diamond cutting questions

[beryl]

Date: 4/21/2008 7:08:44 AM
Author: Serg

Date: 4/21/2008 6:20:18 AM
Author: DiaGem

Date: 4/21/2008 6:09:04 AM
Author: Serg

Date: 4/20/2008 7:26:15 AM
Author: Garry H (Cut Nut)

Date: 4/20/2008 7:21:55 AM
Author: strmrdr

Date: 4/20/2008 7:15:40 AM
Author: DiaGem
Garry..., what is the visual difference between an excellent polish and good polish IF you dont use optic tools to check?

I have seen good graded polish on a crown facet of a EC give it a frosted look on that facet in some lighting that was eye visible.
In other stones where it was a pavilion facet when looking at it lose you could see the frosted effect but face up it was not apparent.
That is why when calling in stones I say to avoid good polish on step cuts because you don''t know what facet it is and the effect it will have.

A perfect example of my dislike for ''features'' based grading Storm.

I would prefer benefit based grading.
We will get there.
It might take decades

Quality surface( flatness and polishing quality ) is very important for brightness of Flashes , specially if distance between diamond and observer is big

Serg..., how big...?

Do you honestly claim that minor polishing lines/fissures will effect the flashes to a noticeable extent that can be differentiated by unaided vision?
Interesting..., and I would be interested to hearing more...

Diagem,

Take distance between source light and observer 3 meters. Pupil size will 0.01 degree

Take 1 ct round cut

Width of girdle pavilion facet is 400 microns
If flatness is 5 microns
Roundness of pavilion facets will 0.7 degree

Such non flat facets will spread energy from 0.01 degree to 1.5 degree. Brightness will in 100 times less

Of course it is very draft calculations for WHITE flash ( for color flash result will in 2-3 times less only) and real roundness could be much less
It is just simple example why flatness is so critical and why diamond could have much more bright flashes than CZ

Hi, Serg; good to hear from you.
Flatness is SO important to apparent brightness. The suddenness of ON-OFF reflections is a major factor in attracting the brain''s attention. This is discussed in "Seeing the Light", Chapter 7. You are familiar with this, but for the interest of readers here are some quotes:
"... the visual system only reports the exciting news, the changes that it sees."
"... the overall light level is less important than the local variations in it."
"... your brain is less interested in the overall illumination than it is in the relative light intensity."
"... an edge, where the light intensity changes rapidly from brighter to darker is more noticeable."
"... your retina ... responds only if there is a change in stimulation in time,"
The flatter the facet, the sharper the edge = the more sudden the flash.
Watch native-cut colored stones on TV marketing shows: as the stone revolves you can see the reflections movel across the facets. On Brazilian stones it is particularly interesting to watch it roll over one edge of each facet - caused by flopping each facet down onto the lap (Glenn Vargas pointed this out years ago - perhaps it has improved).

On the subject of polish smoothness, I show people the light bulb brand and data in its reflection !

It is important to note that flatness and smoothness are two different things; I also look for the light bulb data when polishing a cabochon, which is far from flat.

 

[Garry H (Cut Nut)]

Date: 4/21/2008 11:48:24 AM
Author: Serg

Date: 4/21/2008 9:06:50 AM
Author: DiaGem

Date: 4/21/2008 8:22:05 AM
Author: Garry H (Cut Nut)

DiaGem this is Drena''s diamond sitting between my keys on keyboard facing the halogen bulb directly above me - maybe 2M away. I took this just now, adjusted exposure a little.
Note you can see the little dot dot dots from the ring clip that holds the halogen in place.
The larger white zone is the out of focus table - but I made the camera focus on long distance

Get the idea?
You can read the writting on a bulb across the other side of the room.
Sergey showed me this trick in a great little hotel restaruant in Germany 3 years ago.

Ok..., and you can see these fine miniscule features only reflecting from a EX polish and not on a good one?

Or am I off-track?

take 2 diamonds with good and bad polish ( or CZ)
use white paper to see reflections from diamond facets( ETAS)
For same distance between diamond and paper , reflections from bad polishing diamond will more dull

Here are 3 CZ all facing a venetian blind on a cloudy day.
I focused on the window, held the button down 1/2 way which locks the focus and exposure on my pocket canon camera, and then turned to the stones and pushed it the rest of the way.

You can see the best polish is the stone on the left - sharpest, but convex.
The middle stone is concave (polished on a large drum) and not very well finished - especially in the middle of the stone.
The right side stone is in between and convex.

Interestingly none of this information is able to be seen with a loupe.
Sergeys free naked eye test is better for determining polish and flatness than any gemology test i ever heard of.

Folks - when you try this the diamonds / stones will be out of focus - it is very easy - but most people can not see it at first because they look at the diamond.
If you can see the the light without your specs, then you can see the light in the table without your spec''s.

 

[beryl]

Garry:
I fear that your illustration with slatted blinds may be a bad one because of the diffraction which results when light passes through a grating.

 

[Garry H (Cut Nut)]

Date: 4/21/2008 9:13:54 PM
Author: beryl
Garry:
I fear that your illustration with slatted blinds may be a bad one because of the diffraction which results when light passes through a grating.

You are pulling my leg Bruce / Beryl?
The blinds are about 2M - 7 foot away- photo from where the CZ''s sat.
It is now midday and the cluods have burned off - so the contrast is not as strong as eariler.

 

[beryl]

Garry:
I think that Serg will confirm my comment.

 

[diagem]

Date: 4/21/2008 7:24:54 PM
Author: beryl

Date: 4/21/2008 12:53:06 AM
Author: DiaGem

Date: 4/20/2008 11:37:52 PM
Author: beryl

Date: 4/19/2008 10:12:00 PM
Author:ydiamonds
Just curious and have a couple questions for the diamond cutting experts.

With all the advances in technology, why are diamonds still cut by hand? Wouldn''t a computer be able to determine the best cut for a rough, and then cut it more precisely and perfectly for a given objective?

Secondly, what factors determine how well a diamond is polished? Why can''t all diamonds have excellent polish?

Thanks.

This is the simple original question; somehow the issue got lost.
Garry has answered it well and so has Paul (Infinity). Brian Gavin (WhiteFlash) discussed this extensively - recall the long discussion 2 years ago about ''yawed'' facets.
As a cutter of colored stones I can comment to the idea of automatically-cut stones. It has been done effectively on synthetic stones with perfect preforms (waste involved). However, each natural stone should be cut to maximize its potential and to accommodate its structural idiosyncracies - no two are alike.
Garry''s mention of Princess cuts where polishing may be almost parallel to the cleavage planes, and Paul''s about gripping the stone show real familiarity with the problems.

So if for example (not realistic but lets imagine a perfect world), you could get your hands on perfect octahedron''s (crystals all clean and evenly shaped), it could have been automatically cut by machines (to all the necessary cutting stages)?

DiaGem:
Theoretically this would be possible. Because the round gem is coming from ''square'' rough, the time spent on similar facets of different orientation would vary; it would be a tricky piece of programming.
My hearing of automatic cutting was synthetic corundum in a perfectly round conical preform. Even then, if you cut them in sequence around the preform the time is longer for the first facet than for the last (machines are not perfectly rigid so the time varies slightly according to the amount of stock being removed - what is called ''sparkout'' in the precision grinding industry). It would be necessary to program for cutting facets alternately on opposite sides of the stone instead of sequentially around it. Circa 1980 I did cutting-time tests for DuPont diamond grit vs natural & GE; these factors became very apparent in trying to get consistent test results.
In the case of the synthetic corundum preforms, I also heard that they were using large cylindrical drums to produce near-flat facets, because a flat lap tends to produce convex facets if you polish too fast (polish flowing under facet). Also flat laps tend to wear concave, producing convex facets (I will only try a step-cut stone immediately after re-surfacing a flat lap because it wears concave too fast).
In reality, I think there are too many variables to make the discussion worthwhile. Brian Gavin must have much to say on this. I can imagine what Gaby Tolkowsky would say.

Bruce, thank you for the answer...

Makes complete sense!

I guess the technology is not there yet (or will never be) for what we (cutters) call "provisory cutting (a slang word

)" or the first stage cutting of the initial facet position placement on the rough material...

The technology might have been overcome if we lived in a perfect world...

, but we dont!

Thats why in reality hand Diamond cutting is not done in order of sequence...

 

[diagem]

Date: 4/21/2008 8:10:25 PM
Author: beryl

Hi, Serg; good to hear from you.
Flatness is SO important to apparent brightness. The suddenness of ON-OFF reflections is a major factor in attracting the brain''s attention. This is discussed in ''Seeing the Light'', Chapter 7. You are familiar with this, but for the interest of readers here are some quotes:
''... the visual system only reports the exciting news, the changes that it sees.''
''... the overall light level is less important than the local variations in it.''
''... your brain is less interested in the overall illumination than it is in the relative light intensity.''
''... an edge, where the light intensity changes rapidly from brighter to darker is more noticeable.''
''... your retina ... responds only if there is a change in stimulation in time,''
The flatter the facet, the sharper the edge = the more sudden the flash.
Watch native-cut colored stones on TV marketing shows: as the stone revolves you can see the reflections movel across the facets. On Brazilian stones it is particularly interesting to watch it roll over one edge of each facet - caused by flopping each facet down onto the lap (Glenn Vargas pointed this out years ago - perhaps it has improved).

On the subject of polish smoothness, I show people the light bulb brand and data in its reflection !

It is important to note that flatness and smoothness are two different things; I also look for the light bulb data when polishing a cabochon, which is far from flat.

As per my experience..., this is an issue of other minerals and not so much a Diamonds issue....

 

[Serg]

Date: 4/21/2008 8:14:08 PM
Author: Garry H (Cut Nut)

Date: 4/21/2008 11:48:24 AM
Author: Serg

Date: 4/21/2008 9:06:50 AM
Author: DiaGem

Date: 4/21/2008 8:22:05 AM
Author: Garry H (Cut Nut)

DiaGem this is Drena''s diamond sitting between my keys on keyboard facing the halogen bulb directly above me - maybe 2M away. I took this just now, adjusted exposure a little.
Note you can see the little dot dot dots from the ring clip that holds the halogen in place.
The larger white zone is the out of focus table - but I made the camera focus on long distance

Get the idea?
You can read the writting on a bulb across the other side of the room.
Sergey showed me this trick in a great little hotel restaruant in Germany 3 years ago.

Ok..., and you can see these fine miniscule features only reflecting from a EX polish and not on a good one?

Or am I off-track?

take 2 diamonds with good and bad polish ( or CZ)
use white paper to see reflections from diamond facets( ETAS)
For same distance between diamond and paper , reflections from bad polishing diamond will more dull

Here are 3 CZ all facing a venetian blind on a cloudy day.
I focused on the window, held the button down 1/2 way which locks the focus and exposure on my pocket canon camera, and then turned to the stones and pushed it the rest of the way.

You can see the best polish is the stone on the left - sharpest, but convex.
The middle stone is concave (polished on a large drum) and not very well finished - especially in the middle of the stone.
The right side stone is in between and convex.

Interestingly none of this information is able to be seen with a loupe.
Sergeys free naked eye test is better for determining polish and flatness than any gemology test i ever heard of.

Folks - when you try this the diamonds / stones will be out of focus - it is very easy - but most people can not see it at first because they look at the diamond.
If you can see the the light without your specs, then you can see the light in the table without your spec''s.

Garry,

Did you use manual mode for aperture and exposition time? ( or auto mode)
If you used auto mode, please select manual mode and repeat test and publish new photos

 

[Serg]

Date: 4/21/2008 9:13:54 PM
Author: beryl
Garry:
I fear that your illustration with slatted blinds may be a bad one because of the diffraction which results when light passes through a grating.

Hi Beryl,

I think distance between slatted blinds is so big for interference non coherent light.
( at least we never see it without diamond. Diamond is just mirror in this test)

Diffraction of course present but should be too small and same for all diamonds( do not change results, just could decrease a little bit contrast )

Garry tests is correct to check flatness level. But I am afraid what he used auto mode in photo camera. in such case we can not see correlation between flatness and brightness. ( of course brightness depends from smoothness too and from type flatness. Ideal spherical surface will not reduce brightness, it will just change distance to light source image )

 

[Serg]

re:which locks the focus and exposure on my pocket canon camera

Garry,

Did you use same settings for all 2 shots ? Did you lock aperture too?

 

[Garry H (Cut Nut)]

Date: 4/22/2008 11:48:29 AM
Author: Serg
Garry,

Did you use manual mode for aperture and exposition time? ( or auto mode)
If you used auto mode, please select manual mode and repeat test and publish new photos

I used Auto mode but with exposure and focus distance based on the light from the window.

 

[Garry H (Cut Nut)]

Date: 4/22/2008 12:15:00 PM
Author: Serg
re:which locks the focus and exposure on my pocket canon camera

Garry,

Did you use same settings for all 2 shots ? Did you lock aperture too?

The photo from the window would have been on the same setting - but that one was taken later whn clouds had gone.
I understand what you mean Sergey. It is not a problem - the cloudy blinds look just like the reflection photo.

 

[strmrdr]

That test is kewl when I take my glasses off the difference becomes hugely apparent.
I going too have too dig out my collection of signity stars and try it later myself.

 

[diagem]

Date: 4/21/2008 8:14:08 PM
Author: Garry H (Cut Nut)

Date: 4/21/2008 11:48:24 AM
Author: Serg

Date: 4/21/2008 9:06:50 AM
Author: DiaGem

Date: 4/21/2008 8:22:05 AM
Author: Garry H (Cut Nut)

DiaGem this is Drena''s diamond sitting between my keys on keyboard facing the halogen bulb directly above me - maybe 2M away. I took this just now, adjusted exposure a little.
Note you can see the little dot dot dots from the ring clip that holds the halogen in place.
The larger white zone is the out of focus table - but I made the camera focus on long distance

Get the idea?
You can read the writting on a bulb across the other side of the room.
Sergey showed me this trick in a great little hotel restaruant in Germany 3 years ago.

Ok..., and you can see these fine miniscule features only reflecting from a EX polish and not on a good one?

Or am I off-track?

take 2 diamonds with good and bad polish ( or CZ)
use white paper to see reflections from diamond facets( ETAS)
For same distance between diamond and paper , reflections from bad polishing diamond will more dull

Here are 3 CZ all facing a venetian blind on a cloudy day.
I focused on the window, held the button down 1/2 way which locks the focus and exposure on my pocket canon camera, and then turned to the stones and pushed it the rest of the way.

You can see the best polish is the stone on the left - sharpest, but convex.
The middle stone is concave (polished on a large drum) and not very well finished - especially in the middle of the stone.
The right side stone is in between and convex.

Interestingly none of this information is able to be seen with a loupe.
Sergeys free naked eye test is better for determining polish and flatness than any gemology test i ever heard of.

Folks - when you try this the diamonds / stones will be out of focus - it is very easy - but most people can not see it at first because they look at the diamond.
If you can see the the light without your specs, then you can see the light in the table without your spec''s.

Garry..., is CZ comparable to Diamond material?

 

[beryl]

DiaGem: Thanks for the comment re 'other minerals'.
My cutting experience is exclusively with 'colored stones'; I forget that this forum is specifically diamonds.
The principles are the same but because a diamond is held rigidly by a metal tang a facet does not move during polishing - as I mentioned re Brazilian 'flopping'.
On the other hand, cutting colored stones have problems diamonds do not, such as pleochroism. The worst thing that happens to a colored stone cutter is when the dop wax softens and the stone alignment changes !!! I made a special laser reflection rig to realign - just as when I recut stones.

 

[beryl]

Date: 4/21/2008 9:53:04 PM
Author: Garry H (Cut Nut)

Date: 4/21/2008 9:13:54 PM
Author: beryl
Garry:
I fear that your illustration with slatted blinds may be a bad one because of the diffraction which results when light passes through a grating.

You are pulling my leg Bruce / Beryl?
The blinds are about 2M - 7 foot away- photo from where the CZ''s sat.
It is now midday and the cluods have burned off - so the contrast is not as strong as eariler.

Of humorous interest along this line:
One day the sun was coming in too brightly through a picture window. I put up a 4x8 foot sheet of pegboard temporarily (1/8-inch holes 1-inch apart). On the far side of the room I saw hundreds of pictures of a house 100 yards (meters) away! It was acting like a multiple pinhole camera ! Despite the large hole size, the images were remarkably distinct; each was offset from the others.

 

[Garry H (Cut Nut)]

Date: 4/22/2008 7:04:02 PM
Author: beryl

Date: 4/21/2008 9:53:04 PM
Author: Garry H (Cut Nut)

Date: 4/21/2008 9:13:54 PM
Author: beryl
Garry:
I fear that your illustration with slatted blinds may be a bad one because of the diffraction which results when light passes through a grating.

You are pulling my leg Bruce / Beryl?
The blinds are about 2M - 7 foot away- photo from where the CZ''s sat.
It is now midday and the cluods have burned off - so the contrast is not as strong as eariler.

Of humorous interest along this line:
One day the sun was coming in too brightly through a picture window. I put up a 4x8 foot sheet of pegboard temporarily (1/8-inch holes 1-inch apart). On the far side of the room I saw hundreds of pictures of a house 100 yards (meters) away! It was acting like a multiple pinhole camera ! Despite the large hole size, the images were remarkably distinct; each was offset from the others.

Here is the same photo taken when it is cloudy - camera on auto

 

[Garry H (Cut Nut)]

Date: 4/22/2008 7:04:02 PM
Author: beryl
Of humorous interest along this line:
One day the sun was coming in too brightly through a picture window. I put up a 4x8 foot sheet of pegboard temporarily (1/8-inch holes 1-inch apart). On the far side of the room I saw hundreds of pictures of a house 100 yards (meters) away! It was acting like a multiple pinhole camera ! Despite the large hole size, the images were remarkably distinct; each was offset from the others.

You should have taken a photo!!!!