flr and color grading in GIA or AGS

[Karl_K]

Date: 4/7/2010 11:16:36 AM
Author: michaelgem

Date: 4/7/2010 1:11:07 AM

Author: Karl_K

Date: 4/6/2010 2:39:36 AM

Author: kenny

I wonder if it works in both directions but if sun is allowed to beat on the wrong side it loses its effectiveness after some time.


Or maybe, like you said Garry, there is some coating on one side.



There must be some reason they instruct us to have the light source face a certain side.

Lexan® XL sheet has a coextruded UV resistant surface treatment applied to one side to protect the Lexan against UV degradation (yellowing)


Bare lexan by itself blocks some UV ranges better than others.

Bare lexan is about 85% effective on short wave UV but long wave uv its less than 70% at the most, some sources say less than 25% is blocked. My guess is it depends on the wave length with near visible having little reduction.

The coated ones like the XL are rated at 92% for both long and short wave UV.

The very high end coated lexan as well as the best grades of tempered coated framing glass is rated at 99% for both long and short wave.

Karl,

This is new information that I was not aware of. It makes sense that if the primary UV filtering is accomplished by a coextruded surface treatment, that surface should face the sun to protect the Lexan, which does slowly yellow with UV exposure over time.

I am interested in your findings, as all the information I have come across so far indicates that polycarbonate plastics (Lexan and Makrolan) are opaque to UV from 385nm down. Lexan and Makrolan polycarbonate filters were used in the study when experimenting with the removal of UV from the various lighting used in grading. The attached filter curve shows polycarbonate plastic is particularly suited to removing LWUV without significant or noticeable effect on the visible light spectrum.


Using the same Home Depot Lexan pictured by Kenny, at a two inch distance in the GIA DiamondLite I measured a drop in UV from 170 uW/cm2 to a negligible amount around 1 uW/cm2. Tom Tashey, Professional Gem Sciences, over ten years ago first found a much thinner sheet of Makrolan polycarbonate effectively removed the UV in the DiamondLite allowing a diamond’s true color to be seen and graded.


Although not stated by the manufacturer, perhaps the published curves are the net filter characteristics of the polycarbonate plus coating. I''d like to know. Eye doctors state that polycarbonate lens in sun glasses and prescription clear lens effectively remove all harmful UVA and UVB.


Michael D Cowing

The one pictured by Kenny is coated.
The biggest issue is that lexan is made in dozens of varieties both branded and generic.
For example:
Lexan
Lexan mr10
Lexan xl
Lexan slx series Lexan HP series
Lexan exl series
Then there is specialized versions like the ones for eyeglasses.
http://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/ProductLine/lexan.html#


Glasses are generally made of cr39 and various polycarbonate products all of which have different UV blocking capabilities.
cr39 is highly resistant to some wave lengths of UV but it is also coated in the premium products to raise it to 99.7% of all harmful UV.
Here are the lexan versions used for eyeglasses, again you see varying amounts of UV blocking:

http://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/PerformanceProperties/opticalquality_lexan.html

 

[michaelgem]

Date: 4/7/2010 10:39:28 AM
Author: Karl_K
Well said Michael.

Another problem is the only world wide repeatable method with any degree of accuracy is to block it to 0.
Bulbs will have a huge variation in UV production and it will change as they age even if one could select bulbs that all were in a small range at the start.

Absolutely, this is a very important point.

Representative example measurements of blue sky, northern daylight were 500-600 uW/cm2. The UV rapidly increases as the vicinity of the sun is approached. Near but not including direct sun, the reading quickly exceeded the meter range of 1999 uW/cm2 . Hazy overcast and cloudy skies absorb UV and were observed to drop these figures more than a factor of two. On an overcast day readings of 800 - 1100 uW/cm2 were obtained. This large amount of UV in natural daylight and its high degree of variability makes it clear why this illumination is unworkable for consistent grading of fluorescent diamonds.

Discussions of lighting standards for colour grading are often concerned with the variability of daylight''s colour temperature. The standard lighting (D65) is a colour temperature of 6500K. However, a wide range of colour temperatures from the warmer 4100K "cool white" fluorescent to the 6500K of daylight fluorescent lighting was found satisfactory for accurate colour determination (Cowing,200.

The more problematic, often unknown, and thus neglected consideration for accurate and consistant colour grading is the highly variable stimulation of blue fluorescense by the highly variable amounts of UV and visible-violet" from open sky daylight, from north facing windows, and from the unfiltered fluorescent tube lighting used in diamond colour grading.

The F15T8VLX fluorescent tubes of the DiamondDock or their equivalent is the standard lighting spelled out in the basic technical specifications for D-to-Z colour grading. (G&G, winter 200. The shelf of the DiamondDock enforces a 7 inch grading distance from lamps to grading tray. The exact distance is important to establish, because it in essence defines the chosen "standard" amount of UV and VV. GIA researcher Ronald Geurtz (pers. com.) explained: "With the distance between shelf and the center of the bulb at 8-10 inches, the distance between the diamond and the surface of the bulb is around 7 inches."

He notes an important point about this current lighting standard. The allowed range of light intensity of 2000-4500lux at the surface of the grading tray means the "standard" amount of UV and VV is also allowed to vary over the same 2.5 times range.

Such an allowed large variation of UV and VV defeats standardization of the amount of fluorescence stimulation of blue fluorescent diamonds guaranteeing inconsistent grading results that are higher than the diamond''s true color unenhanced by fluorescence.

Michael D Cowing

 

[Karl_K]

Date: 4/7/2010 11:24:19 AM
Author: kenny
Might concern for this over-grading have something to do with the ''discount'' we see for diamonds with a lot of fluor?

yes, and the the history of fraud surrounding it "blue/white"

 

[Garry H (Cut Nut)]

Date: 4/7/2010 11:50:17 AM
Author: Karl_K


The one pictured by Kenny is coated.
The biggest issue is that lexan is made in dozens of varieties both branded and generic.
For example:
Lexan
Lexan mr10
Lexan xl
Lexan slx series <-- this is what you want to use.
Lexan HP series
Lexan exl series
Then there is specialized versions like the ones for eyeglasses.
http://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/ProductLine/lexan.html#


Glasses are generally made of cr39 and various polycarbonate products all of which have different UV blocking capabilities.
cr39 is highly resistant to some wave lengths of UV but it is also coated in the premium products to raise it to 99.7% of all harmful UV.
Here are the lexan versions used for eyeglasses, again you see varying amounts of UV blocking:

http://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/PerformanceProperties/opticalquality_lexan.html

Thanks Karl,
I will try to track some down here in Oz.

Kenny have you read the fluoro article in the journal section?

 

[Karl_K]

Date: 4/7/2010 5:49:47 PM
Author: Garry H (Cut Nut)
Thanks Karl,

I will try to track some down here in Oz.


Kenny have you read the fluoro article in the journal section?

Here is the contact info for the OZ division.
They should be able to tell you who to buy it from, also ask them for a recommendation on which to use:
Australia

* Brandon Office Park
Building 4, Level 1
530 Springvale Road
Glen Waverley Victoria 3150
Tollfree (domestic): 1-800-649-112
Overseas phone: +613-8561-3600
* [email protected]

 

[Garry H (Cut Nut)]

Thanks Karl,
Ordered a huge sheet chopped up into 10cm x 4cm pieces for about $300

 

[kenny]

Date: 4/7/2010 5:49:47 PM
Author: Garry H (Cut Nut)
Kenny have you read the fluoro article in the journal section?

No, but thanks for pointing me to it.

I will.

 

[Karl_K]

Date: 4/8/2010 5:03:41 AM
Author: Garry H (Cut Nut)
Thanks Karl,

Ordered a huge sheet chopped up into 10cm x 4cm pieces for about $300

Welcome, which did they recommend as being best for blocking UV?

 

[Garry H (Cut Nut)]

Date: 4/8/2010 11:00:45 AM
Author: Karl_K

Date: 4/8/2010 5:03:41 AM
Author: Garry H (Cut Nut)
Thanks Karl,

Ordered a huge sheet chopped up into 10cm x 4cm pieces for about $300

Welcome, which did they recommend as being best for blocking UV?

I took your recomendation and did not ask Karl - the slx

 

[Karl_K]

Date: 4/8/2010 3:35:36 PM
Author: Garry H (Cut Nut)

Date: 4/8/2010 11:00:45 AM

Author: Karl_K

Date: 4/8/2010 5:03:41 AM

Author: Garry H (Cut Nut)

Thanks Karl,


Ordered a huge sheet chopped up into 10cm x 4cm pieces for about $300

Welcome, which did they recommend as being best for blocking UV?

I took your recomendation and did not ask Karl - the slx

ah ok
That is the one that seems to get recommended the most for it online on various forum and the specs look good.
How much they block isn''t something they rate them for however other than optical lexan so it would have been interesting what they say.
The uv blocking is to protect the material itself, that it protects stuff behind it is an added bonus and it is rated the highest for uv exposure protection.

 

[michaelgem]

Date: 4/7/2010 11:50:17 AM
Author: Karl_K

Date: 4/7/2010 11:16:36 AM
Author: michaelgem

Date: 4/7/2010 1:11:07 AM

Author: Karl_K

Date: 4/6/2010 2:39:36 AM

Author: kenny

I wonder if it works in both directions but if sun is allowed to beat on the wrong side it loses its effectiveness after some time.


Or maybe, like you said Garry, there is some coating on one side.



There must be some reason they instruct us to have the light source face a certain side.

Lexan® XL sheet has a coextruded UV resistant surface treatment applied to one side to protect the Lexan against UV degradation (yellowing)


Bare lexan by itself blocks some UV ranges better than others.

Bare lexan is about 85% effective on short wave UV but long wave uv its less than 70% at the most, some sources say less than 25% is blocked. My guess is it depends on the wave length with near visible having little reduction.

The coated ones like the XL are rated at 92% for both long and short wave UV.

The very high end coated lexan as well as the best grades of tempered coated framing glass is rated at 99% for both long and short wave.

Karl,

This is new information that I was not aware of. It makes sense that if the primary UV filtering is accomplished by a coextruded surface treatment, that surface should face the sun to protect the Lexan, which does slowly yellow with UV exposure over time.

I am interested in your findings, as all the information I have come across so far indicates that polycarbonate plastics (Lexan and Makrolan) are opaque to UV from 385nm down. Lexan and Makrolan polycarbonate filters were used in the study when experimenting with the removal of UV from the various lighting used in grading. The attached filter curve shows polycarbonate plastic is particularly suited to removing LWUV without significant or noticeable effect on the visible light spectrum.


Using the same Home Depot Lexan pictured by Kenny, at a two inch distance in the GIA DiamondLite I measured a drop in UV from 170 uW/cm2 to a negligible amount around 1 uW/cm2. Tom Tashey, Professional Gem Sciences, over ten years ago first found a much thinner sheet of Makrolan polycarbonate effectively removed the UV in the DiamondLite allowing a diamond’s true color to be seen and graded.


Although not stated by the manufacturer, perhaps the published curves are the net filter characteristics of the polycarbonate plus coating. I''d like to know. Eye doctors state that polycarbonate lens in sun glasses and prescription clear lens effectively remove all harmful UVA and UVB.


Michael D Cowing

The one pictured by Kenny is coated.
The biggest issue is that lexan is made in dozens of varieties both branded and generic.
For example:
Lexan
Lexan mr10
Lexan xl
Lexan slx series Lexan HP series
Lexan exl series
Then there is specialized versions like the ones for eyeglasses.
http://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/ProductLine/lexan.html#


Glasses are generally made of cr39 and various polycarbonate products all of which have different UV blocking capabilities.
cr39 is highly resistant to some wave lengths of UV but it is also coated in the premium products to raise it to 99.7% of all harmful UV.
Here are the lexan versions used for eyeglasses, again you see varying amounts of UV blocking:

http://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/PerformanceProperties/opticalquality_lexan.html

Karl,

This is very helpful. When I look over the specs on their website of the various series, I have not been able to find the spectral response curves to see which wavelengths are removed and by how much. Have you found any curves like the one I posted? These curves are the key info needed, especially for the Home Depot Lexan most of us are using or have used. All I have is the posted curve that I have been assuming is accurate.

Michael

 

[Karl_K]

Date: 4/8/2010 8:47:41 PM
Author: michaelgem
Karl,


This is very helpful. When I look over the specs on their website of the various series, I have not been able to find the spectral response curves to see which wavelengths are removed and by how much. Have you found any curves like the one I posted? These curves are the key info needed, especially for the Home Depot Lexan most of us are using or have used. All I have is the posted curve that I have been assuming is accurate.


Michael

No I haven't found a source for curves like that for all the different types.

 

[Garry H (Cut Nut)]

Date: 4/7/2010 6:33:48 PM
Author: Karl_K

Date: 4/7/2010 5:49:47 PM
Author: Garry H (Cut Nut)
Thanks Karl,

I will try to track some down here in Oz.


Kenny have you read the fluoro article in the journal section?

Here is the contact info for the OZ division.
They should be able to tell you who to buy it from, also ask them for a recommendation on which to use:
Australia

* Brandon Office Park
Building 4, Level 1
530 Springvale Road
Glen Waverley Victoria 3150
Tollfree (domestic): 1-800-649-112
Overseas phone: +613-8561-3600
* [email protected]

Thanks Karl,
It arrived after being routed to sub, sub, sub agents.

The slx is a little better than the generic Lexan - I think 2 sheets of 3mm taped together is probably adequate to screen out over 90% of the fluoro effect.
I tried 3 different little LED UV lights, and used the one that had the strongest blue effect on the diamond.
The slx is slightly greyer, which does not help - but 2x 3mm is better at screening out than 2x4.5mm and the greyness is not that different.we only need.
I found no difference between which side I used.

 

[Karl_K]

Garry looking at the pics I''m having a hard time separating out the violet light and the effects of the UV.
You need to find a 380nm led rather than the more common and cheaper 400nm.

 

[Garry H (Cut Nut)]

Date: 4/16/2010 2:36:09 AM
Author: Karl_K
Garry looking at the pics I''m having a hard time separating out the violet light and the effects of the UV.
You need to find a 380nm led rather than the more common and cheaper 400nm.

And where (oh great source of buying strange things) would I get one?

 

[Karl_K]

quality 380nm led http://www.weisd.com/store2/ntesemi/NTE30122.php $6.25

typical 400nm 50 cents http://www.quality-deal.com/osCommerce/product_info.php?products_id=179

 

[Karl_K]

Here is the oz distributor for nte
Colourview Electronics
5 Commerce Street
PO Box 228
Salisbury, QLD. 4107 Australia
e-mail: [email protected]

phone: 07-3275-3188

 

[Serg]

Garry,
you need real big gun , take deep UV leds

as

http://www.alibaba.com/product/sodkorea-11543133-10975256/Deep_UV_Led_Lamp.html
- Wavelength : 255nm, 265nm, 280nm,
310nm, 340nm
- Po : upto 650 micro watt at 20mA
- Package type : TO-18 with Flat lens,
TO-39 with Flat/Hemi/Ball lens

and

http://www.alibaba.com/product/sodkorea-101093684-10975256/Power_UV_LED_Lamps.html

365nm Power UV LEDs : 40-75mW
375nm Power UV LEDs : 120-230mW

 

[Garry H (Cut Nut)]

Date: 4/16/2010 2:52:42 AM
Author: Serg
Garry,
you need real big gun , take deep UV leds

as

http://www.alibaba.com/product/sodkorea-11543133-10975256/Deep_UV_Led_Lamp.html
- Wavelength : 255nm, 265nm, 280nm,
310nm, 340nm
- Po : upto 650 micro watt at 20mA
- Package type : TO-18 with Flat lens,
TO-39 with Flat/Hemi/Ball lens

and

http://www.alibaba.com/product/sodkorea-101093684-10975256/Power_UV_LED_Lamps.html

365nm Power UV LEDs : 40-75mW
375nm Power UV LEDs : 120-230mW

Dear sergey, I filled out the request, but probably they will not reply for such a small order. Which actual models do you suggest - there are very many there

 

[Serg]

Date: 4/16/2010 9:23:29 PM
Author: Garry H (Cut Nut)

Date: 4/16/2010 2:52:42 AM

Author: Serg

Garry,

you need real big gun , take deep UV leds


as


http://www.alibaba.com/product/sodkorea-11543133-10975256/Deep_UV_Led_Lamp.html

- Wavelength : 255nm, 265nm, 280nm,

310nm, 340nm

- Po : upto 650 micro watt at 20mA

- Package type : TO-18 with Flat lens,

TO-39 with Flat/Hemi/Ball lens


and


http://www.alibaba.com/product/sodkorea-101093684-10975256/Power_UV_LED_Lamps.html


365nm Power UV LEDs : 40-75mW

375nm Power UV LEDs : 120-230mW

Dear sergey, I filled out the request, but probably they will not reply for such a small order. Which actual models do you suggest - there are very many there

Garry, you need full range waves :255nm, 265nm, 280nm, 310nm, 340nm, 356nm(75mW for example), 375nm( 120mW)

 

[Garry H (Cut Nut)]

Date: 4/17/2010 2:29:22 AM
Author: Serg

Date: 4/16/2010 9:23:29 PM
Author: Garry H (Cut Nut)

Date: 4/16/2010 2:52:42 AM

Author: Serg

Garry,

you need real big gun , take deep UV leds


as


http://www.alibaba.com/product/sodkorea-11543133-10975256/Deep_UV_Led_Lamp.html

- Wavelength : 255nm, 265nm, 280nm,

310nm, 340nm

- Po : upto 650 micro watt at 20mA

- Package type : TO-18 with Flat lens,

TO-39 with Flat/Hemi/Ball lens


and


http://www.alibaba.com/product/sodkorea-101093684-10975256/Power_UV_LED_Lamps.html


365nm Power UV LEDs : 40-75mW

375nm Power UV LEDs : 120-230mW

Dear sergey, I filled out the request, but probably they will not reply for such a small order. Which actual models do you suggest - there are very many there

Garry, you need full range waves :255nm, 265nm, 280nm, 310nm, 340nm, 356nm(75mW for example), 375nm( 120mW)

Dear Sergey,
I do not have the resources to fully conduct this test.
I can not even notice much difference in this very strong blue fluorescent diamond in the other photo''s whan I color grade it with and without Lexan.
The camera could not capture any drop in color with and without.
With my eye I think the stone dropped from a high F to a high G.

My current feeling is that the 4 grade reductions in color reported by Michael Cowing and the task force studying this phenonamon have recorded may be exceptions. I have yet to see more than 2 grades fall when UV is screened out using the 2 Lexan products I have tested. Even a one grade drop in color when UV is screened out is unusual.

My conclusion -

When seen face up in shaded daylight light it is easier to detect small differences in color grade than it is in common indoor lighting environments. In most low Ultra Violet indoor environments it is unlikely that any diamond graded in the GIA environment, fluorescent or not, of say 2 carat +G color or 1/2ct H could be seen to be more tinted in a face up side by side comparison with a non fluorescent D colored diamond. Where-as a G or better color diamond as graded by the GIA system that has Very Strong blue fluorescence will definitely appear to be less coloured in shaded daylight, or may even be percieved to be a ''better'' color than a non-fluorescent D.