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flr and color grading in GIA or AGS

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feidudu

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Hi ,guys . I have heard a strange theory today . it said that the stone''s color grade will be decreased because of it''s str blue flr when certified by GIA or AGS.It means when u buy a I color stone with str b flr with GIA OR AGS ,Its actually color grade maybe H or even G .Is this true ? although I think it is impossible since str b flr will decrease the price . I should ask for accuracy .
thanks for replying
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kenny

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I believe this has been discussed here if you want to do a search... something about controversy over the UV content of the light source GIA uses when graded D-Z stones for color.
 

feidudu

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Date: 4/3/2010 2:26:51 PM
Author: kenny
I believe this has been discussed here if you want to do a search... something about controversy over the UV content of the light source GIA uses when graded D-Z stones for color.
Hi, kenny. thank you for replying .I have searched but too much theory ...I am confused ... can u tell me the conclusion ?
 

LD

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I don''t have the answer I''m afraid but I can tell you that I have a GIA, I colour pear cut diamond that has strong blue fluor. It is exceptionally white and there''s only one particular lighting condition that I see any warmth at all (and even then it''s a struggle). If I put it next to a G (GIA) diamond, there''s hardly any difference, if at all. So I''m guessing that there is some substance to what you''ve heard.
 

Tom Gelb

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Date: 4/3/2010 2:23:29 PM
Author:feidudu
Hi ,guys . I have heard a strange theory today . it said that the stone''s color grade will be decreased because of it''s str blue flr when certified by GIA or AGS.It means when u buy a I color stone with str b flr with GIA OR AGS ,Its actually color grade maybe H or even G .Is this true ? although I think it is impossible since str b flr will decrease the price . I should ask for accuracy .

thanks for replying
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in general blue cancels out yellow when viewing a diamond. Since the vast majority of d-z diamonds have some yellow the prevailing theory is that a strong blue fluorescence will make a diamond look white/higher grade if the light contains some uv. My understanding is that he light the GIA currently uses has some uv content (it is supposed to mimic daylight, which contains uv light also) so a diamond with a strong fluor may get a better grade than if it had no fluor. The strength of the fluor is not taken into account when color grading a the GIA so a strong blue would not get a lower grade because of it.

There is still a lot of controversy surrounding what the "actual" color maybe, but I thinkthis summarizes the current situation as it now stands.

Good luck.
 

Garry H (Cut Nut)

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Hi all,
AGS also uses GIA''s Diamond Dock for color grading and the lamps do have some UV.
There is a US study group looking into it. They use a sheet of Lexan plastic to screen out the UV and they have reported ST and VST stones dropping 4 grades. I carried and used 2x4.5mm sheets with me and looked/color graded a few hundred stones on my last trip, and although the tubes GIA use may be different, I seldom had a drop of more than 1 grade in color, which in my opinion is more than made up for by the rise of often +2 apparent grades in shaded daylight.
In light abset much UV it is usually very hard to see color differences anyway.

Here is my article on fluoro and its history:
http://journal.pricescope.com/Articles/73/1/Blue-Fluorescence-in-Diamonds.aspx

Also if you search MichaelGem (aka Michael Cowing) you will see his opinion on this board.
 

Rockdiamond

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In my experience, GIA's lights must have a good deal of UV based on their grading of Fancy Colored Yellow Diamonds with Fluorescence, which are graded face up.
When you look at SB stones graded Fancy Yellow in normal indoor lighting , containing less UV, a fair percentage look like Fancy Intense Yellow. This is similar to I colors that face up like G colors
It seems to me that GIA's grading through the pavilion eliminates a lot of the color change effect as compared to face up, and this is reflected in the grade.
 

Tom Gelb

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HI David,

While I am not an expert in light and absorption, I can say that the lights used by the GIA Diamond Dock and the Judge II (the fancy color grading environment) are the same. Not sure if this helps.
 

Garry H (Cut Nut)

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Date: 4/5/2010 7:51:19 AM
Author: Tom Gelb
HI David,

While I am not an expert in light and absorption, I can say that the lights used by the GIA Diamond Dock and the Judge II (the fancy color grading environment) are the same. Not sure if this helps.
Tom the Judge II uses several different tubes in comnibation or individually?
http://www.pixl.dk/download_info/xrite/xrite_judge_ii_light_box.pdf

Are these DD lamps readily available?
What lentgh are they?
 

kenny

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Fiedudu wrote, "Hi, kenny. thank you for replying .I have searched but too much theory ...I am confused ... can u tell me the conclusion ?"


That's a common problem here.
The experts speak at a very high level and leave us in the dust.
I wish form time to time they'd translate into simple language for us, perhaps a summary at the end of highly technical threads.
Sometimes the smartest people are the least adept at putting things in simple terms.
Doing this requires a person temporarily pretend they don't know so much when writing.

I think (someone please correct me if I'm wrong) GIA stands accused of selecting light sources that have a high content of ultra violet light.
This makes diamonds with blue fluorescence glow a little blue.
This blue tinge counteracts yellow body color.
This makes, say, an H look like a higher color such as F or G.

I think some people think this is unfair.
I think some people think GIA does this so their clients (diamond sellers) can make more money, unfairly.
This is not the only diamond-seller-friendly (customer-unfriendly) thing they do...... their top cut grade of excellent accepts diamonds many agree are too deep to be considered well cut.
 

kenny

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Actually I was just thinking. . .

GIA graded my asscher F, with medium blue fluor.

I wonder if I sent it to AGS or got it graded with light with no UV content it would be a G or an H or lower.

IOW, I wonder if I paid too much for it because of GIA''s lighting.
Now I''m kind of angry.
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Garry H (Cut Nut)

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Date: 4/6/2010 12:59:25 AM
Author: kenny
Actually I was just thinking. . .

GIA graded my asscher F, with medium blue fluor.

I wonder if I sent it to AGS or got it graded with light with no UV content it would be a G or an H or lower.

IOW, I wonder if I paid too much for it because of GIA''s lighting.
Now I''m kind of angry.
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AGS use GIA''s DiamondDock and same procedures for color grading.

I am findning it is rare to see a drop of more than one color grade even in Very Strong Blue''s when the UV is screened out. But i am still looking into screening materials.
 

kenny

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Thanks Garry.
 

kenny

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BTW Garry and everyone, since we're on the subject Lexan (the plexiglas that blocks UV rays) must be used with the [/b]correct[/b] side facing the light source.
The correct side is labeled on the protective sheet which covers new Lexan.
After you peel the protective sheet there is no way to tell which side is which unless you marked it.
I mark mine with a tiny scratch in the corner.

I only know this because I use it to frame watercolor paintings, which have pigments that can fade when exposed to UV light.
 

Garry H (Cut Nut)

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Date: 4/6/2010 1:17:22 AM
Author: kenny
BTW Garry and everyone, since we''re on the subject Lexan (the plexiglas that blocks UV rays) must be used with the [/b]correct[/b] side facing the light source.
The correct side is labeled on the protective sheet which covers new Lexan.
After you peel the protective sheet there is no way to tell which side is which unless you marked it.
I mark mine with a tiny scratch in the corner.

I only know this because I use it to frame watercolor paintings, which have pigments that can fade when exposed to UV light.

Interesting Kenny, the stuff I have it makes no difference which way round it is - I wonder if yours has an additional coating like some spec''s do?


Here is a series of 3 photo''s with a UV LED (long wave close to visible I guess) shining on a VSB diamond. Sorry one is out of focus.



Lexan none 2 and 4 sheets.jpg
 

kenny

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Date: 4/6/2010 2:15:52 AM
Author: Garry H (Cut Nut)
Date: 4/6/2010 1:17:22 AM
Author: kenny
BTW Garry and everyone, since we're on the subject Lexan (the plexiglas that blocks UV rays) must be used with the [/b]correct[/b] side facing the light source.
The correct side is labeled on the protective sheet which covers new Lexan.
After you peel the protective sheet there is no way to tell which side is which unless you marked it.
I mark mine with a tiny scratch in the corner.
I only know this because I use it to frame watercolor paintings, which have pigments that can fade when exposed to UV light.

Interesting Kenny, the stuff I have it makes no difference which way round it is - I wonder if yours has an additional coating like some spec's do?


FWIW I have some Lexan handy and here is a pic of the Lexan sold at Home Depot in California;
Maybe what is sold in Austraila is different.

Note the instructions, here in Spanish, on which side should face light.

lexanmm.jpg
 

kenny

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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.

lexan2mm.jpg
 

Tom Gelb

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Date: 4/5/2010 8:16:59 PM
Author: Garry H (Cut Nut)
Date: 4/5/2010 7:51:19 AM

Author: Tom Gelb

HI David,


While I am not an expert in light and absorption, I can say that the lights used by the GIA Diamond Dock and the Judge II (the fancy color grading environment) are the same. Not sure if this helps.
Tom the Judge II uses several different tubes in comnibation or individually?

http://www.pixl.dk/download_info/xrite/xrite_judge_ii_light_box.pdf


Are these DD lamps readily available?

What lentgh are they?

Hi Garry,

The tubes used by the judge for colored diamond color grading are the daylight equivalent 6500K ones. I believe they are 24 inches, but they may be 20. I think the diamond dock bulbs are the same length, but I no longer work at the GIA so I cannot confirm. As far as availability of diamond docks I have no idea, sorry.

Kenny,

Well said and simplified. The only thing I would add is that the GIA''s explanation for using this type of bulb is that it mimics daylight, which has historically been the light used for diamond evaluation. What is the true color of a diamond? I would say there are a lot of factors that influence the way a diamond looks, so there is no true answer, in my opinion.

Tom
 

kenny

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Date: 4/6/2010 7:56:48 AM
Author: Tom Gelb
Kenny,
Well said and simplified. The only thing I would add is that the GIA's explanation for using this type of bulb is that it mimics daylight, which has historically been the light used for diamond evaluation. What is the true color of a diamond? I would say there are a lot of factors that influence the way a diamond looks, so there is no true answer, in my opinion.
Tom


Thanks Tom for mentioning this.
They have to select some standardized light source when grading diamonds since only grading them during the day or a certain part of the day is not reasonable.
Selecting lighting that contains UV content simulating that of natural sunlight sounds very reasonable to me.
I'd love to hear argument against it.
 

Rockdiamond

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To me, the bigger question involves how the diamonds are oriented when graded for color.
fiedudu- f I was not clear before: GIA grades the color of near colorless stones face down ( more technically described as through the pavilion).
Fancy Colored diamonds are graded as most people look at them- face up.

IMO this means that fluorescent diamonds GIA grades H-I-J color often times look at least one shade lighter when viewed normally- sometimes as much as 2-3 shades lighter.
This means a Strong blue stone GIA graded I color can look like a G color in many lighting sources.
 

michaelgem

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Date: 4/6/2010 12:24:56 PM
Author: kenny

Date: 4/6/2010 7:56:48 AM
Author: Tom Gelb
Kenny,
Well said and simplified. The only thing I would add is that the GIA''s explanation for using this type of bulb is that it mimics daylight, which has historically been the light used for diamond evaluation. What is the true color of a diamond? I would say there are a lot of factors that influence the way a diamond looks, so there is no true answer, in my opinion.
Tom


Thanks Tom for mentioning this.
They have to select some standardized light source when grading diamonds since only grading them during the day or a certain part of the day is not reasonable.
Selecting lighting that contains UV content simulating that of natural sunlight sounds very reasonable to me.
I''d love to hear argument against it.
Tom, Kenny, Garry and everyone,

Because this topic has aged from the front page, I have addressed the subject in a new topic with heading Color Grading Blue Fluorescent Diamonds.

See you there.
35.gif


Michael D Cowing
 

Karl_K

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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.

Edit: found the info I was looking for.
 

Karl_K

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Date: 4/6/2010 2:15:52 AM
Author: Garry H (Cut Nut)
Here is a series of 3 photo''s with a UV LED (long wave close to visible I guess) shining on a VSB diamond. Sorry one is out of focus.
Garry''s picture show how ineffective it is at blocking near visible UV.
 

Garry H (Cut Nut)

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Date: 4/7/2010 12:49:50 AM
Author: michaelgem

Date: 4/6/2010 12:24:56 PM
Author: kenny


Date: 4/6/2010 7:56:48 AM
Author: Tom Gelb
Kenny,
Well said and simplified. The only thing I would add is that the GIA''s explanation for using this type of bulb is that it mimics daylight, which has historically been the light used for diamond evaluation. What is the true color of a diamond? I would say there are a lot of factors that influence the way a diamond looks, so there is no true answer, in my opinion.
Tom


Thanks Tom for mentioning this.
They have to select some standardized light source when grading diamonds since only grading them during the day or a certain part of the day is not reasonable.
Selecting lighting that contains UV content simulating that of natural sunlight sounds very reasonable to me.
I''d love to hear argument against it.
Tom, Kenny, Garry and everyone,

Because this topic has aged from the front page, I have addressed the subject in a new topic with heading Color Grading Blue Fluorescent Diamonds.

See you there.
35.gif


Michael D Cowing
Hi Michael,
Thanks for dropping in.
I see no reason to start a new thread when there is already a string of information and genuine consumer requests.
We can answer these real questions here?
 

michaelgem

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Date: 4/7/2010 2:02:18 AM
Author: Garry H (Cut Nut)


Date: 4/7/2010 12:49:50 AM
Author: michaelgem



Date: 4/6/2010 12:24:56 PM
Author: kenny




Date: 4/6/2010 7:56:48 AM
Author: Tom Gelb
Kenny,
Well said and simplified. The only thing I would add is that the GIA's explanation for using this type of bulb is that it mimics daylight, which has historically been the light used for diamond evaluation. What is the true color of a diamond? I would say there are a lot of factors that influence the way a diamond looks, so there is no true answer, in my opinion.
Tom


Thanks Tom for mentioning this.
They have to select some standardized light source when grading diamonds since only grading them during the day or a certain part of the day is not reasonable.
Selecting lighting that contains UV content simulating that of natural sunlight sounds very reasonable to me.
I'd love to hear argument against it.
Tom, Kenny, Garry and everyone,

Because this topic has aged from the front page, I have addressed the subject in a new topic with heading Color Grading Blue Fluorescent Diamonds.

See you there.
35.gif


Michael D Cowing
Hi Michael,
Thanks for dropping in.
I see no reason to start a new thread when there is already a string of information and genuine consumer requests.
We can answer these real questions here?
You are right Garry,

Topics seem to age off the page very quickly, not getting enough exposure. Perhaps this topic is important enough to be put in the small group of topics that do not age.

I can move my posts back here.

Michael
 

michaelgem

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They have to select some standardized light source when grading diamonds since only grading them during the day or a certain part of the day is not reasonable. Selecting lighting that contains UV content simulating that of natural sunlight sounds very reasonable to me.

I''d love to hear an argument against it. Kenny




Until the late 90''s GIA and the diamond trade always taught and required the grading of diamonds for their "true body color", the color unimproved by blue fluorescence. This is the color seen at night or out of natural daylight at normal viewing distances from most all forms of overhead illumination including fluorescent lights. Grading for the unenhanced true color was taught and believed to be accomplished by grading in the GIA Lab standard DiamondLite, which was said to have a "minimum of UV" or by grading in lighting filtered to remove the UV.

Both LWUV (Long Wave Ultra Violet) between 330nm and 390nm and VV (Visible Violet) from 390nm to 415nm excite blue fluorescence in many "Cape Series" or Type 1a diamonds, which comprise over 98% of gem quality diamonds. But at normal viewing distances from overhead lighting (3 to 4 feet or more) there is not enough of either to cause grade whitening fluorescence because of the rapid fall off of energy with distance from the light. So the diamond''s true color is seen at night or out of natural daylight.



Unfortunately, since the advent of fluorescent lighting in diamond grading in the 50''s most labs and the diamond bourses have been grading within seven inches of unfiltered tubes where there is significant grade whitening UV and VV causing the highly variable amounts of over grading of many blue fluorescent diamonds, especially those with Strong and Very Strong fluorescence grades.



The discovery of a "good deal" of UV (measured in excess of 150 uW/cm2 at a two inch grading distance from the tubes) in the DiamondLite in the late 90''s resulted in a rethinking and change in GIA lab color grading practice. This change was instituted in 2000 with the replacement of the DiamondLite with the DiamondDock. The new lighting standard to grade diamond color published in G&G Dec 2008 is the equivalent of the DiamondDock''s unfiltered fluorescent tubes having specifications that include:



1. Stable, fluorescent lamps 17 in. (43 cm) or longer
2. An intensity of light in the range of 2000-4500lux at the surface of the grading tray
3. An 8-10 in. Distance between the lamps and the grading tray
4. A color spectrum close to CIE D55-D65
5. An emission for long-wave UV (between 315 and 400nm, close to the reference spectrum of D55-D65)


So, GIA has gone from requiring a minimum of UV in color grading to requiring LWUV close to the CIE reference spectrum for daylight. The Fluorescence Study of over grading found that this amounts to roughly 33 uW/cm2 of fluorescence stimulating UV.



First published in the Austrialian Valuer thanks to the efforts of Garry Holloway and Hylda Bracewell was an IMO "illuminating" article dealing with this whole issue of the current over grading of many blue fluorescent diamonds. Another version just off the press from the British Gem-A''s publication, Gems & Jewellery has been uploaded with permission to my website where you can download a copy at:



http://acagemlab.com/temp/gemsjewellery.pdf



Members of the AGA Task Force on Lighting Standards, Garry, I and others hope to get the word out to the trade, jewelers, and consumers to get back to grading the diamond''s true color unenhanced by fluorescence in order to remove the mystery from the color grading of blue fluorescent diamonds and remove the resulting stigma attached to them.



Would you rather pay for the most often seen true color, or the highly variable fluorescence enhanced color only seen in daylight that is also highly variable? How much UV and VV fluorescence stimulation is that?

33.gif



Let us know what you think.



Michael D Cowing



Will follow with the Fluorescence Study''s recommendations

 

michaelgem

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Together with the AGA Task Force on Lighting Standards, I and a growing international body of gemmologists and appraisers/valuers, recommend a new procedure when examining fluorescent stones. Before grading them for their fluorescence-improved colour in standard daylight-equivalent light, examine them for their unenhanced body colour in lighting both filtered to eliminate UV and diffused to reduce light intensity, so that neither UV nor visible-violet excite blue fluorescence.


Based upon the new investigation and study, we recommend the use of a polycarbonate plastic (Lexan or Makrolan are examples) as an effective and inexpensive filter to remove UV from existing grading illumination. Additionally, a white plastic diffuser is recommended to reduce the visible light intensity below 400 foot-candles (fc). The study found fluorescent light intensities below 400 fc contain insufficient visible-violet to stimulate noticeable fluorescence. In addition to lowering the light intensity, such white diffusers were recommended by GIA to reduce spectral reflections and glare from diamonds being graded and to help filter out UV emissions.


An equally effective solution in concert with the movement to the ''green'' technology of LED lighting is the use of white LEDs such as the investigation''s Dazor LED desk lamp. It not only provides inherently UV-free grading light, but is dimmable without change in colour temperature down to 200-400 fc (2000-4000 lux) to avoid stimulating noticeable blue fluorescence.


A return to lighting standards that allow grading of a diamond''s colour unimproved by blue fluorescence would benefit the diamond industry in a variety of ways. First it would remove the distrust and stigma attached to fluorescent diamonds. Second, the rarer blue-fluorescent diamonds that hold their high-white colour in the absence of stimulation of fluorescence would be recognized once again for their superior beauty and rarity. Thirdly, diamonds graded without their blue fluorescence would be shown to whiten, and sometimes appear blue-white in natural daylight, giving them the edge in marketing over their non-fluorescent counterparts that they used to enjoy.


In the final analysis, it would be as beneficial as it is simple and affordable to correct the problem of over-grading blue-fluorescent diamonds. By so doing, we would restore the colour-grading of diamonds based on the traditional diamond industry standard. By grading a diamond''s ''true colour'' unenhanced by blue fluorescence the diamond world could once again enjoy worry-free commerce in blue fluorescent diamonds.


In short, using new lighting techniques, we urge a return to the past colour-grading practices that involved emphasis on the diamond''s colour in fluorescence-deactivated lighting to perform fair colour assessments of blue fluorescent diamonds and to ferret out the true blue-whites. By so doing, the diamond trade would be creating a wider canopy of consumer protection than presently exists.

36.gif


Michael D Cowing
 

Karl_K

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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.
 

michaelgem

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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


lexan7.gif
 

kenny

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Might concern for this over-grading have something to do with the "discount" we see for diamonds with a lot of fluor?
 
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