

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I agree too - but i also disagree.

Cutting for predetermined range of certs has narrowed the range of acceptable options and resulted in more diamonds close to tolkowsky proportions - but reduced the yield compared to when clever manufacturers had more scope.

But now that we have some labs introducing more sensible less restrictive top cut grade options - there will be an improvement in both yeild and in cut quality.

My crusade is nearing completion
 
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