minor facets

[Stephan]

Sorry, I know this happened a lot of times here on the forum, but I still want to discuss about what they call "minor" facets, as no answer I saw really convinces me.
Most experts here will say minor facets aren''t important, they are just a matter of taste.
Come on guys, if we discuss about 1/10 degree for pavilion angle like "Is 40.6 to shallow?" or "Is 41 to deep?", I think that we, consumers, also have the right to learn more about "minor" facets.
We always consider a crown angle together with the pavilion angle, for example "A 35.2 degree crown is more acceptable if the pavilion is 40.5 than if the pavilion is 41.1" .
So why we just don''t do the same with the minor facets?
Why don''t we consider upper girdle/star facets together with the lower girdle angle, especially when we know they cover more surface than the "main" facets?
Rhino did something like that on his website, and it''s interesting, but he only speaks about LGF/star facets length on his educational page, nothing about angles.
How is it possible that some diamonds with identical main facet angles can have a 41.XX LGF combined to a 40.XX UGF, or 42.XX LGF combined to a 43.XX UGF and both diamonds are sold as ideal?
If 0.5 degree difference can kill a diamond on a "main" facet that covers a small surface, how can the experts tell us that 1.5 degree, 2 degree or even a bigger difference on "minor" facets that cover a big surface are just "a matter of taste"?
I tend to believe that minor surfaces also have a lot of ideal combinations, just like the HCA or Jasper Paulsen believe in ideal pavilion/crown combinations.
I even think that a to shallow/to deep diamond can be improved by cutting the minor facets on a different way: shorter stars and/or longer LGF on a steep/deep, longer stars and/or shorter LGF on shallow diamonds.
That''s also why I prefer shallower diamonds: they allow the cutter to cut bigger arrows (bigger flashes of fire in the arrows) or longer stars and higer UGF angle (nice fire seen in the crown and in the LGF).
That''s only my little consumer experience, but please experts tell me where I''m wrong.
I just can''t believe that such big variances (2 degree) on so many facets are not important.

 

[Stephan]

If I look at this old topic, it is not the first time that shallow diamonds with shorter LGF or longer stars (or both when shallow enough) look very good, but that is only my opinion.
So am I wrong by thinking that minor facet DO matter, and it is not only a matter of taste?

 

[Skippy123]

Bumping for Stephan

 

[Garry H (Cut Nut)]

OK QM - you have to tell us what your preference is for fire or brightness, big or small flashes etc

 

[strmrdr]

The answer is it depends.
In some c/p angle combinations it is a matter of taste in others its a matter of cut quality.
Basically a diamond in the 34.5-34.8 crown range with a pavilion of 40.7 to 40.8 55-57 table is a lot more tolerant of minor facet differences than one outside of that range.

 

[strmrdr]

lets take shallow pavilion diamonds 40.6 and under:
they work better with longer lgf%, why?
shallow pavilion means they react to obstruction more.
To keep them from being even darker up close you cut them with long lgf% unless you want to say who cares about close range veiwing and create an oec with a high crown for the other positive attributes it has.

 

[strmrdr]

next lets talk about 40.9ish to 41.2 pavilion angles with shallowish crowns.
The pavilions on these is makes them directional and a short lgf% can give you a miss-match where the lgf works against the mains.

 

[strmrdr]

Stars - long stars open up the pavilion mains to more light and change the angle of the ugf.
In general there isn't enough difference to matter in the 50% to 60% range with most pavilion angles as far as light to the mains to matter.
The ugf angle can have an effect on the dispersion of the stone, without getting into painting or digging war on this subject and keeping within classic girdle cutting a slightly steeper ugf will have more dispersion up to the point it directs light into a useless zone.
This is seen in detas in diamcalc.
The best compromise for a lot of combinations is ... ~55% which is where a lot of ideal cuts fall.
60% or even 65% may be fine with some c/p combos, usually the steepish/shallowing/long lgf% combos like a 34/41/80.

overall the stars have a minor effect compared to the lgf% and c/p angles and table size.

 

[strmrdr]

What is interesting is that I could take into account someones skin tone, hair color and style, eyesight and lighting envirement most in and balance a diamond just for them that someone else under other conditions may not like but it is the best diamond for that one person.

 

[Stephan]

Thank you strmrdr for your detailed and logical opinion.
One of the best diamond I saw (for my taste) was 33.7/40.8 58% table looong stars and about 80-82% LGF.
It''s very interesting.

Garry, thank you for the HCA, which I believe in and use.
0.1 degrees difference in pavilion mains (40.9 -> 41) can make a difference when calculating the HCA score, sometimes it doesn''t, depending on the crown angle and table size.
Do you mean that with a 42 degrees LGF, the UGF can vary from 39 to 43+ degrees without a drastic change in performance? Perhaps I''m wrong, but it seems like cutters who cut for beauty like WF or 8star use shorter LGF when the UGF is painted (=> shallow UGF w/ steeper LGF).
strmrdr''s answer sounds more logical, and if I have to buy a steep/deep combo, I will avoid short LGF (pale red in the table under IScope when steep/deep) with long stars.

 

[strmrdr]

Simple balance. (short lgf%, painted ugf)
You use short lgf% which gives you more obstruction darkness, cut it to angles that show the stars as often as possible, then you balance it by painting the girdles and removing dark areas from there.
It works sorta.
Some people like me don't like the darker tables even if the overall balance of lightness and darkness is the same.
I also don't like the on/off loss of scintillation off the ugf.

WF new line didnt do it to the extent 8* did/does and was more balanced.

 

[Stephan]

Here is the perfect example of a diamond with a crown shallower than the average of the other "ideal" diamonds sold on the net, especially with such a pavilion. (The most of the diamonds sold as ideal that have a 40.7 pav will have a 34.5-35 crown.)
The star facets are longer.
I saw this diamond, and it was breathtaking, not only because of the nice size.
Here is the link.