question about cut tweak side effect

[elmo]

When a stone''s pavilion is tweaked say to reduce a window and the length/width dimensions are reduced a bit as a result, is it fairly normal practice to leave the crown as-is? I was looking at something yesterday that had been touched up like this...the kite facets were clipped off at the girdle by maybe 10-20% i.e. didn''t come to a point as I expect they did originally. I guess under ideal conditions I would have thought that if someone went to the trouble to recut the bottom, the top would have been touched up as well, given enough additional weight to play with. Not sure what is typical though.

 

[PrecisionGem]

When a stone has a window, it''s because the pavalion angles are cut below the critical angle for the material. This is usually the case with most native cut stones. The cutters are more concerned with weight than the beauty of the stone. So to recut the stone to correct this, you need a greater angle on the pavilion. This usually means the diameter of the stone must also get smaller, and therefore the girdle recut, and the cown. You can''t add more depth to the stone, only change the proportions.
I have recut stones that have lost 60% or more in weight in recutting to correct bad windows.

 

[elmo]

Understood what's being done to the pavilion angle to reduce the window. In the stone I saw that had been recut, the kite facets appeared to be clipped off some at girdle. Kites are normally pointed at the girdle I think. So let me rephrase my first assumption as a question: would that be the side effect of recutting the pavilion without touching up the top?

 

[valeria101]

Date: 12/24/2005 2:11:56 PM
Author:elmo

I was looking at something yesterday that had been touched up like this...the kite facets were clipped off at the girdle by maybe 10-20% i.e. didn''t come to a point as I expect they did originally.

Not sure I understand what exactly the respective tweak is...

About windowing, the main angles would be critical - as it was already explained. I doubt anything else can compensate if these are not right.

That either only the crown or only the pavilion can be recut... either is done. For what reason, it definitely depends on what the stone is, how it looks and what sort of improvement was thought from recutting to begin with. As far as I know, recuting the pavilion is the more drastic measure and is usually expected to waste more weight. If a certain weight has to be maintained and the crown cut is Ok, it would be left as is. Only recuting the crown is more of a cosmetic thing - it may be done to repair wear marks or to improve the apparent symmetry. The darker color stones in which the details of the pavilion are not all that visible face up, improving the symmetry of the crown only is quite effective - IMO, even if the bottom remains uneven and a slight window persists, the overall looks improved allot and with minimal weight loss.

This is about all the generic ''theory'' that comes to mind.

From the description, it sounds like the ''tweak'' is some slight modification of the typical brilliant cut in the upper girdle region. Maybe some small extra facets were cut ? If so, the reason could have well been to avoid an extra thin girdle, or just to give a nicer faceted look to a gem that started out with a very wide girdle. Who knows... As far as I know, there is no point in keeping the ''textbook'' facet pattern. Perhaps for diamonds this is less common - as fancy cuts are less common in the highly standardized cutting context. It may not be worth it to give every single round brilliant special treatment and end up with a ''modified brilliant'' description on the lab report when there is a premium on getting certain standard names (thinking of what ''modified round brilliant'' would be versus the premium on precision cut standard RBC).

Just a thought...

Any chance to show what the respective cut looks like?

 

[valeria101]

Hm... is this it?

If so, I can''t see any profound reason to do it this way other than... the fewer meet points there are, the easier the cut. It doesn''t look any better or worse to me.

 

[elmo]

Stone is on its way home so I can't post a photo...was a cushion-cut sapphire, typical step cut pavilion and brilliant crown. The question is really why the kite facets were clipped at the girdle not pointed, and if this would have resulted from the recut I was told had been done. Not sure how I can describe more clearly with just words

.

Edit: yes that's it except in this case there were two upper girdle facets between two kites as expected - a typical cut brings the kites to a point, those are clipped. From a cutter's perspective why would that be done if not recut side effect? Looked sloppy to me but I'm not a faceter.

 

[Richard M.]

>Date: 12/24/2005 2:11:56 PM
Author:elmo
When a stone''s pavilion is tweaked say to reduce a window and the length/width dimensions are reduced a bit as a result, is it fairly normal practice to leave the crown as-is?

No, it''s not normal practice in the U.S. If a pavilion is recut and L/W is changed, it''s normal to recut the crown as well. A gem''s brilliance/windowing are determined by the angles of the pavilion facets and the crown facets are considered less important optically. They can have an effect on dispersion in stones that display it, but corundum isn''t particularly dispersive.

Weight retention was probably the reason for not recutting the crown in this case. When it comes to high-value stones, weight usually takes precedence over textbook cutting rules. Was the stone pleasing to you from the standpoint of cut?

 

[elmo]

Richard, you're saying that's potentially a side effect of the recut then (clipped kite facets)?

My guess too about weight retention - this was pretty serious color and unheated. Even with the recut though it seemed a little dark in the center with more extinction than I'd like. This question was only a minor detail / technical question, not the reason for returning - stone was nice but just wasn't talking to me

.

 

[Richard M.]

Date: 12/25/2005 6:37:17 PM
Author: elmo
Richard, you''re saying that''s potentially a side effect of the recut then (clipped kite facets)?

That would be my guess. When you reduce L/W the circumference of the girdle is also reduced. In recutting the girdle outline you''d automatically chop off the part of the crown main facets (what you call ''kite'' facets) that normally ''points'' at the girdle. The only way to compensate would be to entirely recut the crown, which would reduce weight even more.

All this is theoretical without actually seeing the stone, of course.