Treatments

• Enhancement and treatments are done on gemstones to improve their appearance, properties and consequently their value. This is generally practiced on lower grade goods so as to increase their salability.
• In actual terms, improvements in a gem material may be specifically related to improvement in Colour and / or Clarity and / or Phenomenon and / or Durability. In some cases a stone is subjected to more than one form of treatment.
• A number of classifications have been put forward by ICA, GIA, CIBJO, jewelers associations in different countries etc. As yet no single classification is considered as a standard.
• The terms enhancement and / or treatment are used ambiguously by members of the trade, though there is a general concept that the acceptable ones such as oiling may be considered as an enhancement while glass fillings, irradiation etc. as a treatment. The technical concept remains that - whether you call it enhancement or treatment - they basically mean the same.
• The important factor is that total disclosure of whatever has been done to the stones is absolutely necessary and is the general attitude of most jewelers these days.

Basic definitions of possible enhancements / treatments are as follows:

1. Bleaching: The use of chemicals or other agents to lighten or remove the colour of a gemstone.
2. Coating: The use of such surface enhancements as lacquering, enameling, inking, foiling or sputtering of films to improve appearance, provide colour or add other special effects.
3. Colourless impregnation:
   • The filling of surface breaking cavities or fractures usually with colourless oil, wax, plastic, natural or synthetic resin (with or without hardeners), other man-made materials and glass, to improve durability and appearance.
   • The use of a colourless bonding agent (wax, polymers, plastic etc.) within a porous gemstone to give it durability and improve appearance.
4. Coloured impregnation (Dyeing): The use of colouring matter to improve the colour by darkening the original colour or improve colour uniformity in stones containing surface reaching fractures and cavities, or in porous gemstones.
5. Lasering or Laser drilling: The use of a laser and chemicals to reach and alter inclusions in diamonds.
6. High Pressure High Temperature (HPHT): The use of a variety of high-temperature annealing techniques at different pressures to enhance optical properties such as the colour and brilliance of certain types of diamonds.
7. Graphitization: The use of high temperature on poor quality yellow to brown diamonds to change the colour to black.
8. Heating: The use of heat to effect desired alteration of colour, clarity and / or phenomena.
9. Irradiation:
   • The use of gamma and / or electron bombardment to alter a gemstones color may be followed by a heating process.
   • The use of neutron bombardment, with the combination of any other bombardment and /or heat treatment to alter a gemstone's colour (In U.S.A. such stones require an environmental safety release from the Nuclear Regulatory Commission).
10. Diffusion: The use of chemicals in conjunction with high temperatures to produce colour and / or asterism - producing inclusions.

The techniques are explained with respect to the nature of the gemstone being enhanced, the materials used, the possible effects and the general identification of the enhancement.

Read more »

Diffusion Treatment

Diffusion treatment is divided in two parts:

1. Surface Diffusion
2. Beryllium Diffusion (also known as Bulk Diffusion)

Surface Diffusion

• Nature of gemstone: This is applied basically on corundum. Experiments are also being conducted on other stones such as topaz.
• Materials used: High temperature furnace along with relevant chemical agents.
• Possible effects: Involves the addition of colour-causing chemicals by diffusing them into the stone by heating. This results in a thin layer of colour at the surface of colourless or light coloured corundum.
• Stones enhanced: Currently this treatment is applied to obtain blue sapphire and ruby, both natural and synthetic.
• Identification:
  • Magnification: The most effective means of detecting a diffusion treated stone is its appearance in Methylene Iodide liquid or in glycerin.
    1. Greater relief, as indicated by a concentration of colour along facet junctions and around the girdle, uneven or patchy facet-to-facet coloration.
    2. Healed fingerprints, burst halos, melted crystals, partially absorbed and dot like (diffused) silk inclusions are typical.
    3. Localization, blotchiness of colour (caused by uneven diffusion and repolishing) seen just below the surface or as colour bleeding in surface reaching fractures or cavities.
    4. Pock marked and burnt surfaces on facets or over the girdle.
    5. Dense concentration of very small, white inclusions with colour spotting just below the surface and covering entire facets.
  • U.V. Lamp: It does not provide diagnostic information for the identification, but some times - weak to moderate, chalky bluish, white to yellowish white under short wave is seen.
  • Refractometer: In case of diffusion treated ruby, multiple readings on individual facets and readings over the range are seen.
• Certification: Such diffusion treated gemstones are certified as per CIBJO rules and regulations.
  • Natural sapphire as artificially coloured sapphire
  • Natural ruby as artificially coloured corundum
  • Synthetic sapphire as artificially coloured sapphire
  • Synthetic ruby as artificially coloured corundum
• Procedure: Currently, this treatment is applied to obtain blue sapphire and ruby.
  • The colour of corundum is due to transition elements Iron, Chromium, Titanium or Nickel.
  • Diffusion treatment first brings the necessary colouring agents (chemicals) into contact with the stone's surface.
  • The stone is then heated to high temperature, causing the lattice structure to expand and allow the energized transition ions to migrate within the surface and hence a thin layer of colour develops around the stone.
  • The higher the temperature and longer the time used, the greater the depth of colour penetration.
• Method: To get blue / red colour, commonly colourless or light coloured faceted corundum is embedded in a powder.
  • For blue colour this powder consists of a major amount of aluminium oxide, a minor amount of titanium oxide, and lesser amount of iron oxide.
  • In case of ruby 3 - 6% of chromium oxide and 22 - 24% titanium oxide is taken in powder form.
  • The samples embedded in powder are kept in an alumina crucible. The crucible is then subjected to extend heating in a furnace.
• Conditions:
  • Temperature: The elevated temperature ranges from 1600°C to about 1850°C (almost near melting point of corundum).
  • At temperatures below 1600°C, the process becomes uneconomically slow and at high temperatures the surface may be damaged.
  • Time: Heating time can vary from 2 hours to 200 hours.
  • Atmosphere: Oxidizing.
• Results:
  • The thickness of the colour layer varies from 0.07mm, (weak colour) to 0.42mm, (deep color) in corundum.
  • After this process, the stones become pockmarked, have a burnt and crazed surface and show some melting.
  • Light repolishing removes these features.

Beryllium Diffusion

• Nature of gemstone: This is applied basically on corundum.
• Materials used: High temperature furnace along with relevant chemical agents like beryllium, lithium, magnesium, etc.
• Possible effects: Involves the addition of colour-causing chemicals by diffusing them into the stone by heating. This results in a penetration of colouring elements upto the core of the stone.
• Stones enhanced: Initially the treatment performed on pink sapphires to turn into pinkish orange "padparadscha" shade. Now this treatment is being performed on all the colours of corundum to get different fancy shades.
• Causes: The lighter element penetrates into the crystal lattice and takes the position of aluminium, changing the colour. When beryllium enters the crystal of corundum, it imparts yellow color to the stone. When this yellow colour mixes with the pink already present, it gives a pink orange "padparadscha" shade.
• Identification: The identification of these stones is very difficult with the classical instruments or routine tests.
  • Like in the case of simple surface diffusion of blue sapphires and rubies, this treatment does not show any colour concentrations on girdle or patchy facets.
  • If present, these stones might show an internal colour rim when immersed in bromoform or methylene iodide liquid and viewed in diffused white light.
  • The treatment can be detected by a highly sophisticated technique known as LA-ICP-MS stands for Laser Ablation Inductively Coupled Plasma Mass Spectroscopy.
  • The other way if one can get features like the characteristic body colour of the stone and inclusions of heat treatment like diffused silk, burst halos, healed fingerprints, then it may be possible to identify.

---

• Modifications: Both rough and cut gemstones are modified externally to imitate natural gemstones. Such modified materials require careful examination under magnification.
• For e.g. a cheap quality green beryl is surface modified:
  • First drilling a hole at the centre.
  • A deep green coloured glass is inserted into the hole.
  • It is then coated with mud to give appearance of natural rough emerald crystal.
• A synthetic ruby is cut into hexagonal form to imitate red beryl.

Read more »

Irradiation Treatment

• Nature of gemstone: Almost any gem material.
• Material used: Radiations used can be produced in a gamma cell, a linear accelerator, cyclotron, synchrotrons and nuclear reactors or from atomic piles.
• Possible effects: In general, when a gemstone is exposed to some form of radiation for a period of time, in almost all the cases:
  • There is a change of colour.
  • After irradiation the stone is subjected to heating to either obtain the desired colour change or to stabilize the colour center formed.
  • High energy radiations which affect the nucleus giving a good coloration can induce radioactivity in the stone.
• Stones enhanced:
  • X-Rays: These produce a surface coloration which is short lived and tend to fade either immediately, or within a few hours or when opposed to strong heat. E.g.
    • Light yellow sapphire irradiated to orange yellow
    • Lilac pink kunzite irradiated to green
    • Colourless topaz irradiated to brown
  • Gamma Rays: These rays produce a uniform coloration in a stone without any localized heat being generated. These rays in general do not induce radioactivity and are thus safer. E.g.
    • Rock crystal irradiated to brown smoky quartz
    • Light pink tourmaline irradiated to dark pink/ red
    • Diamond irradiated to a uniform blue-green colour, on annealing, it becomes dark green.
  • Electrons (also known as cathode rays or beta rays): These radiations produce only a surface coloration and tend to generate localized heat. E.g.
    • Colourless topaz irradiated to blue
    • In diamonds, changes obtained are blue, blue-green, green (after annealing to about 800) type 1a - yellow / type 1b brownish red / type 2a - brown.
  • Neutrons: These are highly energetic uncharged particles which produce a uniform coloration. They induce radioactivity in the stone. E.g.
    • colourless topaz irradiated to blue (some common trade names are cobalt blue, sky blue, London blue, Swiss blue etc.)
    • Diamond changes obtained are green (after annealing to about 800), type 1a - yellow / type 1b - brownish red / type 2a - brown.
  • Other Radiations: such as high energy fast moving protons, deutrons alpha particles (helium ions) etc. are also used, though they may induce radioactivity.
• Identification: The identification of irradiated stones is not possible with conventional gem testing equipment.
  • In the case of gemstones which have just been irradiated or those with residual radioactivity, it may be possible to detect signs of activity with a Geiger Mueller counter (measures radioactivity).
  • Structural imbalances which are caused as a result of irradiation can be identified in some cases with the help of spectroscopy - infrared and Raman spectrums. In irradiated diamonds the characteristic absorption spectrum for yellow to brown irradiated stones is 594nm, 498nm; Brown: 498nm, 504nm (both of equal intensity); Green: 504nm, 741nm.
  • In the case cyclotron treated diamonds, under magnification:
    • Those irradiated from the crown, show a dark ring within the girdle.
    • Those irradiated from the pavilion show an umbrella effect or a number of dark shadow lines around the culet.
    • Those irradiated through the side, there will be a zone of colour near the girdle.
  • A destructive technique would be to heat the specimens and observe the color change. This is not always reliable.

In most cases the stones are annealed and also allowed to cool before they are used for trading. The legal release levels set by authorities in different countries varies. Some are as follows:

Country	Nanocuries/Gram
U.S.A.	1.0 nci/g
U.K.	2.7 nci/g
Asia	2.0 nci/g

Read more »

Heating Treatment

Some common terms used for heat treatment are baking, annealing, heating, browning, combusting, cooking, firing, toasting and roasting.

• Nature of gemstone: Almost any gem material can be heated, except those that are affected by heat such as emerald and opal.
• Materials used: Equipment can be a cooker, furnace, kiln, muffle, pot, oven, roaster, brazier etc. The heating agents used include gases, oils, charcoal, wood, coal, heating coils etc.
• Possible effects: It is the process that causes alteration in physical and chemical structure of the gemstone by the use of heat thereby changing the optical properties like colour or clarity. A wide range of changes are being induced today by heat treatment. Among them a few important ones are as follows.
  

  S.No.	Change	Example
  1.	Darken Color	Light blue sapphire to dark blue sapphire
  2.	Lighten Color	Dark pink tourmaline to light pink tourmaline
  3.	Color Change	Amethyst to Citrine
  4.	Removal of Secondary Color	Removal of purplish hue from ruby, green color from aquamarine
  5.	Development of Asterism	Corundum
  6.	Removal of Asterism	Corundum
  7.	Structural Change	Low zircon to high type zircon
  8.	Crackling	Iris quartz, synthetic ruby

  
  
• Conditions: The effects induce depends upon the following:
  1. The maximum temperature reached.
  2. The time for which the maximum temperature is maintained.
  3. The rate of heating.
  4. The rate of cooling.
  5. The chemical nature of the atmosphere
  6. The pressure of the atmosphere
  7. The nature of the material in contact with the gemstone.
  8. The quality of gemstone used.
• Identification:
  • Magnification: The most useful and valuable data is obtained from inclusions and surface features. These are more clearly observed in corundum. The following features are seen:
    • Pock marked girdle.
    • Chatter marks or burn marks.
    • Diffused silk.
    • Partially melted inclusions.
    • Burst halos around certain inclusions.
    • Healed fingerprints.
  • U.V. Lamp: Some heat treated gemstones show fluorescence characteristics which are different and distinct from their unheated natural counter parts. Unless strong evidence from other sources suggests otherwise, such observations in ultraviolet lamp should be considered an additional clue, though not conclusive proof, of heat treatment.
  • Characteristic spectrums are seen in heated stones using U.V. or Infrared Spectroscopy.
  • Some gemstones show weak dichroism when compared with untreated natural counter parts.

Heat Treated Gemstones

• Amber
  • Possible Changes: Darkening, Clarification, Sun-Spangled cracks.
  • Conditions: Temperature: 175 ± 25°C, Chemicals: Rapeseed oil.
  • Environment: Long but slow heating in sand.
  • Stability: Quite stable till heated again.
• Beryl
  • Possible changes:
    1. Change yellow green to blue (aqua); yellow to colourless; orange to pink.
    2. Change pink to colourless.
    3. Remove maxixe blue; blue to pink, green to yellow.
  • Conditions: Temperature: 450°C ± 50°C; Environment: oxidizing atmosphere.
  • Causes: Iron is present within beryl in two types of locations.
    1. One type is located on an aluminum site and gives a yellow colour if present as Fe³⁺. Heating produces the change from Fe³⁺ to Fe²⁺ and hence the colour changes from yellow to deeper yellow.
    2. The other type of iron is situated in a channel site and gives a blue colour that is unaffected by heating. If both types are present, heating changes green aquamarine to blue aquamarine.
    3. Heat also bleaches the colour due to a colour center in maxixe beryl.
  • Stability: All treatments are stable.
• Chalcedony
  • Possible changes:
    1. Pale colors to brown and red.
    2. Pale colors to milky white.
  • Conditions: Ordinary temperature pressure conditions.
  • Causes: Basically hydration alteration, usually limonite to hematite.
  • Stability: Stable.
• Corundum
  • Possible changes & Conditions:

    S.No.	Change	Temperature	Atmosphere	Time
    1.	Lightening of dark blue.	1700°C	Oxidizing	20hrs
    2.	Darkening of light blue.	1770°C	Reducing	6hrs
    3.	Reduction of color zoning / yellow patch.	1800°C	Oxidizing	3hrs
    4.	Reduction of blue patch.	1800°C	Oxidizing	4hrs
    5.	Development of pink.	1800°C	Reducing	3hrs
    6.	Intensification of yellow.	1800°C	Oxidizing	2hrs
    7.	Development of blue.	1600°C	Reducing	2hrs
    8.	Removal of silk.	1650°C	Oxidizing	2hrs
    9.	Development of silk.	1500°C	Oxidizing	2hrs

    
    
  • Stability: All are stable to ordinary temperature but a few fade in months.
  • Causes: The typical cause of most blue sapphires is caused by (Fe⁺² - O - Ti⁺⁴) inter valence charge transfer (IVCT) process. Varying ratios of Fe⁺³, with Fe⁺²/Ti⁺⁴ produce - blue / green, green / blue, to green and similarly appearing colours. Certain types of corundums contain in their crystals lattice
    
    • Various amounts of Titanium oxide (silk) and Iron.
    • When these corundums are heated at elevated temperatures under reducing atmospheric conditions, the Ti⁺⁴ atoms from the rutile are dissolved into the corundum crystal lattice, where the Fe⁺³ ions are already in solution.
    • As result pairs of ions form and produce blue colour.
    • In case of yellow sapphire the change is due to Fe⁺² / Fe⁺³ pairs of unstable colour centres or traces of Fe+3 and colour centers.
• Diamond
  • Possible changes:
    1. Alter the surface by burning.
    2. Change colour in chameleon diamond.
    3. Modify natural yellow colour.
    4. Modify irradiation colours to produce green, brown, orange, yellow, pink, red, purple etc.
  • Conditions:
    1. Warmed slightly with an alcohol flame or on exposure to light in case of chameleon diamond.
    2. High temperature and high pressure to convert type 1a to 1b or vice-versa (yellow colours).
  • Causes: Change in platelet structure, converts to bright yellow (Type 1a)
  • Stability:
    1. Chameleon diamonds very unstable even at room temperature.
    2. Yellow colour is stable.
• Jade
  • Possible changes:
    1. Lightening green colour.
    2. Darkening yellow and brown colours.
  • Conditions: Varying.
  • Cause: Yellow / brown inclusions on heating get oxidized and become more dark.
  • Stability: All are stable.
• Quartz
  • Possible changes:
    1. Amethyst (violet) to Citrine (yellow) or bicolor amethyst-citrine (ametrine).
    2. Amethyst to colourless to green.
    3. Smoky to paler to greenish yellow to green to colourless.
    4. Rose to lighter to colourless.
    5. Blue to modified or colourless.
    6. Yellow or brown to red-brown or red.
    7. Crackled for Iris quartz.
  • Conditions:

    S.No.	Change	Temperature	Atmosphere
    1.	Smoky to pale brown	280°C	Oxidizing
    2.	Smoky to blue green	280°C	Oxidizing
    3.	Smoky to colorless	400°C	Oxidizing
    4.	Amethyst to Citrine	450°C ± 50°C	Oxidizing
    5.	Amethyst to Colorless	600°C	Oxidizing
    6.	Pink to light pink	450°C	Oxidizing
    7.	Pink to colorless	550°C	Oxidizing
    8.	Deep blue to light blue	300°C	Oxidizing
    9.	Colorless to Iris quartz	300°C	Oxidizing

    
    
  • Causes:
    • The cause of colour in smoky quartz is colour centre, equivalent to Al3+. On heating, the electrons are displaced and destroy the whole colour centers as all the electrons get paired with each other.
    • In case of amethyst, the cause of colour is somewhat similar. A transition metal ion (Iron) is the defect and can be removed on heating partially or completely.
    • In deep blue the colour is again due to a colour centre.
    • In pink quartz the cause of colour is due to Mn as an impurity. A change of valence state of Mn gives a light pink.
• Topaz
  • Possible changes:
    1. Brown or orange to pink
    2. Yellow or green to colourless.
    3. Brown (Irradiated) to blue.
    4. Blue to brown.
  • Conditions:

    S.No	Change	Temperature	Atmosphere	Time
    1.	Brown or orange to pink	500°C	Ordinary	Minutes to Hours
    2.	Yellow or green to colorless	400°C	Ordinary	Minutes to Hours
    3.	Brown (Irradiated) to blue	200°C ± 50°C	Ordinary	Minutes to Hours
    4.	Blue to brown	450°C	Ordinary	Minutes to Hours

    
    
  • Causes: All colors, except pink, the color is due to color centers. There are two types of color centres. BFCC (brown fading color center) and BSCC (brown stable color center). In case of pink / orange topaz, the color is due to chromium as an impurity.
  • Stability: When BFCC topaz is exposed to sunlight for a few days, the color of the treated topaz fades, while others are stable to light.
• Tourmaline
  • Possible changes:
    1. Red/pink to lighter shades to colourless.
    2. Purple to blue or dark green.
    3. Dark blue to light blue.
    4. Dark green to light green / yellow green.
  • Conditions: Due to the complex structure of tourmaline, the temperature for some colours varies from 260°C to 1000°C.
  • Causes: Complex, but most of the blue or green is due to Iron as an impurity, red or brown is due to iron and manganese together as impurities. Heating alters the valence state.
  • Stability: Stable to ordinary temperature / pressure conditions.
• Zoisite
  • Possible changes: Yellowish brown / greenish brown to deep blue (tanzanite).
  • Conditions: Oxidizing atmosphere, temperature between 350° and 600°.
  • Causes: Heating alters the change of state.
  • Stability: Stable to ordinary temperature / pressure conditions.

Read more »

Graphitization Treatment

• Nature of gemstone: This technique is applied on diamonds.
• Possible changes: Poor quality yellow or brown coloured diamonds changes to black.
• Conditions: Exposure of diamonds to high temperature ranging from 900°C - 1650°C in a vacuum, for a period ranging from few minutes to several hours.
• Cause: Due to increase in temperature, without the application of pressure, diamond starts turning into graphite, especially where there is some spaces in the stone like cleavage or feather.
• Identification: Concentration of black to gray graphite along the fractures and cleavages, sometimes form black lines along the edges of fractures or cleavages.

Read more »

High Pressure High Temperature (HPHT) Treatment

• Nature of gemstone: This technique is applied to diamonds.
• Possible changes: Type 2a high colour (brown) diamonds to colourless or near colourless. Type 1a brownish colour diamonds to yellowish green.
• Conditions: High temperatures (1600°C - 2000°C) and high pressures up to 70,000 atmospheric pressure) for several hours to days. These are the conditions required for diamond to crystallize whether naturally or synthetically.
• Cause: The cause of colour in diamond is the vacancies and defects. When diamond is exposed to HPHT conditions, the crystal lattice undergoes through the process of reconfiguration, which results in the destruction of vacancies thereby changing the colour of the stone.
• Identification: The conclusive identification of these treated stones is very difficult or even impossible with classical instruments. Sometimes, identification can be made if internal features like graining and strain patterns are observed. Graphitization along cleavage cracks or feathers, melted crystals and burst halos are some other features that may be encountered in HPHT treated stones. A conclusive identification can be made with photoluminescence or cathodoluminescence spectra. They contain an almost negligible nitrogen percentage which is observed in the spectra.

These treated diamonds were launched in 1999 A.D. by Lazare Kaplan International (LKI) and General Electric (GE). These diamonds were marketed with a branding on the girdle GEPOL to represent General Electric and Pegasus Overseas Ltd. (the marketing firm). In 2000 A.D., they were marketed under the name of Bellataire diamonds.

Read more »

Laser Drilling Treatment

• Nature of gemstone: This technique is usually applied to diamonds.
• Materials used: A strong and thin laser beam for the drilling process, a vacuum furnace for cleaning & lead glass for final filling.
• Possible effects: Generally used to remove coloured impurities in diamonds and thereby improve the clarity.
• Identification:
  • Under magnification a difference in the lustre of lead glass and the diamond on the surface is noticeable.
  • Colour flashes along the drill hole is seen on rotating the stones at varying angles namely yellow, orange and blue colour flashes.
  • Discoloration along the drill hole
  • The drill hole maybe a single channel drill hole or a series of laser drill holes in a single plane giving a fan like pattern and a surface break which appears as a thin rectangular depression.

KM treatment: Recently a newer technique has been introduced in 2000 A.D. known as KM treatment. This treatment is used on black inclusions accompanied by internal fractures. One or more pulsed laser beams are focused on the inclusion itself with the resulting heat creating an internal fracture. The point of focus of beam is then moved towards the closest surface of diamond at the same time creating a continuous fracture from the inclusion to the surface. After this, diamond is boiled in strong acid with pressure, to allow the solution to bleach out the inclusion. Identification of treatment is almost impossible.

Read more »

Colorless Impregnation Treatment

For simplification, enhancement of a gemstone using any colourless material in the filling of fractures, cavities or voids and for the compaction of porous materials is considered under a single heading.

• Nature of gemstone:
  • Any stone which contains surface reaching fractures.
  • Porous stones.
• Materials used: Oil (cedar wood oil, linseed oil etc.), Canada balsam, wax, plastic, polymers, resins, glass etc.
• Possible effects:
  1. Usage of fracture filler having a similar refractive index as that of the stone reduces the visibility of the fractures and thereby improves the clarity of the stone.
  2. In the case of porous stones, the internal pores and those on the surface are sealed, thus improving the overall durability of the stone as well as its surface lustre.
  3. Porous stones which exhibit a phenomenon can be stabilized by bonding as a result of which the phenomenal effect is also enhanced.
• Stones enhanced: Almost any stone can be enhanced in this manner. For convenience, only a few of the most routine stones are considered with respect to the materials used.
  • Colourless oil: As per CIBJO regulations, the colourless oiling of emerald, aquamarine, ruby, sapphire etc. is an accepted trade practice and does not require to be disclosed. Most of the oils used are those which are not affected by temperature changes i.e. they do not freeze and solidify in cold weather.
  • Colourless Resin: Organic resins, such as epoxy resins are being used more often as they are more stable as fracture fillers. Emerald, Aquamarine, Iolite, Amethyst, Peridot and Tourmaline are some of the stones whose fractures are filled with resin. The brand name of opticon has inadvertently got linked up with resin filling, and it is not uncommon to hear the term opticon treated stone among traders.
  • Mixtures of colourless oils and resins.
  • Polymers/wax/plastic: These are basically used as bonding materials for porous stones such as turquoise, coral, opal, jade etc.
  • Glass: Lead glass is currently used as fracture filler for diamond and ruby. The lead glass fracture filling in diamond was originally promoted by Mr.Yehuda and the term Yehuda Diamond is often met with among traders. Glass filling in ruby is done to fill fractures as well as surface pits, twin planes and cavities.
  A large variety of fillers are being made available in the market on a daily basis and identification of each and every one is outside the scope of this book. Needless to say, a student must be aware of the developments in this field. E.g. fillers which harden within a fracture when exposed to ultra violet radiations.
  
• Identification: The criteria used to identify impregnations is quite distinct for fracture filled stones and porous stones.
  • Fracture filled:
    • First locate the surface break of the fracture. It appears as a thin line on the surface and can be better observed by reflecting light off the surface of the stone.
    • Locate the direction in which the fracture is oriented within the stone.
    • Reflect light off the fracture surface and observe any or all of the following:
      • Trapped gas bubbles in the fracture due to incorrect filling.
      • A single colour flash is seen which changes when the stone is rotated 90°. Common colour flashes seen are yellow / orange to blue, or violet to pink.
      • Lumpy and unequal patches within the fracture indicate incorrect filling.
    • U.V. Fluorescence: Some filler may fluoresce distinctly different from the body colour of the stone.
    • Hot Point: This may help to identify a filling in a fracture, but is a destructive test and should be used as a last resort.
    • Surface Lustre: In some cases, a distinct lustre difference is observed between the stone and the filled fracture.
  • Porous stones:
    • Magnification: Under low magnification the impregnated porous stones may show a speckled or slightly sugary appearance.
    • U.V. Fluorescence: Some filler may show distinctly different fluorescence from the body colour of the stone.
    • Hot Point: This may help to identify different impregnating material - polymer, wax and plastic will give a peculiar and distinct odour and may melt where the hot point is applied.
    • Surface luster: Porous stones impregnated with wax generally have a waxy lustre.
    • Other techniques: To conclusively detect the exact nature of impregnated materials (whether oil, resin or wax) it is necessary to resort to Infra-Red and / or, Raman Spectroscopy, X-ray Diffraction or SEM (Scanning Electron Microscope).

The need for identification of the exact nature of the filler material is of prime importance these days and as a result sophisticated equipment are a compulsory feature in laboratories.

Read more »

Colored Impregnation (Dyeing) Treatment

For simplification, enhancement of a gemstone using any coloured material in the filling of fractures, cavities or voids and for the compaction of porous gemstones, is considered under a single heading. This category also includes techniques which involve a chemical reaction within the stone which may or may not be formed as a result of heating.

• Nature of gemstones:
  • Any stone which contains surface reaching fractures.
  • Porous stones.
• Materials used: Oil (cedar wood oil, linseed oil) Canada balsam, wax, plastic, polymer, resin, glass etc. along with additional colour, is introduced as filler.
• Possible effects: An overall enhancement of colour which is localized at fractures in fracture filled stones and in pores in porous stones. The process can involve an additional treatment such as heating and chemical reactions to stabilize the coloured impregnation.
• Stones enhanced: Almost any stone can be enhanced in this manner. For convenience, only a few of the most routine stones are considered with respect to the materials used.
  • Coloured oil / resin/ wax / polymers: The traditional technique of using natural vegetable oils with colour known as Jhoban, as fracture filler for emeralds, rubies, quartz etc. is a major issue in the international markets. This has assumed importance due to the fact that the materials are being used as fracture fillers these days, also includes chemical dyes, paints, inks etc. which in most cases are not the natural vegetable colours. Coloured wax and polymers are commonly used to improve the colour of coral, jade, turquoise, etc.
  • Colour as a result of chemical reactions & / or heating: This category includes stones said to be dyed. A dyed stone is one in which the solvent evaporates and leaves the dye or pigment within pores, cracks or gets attached chemically to the dyed material (Ref: Gem Enhancement by K. Nassau) The most common examples include dyed chalcedony (in almost all colours) dyed quartzite, dyed corundum, sugar / smoke treated opals etc.
• Identification: The criteria used to identify coloured impregnations are very similar to that for colourless impregnation.
  • Fracture filled:
    • First locate the surface break which appears as a thin line on the surface.
    • Locate the direction in which the fracture is oriented within the stone.
    • Reflect light off the fracture surface and observe any or all of the following.
      • Trapped gas bubbles and lumpy fillings in the fracture due to incorrect filling.
      • Colour concentrations in fractures.
  • Porous stones:
    • Magnification: Under low magnification the impregnated porous stones may show a speckled or slightly sugary appearance along with colour concentrations.
    • U.V. Fluorescence: Some filler may fluoresce distinctly different from the body colour of the stone.
    • Hot Point: This may help to identify different impregnating material - polymer, wax and plastic will give a peculiar and distinct odour and may melt where the hot point is applied.
    • Other techniques: To conclusively detect the exact nature of the impregnated coloured materials it is necessary to resort to Infra-Red and / or, Raman Spectroscopy, X-ray Diffraction or SEM (Scanning Electron Microscope).

Some specific examples of gemstones:

• Turquoise: Often porous and is sealed with wax or plastic to stabilize and improve the durability and colour. A new treatment is that known as the Zachary treatment.
• Coral: Often porous and is impregnated with wax or resin to stabilize and improve the durability and colour.
• Black Onyx: Mostly agate which has been impregnated with sugar, which is then carbonized by acid treatment. Similarly green onyx, blue onyx etc. are mostly agates which have been dyed using specific chemicals.
• Lapis lazuli: Very commonly dyed to obtain a uniform deep blue colour, maybe coated with a fine layer of wax, maybe heated to stabilize the chemical reaction.
• Jade: A specific example is that of B-Jade. This is low quality jadeite which is initially bleached and then polymer treated to produce a more uniformly coloured and durable material. Jadeite is dyed in many shades, green and lavender being the most common.
• Opal: Two well know techniques - sugar and smoke treatment improve the phenomenon of play of colour by giving a darker background to the opal. Opals are polymer impregnated to enhance the colour and also the durability of the stone. Sugar treatment is identified by the presence of black peppery effect just below the surface of the stone, while smoke treatment is identified by the presence of cloudy effect.
• Corundum - ruby / sapphire: Glassy fillings in ruby are of two types. Smooth fillings in fractures, twin planes and cavities which exhibit a high mirror like reflection and a difference in the lustre at the surface break. During the heating process, ruby is coated with borax powder. This powder goes into a melt form and enters into any surface reaching fractures. This has the appearance of flux like fingerprint inclusions with higher reflections.

Read more »

Bleaching Treatment

• Nature of gemstone: Stones such as Ivory, Pearl, Tiger's Eye, Coral, Jade.
• Materials used: Hydrogen peroxide or any other bleaching agent.
• Possible effects: Generally used to remove colour discrepancies and provide a uniform coloration. In the case of Tiger's eye the dark brown shade is bleached to a pleasing yellow.
• Identification: This is generally not easy to detect.

Read more »

Coating Treatment

• Nature of gemstone: Coating is done on almost any gem stone. Coating can be performed both on rough and cut stones.
• Materials used: Wax, plastic, paints, resins, reflecting coloured papers and metallic foils, sputtering techniques etc. are used.
• Possible effects:
  1. In diamond, a special coating is performed known as Carbon Vapor Deposition (CVD) where a thin layer of synthetic diamond is deposited over a colourless stone to imitate diamond. One the latest coated colours are the black and green coated diamonds. The black diamonds appear opaque black but may actually be dark browns which are semi transparent in transmitted light. The coating is probably due to a layer of diamond - like carbon (DLC).
  2. In the case of colourless topaz or quartz a thin layer of gold is deposited over the colourless topaz or quartz to produce a blue colour. This has been marketed under the trade name aqua aura. A variety of metallic elements are currently being used to produce different colours which are subsequently marketed as red aura etc.
  3. A coloured paper or metallic foil is pasted on the pavilion facets of cut gemstones or the base of the cabochon to enhance the colour as well as the quality of light reflected from the stone.
• Identification:
  1. Detection in loose stones can be done by boiling with acids or using a hot point or by scratching the stone with a pointed fragment.
  2. In the case of mounted stones, with the help of a lens, examine the back portion of the stone through the table. Some form of crinkling or wrinkling of the coating or foiling is visible.
  3. Identification is also possible by a careful examination of the unevenness of colour on the surface.

Read more »