Real of Synthetic Sapphire

[ChunkyCushionLover]

WOW the cutting is just dreadful, especially on the pink one. And especially on the blue one too. It feels weird though, like it was done by a native cutter who had seen some better cuts and was trying to emulate them, or like it was done by a "western" cutter trying to make it look like a native cut of an unfamiliar sophisticated cut.
Or it could be that the global culture is transitioning and the term "native cuts" (as I used it) wont denote the freehand cutting by highly exploited slightly educated children native to developing countries for much longer. If we choose that interpretation then we might propose that this could be an example of the transition taking place. Still then we would be left wondering if the stones that were cut are natural or synthetic.

Vapid,

I am very interested in learning what makes a well cut colored stone.
What you are seeing from body side views that indicates a poor cut and how this attempted to emulate better cuts.
If you have any suggested links or books I'd be interested in reading them.

I understand this basic concept shown below but probably not much beyond it or how well it can be applied.

 

[ChunkyCushionLover]

WOW the cutting is just dreadful, especially on the pink one. And especially on the blue one too. It feels weird though, like it was done by a native cutter who had seen some better cuts and was trying to emulate them, or like it was done by a "western" cutter trying to make it look like a native cut of an unfamiliar sophisticated cut.
Or it could be that the global culture is transitioning and the term "native cuts" (as I used it) wont denote the freehand cutting by highly exploited slightly educated children native to developing countries for much longer. If we choose that interpretation then we might propose that this could be an example of the transition taking place. Still then we would be left wondering if the stones that were cut are natural or synthetic.

Vapid,

I am very interested in learning what makes a well cut colored stone.
What you are seeing from body side views that indicates a poor cut and how this attempted to emulate better cuts?
If you have any suggested links or books I'd be interested in reading them.

I understand this basic concept shown below but probably not much beyond it or how well it can be applied.

 

[chrono]

ChunkyCushion,
In general, a well coloured stone means that it is symmetrical, shows no windows (neither too deep nor too shallow), little to no extinction and brings out the best colour & characteristics in the stone. Unfortunately, with each gemstone type having different reflective index and other properties to be taken into consideration, there is no cut and dried angles to follow for the perfect cut that will fit all coloured gemstones.

 

[CharmyPoo]

I completely forgotten about these stones! This thread prompted me to actually look for them again since they weren't in my gem box. I never did check them out - just assumed they weren't mined ... and forgot to return them.

 

[ChunkyCushionLover]

ChunkyCushion,
In general, a well coloured stone means that it is symmetrical, shows no windows (neither too deep nor too shallow), little to no extinction and brings out the best colour & characteristics in the stone. Unfortunately, with each gemstone type having different reflective index and other properties to be taken into consideration, there is no cut and dried angles to follow for the perfect cut that will fit all coloured gemstones.

Thanks Chrono for the response. I hoping for more detail considering comments are often made by cutters and experts based on the photographs.

 

[chrono]

I’m not sure exactly how much detail you are looking for. The link below is a low level starting point because I’m not sure how familiar you are at recognizing cut issues from photographs (extinction, off centered culet, windowing, etc)
http://www.palagems.com/quality_4cs.htm

 

[ChunkyCushionLover]

I’m not sure exactly how much detail you are looking for. The link below is a low level starting point because I’m not sure how familiar you are at recognizing cut issues from photographs (extinction, off centered culet, windowing, etc)
http://www.palagems.com/quality_4cs.htm

Thanks Chrono I've seen that nice primer before.

I've already been through this http://www.ruby-sapphire.com/brilliance_windows_extinction.htm as sapphire is my interest.
I ordered the book to get more information was just wondering if you had some more links.

This thread brought a couple questions to mind:

1) Other than to save weight why would a cutter intentionally choose to cut the pavillion using three different angles like in Charmy's blue sapphire. One clearly being too shallow near the culet and another being too steep near the girdle. Why wouldn't they use a more ideal single pavilion main angle of around 42 degrees. Does color retention factor into this?

2) A cutter I respect told me that in lower RI stones(as compared to diamond) like sapphire, physical facets aren't broken up as much into virtual facets. I was wondering why this is? (I can kind of guess it has to do with the lower intensity of light rays that are capable of multiple internal reflections off the pavilion and shorter average ray paths but just guessing)

 

[Largosmom]

I don't envy colored stone cutters their math skills...or perhaps there are tables of information that they use to calculate the right angels for the cut. I suppose software can help, but experience is probably the best teacher...kinda like a pool shark knowing instinctively what angle to hit the ball at after years of practice. With stones, you get a different pool table and different angles each game! I hope I don't have the technical information below wrong...but I can understand and explain it this way.

The refractive index or RI is a measure of the bending of light when it passes into the stone (or other substance, like water). You might remember looking at pictures of an object in a glass of water...like a pencil. The pencil is straight, but when you put it into the liquid, it looks bent...because the water has an RI different from air. It's actually a measure of the speed of light...but the result is what our eyes see...a different angle due to the different light speed. Different species of gemstone such as corundum (sapphire, ruby, etc.), or quartz (amethyst, citrine, etc.) have different RIs due their physical and/or chemical properties. If you had two clear stones of different species and could hold them over that pencil or over a straight line, you might notice that the angle of the bend is different in each those two clear stones. That is because their RI is different.

Light bends when it passes into the stone...and that "refraction" property is used by cutters to reflect the light back to your eyes. If the angles are wrong for that stone's RI, then the light doesn't bounce back into your eye, it might go out through the bottom of the stone (creating a window), or it might leak out the sides of the stone. Lapidaries learn how to adjust the angles for a particular cut in order to bounce the light back up out the top or table of the stone so that you can see the angles and reflections. If you think about it, a "shallow" stone, doesn't have proper angles in the bottom or culet area to properly reflect the light back out the top...the angles are "shallow" and thus the light goes out the bottom and doesn't reflect back up so that we can see the surface of the bottom of the stone. If you had a tiny flashlight and shone the beam through a windowed stone, you would see the reflection somewhere underneath it. With a properly cut stone, with angles appropriate to the stone's RI, the light comes back out the top. Note...DONT try this with a laser pointer...a properly cut stone will bounce that back into your eyes and that is dangerous and can damage your eyes!

Some stones actually make a double reflection due to their properties...so we see even more light when we look into them, for each beam that goes in, we get two out! Light ray BOGO. Of course there are several other properties of the stone that can effect how it should be cut, like the angles of the crystal, and placement of colors in the stone...they aren't all evenly colored throughout, after all. They have blobs or zones of stronger or weaker color and a good lapidary can make that look beautiful, and a bad one can make it look horrible. I think that proper angles are somewhat a range rather than a precise measure, and the lapidary uses their experience and training to know how to maximize an individual stone's potential for color or light play and it's a game of give and take...lots of brilliance may mean less color, and vice versa.

So, I think that people who cut colored gemstones have a tougher job than diamond cutters. They have to know how to work with so many more stones...oy all those angles!

By the way, I found the 3d pictures rotatable graphs of the stone facets on Natural Sapphire's site very helpful to me to visualize why I was seeing things in their photos...an off-center culet on the 3d view gave a slightly off-center image in the stone.

I am finding I cannot handle asymmetry very well. My eyes much prefer a precision cut even if sometimes I cannot initially explain why when I look at a stone or a photo. When I look at the cut through a loupe, I can see more why my eye loves a particular stone...it's cut well! If I cannot see it much, I can live with it, but in some stones that symmetry is way off and my brain cannot handle it.

Laura

 

[chrono]

I believe there is a thread in the past by a couple precision cutters on how they use a special software which does all the necessary calculations to determine the optimal angle for each stone. Of course, it takes many things into consideration which still requires the lapidary to make his/her best educated assumptions. I’m quite sure it is in one of the hotly debated native vs precision cut threads.

LargosMom,
That is a superb explanation on how RI is taken into consideration during the cutting/planning process. It is clear yet easy to understand.

 

[ChunkyCushionLover]

I believe there is a thread in the past by a couple precision cutters on how they use a special software which does all the necessary calculations to determine the optimal angle for each stone. Of course, it takes many things into consideration which still requires the lapidary to make his/her best educated assumptions. I’m quite sure it is in one of the hotly debated native vs precision cut threads.

LargosMom,
That is a superb explanation on how RI is taken into consideration during the cutting/planning process. It is clear yet easy to understand.

Please link me to this thread Chrono as much as I try the search is difficult to use for me. Largosmom good beginning I aspire to go into greater depth though.

 

[Largosmom]

Gosh, thanks! I've got lots to learn.

 

[chrono]

CCL,
I’d love to help you with the link but the current PS search function is horrible and I cannot find it either.

 

[Arkteia]

Re:

Date: 5/24/2010 3:29:36 PM
Author: LovingDiamonds

Date: 5/24/2010 3:25:59 PM

Author: CharmyPoo

Date: 5/24/2010 3:23:42 PM

Author: LovingDiamonds

Two 4ct natural sapphires without a cert both strongly coloured and fairly inclusion free? My gut feeling is that they''re BE diffused at best. Sapphires? Not sure. What are they registering on the gem tester? Are they registering as Corrundum?

Yeah .. showing up in the ''Ruby, Sapphire'' bar.

Mmmm. I have a synthetic that does this also. However it didn''t have the same RI. Have you got the equipment to do a quick RI test? If not, is there a jeweller near you who can? That''ll give you a much better idea.


If it has the same RI as corrundum then the chances are we''re back to thinking about diffusion.

Synthetic corundum IS corundum. It will always show the same RI as natural corundum and will have the same properties overall because it''s just a lab-created version of the material.

Magnification and practice are the best ways to tell them apart, but you''re best off using a lab.

Lisa, doesn't synthetic corundum have curved growth lines?

And about RI... I learned the hard way. A while ago I bought a cheapo spessartite on ebay and it happened to be colored cubic zirconia! The RI of cubic zirconia starts at 1.8 up to 2.17; the RI of spessartite is about 1.88. Easy to confuse? Yes. A good learning experience for $ 5 + shipping from Thailand.

 

[coati]

Lisa, doesn't synthetic corundum have curved growth lines?

(Did not read the entire thread, so I may be repeating info here)

Different types of synthetic corundum have different inclusions and growth markings.

Flame fusion synthetic corundum has curved color bands, as well as gas bubbles that may occur in lines that look like needles at first glance. Flame fusion synthetics are typically the easiest to identify, because the color is usually too extreme, but I have seen treated flame fusion synthetics that might trick your average consumer. There is also flux grown and hydrothermal synthetic corundum, and these two types are trickier to id. Flux grown synthetics may contain "wispy veils" that resemble fingerprints, if one is not careful. They may also contain platinum platelets or platinum needle like inclusions that may resemble natural inclusions without proper magnification. Flux grown synthetics can resemble heat treated natural corundum-treated Mong Hsu ruby is a good example of this. Hydrothermal synthetics often have a "chevron" looking growth pattern and fingerprint inclusions that look natural.

It is best to send stones to a lab for proper identification. (If you've paid a certain amount, and it is worth your while, of course) Synthetics are just too close in some situations. I've seen synthetics with mediocre coloration as well, so not-so-great color is not always an indicator of natural. Experienced tradespeople and gemologists have been duped, so a reputable lab is generally the best bet.

 

[ChunkyCushionLover]

Lisa, doesn't synthetic corundum have curved growth lines?

(Did not read the entire thread, so I may be repeating info here)

Different types of synthetic corundum have different inclusions and growth markings.

Flame fusion synthetic corundum has curved color bands, as well as gas bubbles that may occur in lines that look like needles at first glance. Flame fusion synthetics are typically the easiest to identify, because the color is usually too extreme, but I have seen treated flame fusion synthetics that might trick your average consumer. There is also flux grown and hydrothermal synthetic corundum, and these two types are trickier to id. Flux grown synthetics may contain "wispy veils" that resemble fingerprints, if one is not careful. They may also contain platinum platelets or platinum needle like inclusions that may resemble natural inclusions without proper magnification. Flux grown synthetics can resemble heat treated natural corundum-treated Mong Hsu ruby is a good example of this. Hydrothermal synthetics often have a "chevron" looking growth pattern and fingerprint inclusions that look natural.

It is best to send stones to a lab for proper identification. (If you've paid a certain amount, and it is worth your while, of course) Synthetics are just too close in some situations. I've seen synthetics with mediocre coloration as well, so not-so-great color is not always an indicator of natural. Experienced tradespeople and gemologists have been duped, so a reputable lab is generally the best bet.

Erika,

Thank-you for the informative post. I am very interested in that above could you please expand on what you mean by "too extreme" in terms of Hue, Tone, and Saturation. As I understand FF synthetic rough is darkest in the rind and coloreless in the centre how does that translate to too extreme in a cut gem?

 

[ChunkyCushionLover]

Gosh, thanks! I've got lots to learn.

I'm picking up Richard Hughes book Ruby and Sapphire today, hopefully this can shed some light.