Girdle Treatments: Cheated Girdles, Tweaked Girdles, Digging & Painting

[JohnQuixote]

GIRDLE TREATMENTS: Cheated, Tweaked, Digging and Painting

DIGGING and PAINTING are descriptive of polishing techniques used on a diamond’s girdle facets. When the direction of polish on the wheel is from girdle to crown (or towards culet) it is called digging. When it is run from star (or from culet) to girdle it is called painting. All manufacturers cut and polish diamonds to acquire reasonable recovery. Digging and painting happens routinely, depending on how thick the girdle is after blocking out. The techniques are not used with light performance in mind, they are for weight retention.

(more elaborate descriptions are given several posts below)

Directions of Polish

 

[JohnQuixote]

WHAT IS A CHEATED GIRDLE?

Diamonds cannot be made with cookie cutters. There will be challenges in the rough that cause some of them to undergo these weight saving techniques in a negative sense.

A cheated girdle is descriptive of one where the digging or painting was deleterious to the diamond’s appearance or proportions. Digging is usually done on diamonds where the rough dictated that the finished product would be deep. If a diamond measures 6.3 mm and there is enough room to have a 16% crown the cutter can dig the girdle from both sides (resulting in shorter lower girdle facets and longer stars) and saving the 1ct mark. The result is a smaller looking diamond with leakage around the edge. If the leakage is more than would help with contrast this was done for the sole purpose of maximizing the rough to hit a certain carat mark. Such diamonds are ‘cheated,’ and these are the diamonds to be cautious of. This treatment is visible in an ideal-scope.

Such diamonds are more common among pedestrian wares found with average dealers. Good vendors screen such diamonds from their inventory.

Further, strong labs with cut grades will penalize such diamonds. The AGS already takes negative cheating into account in the proportions portion of their 2005 assessment and penalizes them. Such diamonds will not receive a top cut grade. GIA will do so as well in their 2006 metric.


WHAT IS A TWEAKED GIRDLE?

A tweaked girdle is one where painting or digging was not deleterious, and may have enhanced the look of the diamond. In a controlled situation where a specific design template is followed and quality controls are in place the painting technique can be used to create tight relationships between main crown and upper girdle (and main pavilion and lower girdle) angles, resulting in almost no light leakage. Premium cuts that have careful attention using these techniques are considered by many to be among the best cut diamonds in the world.

 

[JohnQuixote]

MORE ON DIGGING A GIRDLE

After the diamond is blocked in 8, if the girdle is too thick, the polisher who does the brillianteering will thin out the girdle (known as digging). This involves running the upper girdle halves on the wheel from girdle towards the crown, making the angles steeper, taking more material from the girdle side and resulting in longer stars in most cases. It may not be necessary to dig out a girdle on a 6.5 mm stone that's correctly proportioned, but it may be necessary to do so with a 6.3 mm spread weighing 1.05 if the brillianteerer is trying to save 1 carat. The digging of girdles is not always negative. It can make a diamond more attractive overall in situations where they are well-cut, which would be ‘tweaking.’ If the adjustment was done for the sole purpose of saving weight at the finish line and the effects are negative, the girdle treatment may be thought of as ‘cheating.’ It's not cheating if the diamond's spread and weight are in good proportion to each other.

Digging Out: Directions of polish

 

[JohnQuixote]

MORE ON PAINTING A GIRDLE

This technique is also used to save weight, but works in an opposite direction. When the diamond is done in 8 cut top and bottom and has a thin girdle the brillianteerer may put the facets on very lightly, and will run them from star to girdle on the wheel, taking more material from the star side, resulting in shallower angles and shorter stars in most cases. In this manner he will get the maximum out of the material at hand without removing too much weight from the girdle. Painting, when done with a premium cut, is not cheating. It can improve and/or enhance overall light return in the diamond, and should be thought of as ‘tweaking.’

Painting On: Directions of polish

 

[JohnQuixote]

DIGGING AND PAINTING: EFFECTS ON LIGHT PERFORMANCE

When the girdle is dug (facets polished from girdle to star) the variance is greater between the main crown angles and the adjacent upper girdle angles and you will see points of leakage along the edge of the diamond. Consumers should beware of the ‘cheating’ aspect of digging that is done to save weight at the expense of diamond beauty. An ideal-scope or ASET image will reveal the severity of digging. As mentioned, AGS already takes such things into consideration when assigning their cut grade, and GIA is expected to in 2006. If the digging is not severe, these diamonds may show good contrast and can be top performers when well cut.

When the girdle is painted (facets polished lightly from star to girdle) the upper girdle facet angles are closer to the adjacent main crown angles. With this tighter relationship there is less light leakage. In a well-patterned diamond with ideal crown and pavilion relationships and minimal yaw/azimuth shift this can result in no (or almost no) light leakage with the close angular relationships. This creates larger, broadfire scintillation that has been described as fluid and colorful, as opposed to the sharp on/off contrast in diamonds with ‘contrast leakage’ points observable in an ideal-scope. This technique of acquiring minimal/no light leakage is used in the styling of ACA New Line and Eightstar brands.


FURTHER NOTE:

In the same way a symbiosis exists between main crown and main pavilion angles there is a relationship between upper girdle halves and lower girdle halves that can be considered in the optimization of a diamond’s overall light return. These angular relationships may be influenced with girdle treatments as well.

 

[JohnQuixote]

EXAMPLES OF WELL-CUT DIAMONDS WITH GIRDLE TREATMENTS

Or "TWEAKED" GIRDLES

Here are DiamCalc examples of two well-cut diamonds with girdle treatments.

On the left is a 1.01 ct. The girdle was dug out.
On the right is a 1.59 ct. The girdle was painted.

Both are very high quality.

 

[JohnQuixote]

Scanned profiles.

 

[JohnQuixote]

Proportions.

 

[JohnQuixote]

Crown details.

 

[JohnQuixote]

Pavilion details.

 

[JohnQuixote]

Girdle details.

 

[JohnQuixote]

DiamCalc Ideal-Scopes.

 

[JohnQuixote]

DiamCalc ASET images.

 

[JohnQuixote]

DiamCalc pavilion patterning images.

 

[JohnQuixote]

DiamCalc performance predictions.

Notes

1. These well-cut diamonds have been 'tweaked' with digging and painting treatments, with no adverse influence on performance.

2. The differences in these two high-performing diamonds is calculated to be very slight and may not be noticable to the casual observer, who may simply see them on equal levels of beauty.

Fine details: As expected, you can see where overall light return is calculated as marginally higher in the diamond on the right, which was painted and so has no leakage points. Meanwhile, contrast is marginally higher in the diamond on the left, which was dug and has elements of 'contrast leakage' along the girdle.

 

[JohnQuixote]

MORE ON THE DUG-OUT DIAMOND

In the 1.01 diamond with the dug out girdle the crown angle is 34.5 and the ugf average is 40.55, for an average difference of 6.05 degrees. The pavilion is 40.7 and the lgf average is 41.95, for an average difference of 1.25 degrees. The star to ugf ratio is 54:46 (the stars are longer because it was dug, or polished from girdle to star). The difference between ugf and lgf is 1.4.

Why was this diamond dug?

The diamond had a thick girdle, but the cutter saw it was possible to retain the 1.00 ct weight. It would not have been a 1 ct if it has been cut with a 14.7% crown, for instance. Of course, the cutter could have made the stars shorter and the halves longer for less light leakage around the girdle, but that would have resulted in a very thick girdle, which would have been ugly for the diamond.

So what is better to have? Longer stars and steeper ugf with medium girdle and contrast leakage, or shorter stars and shallower ugf with a thick, tractor girdle?

A diamond cutter usually does the best he can within a certain range. In this case the diamond was made more attractive by the digging, in the cutter’s opinion, while still maintaining the 1 ct mark.

 

[JohnQuixote]

MORE ON THE PAINTED DIAMOND

In the 1.59 diamond with the painted girdle the crown angle is 34.7 and the ugf average is 37.8, for an average difference of 3.10 degrees - as opposed to the 6.05 variance in the dug out diamond. The pavilion is 40.9 and the lgf average is 42.09, for an average difference of 1.19 degrees. The star to ugf ratio is 51:49 (the stars are shorter since it was polished from star to girdle). The difference between ugf and lgf is 4.29. This is an interesting inverse relationship relative to diamonds with opposite treatments.

 

[JohnQuixote]

In both of the above examples the diamonds received top cut, proportions and performance ratings. The girdle treatments were positive enhancements, not deleterious to the diamond's appearance.

ALTERNATELY,

If a diamond is handled to beat the weight at the finishing line in such a manner that is adverse to the diamond's face-up appearance (or deceptive) the girdle treatment can be thought of as 'cheating.'

 

[JohnQuixote]

EXAMPLES OF DIAMONDS WITH GIRDLE TREATMENTS INTENDED ONLY TO 'BEAT THE WEIGHT' AT THE FINISH LINE

Or "CHEATED" GIRDLES

(stay tuned)

 

[Lynn B]

*whew!* Unbelievable amount of work, John! Thank you so much! So far, I am following you well. And I am "staying tuned" for (and looking forward to) Part 2.

Thanks again for all your time and effort with this!

 

[Mara]

I have to read through all this but just wanted to say thanks John for taking the time to compile and post this.

I know that many newbies will be curious about this terminology and the things that are going on as stones are being cut!

 

[strmrdr]

kewl thanks John

 

[Garry H (Cut Nut)]

What do you do in your spare time John?
I would like to add a little to your excellent work here, if I may. I think it is appropriate as the terms cheated and tweaked I believe were my inventions.

Also you can change azimuth (paint and dig) and make better models in the new version of DiamCalc which you can download from here http://www.octonus.com/oct/download/diam_demo_down.phtml Use the advanced 2 tab - down the bottom.

Date: 11/15/2005 4:38:21 PM
Author: JohnQuixote

WHAT IS A CHEATED GIRDLE?

Diamonds cannot be made with cookie cutters. There will be challenges in the rough that cause some of them to undergo these weight saving techniques in a negative sense.

A cheated girdle is descriptive of one where the digging or painting was deleterious to the diamond’s appearance or proportions. Digging is usually done on diamonds where the rough dictated that the finished product would be deep. If a diamond measures 6.3 mm and there is enough room to have a 16% crown the cutter can dig the girdle from both sides (resulting in shorter lower girdle facets and longer stars) and saving the 1ct mark. The result is a smaller looking diamond with leakage around the edge. If the leakage is more than would help with contrast this was done for the sole purpose of maximizing the rough to hit a certain carat mark. Such diamonds are ‘cheated,’ and these are the diamonds to be cautious of. This treatment is visible in an ideal-scope.

Such diamonds are more common among pedestrian wares found with average dealers. Good vendors screen such diamonds from their inventory.

Further, strong labs with cut grades will penalize such diamonds. The AGS already takes negative cheating into account in the proportions portion of their 2005 assessment and penalizes them. Such diamonds will not receive a top cut grade. GIA will do so as well in their 2006 metric.
The word cheating will soon not be relevant on GIA, and is already redundant for AGS graded stones. Both labs in the past measured the girdle at the thin valley - and digging out made it possible to have say 63% total depth and a medium girdle at the valley. Now both labs will / do measure at the average of the ticker parts. This also means Fred Cuellar''s business might grind to a halt as there will be no more warped diamonds.
It is possible to cut a slightly shallow diamond and improve its performance by digging the upper girdles and or lower girdles - this can increase the angles of those facets and improve the appearance - AGS will allow this, which is good because creativity can rise to the fore.

WHAT IS A TWEAKED GIRDLE?

A tweaked girdle is one where painting or digging was not deleterious, and may have enhanced the look of the diamond. In a controlled situation where a specific design template is followed and quality controls are in place the painting technique can be used to create tight relationships between main crown and upper girdle (and main pavilion and lower girdle) angles, resulting in almost no light leakage. Premium cuts that have careful attention using these techniques are considered by many to be among the best cut diamonds in the world.

I used this term to politely try not to offend 8* originally - Peter Yantzer posted a side profile of an 8* tweaked stone way back in about 1999 on a forum called GemKey asking if anyone knew what it was. "There was a kinda hush all over the world". but many of us twigged (or is that tweaked).
I never spoke to anyone, because this was 8*''s trade secret - the shallower upper girdle facets gave their stones a certain ''look'' and distinctive marketing angle - it was only right to keep it as their little secret, although at times this was a bit of a pain as various people associated with and running 8* were regular pains in the butt - one gorilla at their trade fair stand was even physically threatening to me when I introduced the ideal-scope to them. I think it was about the time Rhino started (or stopped) selling 8* that all became revealed - or was it when Brian added the "new line"?

 

[strmrdr]

John can you post gem files for those diamonds and or post the light return stereo and the contrast tabs from the cut quality score?

 

[JohnQuixote]

Date: 11/16/2005 5:16:55 AM
Author: Garry H (Cut Nut)

What do you do in your spare time John?

I would like to add a little to your excellent work here, if I may. I think it is appropriate as the terms cheated and tweaked I believe were my inventions.

Also you can change azimuth (paint and dig) and make better models in the new version of DiamCalc which you can download from here http://www.octonus.com/oct/download/diam_demo_down.phtml Use the advanced 2 tab - down the bottom.

Thank you Garry. I appreciate your feedback, particularly how girdle measurements are being handled. It would have been polite of me to mention your coinage of terms - an oversight.

 

[JohnQuixote]

Date: 11/16/2005 8:08:11 AM
Author: strmrdr

John can you post gem files for those diamonds and or post the light return stereo and the contrast tabs from the cut quality score?

Here you go.

Dug.

 

[JohnQuixote]

Painted.

 

[strmrdr]

kewl thanks John,
cant wait to get home tonight and check them out.
Am I pathetic or what? .... dont answer that

 

[valeria101]

Date: 11/16/2005 11:49:43 AM
Author: strmrdr

kewl thanks John,
cant wait to get home tonight and check them out.
Am I pathetic or what? .... don't answer that

Whatever that is... you've got company!

Today I forgot to take that HASP key off the laptop before a presentation and everyone kept asking 'what is that'. That was easy to ward off, but...

How do you tell ?

 

[Garry H (Cut Nut)]

Ignore this post and attachment