Color changing treatment.

By Semyon Felshyn

A new color changing treatment was discovered in diamonds brought to the GCI – Gemological Centers Lab for inspection.
The treatment involves coating the diamond with a thin layer of foreign material.
The treated stone seems fancy colored, transparent and the color is evenly spread throughout the stone.
The coating is easily seen when scratched with tweezers.
The diamonds changes its color after long exposure to UV and peels off completely in ordinary boiling.
Diamonds treated by this process were mostly purple, pink and fancy brown.

מרכזים גמולוגים. GCI טיפול חדש לשינוי צבע נתגלה ביהלומים שנכנסו לבדיקה במעבדת
הטיפול כולל ציפוי האבן במעטה צבעוני דק המורכב חומרים זרים. האבן המטופלת נראית בעלת צבע, שקופה, כאשר הצבע נראה מפוזר באופן אחיד בכל האבן. הציפוי מתקלף בקלות כאשר שורטים אותו עם פינצטה ולכן קל לזיהוי.
היהלום משנה את צבעו בחשיפה ארוכה לקרני אולטרה וויולט ומתקלף לחלוטין בהרתחה רגילה. בשיטה זו נתגלו בעיקר יהלומים בגוונים שונים של סגול וורוד וחום.
The coating is almost unseen, but if we change the angle little bit..
The coating is easily scratched with tweezers.
Not valuable brownish stones getting attractive fancy colorsCapture_849
Internal graining inside the brown diamond.
If we change focus on the surface, we can easily see the coating.

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Would you pick it up from the ground?

By Semyon Felshyn

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A rare blue diamond has been discovered in the Cullinan mine in South Africa.


A 29.6-carat blue diamond, one of the rarest and most coveted in the world with a possible price tag of tens of millions of dollars, has been discovered at a South African mine by London-listed Petra Diamonds.

The miner said the "exceptional" acorn-sized diamond, small enough to fit into the palm of a hand, was unearthed at the Cullinan mine near Pretoria.

The mine, owned by Petra since 2008, was also where the Cullinan Diamond was found in 1905 — described as the largest rough gem diamond yet recovered and weighing 3,106 carats.

Other notable diamonds found in the mine include a 25.5-carat Cullinan blue diamond, found last year and sold for $16.9m, and a diamond found in 2008, known as the Star of Josephine, which was sold for $9.5m.

CEO Johan Dippenaar said the latest blue-diamond discovery could outstrip recent finds.

"By some margin ... this is probably the most significant stone we’ve ever, in terms of blue stones, recovered," he said.

"The stones in the past year or so are selling well above $2m per carat. That’s not my quote, that’s updates in the market," he said ahead of the company’s first-half trading statement.

Petra Diamonds is due to release figures on production and sales for the six months to December 31 on Thursday, but these will not take into account the latest find, which occurred in January.

Analyst Cailey Barker at broker Numis believes the diamond could fetch between $15m and $20m at auction.
Lately the owners of Petra diamonds refused to accept $12.500.000 offer for this stone.

Diamonds from both the Cullinan mine in South Africa and the Williamson facilities in Tanzania, both owned by Petra, have been displayed at London’s Buckingham Palace and are regarded as among the rarest and most valuable in the world.

Amber and imitations.

By Semyon Felshyn

Gas bubles inside the stone.                                                                              בועות גז בתוך האבן
What kind of spiders they were? Does anybody remember biologia lessons from the school?
                                                                            ? איזה סוגי עכבישים אלה? מישהו זוכר משיעורי ביולוגיה
At this stage we found mosquito close to head of spider.
                                                                                  בשלב הזה אנו רואים יתוש קרוב לראש של עכביש
Fractures on the surface.                                                                                   סדקים על פני השטח

עם צאתו לאקרנים של הסרט "פארק היורה" נחשף הציבור הרחב לעובדה שהטבע משמר בתוכו "מזכרות" מהעבר.
אחת מהדוגמאות הבולטות הנן אבני האמבר .
אמבר הינו שרף עצי מאובן בן 30-50 מיליון שנה.
אבני אמבר המכילות "שאריות" וחלקים מתוך עולם היער הקדמון בו הן נוצרו הינן נדירות.
לפנינו שלוש חתיכות אבני אמבר במשקלים של 35 קרט, 135 קרט, ו-165 קרט בהם ניתן לראות בברור את אותם "יצורים" וחלקי עלים שחיו בסביבה הטבעית של יערות קדמונים. חתיכות אמבר אלה מכילות לטאה, עכביש ויתוש שנלכדו בשרף הדביק.
גושי אמבר אלו הגיעו מאזור הים הבלטי.
גודלם והממצאים שבתוכם הופכים אותם ליקרים ומבוקשים בקרב אספנים.מחיר אמברים בגדלים כאלה יכול להגיע לעשרות אלפי דולרים. מחיר כל פריט יהיה תלוי בצבעו, שקיפותו כמו גם באופיו, סוגו ושלמותו של האורגניזם שנלכד בתוכו
אמבר – שרף עצים מאובן
חומר אורגני בעל שבירה יחידה של קרן האור SR
RI - 1.540
SG - 1.08
בגלל משקלו הסגולי הנמוך הוא נוטה לצוף במי מלח ולכן לרוב הוא מתגלה לחופי הים הבלטי.

When the film ‘Jurassic Park’ came out in 1993 many of us were exposed for the first time to some of nature’s ways of preserving traces of history. One of the most incredible ways is the Ambers.
Amber is a 30-50 million years old fossilized pine tree resin.
The Ambers often contain animal and plant material as inclusions, left as a testament to the ancient world in which they were created.
Presented here are 3 Ambers, weigh 952, 355 and 769 carats, in which embedded creatures and leaf fragments of the prehistoric forests are clearly visible.
These Ambers contain a lizard, a spider and a mosquito that were captured in the fossilized resin, and originated in the Baltic Sea region.
The odd size and the elements captured in these Ambers make them exceptionally expensive and desirable among collectors.
The value of Ambers like these can reach to tens of thousands of dollars, and is influenced by their colour and clearness, as well as the type and condition of the captured organism inside.

Amber -  fossilized tree resin.
*Organic matter with a single refraction of light - SR

RI - 1.540
SG - 1.08

Due to their relatively low specific gravity Ambers tend to float in salt water, and as such often discovered on the shores of the Baltic Sea.


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Synthetic ruby curved lines                                                                       קווים מעוגלים ברובי סינטתי
Doubling                                                                                                                              הכפלות
Fractures caused by quench crackled treatment.
                                                                                                .גלצים ברובי שנגרמו על ידי חימום וקירור
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Antique necklace

By Semyon Felshyn

Black and Yellow metal necklace set with thirty eight Old European cut and two hundred thirty one Rose cut.
The necklace can be separated appart. (Center Part + two Wings + Chaine).
ענק מתכת שחורה וצהובה, משובצת עם שלושים ושמונה יהלומים בליטוש אירופאי ישן ומאתיים שלושים רוזתות.
הענק מתפרק לחמש חלקים : חלק מרכזי + שתי כנפיים + שרשרת

Necklace chaine set with sixteen Old European cut diamonds appart, turns to a nice bracelet.
שרשרת עליונה בנפרד הופכת לצמיד.
A stamp of a French boar's head mark was taken with a x60 microscope.
חותמת של ראש חזיר בר מצולמת בהגדלה כפול שישים.
On French silver jewelry, the most often-seen mark is the boar's head, the mark of the Paris Assay Office,
indicating a fineness of 800 or higher on small articles (such as jewelry). This mark was in use from 1838 to 1961.
Outside of Paris, the crab mark was used from 1838 to 1961, and since 1962, has also been used by the Paris Assay Office.
. על תכשיטי כסף מתוצרת צרפת, חותמת הכי נפוצה היא ראש של חזיר בר, סמל של מכון התקנים הפריזאי.
חותמת הייתה בשימוש משנת 1838 עד 1961

Center stone: Old European cut diamond.
Color  : I
Clarity: SI1
Est.Weight: 0.60 carats.
Measurements: 7.10 X 6.49 X 1.98(!!!) mm.
The diamonds in necklace are H - J colors.
Pay attantion: Black silver metal setting makes diamonds looks "whiter".
: יהלומים בענק הם בצבעים
H - J
אנא שימו לב, כסף מושחר גורם ליהלומים להראות יותר לבנים
Old European cut and Rose cut diamonds.
Old Style diamonds setting.
שיבוץ יהלומים בסגנון ישן
Gold and Silver metals combination.
שילוב של זהב וכסף בתכשיט
Golden screw connect Center Part of necklace with one of the Wings.
בורג מזהב, המחבר בין חלק מרכזי של ענק לבין אחת הכנפיים
Eagle's head. French hallmark that was/is struck in gold jewelry containing gold parts.
It is used since 1838 with minor variations in it's design.
ראש נשר. חותמת צרפתית משנת 1838 על חלקי תכשיטים המכילים זהב
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A Lexicon of Diamond Treatment Terms

A Lexicon of Diamond Treatment Terms

by Yehuda Yacar, G.G.

Here we present the first fruits of our project aimed at compiling the gemological terms related to diamond treatments – processes, devices and companies

Apollo (today, SCIO)

The Apollo Diamond Company of Boston, Massachusetts produces single-crystal synthetic diamonds of near-flawless clarity. The crystals are used in the optic electronics industry, nanotechnology and more. The company also manufactures gem-quality diamonds. Apollo was also a pioneer in the field of growing diamonds using the CVD (chemical vapor deposition) method. The company specializes in growing colorless synthetic diamonds.

Bearding (Bearded Girdle)

Tiny cracks that may be created in the girdle during the bruting process. The cracks result from the application of excessive pressure by a manual bruter, or by an automatic or semi-automatic machine. The cracks resemble a thin white beard.


See the entry “color change.”

Cleavage, Feather, Fracture

A crack, cleavage, or break in the diamond, sometimes referred to by the Dutch term, gletz (feather). Some of the cracks do in fact resemble feathers.


A process of dividing a diamond crystal into two along one of its four cleaving planes (parallel to the octahedral facets). The cleaving is executed by creating a recess or a groove in the diamond, using laser or another diamond. Then a cleaving blade is inserted into the recess and tapped with a hammer-like instrument. The blade serves as a wedge for splitting the stone into two.

Color Change

Treatments of diamonds intended to alter their color (known in industry jargon – mistakenly – as diamond coloring). In the past it was customary to use radioactive isotopes to create a change in the lattice structure, so that the stone appeared to have a different color. Nowadays, with modern technology, it is possible to change and improve the color of diamonds using electronic accelerators that do not present a health problem, and in some cases render them colorless. Disclosure of color change treatments is required (see also HPHT).

Cubic Zirconia

Zirconia (CZ) is an artificial stone produced in an infinite variety of qualities at a very low price. The most common use of the stone is as a diamond imitation. It stone is composed of ZrO2 and other chemical components such as hafnium, calcium and yttrium, which contribute to the stability of its crystal structure. Zirconia is usually “colorless,” although it is also possible to manufacture it in a range of colors. The optic characteristics of zirconia resemble those of the diamond. Presented to the market in the 1970s, it became the most popular imitation of diamond due to its appearance and its low price. Remember: Cubic zirconia is not synthetic diamond.

CVD – Chemical Vapor Deposition

Plasmic layering – a chemical process for growing synthetic diamonds in plasma, or ionized gases. The growth of the material is achieved by depositing layers on top of one another.

Deep Boiling

An alternative to boiling as a cleaning process, executed by means of high pressure and high temperature for several hours. Deep boiling is capable of removing and whitening sediment from diamond facets or in open cracks on rough and polished.

Diamond Types

Diamond crystals are divided into three types, based on their level of inclusions as well as consideration of the molecular arrangement in the diamond crystal, which affects its physical characteristics. These are the types:
Type I – A diamond whose main inclusion contains nitrogen. Type I is divided into two subtypes: Ia, which contains concentrations of nitrogen atoms in groups, and Ib, in which the nitrogen atoms are spread through the lattice under the carbon atoms, making the diamond absorb light at the ultraviolet end of the spectrum and thus creating the yellow color of Cape diamonds.
Type II – A diamond that does not contain nitrogen inclusions. Type II is divided into two subtypes: IIa, which does not contain any other inclusions, and IIb, which contains boron. The boron atoms in type IIb are located under the carbon atoms in the crystal lattice, causing the stone to become a semiconductor of electricity. Type IIb diamonds are usually blue in color.
Type III – Diamond found in meteorites, which has a hexagonal rather than a cubic structure.

Eight Cut, Single Cut

A stage in the polishing of a stone that contains a table and four other facets on the crown and seven facets on the pavilion. Diamonds that undergo HPHT are entered into the process when they are at this stage.


A polished surface of a diamond.

Fancy Colors

Diamonds of special colors: red, blue, green, yellow, brown, black and others, that are not included in the standard scale of colors (D – Z). Looking at these diamonds from the direction of the crown, they seem to contain a color beyond grade Z on the master stones.

Fracture Treatment, Fracture Filling

Improvement of the appearance of a diamond that has open fractures by injecting it with foreign material. Silicon- or bromide-based material is used for this purpose. The filling withstands daily conditions, but heating at high temperatures or deep boiling extracts the filling and restores the stone to its previous condition. In some cases exposing the filling to UV rays is liable to change its color. Disclosure of this treatment is required.

FTIR – Fourier Transform Infra Red

A device that uses infrared rays to test the presence and quantity of components in a material. The result is a graph of absorption, which enables classification of the diamond type. The device is also used in the food, cosmetics and pharmaceutical industries.
Full Cut

The definition of a cut in which all the facets are on the crown and the pavilion, unlike Single Cut.


A private firm founded by Carter Clark of Sarasota, Florida. In 1995, the company acquired Russian technology that was used during the Cold War to grow synthetic diamonds, due the semi-conductive property of diamonds used in electronic components. The company specializes in manufacturing high-quality synthetic diamonds. At first, the company sold its synthetic polished directly to retailers. Now it sells rough diamonds to diamond manufacturers, who process it. Gemesis specializes in growing colored synthetic diamonds.

Growth Lines

Lines seen on a diamond that reflect the disturbances it underwent during the process of growth and crystallization. The lines – external or internal – may interfere with the polishing of the stone. Brown diamonds are the result of disturbances in the crystal structure; in most cases they have growth lines.

HPHT – High Pressure High Temperature

A process of changing the color of diamonds by using high pressure and high temperature. The process is now used in growing synthetic diamond, as well.


An internal flaw in a diamond. Inclusions are used to identify diamonds and they influence the grade of clarity. The existence, character and location of inclusions must be taken into consideration when deciding about diamond treatments, unlike external flaws, which affect the quality of the polishing and the symmetry and can usually be removed with minimal weight loss.

KM – Special Drilling

KM are the initials for “special drilling” in Hebrew: kiduah meyuhad. This is a laser treatment of diamonds that creates a series of cracks reaching the external facet. In this process, no drilling pipe is left in the stone. The process causes the existing flaw in the stone to open and reach the surface, thus making it possible to whiten it by means of deep boiling. Disclosure of this process is required.

LASER – Light Amplification by Stimulated Emission of Radiation

An energetic ray of light centered on a spot creates heat and causes material to burn. Lasers are used in the diamond industry for drilling, sawing, cleaving, bruiting fancy, creating grooves, and lately – also for diamond marking and inscription (see also: Laser Drilling).

Laser Drilling

Drilling of diamonds with a concentrated, focused ray of light. The ray burns the diamond regardless of the directions of the hardness. The laser serves as a means of reaching flaws in the core of the stone. A drilling pipe is left in the stone, making it possible to clean and whiten the pique using acid. Disclosure of laser drilling is required.

Lazare Kaplan (see Pegasus)

Light Brown

Diamonds of a brown color, corresponding to GIA grades K and J. Type II light brown diamonds become white under the HPHT process.


Pure synthetic moissanite is a polymer of crystal structure with covalent bonds, similar to those in a diamond. Due to these bonds, moissanite is able to withstand high pressure. Transparent, almost colorless moissanite appeared in the market in 1998. Note: Moissanite is not a synthetic diamond.

Patience Lines

Growth lines, which earned their amusing name because polishing them requires a great deal of experience and patience.


A subsidiary of Lazare Kaplan (LKI) that specializes in a process that whitens brown diamonds and makes them colorless. General Electric (GE) scientists perform this HPHT (high temperature, high pressure) process. In accordance with the decision of the World Federation of Diamond Bourses (WFDB), the company is required to mark diamonds that have undergone the process with a GE POL laser inscription. Nowadays, other companies in the market also perform the process.


Small pale or dark inclusions in a diamond. This term is used by European laboratories for grading the clarity of polished diamonds – it corresponds to the GIA’s grade I.


An optical device composed of two polarized lenses or filters, enabling examination of a diamond under polarized light, in order to determine the degree and location of any internal tension in the stone. In some situations, the use of polarized rays may clarify whether the diamond has undergone HPHT treatments.

Special Drilling (see KM)


A device used to test the way light that passes through material is absorbed. The device transmits light of different wavelengths from the UV and visible spectrum and up to near-infrared light. The result of the examination is a graph of the absorption, which provides information about the type of diamond, its color, color authenticity and treatments it has undergone, if any.


A firm that specializes in manufacturing industrial diamonds and offers diamond enhancement treatments and color changes. The company’s main specialization is in HPHT. Located in Utah, US, it recently it changed its name to Suncrest Diamonds.

Synthetic diamond

Diamond grown in laboratory conditions. These conditions imitate those in which diamonds are created in nature; they are created by using high pressure and temperature (HPHT) or chemical vapor deposition (CVD). Such stones may be referred to as man-made or laboratory-grown diamonds. They should not be referred to as cultured diamonds.

Top Light Brown

Diamonds with a very slight brown color. The color is parallel to GIA grades H and I. Type IIa top light brown diamonds are suitable for the HPHT process (see also: Light Brown).

Protrusions and recesses on the face of rough crystal that look like triangles (thus their name). The vertices of the trigon point towards the margins of the octahedral facets. Trigons serve as one of the means for identifying a diamond.

Type IIa
A Type IIa diamond – a diamond that does not include nitrogen in the atomic structure. Diamonds in the brown tones of this type are suitable for the HPHT process.

Ultrasonic device
A device for cleaning jewelry that operates on the basis of ultrasound. The jewelry is placed in a warm watery solution that contains an oil dissolvent. The sound waves create vibrations that push away the dirt that is dissolved.

Ultraviolet (UV) Light

Electromagnetic radiation of wavelengths that are below the level of visible light – lower than 4000 nanometers – and longer than that of an x-ray. LW ultraviolet light, with a wavelength of 3660, is used to test the fluorescence of diamonds.

Zvi Yehuda

An Israeli scientist and diamantaire who in 1982 found a way to improve the clarity of diamonds using a revolutionary process to create an optical phenomenon that “hides” fractures. The result is a diamond that looks better, and therefore is more marketable. In most cases the process is evident only under enlargement with a loupe or a microscope. The process endures regular daily conditions, but deep boiling restores the stone to its condition prior to the treatment. Disclosure of this treatment is required.


Fake Rough Diamonds

By Semyon Felshyn


Last week GCI Gemological Centers received from the Goverment Diamond Control, a parcel of 346.07 carat of crystals, imported as natural rough diamonds from Tanzania. The importer was sure that he got genuine diamonds. The crystals in the parcel had a shape similar to natural rough diamonds, and some of them showed noticeable surface lines, "positive triangles", frosted surfaces, internal inclusions and fractures. Specific Gravity was close to that of natural diamond . After testing and inpection of the goods at GCI laboratory, all the parcel was indetified as  topaz crystals - not even one single diamond !!! , The surface lines were engraved intentionally on the crystals.
Here you can find some pictures of different shapes rough crystals, taken while inspected at GCI.
! אזהרה יהלומי גלם מזויפים
                                                                                                              בשבוע שעבר הגיעו למרכזים גמולוגים חבילה של "יהלומי גלם"  במשקל של 346.07 קרט
(GCI - החבילה הובאה על ידי משרד פיקוח היהלומים הממשלתי והיא יובאה לארץ מטנזניה על ידי חבר בורסת היהלומים (השם המלא שמור ב
.אשר היה בטוח כי ברשותו יהלומי גלם
חבילה זו מצטרפת למספר חבילות קודמות אשר הובאו לארץ ואף הן התגלו כחיקויי יהלום
    גבישי האבנים בחבילה הנדונה היו בצורות דומות ליהלומי גלם טבעיים ובחלקם ניכרו בברור סימנים מוטבעים על פני השטח בצורת פסים, משולשים בולטים
משטחים פרוסטד וכן תכלילים פנימיים וגלצים.
משקלם הסגולי של הגבישים שנבדקו היה מאוד קרוב ואף זהה לזה של יהלומים.
לאחר אבחון ובדיקת החבילה הנדונה במעבדת  גי.סי.אי זוהתה החבילה כולה כגבישי טופז ואפילו יהלום טבעי אחד לא היה בה
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Bulike, Kappe and Crystal
"Bolike", "Kappe" and "Crystal" shapes.                             "צורות "בוליקה", "קאפה" ו"קריסטליות

Three natural diamonds (front line), comparing to similar shapes fake rough crystals (backline)
                    שלושה יהלומים טבעיים בשורה קדמית לעומת צורות דומות בחיקויי היהלום בשורה האחורית  

12.45 carat "Kappe" flat crystal.                                             גביש "קאפה" שטוח במשקל 12.45

Gletz (Feather / Fracture).                                                                             (גלץ (שבר/.סדק

Polariscope reaction: The stone shows light / dark - DR - Double Refraction.
                                                                      DR    תגובת האבן בבדיקת פולריסקופ - חושך / אור

Topaz crystal vs natural Diamond crystal (on the right).    גביש טופז לעומת גביש יהלום טבעי מימין

10.46 carat Octahedral "Crystal".                                        גביש אוקטהידרלי במשקל 10.46 קרט

Pay attantion: "Positive Triangles" engraved on the surface, to look similar to natural rough
diamond.No "Negative Triangles" found on the surface of the stones.
                     .שים לב: משולשים בולטים חרוטים על פני המשטח על מנת לתת מראה דומה לגלם היהלום
                                                                                                     לא נמצאו משולשים שקועים

Gletz (Feather / Fracture).                                                                             (גלץ (שבר/.סדק

Pay attention: Two Phase inclusions, typical to Topaz.    שים לב: תכלילי שתי פזות אופייניים לטופז

Polariscope reaction - light and dark     ->      D.R.                         תגובה בפולריסקופ : אור חושך

Topaz crystal vs natural Diamond crystal (on the right).
Pay attention:Artificial "Positive triangles" surface lines on the left crystal.
                                                                                   גביש טופז לעומת גביש יהלום טבעי מימין
                                            שים לב: קווי משולשים בולטים שנחרטו בצורה מלאכותית בגביש השמאלי

Gletz with yellow color wale.                                                           גלץ בעל הינומה בצבע צהוב

6.41 carat Dodecahedral "Bolike" crystal                     גביש בוליקה דודקהידרלי במשקל 6.41 קרט

Engraved surface lines.                                                                  קוים חרוטים על פני המשטח

Topaz crystal vs natural Diamond crystal (on the right).See the difference between natural
surface lines (on the right) and artificial surface lines (on the left).
                                                                                  .גביש טופז לעומת גביש יהלום טבעי מימין
       שים לב להבדל שבין קוים טבעיים על פני המשטח לבין קוים שנחרטו בצורה מלאכותית על פני המשטח

Polariscope reaction    ->                       DR                                        תגובת האבן בפולריסקופ

All the pictures in this blog are copyright protected
                                                                                 כל התמונות בבלוג זה מוגנות בזכויות יוצרים

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A diamond's color - or lack of color- is one of the components that affects its value. The diamond industry has developed methods to turn yellow and brownish diamonds into the colorless and vivid fancy colors that the public and the market demands.

As a result, the diamond market has seen an ever increasing number of natural diamonds and diamonds types that have been subjected to some form of color changes through High Pressure High Temperature annealing or irradiation.

The synthesis of diamond at high pressures and high temperatures was first demonstrated by ASEA in Sweden in 1952 and at GE in 1955.

The awareness of the market to HPHT color treated diamonds started when General Electric and Lazare Kaplan, in early 1999 introduced a technology to process certain type IIa diamonds and to convert them from brownish colors to a much more marketable colorless range or pink color. As a result of the treatment, the color of a diamond can be improved by several color grades. . General Electric is producing colorless diamonds, called Bellataire, from type IIa diamonds that are nitrogen-free.

Irradiation and HPHT treatment are the color enhancement methods that in recent years have been applied to change the color of natural diamonds as well as laboratory created diamonds. Experiments using irradiation to change diamond’s color began in the early 1900s. The early process produced some good colors but left the gems strongly radioactive for years. Current methods though leave hardly any residual radioactivity. Irradiation produces green and blue colors, and additional treatments can create yellow, orange, and red colors.

The artificial irradiation of diamonds uses high-energy particles to create color centers in the atomic crystal lattice. The most common commercial irradiation treatments involve focusing a beam of accelerated particles (electrons or neutrons) at a diamond, which creates green and blue colors. By following irradiation with annealing via heating to around 800 °C, the green and blue colors can be changed to orange, pinks and reds.

The problem with irradiation is that although the colors are attractive, there is some question about their permanency and the health hazards. Irradiated diamonds are guaranteed to survive the normal, everyday wear and tear, but the color may change when the stone is exposed to high heat.

The more recent option for coloring diamonds, the HPHT treatment is more costly more than irradiation, but it produces colors that are stable even under intense heat and there are no health issues involved. A variety of tests have shown the HPHT color treatment to be permanent and irreversible. The HPHT treatment has therefore proven to be the primary color enhancement method.

How HPHT Works

Initially, General Electric and Lazare Kaplan utilized HPHT treatment to remove color from brown type IIa diamonds, resulting in colorless or near-colorless gems
When the diamond crystal is subjected to very high temperatures, the structure of the dislocations is modified, causing the brown coloration to be reduced. At these very high temperatures, diamonds will convert to graphite unless very high pressure is applied. This is done using the same kind of equipment as is used for diamond synthesis, e.g., the conventional “belt” presses developed by General Electric, the cubic or prismatic presses used by NovaTech or the BARS presses developed in Russia. Such equipment is complex and relatively expensive.

Typical HPHT conditions can be in excess of 2000ºC and 60,000 atmospheres

Less than 1 percent of natural diamonds are type II of adequate quality to be suitable for HPHT treatment. The HPHT color enhancement can also be suitable for converting brownish colored diamonds to fancy colored diamonds. Type IIb brownish diamonds can be enhanced to blue. HPHT can also change Type IaA/IaAB to yellow/orange or yellow-green 

HPHT color treated diamonds - IDENTIFICATION

Gemological laboratories today are required to be able test both whether a diamond is suitable for HPHT annealing, ie. color improvement and whether a diamond has undergone color treatment.

Currently, the recognition of HPHT-treated diamonds involves the determination of various visual properties - such as color and features seen with magnification - as well as characterization by several spectroscopic techniques. HPHT-treated diamonds were introduced into the jewelry trade in the late 1990s, and despite progress in their recognition, their identification remains a challenge. While some detection methodologies have been established, the large number of diamonds requiring testing with sophisticated analytical instrumentation poses a logistical problem for some gemological laboratories.

HPHT will continue to be a controversial topic, with grading labs trying to perfect ways to detect the always-improving process so that consumers can receive full disclosure about the diamonds they purchase. The Federal Trade Commission recommends that HPHT is disclosed. It has become common practice for gemological laboratories to clearly indicate on diamond grading reports if the diamond is "HPHT annealed" or "artificially irradiated". At the Gemological Institute of America (GIA), diamonds are laser-inscribed with the words "HPHT PROCESSED" or "IRRADIATED" on the girdle.

Color treated HPHT diamonds are highly fluorescent and contain observeable absorption characteristics as well as inclusions. The majority of color treated diamonds are type IIa diamonds, which are very rare in nature. They are almost free of nitrogen transparent in part of infrared and have irregular shapes.

Type IIa diamond is the rare type of diamond that can be transformed from brownish to colorless of a higher value — up to D in color — by HPHT treatment. Thus the first step to detect color treated is to determine whether the sample is type IIa. This can easily be done by using the SSEF Diamond Spotter, which is based on the transparency of these diamonds to short-wave ultraviolet radiation (SWUV).
The SSEF diamond spotter provides an inexpensive and convenient first test to determine whether it is not one of these rare types that are suitable for HPHT treatment, but if it is one of the rare types other infrared spectrometric tests must be performed.

The SSEF Diamond Spotter determines whether or not a diamond is one of the rare types that could be treated to produce colorless, near-colorless, pink and blue diamonds. It allows an easy separation into two groups of diamond types: type IaA, IaAB and Ib versus IIa, IIb and rare IaB. The technology is based on the fact that Type II diamonds are transparent to SWUV light, whereas the vast majority of Type I diamonds block SWUV light.

However, it does not determine whether the diamond has been HPHT treated or not.
By placing a diamond into the spotter and switching on the SWUV light source, the diamond will react by transmitting or absorbing the SWUV light, thus fluorescence or no fluorescence on the screen of the spotter

Green fluorescent light spot on the screen during testing with the SSEF diamond spotter identifies the diamond as type IIa or IIb or rare type IaB and at the same provides indication that a colorless diamond may have been “discolorised” by HPHT treatment. Further analysis is required within a specialized gemological laboratory which is equipped with spectroscopic detection instruments.

If no fluorescence reaction shows on the screen in the SSEF diamond spotter, the diamond is of type Ia or Ib, which means that the colorless diamond has not been HPHT treated for discolorisation.

A very similar screening device has most recently been introduced by the HRD. The technology used by the D-Screen is based on optical measurement by projecting shortwave UV radiation through the diamond.

Conclusive identification of HPHT treated diamonds requires low-temperature visible and photoluminescence spectroscopy, techniques normally available only in professional gemological laboratories.

Thus as the diamond is identified as a type that is suitable for HPHT color treatment, the second step is to look for subtle luminescence features related to N-V centers in the type IIa diamonds with a Raman spectrometer.


The real concern in the industry regards the possibility of undisclosed HPHT treated stones and the need for detection. Research in the detection methods are constantly under review to extend capabilities. Laboratories worldwide have therefore invested heavily in the equipment needed to handle detection hand in hand with professional staff that has the necessary knowledge to interpret the available data. The potential of fraud in the industry means that disclosure must be accompanied by a combination of means of identification. In the case of HPHT treated diamonds, this can reliably only be achieved by detailed spectroscopic examination at a fully equipped gemological laboratory.