dgemg- and dsef-information: clarity enhancement of emeralds · 2018-04-17 · emeralds. oil, wax,...

DGemG-information 3/2016 Clarity enhancement of emeralds © DGemG & DSEF

DGemG- and DSEF-information:

Clarity enhancement of emeralds

German Gemmological Association and German Gem Lab www.dgemg.com and www.dsef.de Authors: Dip.-Min. Fabian Schmitz and Tom Stephan B.Sc. (DGemG) Dr. Claudio C. Milisenda, Dip.-Geol. Stefan Koch and Stefan Müller M.Sc. (DSEF) © 2016

Content 1. Introduction: History of clarity enhancement of emeralds 2. Treatment process and filler substances 3. Identification 3.1. Residues of the filler substances 3.2. Flash-effect 3.3. Fluorescence 3.4. Spectroscopic methods 4. Duration of the fillers 5. Nomenclature 6. Literature

Fig. 1: Emerald (Columbia, 1.16 ct) before (left) and after clarity enhancement (right) (sample: Company Lothar Haag GmbH & Co.KG, Idar-Oberstein).

© DGemG


1. Introduction: History of clarity enhancement of emeralds The enhancement of the clarity resp. transparency due to the filling of surface-opened

fissures improves the appearance of a stone distinctly. Furthermore, the filling with

polymers increases the stability.

One of the first descriptions of the use of oil as a filling material for fissures, especially for

emeralds, was given by C. Plinius Secundus (55 AD) in his 37th book of natural history. Other

historic information are the Papyrus Graecus Holminensis (400 AD), as well as Arabian

writings from the 14th century. Since the 1980s artificial resins, which fill the fissures and,

depending on the kind of application, could coat the stone, too, are used to impregnate

emeralds. Oil, wax, soft resins and artificial resins are the common filler substances for the

clarity enhancement of emeralds today.

2. Treatment process and filler substances During clarity enhancement fissures are filled with a filler substance showing a similar

refractive index like emerald. This lowers reflections and total reflection at the former air-

filled fissures strongly.

Fig. 2: Equipment for clarity enhancement of emeralds

(Company Lothar Haag GmbH & Co.KG, Idar-Oberstein).

© DGemG


Basically it is differentiated between fissure fillings with oil or artificial resin. Both treatments

are presented shortly in the following (c.f. RINGSRUD, 1983 & KAMMERLING et. al., (1991):

Treatment with oil • Cooking of the stones in methyl- or ethyl alcohol to clean them • Cleaning in hydrochloric and nitric acid (HCl : HNO3 = 2:1) to remove residues of the

cutting and polishing process (usually Zn, Pb and Cr-oxides) from the fissures • Removing of acid residues from the fissures with alcohol • Oiling of the stones (at approx. 83°C, to increase the viscosity) • Removing of oil residues at the surface by rubbing

Treatment with artificial resin • Cleaning of the fissures with diluted hydrochloric acid • Filling of the fissures in a vascular in the oven at approx. 95°C • Treatment of the surface with a hardness substance or UV-light • Cleaning of the stones in vacuum (also for oil)

• better removal of dirt in fissures • Filling process under pressure (also for oil)

• better infilling and consistent distribution

Filler substances Oils keep their viscosity after the filling process, therefore the transparency may deteriorate

after some time. Besides, oiled emeralds should not be cleaned in the ultrasonic bath.

However, a benefit of oils is, that it is easy to remove and refresh them. Additionally the

natural state of the emerald is recoverable.

Canadabalm, which is listed in the table, is a natural resin. The treatment process is the same

as for oils.

The following oils find a use:

Fillers (Oil): Refractive index:

Paraffin-oil 1.45 – 1.49

Cedar wood oil (various) 1.51

Cosmetic oils >1.50

Corn oil 1.47

Olive oil 1.47

Canadabalm (natural soft resin) 1.52-1.55

Moreover, also coloured oils have an application, but this enhancement is then declared as

dyeing.

Artificial resins on the contrary are hardened, to seal the opening of the fissure at the

surface. This extends the duration of the fissure filling and therefore also the transparency

and stability of the stone. A disadvantage of artificial resin is, that it is harder to remove it

(acid), to recover the stones natural state. Often the only way to remove the artificial resin is

repolishing (JOHNSON, 2007). Some artificial resins contain UV-active addives (“Fluoresin”), to


increase their recognisability (THEMELIS, 1990). The artificial resin “ExCel” does not have these

additives.

The following artificial resins find a use:

Fillers (artificial resin) Refractive index

Opticon 1.545

Permasafe 1.56 – 1.60

Epon 828 (“palm oil“!) 1.573

ExCel (former: “Gematrat“) 1.52 – 1.60

Epoxy resin various

Silicon „DC4“ various

c.f. THEMELIS, 1990 & KIEFERT et.al., 1999.

3. Identification The identification of clarity enhanced emeralds is based on several criteria. Microscopic characteristics, the UV-fluorescence and spectroscopic investigations are used today, to detect not only the filler substance itself, but also the kind of filling material (KAMMERLING et al., 1991). 3.1. Residues of the filler substances

No matter if treated with oil or artificial resin, in both cases the filler substance mutates

afterwards. Because they are usually organic substances, oils and artificial resins can change

their colour and coagulate, which means, that their structures change slightly and show less

transparency. Consequently, structures inside the fissures become visible, which would not

be present in an untreated emerald. These are identifiable in the microscope in both,

transmitted as well as reflected light. Additionally it is observable often that especially oil

begins to dry after a while.

The residues of the filler substances are detectable in particular because of the specific

structures and the dried areas (fig. 3 – 7). Attention should be paid to the fact, that

immersion liquid could also enter open fissures. Therefore, no liquid should be used while

microscoping (RINGSRUD, 1983).

Fig. 3: Residues of oil in an emerald from Colombia.

Fig. 4: Residues of oil (brown) in an emerald from Brazil.

© DGemG © DGemG


Fig. 5: Strongly reflecting residues of artificial resin in reflective light in an emerald from Zambia.

Fig. 6: Fissure filling with artificial resin in an emerald from Colombia.

Fig. 7: Typical “fingerprint-like” structures of artificial resin in an emerald from Colombia.

3.2. Flash-effect

Another important characteristic of with oil or artificial resin filled emeralds is the so-called

flash-effect (fig. 8 and 9), generated through “interference at thin layers”. Here the following

rule counts: The higher the difference between the refractive index of filler and emerald, the

more colours shows the flash-effect. This effect is harder to identify, if the filled fissure is

thicker. But in those cases it is easier to observe it close to the stones surface.

In some cases the flash could be orange, too.

© DGemG © DGemG

© DGemG


Fig. 8: Blue flash-effect in a fissure in an emerald from Colombia.

Fig. 9. Orange-blue flash-effect in a clarity enhanced emerald from Colombia.

3.3. Fluorescence

Some filler substances show fluorescence when stimulated with ultraviolet light or with a

405 nm – laser. Attention should be paid to the fact, that these lasers can harm the human

eye heavily. When using such an instrument, one should always wear safety-googles. It is

also useful to observe the fluorescence with the help of an imaging-system, e.g. a

microscope with camera and monitor. UV-radiation, especially short-waved UV, can harm

the eyes, too (c.f. THEMELIS, 1990 & KAMMERLING et. al. 1991).

Fig. 10: Fluorescence of a filler substance in an emerald from Colombia in laser light (405 nm – laser

pointer).

Fig. 11: Fluorescence of artificial resin in a cavity in laser light (405 nm – laser pointer).

© DGemG © DGemG

© DGemG © DGemG


3.4. Spectroscopic methods The Raman-spectroscopy is an established method for the identification of materials. Most of the filler substances, which are used today, can be identified with this method, too. The filler substances show their characteristic peaks especially in the spectral areas between 1200 – 1800 cm-1 and 2700 – 3200 cm-1. After the measurements the substances are identified through comparison with literature data (c.f. JOHNSON et al., 1999, KIEFERT et al., 1999) and/or with the in-house database. Figures 12 and 13 show each a characteristic Raman-spectrum for paraffin-oil, Canada-balm and ExCel in the discussed spectral areas.

Fig. 12: Raman-spectra of different filler substances in emerald in the spectral area from 1200 – 1800

cm-1 (green = paraffin oil, blue = Canada balm, red = ExCel).

1200 1300 1400 1500 1600 1700 1800Raman shift (cm-1)

Co

un

ts

Raman shift (cm-1)

Co

un

ts

Raman shift (cm-1)

Co

un

ts


Fig. 13: Raman-spectra of different filler substances in emerald in the spectral area from 2700 – 3200

cm-1 (green = paraffin oil, blue = Canada balm, red = ExCel).

Likewise it is also possible to identify most of the filler substances with the infrared-

spectroscopy. Here especially the spectral area between 3300 – 2600 cm-1 is analyzed,

because in this area the emeralds have a high transparency and the fillers show their

characteristic peaks. Similar like for the Raman-spectroscopy the identification of the fillers is

done through comparison with literature data (c.f. HENN & REDMANN, 1993) and/or with the

in-house database.

Figure 14 shows the infrared-spectra of the filler substances paraffin-oil, Canada-balm and

Opticon.

2700 2800 2900 3000 3100 3200

Co

un

ts

Raman shift (cm-1)

Co

un

ts

Raman shift (cm-1)

Co

un

ts

Raman shift (cm-1)


Fig. 14: Infrared-spectra of different filler substances in emerald in the area between 3300 – 2600

cm-1. (green = paraffin oil, blue = Canada balm, red = Opticon).

4. Duration of the filler substances Especially oil is very susceptible for alteration processes through which the transparency decreases after some time. Artificial resins are less vulnerable, because they are hardened after the filling process. Oil on the contrary can easily be removed and refreshed if wanted, which is much harder for artificial resin. However, generally speaking when working with fissured resp. fissure filled materials special care should be taken, because they are vulnerable for fractures. Particularly cleaning with the ultrasonic bath could extend fissures. Furthermore acidic or alkaline cleansers could attack resp. dissolve the oil or artificial resin, whereby the clarity of the stone could decrease significantly (JOHNSON, 2007). Also in the “Gemstone charts” of the CIBJO (2015) is written, that it is required to treat emeralds with special care because of their brittleness. Additionally the information are given, that they should not be cleaned in the ultrasonic bath and that they should be kept away from cleaning solutions (some detergents, too), chemicals and heat.

5. Nomenclature According to the current CIBJO-standards (The World Jewelry Confederation – Gemstone Book) emeralds which have been clarity enhanced with colourless organic substances (resp. a nearly colourless organic substance, which does not improve the colour), are classified as gemstones requiring general information about their treatment. If the fissure or cavity fillings are detectable by a trained observer with a 10x magnifying loupe because of a different surface luster in comparison to the emerald itself, then the treatment has to be classified as a specific information. The same is valid for dyeing, too.

26002700280029003000310032003300Wellenzahlen (cm-1)

Ab

sorb

anz

Wellenzahlen (cm-1)


The gemmological laboratories, which are member of the LMHC (Laboratory Manual Harmonization Committee), like the German Gem Lab (DSEF), divide the following categories on their certificates: - “Emerald - indications of fissure filling/clarity enhancement“

For these stones the mineral species “(Natural) beryl” with the variety “emerald” is given in

the certificate, together with the remark: “fissure filling” or “indications of clarity

enhancement/modifications” as well as a quantification of the clarity enhancement. Latter is

done as a text description and/or alphanumerically as follows: “minor (F1)”, “moderate (F2)”

or “significant (F3) amount of oil/resin in fissures” or “indications of

minor/moderate/significant clarity enhancement/modification”.

- “Emerald - indications of cavity filling“

If additionally cavities or hollow spaces are filled with filler substances, then another

information appears in the certificate: “minor”/”moderate”/”significant amount of

resin/wax in cavities” and/or the alphanumeric description C1/C2/C3.

- “Emerald - indications of coloured fissure filling/clarity and colour enhancement“

In this case the comment “Coloured filler in fissures/fractures” or “Indications of clarity and

colour enhancement/modification by a coloured substance” as well as the grade of

enhancement appears in the certificate. Additionally the variety is described as treated.

- “Emerald with/and resin“

Sometimes emeralds with a very high amount of hardened artificial resin are observed. The

original materials are extremely fissured rough stones which are stabilized with artificial

resin before the cutting process.

These stones are described as “Manufactured product” or “(Natural) beryl with/and resin”.

Additionally the variety could be declared as “Emerald with/and resin”. As a comment it is

written “This stone is a combination of resin and emerald”.

6. Literature HENN, U. & REDMAN, M. (1993): Smaragde mit künstlich behandelten Rissen und deren Erkennung.- Z. Dt. Gemmol. Ges., 42/1, 17-25. JOHNSON, M.L. (2007): Durability testing of filled emeralds.- Gems & Gemology, 43, 120 - 137. JOHNSON, M. L., ELEN, S. & MUHLMEISTER, S. (1999): On the identification of various emerald filling substances.- Gems & Gemology, 35, 2, 82 - 107. KAMMERLING, R.C, KOIVULA, J.I., KANE, R.E., MADDISON, P., SHIGLEY, J.E. & FRITSCH, E. (1991): Fracture filling of emeralds – Opticon and traditional oils.- Gems & Gemology, 27, 70 - 85.


KIEFERT, L., HÄNNI, H.A., CHALAIN, J-P. & WEBER, W. (1999): Identification of filler substances in emeralds by infrared and Raman spectroscopy.- Journal of Gemmology, 26, 501-520. MCCLURE, S.F., MOSES, T.M., TANNOUS, M. & KOIVULA, J.I. (1999): Classifying emerald clarity enhancement at the GIA Gem trade laboratory.- Gems & Gemology, 35, 176 - 185. NASSAU, K. (1994): Gemstone Enhancement: History, Science and State of the Art.- Oxford and London (Butterworth Heinemann), England. RINGSRUD, R. (1983): The oil treatment of emeralds in Bogota, Colombia.- Gems & Gemology, 19, 149-156. THEMELIS, T. (1990): Emerald oiling (In-Fill) process.- Modern Jeweler, 5, 1990 http://www.cibjo.org/introduction-to-the-blue-books/

http://www.lmhc-gemology.org/pdfs/IS5_20121209.pdf

dgemg- and dsef-information: clarity enhancement of emeralds · 2018-04-17 · emeralds. oil, wax,...

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