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244 Blue Fluorescence in Diamond GEMS & GEMOLOGY Winter 1997

any factors influence the color appearance ofcolorless to faint yellow diamonds.Typically, such diamonds are quality graded

for the absence of color according to the D-to-Z scale devel-oped by the Gemological Institute of America in the 1940s(Shipley and Liddicoat, 1941). By color appearance, however,we mean the overall look of a polished diamond’s color thatresults from a combination of factors such as bodycolor,shape, size, cutting proportions, and the position and light-ing in which it is viewed. When exposed to invisible ultravi-olet (UV) radiation, some diamonds emit visible light,which is termed fluorescence (figure 1). This UV fluores-cence arises from submicroscopic structures in diamonds.Various colors of fluorescence in diamond are known, but

blue is by far the most common.The response of a diamond to the concentrated radia-tion of an ultraviolet lamp is mentioned as an identifyingcharacteristic (rather than a grading factor) on quality-grad-ing reports issued by most gem-testing laboratories. Otherlight sources—such as sunlight or fluorescent tubes—alsocontain varying amounts of UV radiation. Although therehave been instances where the color and strength of the flu-orescence seen in diamonds observed in these other lightsources are also believed to influence color appearance, inrecent years the fluorescence noted on grading reports hasbeen singled out by many in the diamond trade and appliedacross the board as a marker for pricing distinctions.

Generally, these distinctions are applied in the direction oflower offering prices for colorless and near-colorless dia-monds that exhibit fluorescence to a UV lamp (MannyGordon, pers. comm., 1997). Other trade members contendthat the overall color appearance of a diamond typically isnot adversely affected by this property (William Goldberg,pers. comm., 1997); many even say that blue fluorescenceenhances color appearance.

A CONTRIBUTION TO U NDERSTANDING

THE EFFECT OF BLUE FLUORESCENCEON THE A PPEARANCE OF DIAMONDS

By Thomas M. Moses, Ilene M. Reinitz, Mary L. Johnson, John M. King, and James E. Shigley

ABOUT THE AUTHORS

Mr. Moses is vice-president of identification ser-vices, Dr. Reinitz is manager of research and development, and Mr. King is laboratory projectsofficer at the GIA Gem Trade Laboratory, New

York. Dr. Johnson is manager of research and development at the GIA Gem Trade Laboratory,Carlsbad, California, and Dr. Shigley is director of GIA Research in Carlsbad.

Please see acknowledgments at the end of the article.

Gems & Gemology , Vol. 33, No. 4, pp. 244–259

© 1997 Gemological Institute of America

Some gem diamonds fluoresce, most commonly blue, to the concentrated long-wave ultraviolet

radiation of a UV lamp. There is a perception inthe trade that this fluorescence has a negativeeffect on the overall appearance of such a dia-mond. Visual observation experiments were con-ducted to study this relationship. Four sets of very similar round brilliant diamonds, coveringthe color range from colorless to faint yellow,were selected for the different commonly encountered strengths of blue fluorescence they represented. These diamonds were then observedby trained graders, trade professionals, and aver-age observers in various stone positions and lighting environments. For the average observer,meant to represent the jewelry buying public, nosystematic effects of fluorescence were detected.

Even the experienced observers did not consis-tently agree on the effects of fluorescence fromone stone to the next. In general, the results revealed that strongly blue fluorescent diamondswere perceived to have a better color appearancewhen viewed table-up, with no discernible trendtable-down. Most observers saw no relationshipbetween fluorescence and transparency.

M



Blue Fluorescence in Diamond GEMS & GEMOLOGY Winter 1997 245

To date, however, there have been no studies

that examine the influence of blue fluorescence onthe appearance of a diamond under normal viewingconditions. To this end, we identified certain funda-mental variables that we needed to investigate as afirst step in understanding this complex issue. Forexample, a grading laboratory such as the GIA GemTrade Laboratory (GIA GTL) assesses color undercarefully controlled lighting and viewing conditionsand mainly with the diamond positioned table-down. In a retail jewelry store, when a diamond isexamined for its overall color appearance in mount-ed jewelry, viewing normally occurs with the dia-mond table-up in any of a variety of lighting condi-

tions, as it does for the wearing of jewelry. Also,because it is within the D through J range that fluo-rescence has become a greater influence on pricing(Don Palmieri, pers. comm., 1997), we decided tofocus our initial investigation on diamonds that rep-resent this end of the color scale. Thus, the purposeof this study was to explore the perceived influenceof reported blue fluorescence in colorless to faint

yellow diamonds when viewed in different posi-

tions and under different lighting conditions byobservers from both within and outside the dia-mond industry.

BACKGROUND

Industry Perception of Fluorescence in Diamonds.Historically, the trade has given names to certaintypes of fluorescent diamonds based on the minesthat produced significant numbers of such stones.The term premier, for example, has been used todescribe light yellow diamonds with strong blue flu-orescence, because such diamonds were often

recovered from South Africa’s Premier mine. Theterm jager has been used to describe colorlessstones with strong blue fluorescence; the name orig-inates from the Jagersfontein mine in South Africa,where such diamonds were once common (Bruton,1978). Historically, some diamond merchantswould seek out near-colorless to light yellow dia-monds with strong blue fluorescence because they

Figure 1. Blue is by farthe most common fluorescence color encoun-tered in gem diamonds

when they are exposed tothe concentrated long-

wave ultraviolet radia-tion of a UV lamp. In

recent years, this proper-ty of many diamonds hasbeen the subject of muchdebate with regard to itseffect on appearance and

value. Photo by Harold &Erica Van Pelt.




Fluorescence is a form of luminescence. For the purpos-es of this paper, luminescence is defined as the emis-sion of light by a substance that has absorbed UV radia-tion. A substance is fluorescent if the emission of lightstops when the energy source causing it is removed. (Incontrast, if a substance continues to glow after the

energy source is removed, it is phosphorescent.)In a luminescent substance, the absorption of UVradiation causes an electron to move from its stablelow-energy position (“ground state”) into a temporaryhigh-energy (“excited”) state (figure A-1). This high-energy state is unstable, so the electron relaxes into alower-energy excited state that is slightly more stable.As the electron falls back to the ground state, the sub-stance emits light. This emitted energy is always lessthan excitation energy. Since wavelength increases asenergy decreases, emission occurs at longer wave-lengths than the excitation wavelength (again, see fig-ure A-1). Submicroscopic structures that allow thismovement of electrons are called luminescence cen-ters. These centers arise from certain defects in the

crystal lattice, such as electrically charged ions, oratomic vacancies or substitutions (see Nassau, 1983;Waychunas, 1988).

Gem diamonds typically contain a variety of struc-tural defects, most involving impurity atoms such asnitrogen, hydrogen, and boron. Nitrogen-related defectsare the most common of these, and only some of theresulting defects cause luminescence (Clark et al.,1992; Collins, 1992; see also Davies et al., 1978). Thenitrogen-related defects, and their association with flu-orescence, are described as follows:• A single nitrogen atom substituting for carbon in a

diamond that is partly type Ib (see, e.g., Fritsch andScarratt, 1992) produces orangy yellow fluorescence.• A group of two nitrogen atoms, the A aggregate, tendsto quench—that is, extinguish—fluorescence.• A group of three nitrogen atoms is called the N3 cen-ter, and produces blue fluorescence.

• A group of four nitrogen atoms is called the B aggre-gate, and is not known to cause luminescence.• A lens-shaped cluster of nitrogen atoms is called aplatelet, and is associated with yellow fluorescence.• A single nitrogen atom trapped near a carbon vacancycauses bright orange fluorescence.• A vacancy trapped near an A or B aggregate is calledthe H3 (H4) center, and generates green fluorescence.

A single diamond may contain several differentkinds of defects, leading to a range of complex relation-ships between nitrogen content, nitrogen aggregationstate, diamond color, and fluorescence color andstrength. A diamond may also display two different flu-orescence colors, either clearly zoned or closely mixedtogether. As described in the Background section of the

text, of 5,710 colorless to near-colorless diamonds thatfluoresced a noticeable color, 97% showed blue fluores-cence, which is caused by the N3 center. Of 16,835 dia-monds in the same study that did not fluoresce, manycontained N3 centers, but they also contained enoughA aggregates to prevent any visible luminescence. Theexistence of N3 centers in these diamonds is suggestedby their yellow bodycolor (most commonly caused by“Cape” absorption bands, which are related to thesecenters); the existence of A aggregates (or other centersthat quench luminescence) is evident from the fact thatthe stones do not fluoresce. These complexities con-

found the trade notion that nonfluorescentdiamonds are more “pure” than those that

fluoresce, since there are nitrogen-relatedcenters that extinguish fluorescence, aswell as those that cause blue fluorescence.

BOX A: FLUORESCENCE IN DIAMOND

Figure A-1. The diagram on the left showsthe relationship of visible light to ultravio-

let and infrared radiation. The wavelengthof light is related to its energy in an

inverse manner: the longer the wavelength, the lower the energy. Visible light

has longer wavelengths than UV radiation, but is lower in energy. The energy

diagram on the right shows the relationship between absorption and lumines-cence. When UV radiation is absorbed at a luminescence center, it causes anelectron to move from the ground state to an excited state (straight up arrow).No light is emitted as the electron moves to a slightly lower state, losing someof its energy (wavy down arrow). From this lower state it returns to the groundstate (straight down arrow), releasing energy as fluorescence (visible light). Both

figures are adapted from Nassau (1983).

E N E R G Y

A b s o r p t i o n

F l u o r e s c e n c e

Ground state

Relaxation

10,000

2000

1000

700

600

500

400

ENERGY(electron

volts)

WAVELENGTH(nanometers)

ULTRA-

VIOLET

INFRA-

RED

VIOLET

BLUE

GREEN

YELLOW

ORANGE

RED

300

2505

4

3

2

1

0

Excited states




believed that such fluorescence gave rise to a dia-mond that appeared “more colorless” (i.e., “less yel-low”) under lighting with a high UV content. Firmssuch as C. D. Peacock were known to actively lookfor such fluorescent diamonds (Joe Samuel Jr., pers.comm., 1997). Often these diamonds were market-

ed as “blue-white,” a term that was prohibited byU.S. Trade Practice Rules in 1938 (U.S. FederalTrade Commission, 1938). Recognizing that somehighly fluorescent diamonds might have a slightlydifferent color appearance when viewed under lightsources with differing UV content, Shipley andLiddicoat (1941) emphasized the importance of con-trolled lighting conditions for consistent color grad-ing of faceted diamonds.

Tradespeople further observed that some gemdiamonds with a hazy appearance also fluorescedstrong blue to UV radiation. In the dynamic marketof the late 1970s, some dealers began offering sub-stantially lower prices for what they called “milkyDs” (diamonds with a color grade of D, very strongblue fluorescence, and reduced transparency). Overthe next decade, the perceived negative impact offluorescence spread down the color grade scale (asfar as F) and eventually also included stones withweaker fluorescence (M. Rapaport, pers. comm.,1997). In recent years, fluorescence has had moreimpact as a value factor because of the influx oflarge quantities of high-quality diamonds fromRussia. Many of these diamonds exhibit moderateto strong blue fluorescence to the UV lamp (Kevo

Ayvazian, pers. comm., 1997).The concerns about fluorescence can be

attributed to a number of factors. These includenotions that: (1) nonfluorescent diamonds are more“pure” than those that fluoresce, (2) nonfluorescentdiamonds (in the colorless range [D–F]) are rarerthan fluorescent diamonds in the same color range,and (3) the hazy appearance seen in some stronglyfluorescent diamonds must exist in more weaklyfluorescent diamonds as well. With the airing of atelevision “exposé” in South Korea in 1993 (WeWant to Know That), the negative image of fluores-cent diamonds was brought to the attention of con-

sumers as well.An indication of the extent to which fluores-

cence influences market value is found in theRapaport Diamond Report weekly price guide. Inthe November 7, 1997, Report, for example, somehigher-color (D-H) diamonds with very strong fluo-rescence were listed for up to 15% less than compa-

rable nonfluorescent stones. From the spring of1993 until the present time, the Report has statedthat “the impact of blue fluorescence on pricedepends on its noticeability.” Although the fluores-cence description (which is based on observationsmade under a long-wave UV lamp) can be read from

a laboratory grading report, “noticeability” refers tothe direct observation of the diamond under thelighting conditions of a normal trading environ-ment. In that same issue of the Report, lower-color(I–N) diamonds with very strong fluorescence car-ried a premium of up to 4% over similar nonfluo-rescing stones. This may be due to the continuingperception of many in the trade that blue fluores-cence acts to mask or offset the faint to very lightyellow bodycolor of some gem diamonds.

Observation of Fluorescence. Fluorescence is the

“emission of visible light by a material such as dia-mond when it is stimulated by higher-energy X-rays, ultraviolet radiation, or other forms of radia-tion. Fluorescence continues only as long as thematerial is exposed to the radiation” (Liddicoat,1993, p. 91). In gem testing, the ultraviolet unit thatis commonly used provides two types of UV radia-tion. These two types are normally referred to bytheir most intense excitation wavelengths: 365 nm,or long-wave UV (also an important component ofdaylight); and 254 nm, or short-wave UV. Althoughthe latter provides identification data for the labora-tory, it is long-wave UV fluorescence that is meant

when fluorescence is discussed in the diamondtrade or described on a diamond grading report. (Formore on fluorescence in diamonds, see Box A.)

Depending on the viewing conditions and theobserver’s visual perception, the reaction of a dia-mond to long-wave UV radiation may vary in bothstrength and hue. Both colorless and colored dia-monds can fluoresce several hues, most commonlyblue, yellow, orange, and white. Some pink (and, onrare occasions, colorless and near-colorless) dia-monds fluoresce bright orange. Some blue dia-monds, such as the Hope, fluoresce (and phospho-resce) red to short-wave UV. These different colorsof UV fluorescence arise either from trace impuri-ties (mainly nitrogen and boron, possibly hydrogen)or from other submicroscopic defects in the dia-mond crystal structure (again, see Box A). In theexperience of GIA GTL, strength of fluorescencedoes not directly correlate to either color or clarity.For example, a diamond with a clarity grade of




internally flawless and a color grade of D can exhib-it the same strength of blue fluorescence as anotherdiamond with a clarity of I1 and a color grade of J.

A gemological report assigns grades so that thequality of one diamond may be assessed relative toothers, but it also provides information that

describes the stone and helps separate it from otherdiamonds. At GIA GTL, the fluorescence entry on adiamond grading report is considered to be adescription, not a grade. In fact, the laboratory hasused fluorescence to help clients recover diamondsthat were lost or stolen.

At GIA GTL, the standard procedure for observ-ing UV fluorescence includes use of a long-wave UVlamp in a darkened viewing environment. Factorssuch as the distances and viewing angles betweenthe UV lamp, the diamond, and the observer arespecified to maintain consistency betweenobservers. A set of reference diamonds is used toestablish the intensity of the fluorescence exhibitedby a stone within the ranges none, faint, medium,strong, and very strong. In a procedure similar tothat employed for color grading with the D-to-Zscale, the diamond being examined is placed table-down and moved between the reference stones untilthe intensity of the fluorescence is stronger than the

reference stone on the left, and weaker than the ref-erence stone on the right (figure 2). As with colorgrading, the trained eye adjusts for differences infacet arrangement, size, and shape between the dia-mond and the reference stones. This procedure fol-lows the standard methodology recommended by

the American Society for Testing and Materials(ASTM, 1996) for comparing the colors of objects.

To better understand how common UV fluores-cence is among colorless to faint yellow diamonds,we reviewed a random sample of 26,010 GIA GTLgrading reports for diamonds in this range. The datarevealed that approximately 65% of these diamondshad no reported fluorescence to long-wave UV radi-ation. (Note that a report description of “none”means that any fluorescence exhibited is weakerthan that of the reference stone that marks thenone/faint boundary.) Of the 35% (9,175 diamonds)for which fluorescence was reported, 38% (3,465)were described as having faint fluorescence and62% (5,710) had descriptions that ranged frommedium to very strong. Of the 5,710 diamonds withmedium to very strong fluorescence, 97% (5,533)fluoresced blue (in varying intensities) and only 3%(162 stones) fluoresced another color (yellow, white,or orange; no color is reported for descriptions offaint fluorescence.). Therefore, only 35% of the26,010 diamonds fluoresced, and less than 1% fluo-resced a color other than blue. Of the 11,901 dia-monds in the D-to-F range, a similar proportion flu-oresced (4,250 diamonds, 36% of the total).

Although yellow fluorescence is also a concernin the industry (see, e.g., the June 1997 issue of theDiamond Value Index ), our decision to limit thepresent study to diamonds with blue fluorescencewas based on the preponderance of such diamondsand the difficulty of finding sufficient numbers ofyellow-fluorescent stones to conduct a parallelstudy. Diamonds with extremely strong blue fluo-rescence and a distinctive oily or hazy appearance,often referred to as “overblues,” are also a concernto the industry. In our experience, however, they areeven rarer than diamonds with yellow fluorescence.

MATERIALS AND METHODSDiamond Samples. From an initial population ofmore than 1,000 diamonds made available forstudy, we identified approximately 300 stones withvarying degrees of blue fluorescence. From these,we assembled four sets of six stones each that werevery similar to one another in all respects excepttheir fluorescence (see figure 3 and table 1). Based on

Figure 2. As with diamond color grading, both thecontrol of observation variables (light source, envi-

ronment, viewing geometry) and the use of known reference stones are required to make consistent

fluorescence observations. At GIA GTL, the diamondbeing examined is placed table-down and movedbetween the fluorescence reference stones until the

intensity of the fluorescence is stronger than the reference stone on the left, and weaker than the ref-erence stone on the right. Photo by MahaDeMaggio.



E Color Set G Color Set

K Color Set

Figure 3. The four color sets of diamonds used for the observation experiments are seen here table-up andtable-down under normal lighting conditions, and under the long-wave UV lamp used to make fluores-cence determinations in the laboratory. See table 1 for precise descriptions of these stones as they are pre-sented here, which is the same arrangement within each set shown to the observers. From left to right, topto bottom: the six stones in the E set show strong, medium, very strong, none, faint, and strong fluores-cence; the G set stones show faint, very strong, medium, medium, none, and strong fluorescence; the I setstones show medium, very strong, faint, strong, none, and strong fluorescence; and the K set stones show very strong, faint, strong, strong, faint, and strong fluorescence. (Because of the inherent difficulties of controlling color in printing, the colors in this illustration may differ from the actual colors of the stones.)Photos of diamonds in normal light are by Harold & Erica Van Pelt; and in UV light, by Maha DeMaggio.

I Color Set





TABLE 1. Description of the 24 faceted diamonds used in this study.a

E color (Set 3) G color (Set 2) I color (Set 1) K color (Set 4)

Letter Fluor.b Clarity Wt. (ct) Fluor. Clarity Wt. (ct) Fluor. Clarity Wt. (ct) Fluor. Clarity Wt. (ct)

A Strong VS1 0.76 Faint VVS1 0.60 Medium SI1 0.79 V. strong SI2 0.56

B Medium VVS1 0.68 V. strong VS2 0.62 V. strong VS2 1.15 Faint SI1 0.56

C V. strongc IF 0.70 Medium IF 0.63 Faint VS1 1.01 Strong VS2 0.47

D None VVS1 0.69 Medium VS2 0.50 Strong VS1 1.19 Strong SI1 0.59

E Faint VS1 0.65 None IF 0.72 None VS1 1.03 Faint VS2 0.48

F Strong VVS1 0.77 Strong VS1 0.51 Strong VS2 0.80 Strong VS2 0.65

aThe letters represent how the diamonds were referred to in answering our questionnaire and their order from left to right as they were placed in trays or ring

mounts for viewing (i.e., the diamond labeled “A” was on the left,“B” next, etc.). The set numbers refer to the order in which each color set was given to the

observer. For all four sets of diamonds, polish and symmetry were good, very good, or excellent. bFluor. = strength of fluorescence to a long-wave ultraviolet lamp.cV. Strong = very strong.

our experience grading millions of diamonds, theselection was typical of those encountered in thetrade. All 24 diamonds were round brilliants; mosthad clarity grades at or above the VS range, were of

good or better symmetry and polish, had similarproportions, and fell within similar size ranges.Each set comprised a different color grade—E, G, I,and K—representing important commercial break-points. Within each of the four sets, the six dia-monds represented a wide range of intensity of blueUV fluorescence (from none to very strong). For allobservations, the diamonds were arranged in eachset so that there was no particular order to thestrength of their fluorescence. As noted above, wedid not include those diamonds with extremelystrong blue fluorescence and a hazy appearance(“overblues”—see, e.g., figure 4), because we could

not obtain sufficient numbers of such stones.However, the diminished transparency of theseextreme examples prompted us to investigate trans-parency as well as color in this study. Although wewould have preferred a larger sample of diamonds,we felt that this initial study should focus on con-trolling those other variables that could affectappearance, leaving fluorescence as the variable tobe studied. Despite the large number of blue fluores-cent diamonds that were available, potentiallyinfluential factors such as size, proportions, polish,symmetry, and clarity considerably narrowed ourfinal selection.

Viewing Environments and Methodology. Becausefaceted diamonds are observed under different light-ing and viewing situations in different parts of thetrade, we identified five representative viewingenvironments for this experiment (see table 2 andfigure 5). These environments cover the range of

lighting and viewing situations commonly encoun-tered in the industry. (Although incandescent lightsare frequently used in retail jewelry stores for dis-play purposes, diamond value judgments made by

jewelers are typically made with daylight or fluores-cent light.) The viewing environments that we usedfall into two general categories: “grading environ-ments” and “appearance environments.”

In grading environments, an attempt is made tocontrol, as much as possible, all observation vari-ables to achieve consistent, repeatable results dur-ing the evaluation of a diamond’s color grade. Here,as in standardized GIA color grading, the faceteddiamonds were viewed table-down through thepavilion facets, so that the effects of cutting, such asfacet reflections, would be minimized. Two suchenvironments were used:

1. A GIA GEM DiamondLite viewing unit, with anonfluorescent white interior and two overheadVerilux (daylight equivalent) fluorescent tube-type lamps, was placed in an otherwise dark-ened room. In this configuration, the six dia-monds in each set were positioned table-downon the floor of the viewing box, 5–10 cm (2–4inches) below the lamps, with the observerlooking at the diamonds in profile view (again,see figure 5). This is the standard position andenvironment for color grading diamonds in theD-to-Z range at GIA GTL.

2. An overhead, desk-mounted, Phillips F15T8/D15-watt (daylight equivalent) fluorescent tube-type lamp was placed in a standard office set-ting. In such an environment, there may ormay not be ambient light sources nearby (inthis instance, there were). The diamonds werepositioned table-down in a grooved, white, non-fluorescent plastic tray and observed in profile




view. (Although many diamond dealers regular-ly use a folded business card for such observa-tions, most white card stock itself fluorescesbluish white and thus adds its own emittedlight to the diamond being observed, potential-ly altering the color appearance.) This is thestandard position and environment for diamondcolor grading used in diamond bourses around

the world and in retail jewelry stores.In appearance environments, there is less

attempt (or opportunity, or perceived need) to con-trol the observation variables that can affect the dia-mond’s color appearance. Typical situationsinclude: informal color grading of D-to-Z diamonds;observations of color appearance made at the time adiamond is bought or sold; and, for the jewelry-buy-ing public, how a diamond might appear whenworn in jewelry. Here, the diamond is viewed table-up through the crown facets, where the cuttingstyle has more influence on the perceived color.Three such environments were used in our experi-ment:

3. Observations were made with an overhead,desk-mounted, Sylvania Cool White F15T8/CW15-watt (daylight equivalent) fluorescent tube-type lamp in a standard trading environment.(Recognizing that different offices have differentoverhead fluorescent lighting, we felt that theuse of different bulbs for environments 2 and 3provided a broader representation of trade envi-ronments. Again, in such a setting, there may ormay not be ambient light sources nearby. In thisenvironment, we did not have ambient light.)For this experiment, the diamonds wereobserved table-up in a grooved, white, nonfluo-

Figure 4. The 127 ct Portuguese diamond at theSmithsonian Institution in Washington, DC, is a classicexample of a blue fluorescent diamond referred to as an

“overblue.” These diamonds of extremely strong blue flu-orescence may exhibit a noticeable oily or hazy appear-ance when excited by any of a number of light sources.

Although diamonds described on a laboratory report as having very strong blue fluorescence are routinely seen in

the trade, a true “overblue” is not commonly encoun-tered and was not part of our study. Photo © Harold &Erica Van Pelt.

TABLE 2. The five viewing environments used in this study.

Distances:Lighting Observer type Stone light-to-object /

No. environment Light source (no.) orientation observer-to-object

1 DiamondLite, Verilux type Laboratory grader (5) Table-down, floor 2–4 in. / 12–18 in.in a darkened room fluorescent tubes (2) Trade grader (2) of viewing box (5–10 cm / 30–45 cm)

2 Overhead desk- 18” Phillips Laboratory grader (6) Table-down, 12–18 in. / 6–18 in.mounted light, F15T8/D 15-watt Trade observer (4) grooved tray (30–45 cm / 15–45 cm)in a lighted room fluorescent tube

3 Overhead desk- 18” Sylvania Laboratory grader (8) Table-up, 12–18 in. / 6–18 in.

mounted light, F15T8/CW 15-watt Trade grader (2) grooved tray (30–45 cm / 15–45 cm)in a darkened room fluorescent tube Trade observer (2)

4 Ceiling-mounted Phill ips FB40CW/6 Laboratory grader (6) Table-up in ring, Approx. 6 ft. / 6–18 in.room lighting 40-watt fluorescent Trade grader (1) ring tray (Approx. 2 m / 15–45 cm)

tubes Average observer (5)

5 Window South daylight Laboratory grader (3) Table-up in ring, Not applicable / 6–18 in.(indirect sunlight) (1:00–4:00 pm, July, Average observer (6) ring tray (NA / 15–45 cm)

in New York City)




rescent plastic tray. This is a standard environ-ment for evaluating diamonds in the trade.

4. Observations took place in a room with PhillipsFB40CW/6 40-watt fluorescent tube-type ceilinglights. Each of the diamonds was placed in aspring-loaded white metal display mounting,and each set was placed in a neutral gray ringtray. This also is a standard condition for buyingand selling diamonds in the trade; in addition, itapproximates the lighting conditions for typicalindoor wearing of diamond jewelry.

5. Observations were made in a room where theonly light was external, indirect sunlight com-ing through a window (July afternoon daylight,on a sunny day, from a southerly direction inNew York City). Each of the diamonds wasplaced in a spring-loaded white metal displaymounting, and each set was placed in a neutral

gray ring tray. This is a standard position andenvironment for buying and selling diamonds inthe retail jewelry industry. Although partial fil-tering of UV radiation occurs through a window,this approximates typical outdoor wearing ofdiamond jewelry.

Because different intensities of ultraviolet radia-tion in the light sources could affect the diamonds’fluorescence reaction, we used a UVX digitalradiometer manufactured by Ultraviolet Products,Inc., to measure the UV content in each of the lightsources chosen. The measurements revealed noappreciable differences in long-wave UV content

from one fluorescent light source to the next. Theyalso revealed that these light sources emit approxi-mately 5% as much UV radiation as the UV lamp,at the light-to-object distances used in the laborato-ry. According to our measurements, indirect day-light through our windows has about as much UVradiation as the fluorescent light sources.

Observers. We assembled four groups of observers, atotal of 46 individuals, to represent both the dia-mond industry and the diamond-buying public, asfollows:

1. Laboratory Graders (25 total)—trained individu-als employed by GIA GTL, who routinely per-form diamond color grading using the D-to-Zscale and GIA’s standard grading procedure.Because of their experience in diamond gradingand the fact that they are constantly monitoredfor consistency, we felt that the members ofthis group would best be able to make the dis-

tinctions we were investigating. Consequently,members of this group participated in everyviewing environment.

2. Trade Graders (5 total)—trained individualsemployed by diamond manufacturers, who rou-

tinely perform diamond color grading using theD-to-Z scale and a standard grading procedure.

3. Trade Observers (5 total)—individualsemployed by diamond manufacturers or dia-mond brokers, who have a working knowledgeof diamond color-grading practices but either donot carry out color grading on a daily basis or, ifthey do color grade, they use less stringentguidelines than those used by the Laboratoryand Trade Graders.

4. Average Observers (11)—individuals who repre-sent the diamond-buying public. Some of these

had limited knowledge of diamond color-grad-ing procedures, while others had none. In eithercase, none of these individuals had previouslymade observations of color appearance in dia-mond in any systematic way.

We asked these four sets of observers to viewthe four sets of diamonds in one or more of theviewing environments. Because some observersbrought their own trade practices to the experi-ment, and others had no prior experience with someof the environments, we did not ask all observers tomake observations in each type of environment.Nor do we have equal numbers of observations for

each group of observers and viewing environment.However, we did ask four observers (threeLaboratory Graders and one Trade Observer) whohad both laboratory and extensive trade experienceto look at the diamonds in more than one viewingenvironment. All told, the final data represent atotal of 50 observations for each of the four sets ofdiamonds (i.e., 46 observers, four of whom viewedthe diamonds in two environments).

Observer Questionnaires. We gave each observer asheet of instructions that briefly stated that the

research project concerned diamond fluorescenceand then asked questions regarding his or her obser-vations (table 3). The observer was verbally instruct-ed not to alter the geometry of the environment (thearrangement of the light source, diamond, and eye)in which the observation was being made. Termssuch as hue (color), depth (strength) of color, andtransparency (in this instance, the presence or




absence of haziness or oiliness) were defined so thatall observers were responding to the same character-istics. Our concern was to determine whether theseobservers could perceive any effect from fluores-cence on the appearance of the diamonds (that is,more or less colored or more or less transparent)under normal lighting conditions.

We presented the diamonds to each observerone set at a time, and then asked the individual toanswer the same group of questions for each set.Observers were allowed to select more than onestone as “most colored,” “least colored,” etc. No

time limit was given to view the sets of diamonds.RESULTS

Analysis of the Data. Questions 1, 2, and 6 weredesigned to focus the observer’s attention on theproperties we wanted to test: color and transparen-cy. Questions 3 and 4 provided us with quantifiabledata on color that could be statistically analyzed.

The answers to question 5 were not statisticallymeaningful. Questions 7 and 8 provided quantifi-able data for transparency.

We analyzed the combined results for allobservers and all viewing environments to seewhether there was an overall trend in (A) perceivedstrength or weakness of color in relation to fluores-cence; and (B) perceived transparency in relation tofluorescence. Next, for questions 3, 4, 7, and 8(again, see table 3), we tallied the number ofobservers who chose a particular diamond inresponse to each question. Since we had different

numbers of stones in each fluorescence category(e.g., two diamonds with “strong fluorescence” inthe E color set), we used a statistical normalizingtechnique to correct for the number of observations,so that each fluorescence category had the samechance of being considered as most colored, leastcolored, most transparent, or least transparent. Thisnormalization was important because certain fluo-

Figure 5. Gem diamonds are viewed in various environments and positions. These range from a highly controlled grading environment (DiamondLite, upper right) through more variable environments such as the diamond bourse (at Antwerp, above left) to the more generalized environ-ment of the retail jewelry store (lower right). DiamondLight photo by Maha DeMaggio, jewelry store photo by James Aronovsky, and bourse photo courtesy of the Diamond Bourse, Antwerp.




rescent stones were picked more often than othersof equal fluorescence strength in the same color set.We also adjusted the totals where needed to accountfor a single observer “splitting his or her ballot”—that is, choosing more than one stone as most col-ored, least colored, most transparent, or least trans-

parent. We used this corrected data set to build dis-tributions of the number of observations versus flu-orescence strength, for each question and a varietyof groupings (across observer types and viewingenvironments).

With this analytical technique, key trends inthe data can be readily discerned. These trends arebest seen as bar graphs of the (normalized) numberof observations for each fluorescence category. Theanswers to the two questions “most colored” and“least colored” (or “most transparent” and “leasttransparent”) actually constitute one set of observa-tions; that is, if a fluorescent effect exists, it shouldbe evident in the choice of both “most color” and

“least color.” To see this, the data are plotted on thesame graph, with more desirable attributes (leastcolor and most transparency) plotted above the axis,and less desirable attributes (most color and leasttransparency) plotted below the axis (see, e.g., figure6). A trend is indicated when the averages for each

category (above and below the axis) form a slopedline. For instance, figure 7A does not show a trend,whereas the trend in figure 8A is pronounced.

We first compared the Laboratory Graderresponses to questions 3, 4, 7, and 8 to those of eachof the other groups (Trade Graders, TradeObservers, and Average Observers). We found thatthe observations by the Trade Graders and TradeObservers showed trends similar to the observa-tions by Laboratory Graders. However, observationsby Average Observers were randomly distributed(that is, even in a color set and viewing environ-ment where trained Laboratory Graders detected atrend in stone color or transparency, averageobservers did not). Therefore, the results for AverageObservers were excluded from the remainder of theanalysis. It is apparent that the Average Observerswere not able to consistently discriminate any fluo-rescence-related effects in the viewing environ-ments most similar to those in which jewelry ispurchased and worn.

Assessing the Fluorescence Effect. Questions 1 and6 provided a general measure of the strength of theeffect fluorescence might have on color and trans-

parency. Seventy-one percent of all observers(excluding Average Observers), across all environ-ments and sets, said that stones in a given setappeared to have different depths of color. Twenty-nine percent reported that all the stones in a set hadthe same color appearance. However, when theanswers for each color set were examined separate-ly, it became evident that these results were relatedto color grade: 46% of the observations indicate nodifference for the E-color diamonds, 41% for the G-color diamonds, 15% for the set with an I colorgrade, and 10% for K color. No difference in trans-parency was reported by 62% of the observers in

response to question 6. This result also varied bycolor set, from 72% for the E set to 56% for the I set.

The data revealed a weak “fluorescence effect”in color appearance over all five viewing environ-ments considered together (figure 6). Althoughresponses to strongly fluorescent stones weremixed, in general, observers were more likely to

TABLE 3. The observer questionnaire.

Name:

Viewing Method:

Diamond Series:

1. Do all the diamonds in this group appear to have the samedepth of color? (Yes No)

If yes, please proceed to question 6.

If not, circle the corresponding letter for the one or ones

which appear different.A B C D E F

2. Do any of the diamonds have a different hue (color)? (Yes No)

If yes, which one or ones?

A B C D E F

3. Which diamond (or diamonds) has the most color?

A B C D E F

4. Which diamond (or diamonds) has the least color?

A B C D E F

5. Of the diamonds that remain, are any more colored thanthe rest? (Yes No)

If yes, which one or ones?

A B C D E F

6. Is there a difference in the transparency of any of thesediamonds? (Yes No)

If yes, please answer the next two questions.

7. Which diamond (or diamonds) appears the most transparent?

A B C D E F

8. Which diamonds appear the least transparent?

A B C D E F




choose inert and faintly fluorescent stones as “mostcolored” and very strongly fluorescent stones as“least colored” within each color set. For trans-parency, the “fluorescence effect” appears evenweaker, since most observers detected no effect at all.

Because all the viewing environments were

included in the above analyses, further evaluationwas needed to determine whether any particularfactor—viewing position, light source, and/or stonecolor—influenced the perceived effects of fluores-cence on color and transparency.

Viewing Position. Observations made with similarlighting conditions, but with the stones observedtable-down in environment 2 and table-up in envi-ronment 3, showed noticeably different results.Table-down yielded no trend in color with respectto increasing strength of blue fluorescence. How-ever, table-up showed a trend of better color appear-

ance with greater strengths of fluorescence. Wethen grouped the color observations for all lightsources for each of the two positions, with theresults shown in figures 7a and 8a. Viewed table-down, neither the most colored nor the least col-ored choices show a trend with fluorescence. In thetable-up position, there is a clear trend for stronglyfluorescent diamonds to look less colored, and fordiamonds with no to weak fluorescence to lookmore colored.

Across both viewing positions, most observerssaw no effect of fluorescence on transparency. Halfthe observers saw no difference in transparency in

the table-down position; the other half observed aclear trend toward lower transparency with strongerfluorescence (figure 7b). As seen in figure 8b, 71% ofthe observers saw no difference in transparencytable-up in similar lighting, and there was no dis-cernible trend in the observations of those who didperceive a difference.

Light Source. We saw no difference in the relation-ship between apparent color and strength of fluores-cence in diamonds observed table-down in aDiamondLite unit (environment 1) as compared tofluorescent overhead illumination (environment 2).

Nor did we see different relationships between colorand fluorescence in stones viewed table-up with flu-orescent overhead illumination as compared toexternal window light (environments 3, 4, and 5). Inother words, there did not appear to be any differ-ence among the light sources we used in their effecton perceived color relative to fluorescence.

By contrast, the results for transparency sug-gested a difference between daylight (environment

5) and artificial light (environments 1–4). Non-fluorescent and weakly fluorescent stones werereported by some observers to be more transparenttable-down in artificial light (environments 1 and 2;figure 7b), but less transparent table-up in indirectsunlight (environment 5; figure 8c). Although wewere not able to make any definitive conclusionsbecause of the limited number of usable observersfor the indirect sunlight environment, the prelimi-nary correlation of greater transparency withstronger fluorescence in the table-up position meritsfurther investigation.

Diamond Color. For each of the four color sets (E,G, I, and K) taken separately, we also saw no rela-tionship between strength of fluorescence and colorappearance with the diamonds viewed table-down,but we again saw a trend toward better color appear-ance with stronger fluorescence when the diamondswere viewed table-up, regardless of light source. It

Figure 6. This bar graph illustrates the observa-tions of color appearance in which color differ-ences were noticed, for the various fluorescencecategories across all color sets and all experiencedobservers. Strongly fluorescent diamonds are more

likely to be considered “least colored”––that is, to have a better color appearance––in contrast toweakly fluorescent stones, which were somewhat

likelier to be considered “most colored.”

Least

color

Most

color

40

30

20

10

0

10

20

30

O b s e r v a t i o n s

None Faint Medium Strong Very

strong

40

All EnvironmentsNo. observations = 110




appears that fluorescence had a weaker effect ontable-up color appearance for the diamonds in the Eand G color sets than for those in I and K. However,as there were far fewer observations for a singlecolor set than for all sets taken together, theseresults are less definitive.

DISCUSSION

For the observers in this study, the effect of blue flu-orescence on color appearance and transparency incolorless to faint yellow diamonds was subtle. Infact, our results indicate that Average Observerscould not make the fine distinctions sought in thisstudy. Of the experienced observers, most saw aneffect on color appearance, but far fewer saw anydifference in transparency. Even among the experi-enced observers, responses varied from stone tostone. Because some highly fluorescent diamonds ina set were singled out and others were not, it is pos-

sible that other factors are affecting color appear-ance more strongly than fluorescence strength.The results of this study indicate that there is a

perceptible relationship between blue fluorescenceand color appearance, which depends on viewingposition. On average, strongly fluorescent diamondshave a better color appearance table-up, and this

effect is most noticeable at lower color grades. Mostobservers did not detect any differences in trans-parency among diamonds in a given color set. Ofthose who did see a difference under fluorescentlighting, it was only apparent in the table-downposition. These results challenge the notion thatstrongly fluorescent diamonds typically have a hazy

appearance.Classic examples of fluorescent and nonfluores-cent diamonds that have similar color appearanceand transparency can be seen in many pieces of finejewelry. Figure 9 shows two complete views of thediamond necklace and earrings from the cover ofthis issue: one view under normal lighting condi-tions and the other under the long-wave UV lamp.Clearly, there is a range of fluorescence strengths tothe diamonds brought together in these pieces;however, there is a generally uniform overallappearance to the diamonds under normal lightingconditions.

CONCLUSION

Documenting the effects of blue fluorescence on theappearance of gem diamonds is a difficult and com-plex process. In this study, we screened more than1,000 polished diamonds to find 24 that fit the cho-sen color grades, clarity, cutting style and quality,

Figure 7. These graphs show the results of the observations on the diamonds positioned table-down. (A) Although color differences were seen in most cases (across all experienced observers and color sets), as indicated

by the pie chart, there is no clear trend in color appearance with strength of the fluorescence. (B) In half thecases, no differences in transparency were seen in the diamonds positioned table-down; however, the remainingobservations showed a clear trend for weakly fluorescent diamonds to be considered more transparent thanstrongly fluorescent stones.

Least

color

Most

color

15

10

5

0


strong

A. Perceived Color: Environments 1 and 2No. of observations = 68

Any Differences?

no19%

yes

81%


20

25

30

20

25

30

15

10

5

Least

transp.

Most

transp.

15

10

5

0

5

10


strong

B. Perceived Transparency: Environments 1 and 2No. of observations = 68

15

Any Differences?

no50%

yes

50%





and size range while representing the variousstrengths of fluorescence. Although yellow fluores-cent diamonds and “overblues” are also of concernin the trade, such stones are so rare that we couldnot assemble appropriate examples to perform acomparable study. We obtained the cooperation of46 observers from a wide variety of trade and non-trade backgrounds. One interesting aspect of thisstudy was that the nontrade observers could notmake meaningful distinctions. For this group,which would be considered most representative ofthe jewelry-buying public, fluorescence had no over-all effect on color appearance or transparency.

For the experienced observers, we found that, ingeneral, the strength of fluorescence had no widelyperceptible effect on the color appearance of dia-monds viewed table-down (as is typical in laborato-ry and trade grading). In the table-up position (as iscommonly encountered in jewelry), diamondsdescribed as strongly or very strongly fluorescentwere, on average, reported as having a better colorappearance than less fluorescent stones. In thisstudy, blue fluorescence was found to have evenless effect on transparency. These observations con-firm GIA GTL’s experience grading millions of dia-monds over the decades.

Figure 8. The results were also graphed for obser-

vations on diamonds positioned table-up with thedifferent types of fluorescent light and indirectsunlight. (A) Differences in color appearance were

noted in all three environments; they showed aclear trend for strongly fluorescent diamonds to beconsidered less colored than weakly fluorescentstones. (B) In most cases, no differences in trans-

parency were seen for diamonds positioned table-up in fluorescent light environments; for observa-tions in which differences were noted, no trendwas seen. (C) In half the observations, no differ-ences in transparency were seen; for diamonds

positioned table-up in indirect sunlight, the few observations in which differences were seen sug-

gest that strongly fluorescent diamonds were likelier to be considered most transparent.

Least

color

Most

color

20

15

10

5

0

5

15

20

None Faint Medium Strong

Very

strong

A. Perceived Color: Environments 3, 4, and 5No. of observations = 90

10

Any Differences?

no36%

yes

64%

25

30

O b s e r v a t i o n

s

25

30

Least

transp.

Most

transp.

15

6

3

0


strong

B. Perceived Transparency: Environments 3 and 4No. of observations = 64

15

Any Differences?

no71%

yes

29%


9

12

3

6

9

12

6

3

0


strong

C. Perceived Transparency: Environment 5No. of observations = 24

Any Differences?

no50%

yes

50%


9

12

3

6

9

12

Least

transp.

Most

transp.

15

15




Although we identified general tendenciesacross all diamonds and experienced observers, wealso identified apparent variations in fluorescenceeffect for different color sets. For instance, the effectof fluorescence on color was most noticeable in thelower (I and K) colors, although in the marketplacethe influence on price is greater in the higher(D through H) colors.

Unlike the notion held by many in the trade,

fluorescent diamonds are not as prevalent as nonflu-orescent stones, as the GIA Gem Trade Laboratorysample data for more than 26,000 diamondsshowed. The present study also challenges the tradeperception that fluorescence usually has a negativeeffect on better-color diamonds. Our results showthat the diamond industry would be better servedby considering each individual diamond on its ownvisual merits.

Figure 9. The necklace and earrings reproduced on the cover of this issue of Gems & Gemology areseen here in their entirety under normal lighting conditions (left) and under the long-wave UV lamp(right). Quite often, diamonds in a range of fluorescent strengths and colors are placed next to inertdiamonds, yet the piece maintains a uniform overall appearance under normal lighting conditions.The diamonds in the necklace weigh a total of 132 ct; the diamonds in the earrings weigh 23 ct, withthe two large pear shapes 3.04 and 3.20 ct. Jewelry courtesy of Harry Winston, Inc.; photos by Harold& Erica Van Pelt.

Acknowledgments: At the GIA Gem TradeLaboratory, Michael R. Clary and Joshua Cohn coor-dinated and administered the visual observationexperiments, and Mark Van Daele assisted with the

light source analysis. Scott Hemphill, a consultant inLexington, Massachusetts, extracted the statistics on

large numbers of fluorescent diamonds from the GIAGem Trade Laboratory database. Shane Elen of GIAResearch helped characterize some of the diamonds.The following firms kindly loaned diamonds for the

observation experiments: T. Gluck & Co., Good FineDiamond Corp., Gregric Diamond Co., LazareKaplan International., L.I.D. Ltd., E. Schreiber Inc.,and United Gemdiam. Dr. Emmanuel Fritsch, pro-

fessor of physics at the University of Nantes inNantes, France, contributed useful suggestions dur-

ing the early formation of this research.GIA thanks Hasenfeld-Stein, Inc. for financial

support of this research project and for loaning dia-monds for the observation experiments.




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luminescence spectroscopy. In J. Field, Ed., Properties of Natural and Synthetic Diamond, Academic Press, London,pp. 35–80.

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Waychunas G.A. (1988) Luminescence, X-ray Emission and newspectroscopies. In F.C. Hawthorne, Ed., Reviews inMineralogy , Vol. 18, Spectroscopic Methods in Mineralogyand Geology, Mineralogical Society of America, Washington,DC, pp. 639–698.

We Want to Know That (1993) SBA-TV, South Korea, broadcastMay 9.

gia - a contribution to understanding the effect of blue fluorescence on the appearance of diamonds...

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