Long stars

[strmrdr]

For the following images the Pavilion angle was 40.8 for all images.
Girdle thin and cutlet pointed.
Weight .79ct diameter 6.00mm depth 3.66 and 3.68
Crown angles 34.4% and 35%
LGF% 78 and 80

 

[strmrdr]

C: 35 star 50% lgf 78%

 

[strmrdr]

c: 35 star 50% lgf 80%

 

[strmrdr]

c: 35 star 60% lgf 78%

 

[strmrdr]

C 35 star 60% lgf 80%

 

[strmrdr]

c: 34.4 star 50 lgf 78

 

[strmrdr]

c: 34.4 star 50 lgf 80

 

[strmrdr]

c: 34.4 star 60 lgf 78

 

[strmrdr]

c: 34.4 star 60 lgf 80

 

[strmrdr]

35 50 78 vs 35 60 78

 

[strmrdr]

34.4 50 78 vs 34.4 60 78

 

[strmrdr]

34.4 50 80 vs 34.4 60 80

 

[belle]

pretty pictures strm

you''ve been busy!

 

[Garry H (Cut Nut)]

1. I would be happy with any one of them Storm.

2. try this - increase the carat weight to 100ct or 1,000 ct and see how little difference the upper and lower girdles make to weight and therefore cutters yeild.

3. Others have suggested that incorrect minor facets are cut for getting better yeilds and disguising weight. This is simply wrong. I have worked with many manufacturers who are now aware that lower girdles neeed to be adjusted for different table sizes to keep a nice star width. They all want to get the best looking diamonds they can when there is no cost disadvantage.

But of more interest is to play with slightly shallow or slightly deep diamonds - not ones near a sweet spot. Then the minor facets can really make a difference, which is why I always have said that in the sweet spots of HCA the minor facets do not make much difference.

 

[strmrdr]

Yea Garry the difference that are showing up are personality tweaks nothing more.
I ran a much wider range thru various combos and like you said until you go to the extremes it was pretty much personality tweaks because the differences weren''t big enough to be called performance differences.

 

[JohnQuixote]

Date: 8/8/2005 5:36:51 PM
Author: Garry H (Cut Nut)
1. I would be happy with any one of them Storm.

2. try this - increase the carat weight to 100ct or 1,000 ct and see how little difference the upper and lower girdles make to weight and therefore cutters yeild.

3. Others have suggested that incorrect minor facets are cut for getting better yeilds and disguising weight. This is simply wrong. I have worked with many manufacturers who are now aware that lower girdles neeed to be adjusted for different table sizes to keep a nice star width. They all want to get the best looking diamonds they can when there is no cost disadvantage.

But of more interest is to play with slightly shallow or slightly deep diamonds - not ones near a sweet spot. Then the minor facets can really make a difference, which is why I always have said that in the sweet spots of HCA the minor facets do not make much difference.

Strm asked me to comment in this thread.

I'd be happy with these as well...Of course I'd rather see actual diamonds than models.

Diamonds are not stamped out, and recovery for any manufacturer is prime importance. It's a matter of cost. The weight recovery for the rough will dictate whether they make nice stones or just commercially viable hepgush. Smaller goods produces en masse will show more variance. Most fine make diamonds are already slated for less weight recovery.

Incidentally, my understanding about saving weight with longer LGFs was derived from the fundamental that they are closer in angle to the pavilion mains when longer, thus less must be polished away. However, running your 100ct experiment in DC it calculates more weight saved with short LGFs (?).

Any insight Garry? I know pavilion mains are put on first when it's blocked in 8. Is this DC not emulating rough-to-polished planning/design or am I backwards here?

As for minors making a difference near sweet spots. Some of us who are into precisely patterned diamonds note differences in different lighting conditions that correlate to the minors. This relies on combos of majors, minors and the level of patterning.

 

[mkb]

John,
as Gary said in reality there is very little to gain in weight with the length of the bottom halves (lower girdles). If weight is that critical in a particular stone (eg. Risking a 0.99 instead of a 1.00 ct) the cutter would be better off to cut the halves say 9.5 degrees away from the pavilion (instead of 11.25), H&A would then be out of the question, but would probably still get a better price without certification.
Although stones are blocked on the pavilions, in these ‘super cuts’, while finishing halves are cut first.
I’ll ad a few pages out of my training manual (not aimed at H&A), here the halves are 80%, as is usually used in smaller goods (VG).
Sorry it seems that the file is too big, I''ll mail it to you if you wish
Br
luc

 

[JohnQuixote]

Luc,

Got it. That percentage jives with my understanding about halves.

In the big picture my impression is that for large cutting houses even the slightest weight recovery is considered, especially with modern tools and measures. Take a smalls manufacturer who saves even 0.01 per carat of goods produced due to such minor adjustments. If he produces 10,000 carats per year he’s recovered 100 carats. At $600 per, he''s gained $60,000 that would have been wasted if he didn''t make that decision. In a factory producing 100,000 carats per year that’s $600,000. However, as Garry said, manufacturers are becoming aware of the need for better cut. Times change.

Thanks for your cutting description... I see now where my understanding differs. What you say makes sense - especially with semi-automatic machines that block in 16 - but that''s not the process that we follow on larger diamonds, say anything above .30. Brian has said that blocking in 16 works quite well in the faceter’s world of colored stones, but we’re still following a traditional method of blocking and brillianteering with our goods- mainly because of graining which Brian is very sensitive to because of facet yaw.

I look forward to getting the manual! Thanks for that, and thanks for being my ‘surrogate cutter’ today

 

[mkb]

John,
interesting point about the graining, I would very much like to discuss that with Brian.
I know that in the traditional -big stone- centers (Antwerp, NY, Amsterdam, Tel Aviv) the ''old'' (no offence meant) way is still being followed, I was trained that way too. But as you partly stated, in smaller goods even for H&A the need for production is already taking the front seat.
On the little ''swindling'' to gain these extra few ''points'', garry is right. Manufacturers are paying more attention to the cut now, question of otherwise not being able to sell your goods. If one has a large production, nowadays one is better off being a banker

.
Looking forward to the discussion with you and Brian.
TYVM
luc

 

[JohnQuixote]

Date: 8/9/2005 12:59:12 AM
Author: mkb
John,
interesting point about the graining, I would very much like to discuss that with Brian.
I know that in the traditional -big stone- centers (Antwerp, NY, Amsterdam, Tel Aviv) the 'old' (no offence meant) way is still being followed, I was trained that way too. But as you partly stated, in smaller goods even for H&A the need for production is already taking the front seat.
On the little 'swindling' to gain these extra few 'points', garry is right. Manufacturers are paying more attention to the cut now, question of otherwise not being able to sell your goods. If one has a large production, nowadays one is better off being a banker

.
Looking forward to the discussion with you and Brian.
TYVM
luc

Luc,

Well, Garry is the most world-travelingest cut nut ever, so he'd know. I understand his frequent flier miles are counted in parsecs now, and instead of a passport he just flashes his ideal-scope and pocket CZs.

No offense at all regarding the 'old' way. Brian prefers it, and I know he'd be delighted to visit with you about graining & yaw.

 

[Garry H (Cut Nut)]

Nice insights guys.

John an easy way to understand the LG wieght loss:

the mains are cut first - and once the stone is blocked out with its 8 facets the halves are added.
Now if the halves only run 1/2 way down (50% and very short like the olden days) then less material is removed.
But if you polish them to 99%, then you take away more stuff.

But as we know - there are more lower girdles around that are too long - so any theory about cutters deliberately adding weight is plain wrong.

And using 80% as a yard stick - 10% variation either side only results in 0.5% weight variation. As Luc says, selling goods is more important than trying to dud people who will not like your stones because they look too dark with 70% LG''s