Blue Fluorescence in Diamonds

Published on 14/06/2009

Historically ‘blue white’ fluorescent top coloured (D to F on the GIA colour grading scale) diamonds were once priced around 10% more than non fluorescent diamonds. Today D to F coloured blue fluorescent diamonds are usually discounted on wholesale markets. There are two main technical reasons why fluorescent diamonds would be discounted. The diamond’s body colour may have been ‘over-graded’ or its transparency may have been impaired.

A thank you to the The Australian Gemmologist for allowing Pricescope to post this article from Vol 23 Number 9, January - March 2009

Abstract:

There are also several possible “commercial” reasons why high coloured (D-F) blue fluorescent diamonds are often discounted. For example, they may be more difficult to sell. This article will review the complex and often contradictory history.

Introduction:

In the USA the Federal Trade Commission banned the use of the term ‘blue white’ in 1938. In 1993, Martin Rapaport added a fluorescence price guide to the Rapaport Diamond Report apparently as a response to events in Korea. In 1997 the Gemological Institute of America (GIA) published a survey in Gems & Gemology indicating that blue fluorescence was a benefit to diamond face up colour appearance. Shortly after, without declaration, the GIA Gem Trade Laboratory changed its grading illumination environment used to grade D-Z coloured diamonds to include more ultra violet light. Cape or yellowish diamonds that exhibit blue fluorescence are believed by many to receive higher colour grades than when ultra violet light was absent. The author solicited opinions while researching for this article concerning possible links between fluorescence and transparency from several respected lab directors and trade experts. Worryingly, the views differed widely. The history, pricing and related issues are discussed and some conclusions are offered.

What causes fluorescence?

Diamond is a very pure mineral. The most common impurity is a tiny amount of nitrogen (0.0001% to 0.01%) dispersed throughout the crystalline structure. When white light traverses a yellowish diamond some blue light is absorbed by the deformities in the crystal associated with the nitrogen causing a slight yellow appearance. Higher energy ‘light’ like x-rays or short wave ultra-violet can also cause the diamond to fluoresce and emit in the same frequency range that was previously only absorbed. Natural ultra-violet from daylight or even from some light globes is enough to make a fluorescent yellowish diamond appear whiter. Nitrogen can also occur in various ‘states’ with different electronic properties within a diamond so that it is possible for one D coloured non-fluorescent diamond to have 10 times more nitrogen than another that is K colour and fluorescent.

History

Background

After the discovery of diamonds in South Africa in 1867 some mines were renowned for producing a percentage of high colour diamonds that exhibited a bluish appearance in daylight as a result of their fluorescence. It came to be that these diamonds, especially those that were otherwise colourless, were termed ‘blue white’ and sold at a premium price.[1] However, human nature being what it is, some marketers of diamonds indulged in “bracket creep” and began to call diamonds of lower colours “blue white” in order to achieve a higher selling price and more profit. This led the United States of America Federal Trade Commission (FTC) to ban the use of the term ‘blue white’ on March 18, 1938 with the following resolution 23.14, (Trade Practice Rules for the Wholesale Jewellery Industry, Rule No. 6, p4:

23.14 Misuse of the term “blue white.” [2], [3]

It is unfair or deceptive to use the term "blue white" or any representation of similar meaning to describe any diamond that under normal, north daylight or its equivalent shows any color or any trace of any color other than blue or bluish.

Interestingly under this definition there are diamonds that could still be legally described as blue white, however it seems that the intention of the legislation has been observed, and, if anything, there has been an over-reaction. The FTC also made an attempt to define the type of lighting that might cause a diamond to fluoresce and appear ‘blue or bluish’. The detail however did not include terms such as ‘shaded’ or ‘indirect sunlight’ or make any reference to the time of day or atmospheric conditions. The quality of published industry and gemological opinion about the type of natural light that diamond colour ought to be judged or graded in, is poor and often contradictory, as can be noted in the following quotes.

Eric Bruton wrote in 1978 in ‘Diamonds’: [4]

“A very important consideration is that any fluorescence in the stone must be suppressed. A visible blue fluorescence can be caused in a yellowish diamond when ultra-violet light, which is invisible, falls on it. If the diamond is examined in sunlight, even reflected light, which contains ultra-violet light, the blue fluorescence will tend to cancel the yellowish body colour because the colours are nearly complementary, and the stone will appear to be whiter than it is. These stones are often mistakenly called ‘blue-white’. It is therefore important to grade stones in white light that is relatively free of ultra-violet and the orthodox method is to use daylight from a north-facing window in the northern hemisphere and from a south-facing one in the southern, i.e. with one’s back to the sun.”

“…but it must be remembered diamonds are rarely seen in such ideal conditions in wear because there is some ultra-violet in most daylight.”

“False White” Stone: If a stone has blue fluorescence and a tinted yellow body colour, the colours being complementary may cancel each other so that in some conditions the stone appears white. The experienced grader will recognize such stones because their colour grade appears to vary in different light intensities. A white light free of ultra-violet will disclose the true body colour and an ultra-violet lamp the fluorescence.”

Mr. Bruton is the only author who attempts to describe an orthodox and accepted colour grading environment of shaded daylight which has often been referred to as the environment that artificial light should mimic. However, Bruton then seems to contradict his own comments: “even reflected light, which contains ultraviolet light”….. “A white light free of ultra-violet will disclose the true body colour….” “but it must be remembered diamonds are rarely seen in such ideal conditions in wear because there is some ultra-violet in most daylight…..”

In 1986 Eddy Vleeschdrager wrote in ‘Hardness 10: Diamond’[5]

“A polished diamond is less valuable if its fluorescence is too high, for it will give the impression of having a better colour than it actually has in normal light conditions. The colour of a diamond has to be determined using a normalised artificial light source which corresponds to daylight. Because this light source simulates day light, it contains an amount of ultra-violet light. It is evident that the ultra-violet light will contribute to fluorescence.”

It is interesting to note the contradictions in Mr. Vleeschdrager’s quotes. A diamond should be less valuable if its colour is better in normal lighting? A diamond’s colour should be determined in ‘normalised’ artificial daylight which should contain an undefined amount of ultraviolet light. Did Mr. Vleeschdrager really intend to say that blue fluorescent diamonds will be overgraded in a normalised artificial light source, which by his own definition, should contain some unspecified content of ultra-violet light?

In 1980 Verena Pagel-Theisen in the 7th edition of ‘Diamond Grading ABC’[6] wrote:
“the body colour observed in normal light determines the colour grade of fluorescent diamonds” although there is no description in this book as to what constitutes ‘normal light’.

In the 9^th edition of the same book, in 2001: [7]

“…the body colour observed in standardized light determines the fluorescent diamond’s colour grade.” ‘Normal light’ has become ‘standardized light’, but there is still no attempt to define a standard.

There is however an additional notation that “In the upper colour grades up to ‘white’, fluorescence means a reduced price because clear fluorescence can affect the transparency and clarity of the stone.” There is a recurrent theme in “Diamond Grading ABC” that fluorescence may affect the transparency of higher colour and clarity stones more than in the case of lower grades. If this is so then it has neither been discussed nor validated in the literature. In this writer’s diamond grading experience it does not appear to be the case. One can also only wonder why the term “clear fluorescence” was used in the same sentence as “transparency”

It becomes apparent from a review of the literature that there is no clear idea of what type of natural or artificial light should be used for diamond colour grading. It should also be noted that there have been no attempts by gemmologists or diamond grading laboratories to clearly define, describe or rate the levels of transparency that may be reduced in diamonds that fluoresce, or for that matter even in those that are inert. Transparency will be a recurring topic in this article.

‘KoreaGate’ In an interesting case study, prior to 1993, Korean retailers and consumers exhibited a preference and paid a premium for blue fluorescent diamonds. However a Korean current affairs TV program[8] in 1993 accused local Korean grading laboratories of over-grading the colour of fluorescent diamonds, suggesting for instance that “your G is really H”. Korean traders replaced many of the fluorescent diamonds they had sold earlier, becoming net sellers of fluorescent goods and buyers of non-fluorescent diamonds. This simultaneous dumping and demand of the different grades of goods seemingly contributed to an adjustment in the Rapaport Diamond Report price guide. A month or two later a chart appeared (Table 1) with price guides for blue fluorescent diamonds of different colours and clarities. This guide is still in place today, having had only some minor adjustments from time to time which presumably only reflect fluctuations in supply and demand.

In an article written by Martin Rapaport 1998 in the Rapaport magazine, entitled ‘Blue White’ [ix] Martin wrote: “Once upon a time, before the diamond industry standardized to GIA color grading terminology, the term Blue White (Blauweiss) was used to described the finest color white diamonds. The original Blue White diamonds came from South Africa's Jagersfontein mine. The best Jager stones were highly transparent (clear and colourless) with a bluish tint due to fluorescence. Ironically, during the early part of the 20^th century, fluorescence was seen as something that had a very positive impact on top colors”. And: “While education can play an important role, changing buyers’ perception about the negative impact fluorescence has on higher color diamonds will have to be backed up by solid results. In other words the labs are going to have to be very serious about not over-grading the color of fluorescent stones, even though these stones tend to appear whiter than they really are”.

Table 1 – Rapaport Diamond Report Price Indications for Blue Fluorescent diamonds[i] commenced in June 1993, immediately after a negative Korean current affairs TV broadcast highlighting the possible effect of fluorescence on colour grading of fluorescent diamonds.

The impact of fluorescence on price depends on its noticeability. For some higher-colour stones, fluorescence gives the stone a milky white appearance which greatly lowers value. In some instances the fluorescence is hardly noticeable and has minimal impact on the stone’s brilliance and value. Blue fluorescence may add value to lower-colour stones as it gives the stones a whiter, brighter appearance. Some buyers regularly pay increased prices for highly blue-fluorescent J and lower-colour diamonds. Conversely, yellow or white fluorescence may attract a 5 to 10 percent discount. Generally the higher the quality and price per carat, the more any such non-blue fluorescence will lower the value. The Price List is based on stones without strong or medium fluorescence. A table (see table 1) with estimates of discounts and premiums for fluorescent stones is presented in a monthly Report.

While it is likely that Mr. Rapaport does influence market prices, it is also clear that his intention is to simply report on market pricing. Traditionally, top colour (D to F) fluorescent diamonds received a premium but now they are discounted and fluorescent diamonds with a colour grade lower than ‘I’ earn a premium.

Interestingly Mr. Rapaport, like so many others, focuses his attention on high colour grade diamonds and warns labs they should not “overgrade fluorescent stones, even though these stones tend to appear whiter than they really are”. To this observer it seems contradictory that we should discount high colour diamonds because they appear “whiter than they really are” while we should add value to low-colour blue fluorescent stones because they too appear whiter than they really are.

While Mr. Rapaport mentions transparency in passing, he does not raise the obvious issue of grading reports for not rating or warning with a comment when a diamond exhibits reduced transparency. As an industry, diamond grading laboratories are very good at noting features that they are able to report with some consistency and accuracy. Many of these features are of little interest to consumers and could be described as hair splitting; the difference between Excellent and Very Good polish for example has no bearing on a diamond’s appearance to a consumer, but the mere fact that this distinction is made on a diamond grading report affects the diamond’s price. However, any cause of the reduction of a diamond’s transparency and sparkle is important to all consumers and the inability of laboratories to provide this information is, in this writer’s opinion, a deficiency that could compromise consumer confidence.

Are Fluorescence and Haziness linked?

While researching for this article the author solicited opinions as to possible links between fluorescence and transparency from several respected laboratory directors and trade experts. This is the final question that was asked in an email:

“Please estimate / guesstimate the percentage of diamonds that are hazy / oily with reduced transparency when viewed in shaded daylight for Very Strong, Strong, Medium, Faint and negligible fluorescent diamonds”?

Because some respondents requested anonymity their identities have not been divulged.

For diamonds with ‘Very Strong’ fluorescence the experts opinions ranged widely from “very small”, and “a small fraction” to “almost all the Very Strong fluorescent stones (±90%) have an oily look, especially visible in lower colours such as J, K, L..., they're also called "over-blue". The majority of replies fell in the range of 20% to 40% of Very Strong blue fluorescent diamonds suffered from a noticeable reduction in transparency. Of those respondents who indicated that 20% or more of ‘Very Strong’ fluorescent diamonds had reduced transparency, the response for ‘Strong’ was around one half of the percentage for ‘Very Strong’ or in the range of 10 to 20% visibly affected.

Interestingly one expert mentioned that oily appearance is more common in diamonds with a lower colour than ‘J’. This is contradictory to the Rapaport price guide and the generally held opinion; the market usually places a price premium on yellow tinted blue fluorescent diamonds.

Some of those surveyed also mentioned that reductions in transparency or hazy affects also can be caused by graining that results from crystal growth, or clouds of very fine pin point inclusions that can sometimes be too small to see with a 10x loupe.

A study of blue fluorescence conducted by the Gemological Institute of America (GIA) and discussed in the next section of this article, briefly dealt with transparency. The article supports the idea that a “very small” number of blue fluorescent diamonds suffer reduced transparency.

Given the diverse responses in the informal survey of experts for this article it seems this is an area that would benefit from further study.

Figure 1. An extremely strong blue fluorescent diamond ring owned by American gemmologist David Atlas was photographed on the left, in direct sunlight, and on the right in shaded daylight. Even in the photograph on the right the diamond is slightly hazy (the pink colour is from the surrounding environment).

A large diamond manufacturer, Venus Jewel in Surat India, provides very detailed grading reports covering 16 grading parameters with each of the diamonds it polishes. One of those parameters is ‘Luster’ which is their measure of a diamonds transparency[i]. The Venus system rates a diamonds luster in 11 grades from excellent, very good, good and fair, followed by seven more grades from ‘very slightly milky’ to ‘strong milky’. If a vendor can grade transparency then commercial grading labs, who proclaim they work to maintain consumer confidence, should also be able to report this feature?

The authors occasional analysis of Venus Jewel’s extensive (but not necessarily representative) on-line inventory indicates that the percentage of very strong and strong fluorescent diamonds with reduced ‘luster’ lies within the mid to lower ranges of the experts opinions mentioned above. Graining (visible crystal growth planes) is another feature graded by Venus Jewel; it is clear from limited analysis of diamond listed on their website that diamonds with pronounced graining are also more likely to receive a lower grade for ‘luster’ or transparency.

A review of the GIA’s fluorescence study

Trade perceptions that ultra-violet fluorescence has a negative effect on diamond appearance. The results support an older belief that strong and very strong blue fluorescence can improve a diamond’s appearance, especially those with faint yellow body colour. In the study, the benefits of blue fluorescence in colourless to near-colourless diamonds were also evident. In the GIA team’s opinion this brought into question the trades’ lower ‘bid’ prices for moderate to highly fluorescent diamonds in the better colours.

To find out how many diamonds fluoresce the GIA team examined a random selection of 26,010 stones graded by the GIA’s Gem Trade Lab. Of the 35% that fluoresced, 22% ranged from medium to very strong of which almost all fluoresced blue. Only 0.6% fluoresced a colour other than blue (yellow, white, green or orange). 11,901 of the diamonds were in the D-to-F range and of these the same proportion fluoresced, see Table 2

In 1997 the Gemological Institute of America (GIA) published a study in Gems & Gemology By Thomas M. Moses, Ilene M. Reinitz, Mary L. Johnson, John M. King, and James E. Shigley titled “A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds”.[ii] This article was based on an extensive survey and challenged trade perceptions that ultra-violet fluorescence has a negative effect on diamond appearance. The results support an older belief that strong and very strong blue fluorescence can improve a diamond’s appearance, especially those with faint yellow body colour. In the study, the benefits of blue fluorescence in colourless to near-colourless diamonds was also evident; in the GIA team’s opinion this bought into question the trades lower ‘bid’ prices for moderate to highly fluorescent diamonds in the better colours.

To find out how many diamonds fluoresce the GIA team examined a random selection of 26,010 stones graded by the GIA’s Gem Trade Lab; 65% had no fluorescence and of the 35% that fluoresced, 22% ranged from medium to very strong, almost all fluoresced blue. Only 0.6% fluoresced a colour other than blue (yellow, white, green or orange). 11,901 of the diamonds were in the D-to-F colour range and of these the same proportion fluoresced. See Table 2.

Sample Size	Nil Fluor.	Faint Fluor.	Medium to Very Strong Fluorescence
Sample Size	Nil Fluor.	Faint Fluor.	Medium to Very Strong Fluorescence
26,010	16,835	3,465	5,710
100%	65%	13%	22%

Table 2. To find out the proportion of diamonds that fluoresce the GIA team examined a random selection of stones graded by the GIA’s Gem Trade Lab. The results are presented in the table above. A total of 35% were found to fluoresce, and of those around 97% showed a blue colour.

Four sets (colours E, G, I and K) with seven diamonds in each set were selected (see figure 2). The sets ranged from inert to very strong fluorescence. Forty six people were asked to grade these diamonds for apparent colour and transparency.

Grading was performed table down (the usual D-Z colour grading position) with a GIA grading light, at a dealer’s desk, and ‘face up’ with a dealer’s typical double row fluorescent desk lamp. In addition in the face up viewing environment grading was performed in a regular office with fluorescent ceiling lights and near a window, in summer and in shaded daylight.

One interesting aspect of this study was that the non-trade observers could not make meaningful distinctions. For this group, said to be representative of the buying- public, fluorescence had no overall effect on colour appearance or transparency. ‘Average observers’ did not notice the colour or transparency trends detected by trained graders. Therefore, the results for ‘average observers’ were excluded from the analysis.

Sometime after the publication of this article the GIA Gem trade Lab (GIA GTL) began grading diamond colour with lamps that emitted more ultra violet light. It is possible that those diamonds used in the study that had stronger fluorescence would receive higher colour grades if they were resubmitted today.

The reported results of this study indicate that there is a perceptible relationship between blue fluorescence and colour appearance, which depends on viewing position. On average, strongly fluorescent diamonds were found to have a better colour appearance face up. This effect was seen across all colours, but was most noticeable at lower colour grades

Most observers did not detect any differences in transparency among diamonds in a given colour set. Of those who did see a difference under fluorescent lighting, it was only apparent in the table-down position. This challenged the notion that strongly fluorescent diamonds typically have a hazy appearance.

When viewed face up with artificial light and in shaded sunlight (containing ultra-violet) observers noted respectively a 29% and a 50% difference in transparency although these expert observers as often as not made contradictory assessments. The conclusions drawn in this study indicated that very strongly fluorescent diamonds set in jewellery are not less transparent.

Diamonds showing extremely strong blue fluorescence with an oily or hazy appearance were found to be so rare in fact that the GIA team abandoned a proposed extension to the study because they were unable to locate sufficient samples for each colour. In this writer’s opinion, that finding contradicts the author’s own experience and those of a few senior laboratory directors who report reduced transparency among a considerable proportion of strong and very strongly fluorescent diamonds. It is important to remember that it is common for GIA to base studies on populations of diamonds that are submitted to the GIA GTL for grading and these sample assortments may not be representative of all polished diamonds.

Cut-related factors can also affect the colour appearance of diamonds. The longer the average ray path the more apparent will be the colour of a diamond. A well cut round brilliant usually has a shorter average ‘face up’ ray path length than that of the table down colour grading position. Therefore it is likely that the better cut diamonds in the sample-set would face up with a better colour. There was no information provided in this study on the quality of cut. Additionally, if this survey been conducted with fancy shaped diamonds with different proportions to the round brilliant it is possible that the results would have differed.

Seven of the diamonds in the sets I and K coloured series were Very Strong or Strongly fluorescent compared with only five Very Strong and Strong stones in the sets E and G. Since the more strongly coloured fluorescent diamonds (the I and K stones) were perceived to be of markedly better colour, the reported comment may have been biased by the sample selection.

The conclusion of the GIA study included the following statement:

“For the experienced observers, we found that, in general, the strength of fluorescence had no widely perceptible effect on the color appearance of diamonds viewed table-down (as is typical in laboratory and trade grading). In the table-up position (as is commonly encountered in jewelry), diamonds described as strongly or very strongly fluorescent were, on average, reported as having a better color appearance than less fluorescent stones. In this study, blue fluorescence was found to have even less effect on transparency. These observations confirm GIA GTL’s experience grading millions of diamonds over the decades.”

Figure 2. Photographs face up and table down in normal light and ultra violet light of the diamonds used in the GIA fluorescence study. Image has been supplied by Gems & Gemology. Photos of diamonds in normal light are by Harold & Erica Van Pelt; photos in UV light are by Maha DeMaggio. Image © GIA.

A Critique of the GIA’s Policy on Fluorescence:

Martin D. Haske, GG, NGJA, MS has closely studied the GIA’s approach to fluorescence and makes a claim that GIA’s Gem Trade Laboratory (GIA GTL) introduced new grading lamps with more ultra violet radiation after its 1997 article in Gems & Gemology was published. After this time Mr. Haske claims blue fluorescent diamonds graded by the GIA GTL are generally graded one to two colour grades higher than with the earlier lamps that had lower levels of ultra violet depending on the grading technique used.

Mr. Haske has chronicled reported changes in GIA’s approach on his website[i] indicating that in 1972 GIA taught "Fluorescent diamonds should be graded at their poorer color in artificial light devoid of ultraviolet radiation, rather than at their daylight grade".

“Filtered, cool white balanced fluorescent light is best: unlike sunlight, it is nearly free of ultraviolet”.

Then by 2002 “The most widely available and accepted lighting for color grading diamonds is balanced, daylight equivalent, fluorescent light”.

Mr. Haske claims that the GIA GTL did not formally announce any change in policy.

Competitive retail practice and sales training

In an article in Rapaport magazine in 1997[ii] Elly Rosen pointed out: “The biggest real problem is the danger that another merchant, a gemological lab or an appraiser will transmit his own view to a recent purchaser in a manner that creates the impression that the seller was “less than honest” even if such is not the case and even if this implication was totally unintended.”

Many small and also large influential branded jewellers, including Tiffany & Co, do not stock diamonds with ‘Strong’ or ‘Very Strong’ fluorescence. One reason could be that big companies buy in large quantities ‘by system’ as a matter of supply chain simplification. This could contribute to a negative message perceived by dealers and consumers, as mentioned by Elly Rosen, such that there must be something wrong with fluorescent diamonds. There is abundant anecdotal evidence that salespeople in stores where there is a policy not to sell strongly fluorescent diamonds denigrate the goods of competitors who offer strong and very strong blue fluorescent diamonds.

Mr. Wink Jones, a US jeweller in Boise, Idaho comments[iii]: “In the 70’s I paid a premium for fluorescent diamonds and proudly passed it on to my clients who loved that extra touch of beauty. During the investment craze, late 70's, ladies’ shoe sellers were now selling diamonds from boiler room phones – they had no clue what fluorescence was or how to explain it. It came to be viewed as a bad thing.” It would seem that this staff training problem is even worse now because staff turnover rates are higher today. A related issue is that during the sales process, or even after a diamond is sold, a diamond grading report is often produced and a less knowledgeable salesperson may be faced with explaining fluorescence and all its complexity.

There is also abundant anecdotal evidence that many diamantaires and their wives prefer blue fluorescent diamonds for their own personal use. Store owners, gemmologists and salespeople should, if they have not already, decide if they should or should not sell blue fluorescent diamonds. The ethical businesses that have decided to include fluorescent diamonds in their offering should be practiced in identifying those diamonds with hazy milky appearances and reduced transparency. Some stones are so obviously over-blue that their different appearance in daylight when non fluorescent diamonds are set nearby in a piece of jewellery. Such careful consideration and staff training will help establish much needed trust and confidence in our industry.

The authors advice to those who do not like and prefer not to stock or sell blue fluorescent diamonds is they should not be derogatory to other jewelers’ customers who have or may purchase diamonds that fluoresce, for just as the tide turned against ‘blue white’ diamonds, it could indeed turn again in favor of ‘blue white’. With the advent of the Internet and education websites, it is common for knowledgeable consumers (called ‘prosumers’ on Internet forums)to not only be aware of fluorescence, but to actively seek out these diamonds.

For example a poll conducted between the 9^th and 11^th of May 2008 on Pricescope.com,[iv] the leading consumer advocate website, 75% of respondents preferred fluorescent diamonds. Many of these diamond buying members of the public state they would pay more to buy blue fluorescing diamonds and the current discount on D-F high colours is an added bonus. See Table 3.

Question: Do you like fluorescence?

Answers:	%	Votes
Yes	75%	89
No	25%	30
Total Votes:		119

Table 3 - The results of a poll conducted over two days on consumer diamond information site www.pricescope.com which is frequented by well educated diamond consumers.

Conclusion:

The outlawing the use of the term ‘blue white’ by the Federal Trade Commission of the USA had a profound effect on trade practices and effectively reversed the premium that was once placed on many high coloured blue-fluorescent diamonds.

A review of the literature indicates that there are no clear guidelines on the type of lighting used for grading diamond colour. Should ultra violet light be present, if so what frequency and strength, and how far from a lamp should a diamond be held? This writer believes the answer lies in digital or spectrophotometer machine based colour grading, in the face up position, with perhaps half the radiation strength of long wave ultra violet light as found in shaded daylight. lf industry standards bodies like CIBJO could agree on an appropriate standard light source for face up colour grading, then the industry may not need to price fluorescent diamonds differently. Certainly consumers would prefer that the face up colour of a diamond was reported on lab diamond grading reports or certificates because differences in face up colour can also be caused by factors other than fluorescence. (Diamonds of different cut type, e.g. step vs brilliant styles, and varied cut qualities present different side view to face up colours. Size also makes a difference; face up a G colored half carat diamond appears more colourless than a 10ct G of the same cut type and quality). A better colour grading method may have avoided the events that occurred in Korea in 1993 which led to a price guidance table being added in the Rapaport Diamond Report formalizing discounts for colourless blue-fluorescent diamonds and premiums for the lower coloured blue-fluorescent diamonds.

It appears that the GIA attempted to solve the colour grading and transparency issues with its study published in 1997. However Mr. Haske has shown that after this report the GIA, apparently, without adequate notification, introduced grading lamps with a similar amount of long wave ultra violet radiation as found in indirect daylight.

In researching this article a discrepancy in experts’ opinions on the transparency of fluorescent diamonds was discovered suggesting that development of non-subjective digital spectrophotometer based grading methods. In the interest of promoting consumer confidence, laboratories should grade, rate or make a comment on any perceived reduced transparency in diamonds whether it is as a result of fluorescence or any other cause, in view of its consequent detraction from the desirability and the value of a stone.

References

1 Gilbertson A. (2007), American Cut The First 100 Years, Gemological Institute of America, California

2 US Federal Trade Commission (1938) Trade Practice Rules for the Wholesale Jewelry Industry. Rule No. 6, p.4, as promulgated March 18, 1938.

3 FTC USA www.ftc.gov/bcp/guides/jewel-gd.shtm

4 Bruton E. (1978), Diamonds, 2^nd Edn. Radner, Pennsylvania

5 Vleeschdrager E. (1986), Hardness 10: Diamond, Gaston Lachurie, Paris

6 Pagel-Theisen V. (1980), Diamond Grading ABC, 7^th Edn, Rubin & Son, New York, Antwerp, Belguim

7 Pagel-Theisen V. (2001), Diamond Grading ABC The Manual 9^th Edn. Rubin * Son, Antwerp, Belgium

8 We Want to Know That (1993), SBA-TV, South Korea, broadcast May 9

9 Rapaport M. www.diamonds.net/news/Default.aspx?Search="blue%20white

10 Currently Published in Rapaport Guide to the Rapaport Price Lists

11 Venus jewel grading system information http://www.venusjewel.com/openframe.htm

12 Thomas M. Moses et al A contribution to understanding the effect of blue fluorescence on the appearance of diamonds, Gems & Gemology (Winter1997) http://lgdl.gia.edu/pdfs/W97_fluoresce.pdf

13 Haske M. http://www.adamasgem.org/giafluor.html

14 http://www.diamonds.net/news/NewsItem.aspx?ArticleID=1635

15 Personal communication

16 Pricescope survey www.pricescope.com/idealbb/view.asp?topicID=84923 9 - 11 May, 2008

Discuss on the forum