Princess breakage and extra corner facets

[Garry H (Cut Nut)]

It is common that the girdles of princess cuts are thinner at the corners than in the middle of the stone.
This is because of the shape of the rough is usually not perfectly square or rectangular - so inorder to get the largest shape the corners are made a little thinner.
This leads to more likely-hood of chipping at the corners, either during setting, or subsequent removal and resetting which we know is common (many diamonds will have several owners over hundreds of years).

I am going to propose that a very small additional facet (or small set of facets) be used on the corners of all square and many other pointy diamond cuts.
The beneftis:

1. less than 1/2 the likelyhood of chipping
2. slightly better cutting yeilds on some stones
3. easier to hold and set stones in prongs
4. not a problem in rubbed over bezel settings as the metal would cover that area anyway

Before contacting many of my associates diamond grading labs, and making a submission to the WFDB"s, I would like to guage the opinion here on Pricescope (consumers, vendors appriasers etc).

I guess what i would like to see is no comments if the corners are removed - and a warning comment if they were left sharp. that way the public will be protected by default.

 

[Garry H (Cut Nut)]

Here is an example of the very small scale of extra facets.
I have had this done with less than 0.01ct of loss, and in some cases the polisher could make a slightly (1%) heavier stone because they could pushe the dimensions out a little.

 

[PhillipSchmidt]

You get my vote. I have seen far too many chipped corners in my lifetime. I know setters who already blunt the corners by hand, and that helps them avoid potential chipping. It will work and save many headaches for jewellers and consumers alike.

I dissagree that it isn''t necassery for rubbed over stones. The points therein require a cavety drilled into the hole to take any pressure away from the point. It would help a little there too.

Cheers,

PS

 

[strmrdr]

I dont care much for princess cuts but agree with you that its a good idea.
Im thinking that as long as it isnt cut back too far that most of the time there would be no real difference in appearance when mounted anyway because the prongs cover the points.
Correct?

I would like to hear Paul's and Brian's comments on this idea.

 

[PhillipSchmidt]

Yes correct,

The point need only be dulled rather then taking a big bit off. I don''t know how large a facet Garry suggests. I suppose that is a question for the cutter.

Can you think of any examples of settings where the corners are exposed?

 

[PhillipSchmidt]

Somebody has got CAD software

 

[PhillipSchmidt]

LOL seemless topic swap

Setting a p'cut without making a hollow for the point is a dissaster waiting to happen. The more preparation you do the better, best is if you can close the setting flush to the diamond without using any force. Then it is easy

Good point about the settings angle Dave. People often don't know what they sacrifice in strength to get that racy look. It is often usefull to pierce the prong and bring over two pieces of metal at right angles to the point, thus not pushing against the corner, and solder the split after. Obviously, due to heat, it is only possible in gold (and maybe in plat with a laser welder) This gives a very good hold and allows you more control over metal thicknesses.

Cheers,

Phillip

 

[JohnQuixote]

Date: 12/5/2004 4:43:21 AM
Author: strmrdr
I dont care much for princess cuts but agree with you that its a good idea.

Im thinking that as long as it isnt cut back too far that most of the time there would be no real difference in appearance when mounted anyway because the prongs cover the points.

Correct?

I would like to hear Paul's and Brian's comments on this idea.

Strm - From the cutter's perspective this is more of a setting issue than one of cutting, since natural cleavage planes will always be the prime factor in such breakage. Brian has discussed this in meetings with production staff and with our setters.

Feydakin's setting example is excellent - it's the way all princess stones should be set! Breakage of stones and chipping of princess cuts is largely due to incorrect setting.

Here is more technical info,

The right rough for princess cuts will be a square octahedron. If the diamond is not seated correctly (or if the seats have not been cut level) there will always be potential for problems: The setter puts pressure on one corner then moves to the next corner and puts pressure there and so on... If the seats are not level in the prongs of the ring - or modified as in the good example Feydakin showed us - or if the stone is not set level in those seats the force will release that pressure along a natural cleavage plane (see diagram).
 
This will occur whether the girdle is thick or thin* or whether it has an extra facet on the end or not. It doesn't matter whether the stone has a sharp point or a flat point: The cleavage plane is the overriding factor. The solution is to cut the seat correctly in order to protect the diamond.

* It may be better to have a girdle that's not "extra thin," but if the stone is a great performer one should not walk away from it providing the person setting it is competent.
 
This was discussed, along with a photo essay, back in April in this Strmrdr-instigated link.

PS...On-topic...Da Bears win!

 

[RockDoc]

All the points you make are excellent but it stil comes down to the experience, ability and interest in doing the work to the finest level you can.

No one is perfect... but a few are damn close


Rockdoc

 

[Garry H (Cut Nut)]

All wonderful sentiments gentlemen - setters should do this and that etc - but the issue is that princess do and will continue to break.

John there is not much we can do to stop octahedral clevage - but as we know the most frequent damag is chipped corners.

What I am looking to do is change the definition and prctice for cutting ALL princess cuts.
I believe that the time to do this is as AGS are introducing their new princess cut grade.

The more setters who follow the excellent advise given here the better - but I am after an holistic solution that works for millions of stones, not hundreds.

 

[JohnQuixote]

Another graphic to illustrate the inherent difficulties.

 

[BrianTheCutter]

All wonderful sentiments gentlemen - setters should do this and that etc

I agree. That is their job. It''s what they are trained to do. When they don''t it''s caused by a lack of education or laziness - and they are failing their profession. We can all help to address that.

but the issue is that princess do and will continue to break.

Again, I couldn''t agree with you more. Princess cuts do and will continue to break because of their octahedral cleavage.

John there is not much we can do to stop octahedral clevage - but as we know the most frequent damag is chipped corners.

Precisely. You cannot stop octahedral cleavage - Princess cuts will always have to be repaired because of that fact.

What I am looking to do is change the definition and prctice for cutting ALL princess cuts.

Good luck on that Garry. The problem is that this is not a line drawing in Diamond Calc, this is a real-world issue that goes to cleavage and graining. Each layer of molecules is a new cleaving plane. These planes merge where the corners are and run beyond them. Placing an extra facet will not alter this natural cleaving area and it may even compromise the integrity of the corner more than if the stone is run naturally.

You have a nice idea in theory, but in practice it is different. With rock climbing it''s all well and good to study the tools and chart a cliff face, but once you try climbing you find that there are more factors in the environment than can be described in a chart or software program.

You have asked for opinions and this goes to real-world cutting. How many princess cuts have you cut lately, and I mean diamond to wheel? Graining is not easily understood. There are soft and hard spots and no two stones are alike. That is why these practices have lasted so long without alterations.

I believe that the time to do this is as AGS are introducing their new princess cut grade.
The more setters who follow the excellent advise given here the better - but I am after an holistic solution that works for millions of stones, not hundreds.

You can do that if you can redesign the octahedron cleavage plane! That would really solve the problem.

 

[Garry H (Cut Nut)]

Thanks Brian, I have a rudimentary crystallograhpers understanding having learned this stuff three times (Geologist and then Gemmology British style, then Diamond Technology).

I think what I am proposing would be valid for marquise and pear shapes also.

But it should, in theory, be particularly effective because princess have 2 or 4 times more corners than marq and pears - so 2-4 times the vunerability before considering cleavage directions.
Also what I am proposing is the addition of a predominantly cube (4 point) facing facet (100). Then presure is applied there is less lielyhood of the pressure being applied paralell to (111).

 

[Garry H (Cut Nut)]

Dave have a look at my first 2 pictures - I put the extra facets on inside the red circles - they probably need only be very small - do you think they would be enough? they would remove about 1/2 a point.

 

[Garry H (Cut Nut)]

I think that is a little large Dave - maybe more like 1/3rd mm.
But consider 1/2mm:
IF a 1.3mm diameter diamond without a crown weighs about .006ct then 1/2mm off the point would be about .0005ct (any mathematicians?) so it is possible we are talking about removal of .002ct.