Gemology Hub / Gems Hub / Minerals Hub: September 2022

Those gems materials which have pores surface or having surface reaching craks are introduction of colouring material into a gemstone to give it a new colour, intensify present colour or improve colour uniformity. For example Agate, carnelian, chalcedony, coral, ivory, jade, opal, pearl, quartz, turquoise etc.

The Quartz bangles which are shown below in picture is colored to make imitation of imperial Jadeite Jade and also sold in the name imperial Jadeite Jade in Market.

For more information of treatment and detectation of treatment please visit the following link

Gemstone Treatment and their Detection Method.

Detection: Magnification (concentrations of dye visible in veins and cracks), Spectroscope (Broad absorption bands due to chromium slats used as a dye), Most organic dyes will stain a swab moistened with acetone.

Dyed pores quartz bangle sold as a natural Jadeite Jade

Dyed pores quartz under microscope

Dyed pores quartz bangle under microscope

Kindly visit my eBay store: https://www.ebay.com/usr/lavish_gems

Finding treatments that may have been made to enhance the color or appearance of the gemstones under examination is one of the gemologist's main duties. We must first understand what a treated gem is in order to understand enhancement or treatment. Thus, the treated gem may be

described as follows

Treated Gem: Any Gem material (Natural) which has been altered by a human, beyond ordinary cutting and polishing: For example, Heat-treatment corundum, oiled emerald, stabilized turquoise, etc

The term "enhancement" is defined to be any treatment process other than cutting and polishing

that improves the appearance (color/clarity/phenomena), durability, or availability of a gemstone

Purpose of Enhancement or Treatment

a. To improve Color and Clarity

b. To enhance Durability

c. To improve optical effects

D, Availbility / Accessablity

Tanzanite in shades of violet and blue depends on heat treatment to produce enough supply to meet the demands of the public.

Pink topaz is another example of a gem that would (not)be available without heat treatment. Not only are these treatments acceptable, they are necessary to keep these products affordable and available.

Nature Citrine the yellow variety of Quartz is rare in nature. Most citrine is prodoced by heating of amethyst which is frequently available in nature.

Gemstone Treatments and Pricing

There are some gemstones that would not even exist if it were not for treatments. The abundance of citrine , in shades of yellow, gold and orange is the result of heat-treating amethyst. Naturally occurring citrine is quite rare in nature. If it was not for treatments the stone would be far more expensive than it is!
Tanzanite in shades of violet and blue depends on heat treatment to produce enough supply to meet the demands of the public.
Pink Topaz is another example of a gem that would not be available without heat treatment. Not only are these treatments acceptable, but they are also necessary to keep these products affordable and available.
Recent demand for unheated sapphires and rubies has caused a price increase of as much as 50%-100% for unheated material. Does this mean that the untreated gem is more beautiful? NO! In most cases the heating enhances the gemstone to make it more beautiful; the price premium is the result of the rarity of being unheated!.

Types of Treatments and their Detection

1. Painting, Foiling or Coating

2. Dyeing

3. Impregnation and Filling using oiling, waxing, resin and polymer fillers

4. Laser treatment

5. Heat treatment

5.(a) Heat treatment without additives in corundum (ruby/sapphire)

5.(b) Heat treatment with additives For example glass filled, surface diffusion,

beryllium treatment etc) in corundum (ruby/sapphire)

6. Irradiation

1.Painting, Foiling or Coating: Adding a shiny backing, such a reflective metal piece is called foiling. The foil reflects light back out of the stone towards the observer. This makes the stone appear more brilliant. A transparent or translucent material is painted or foiled, usually only the back facets of the stones. Use of surface treatments such as films or thin surface layer applied to its entire surface to provide colour or other special effects.

NOTE: This type of treatment is not permanent and can chip or wear off. Do not use harsh solvents or chemicals on jewellery with this type of treatment.

Detection: Careful observation with 10x lens

Enhancement or Treatment of Gemstones and their Detection

paint layer on a quartz surface

Green painting on small colourless quartz crystal which shows the scene of tourmaline/Emerald embedded crystal in mother rock.

Foiling or backing on Red Glass

Closed view of Coated Topaz

a close up of a pink coated topaz in polariscoe

coated pink topaz in polariscoe

2. Dyeing: The introduction of colouring matter into a gemstone to give it a new colour, intensify present colour or improve colour uniformity. For example Agate, carnelian, chalcedony, coral, ivory, jade, opal, pearl, quartz, turquoise etc.

Aquamarine is dyed to resemble Emerald

concentrations of dye visible in veins and cracks

Dyed Quartz (noted the color concentration in cracks)

The low grade Sillimanite are dyed in different colors. Due to fibrious like inclusions it is favourite material for dyeing.

Sillimanite are colored in Red, blue and green which is best imitaion of ruby,

sapphire and Emerald respectivily. India is the main expoter of dyed sillmanite.

Dyed sillimanite .

Dyed Quartz beads String

dyed quatz in polarisocpe

3. Impregnation and Filling using oiling, waxing, resin and polymer fillers: Certain gemstones such as Emerald, opal, turquoise, and agates are permeable (will allow fluids to penetrate and flow through them). These stones can accept dyes, oils and waxes. The filling of the small openings in the stone may allow a new colour to be added or allow a wax into the pores that will then make the stone have a glossy finish or fill cracks. Usually, a regular oil such as olive oil, peanut oil, coconut oil etc is used, but resins (both natural and plastics) have been reported. Almost all emeralds sold are oiled. Since it is standard practice, very little is said about its application and most consumers are unaware.

Detection: Magnification (Darkfield illumination+ fiber optic light. The dried-up filler in emerald's cavities displays white dots that have a unique appearance. Other test includes immersion microscopy. A suitable liquid would be bromoform whose refractive index of 1.56 is very close to that of emerald, which is around 1.57. Once an emerald is observed in bromoform, all that will be visible are those areas that contain lower refractive index filler.

Oil in Emerald (Oiled filled Emerald

Oil in Emerald (Oiled filled Emerald)

Cedar oil, oil with green color, opticon used in emerald treatment

Machine used for emerlad oiling

4. Laser treatment: Diamond are often laser drilled to reduce the visual impact of dark inclusion. A laser beam is used to drill a very fine hole, with a diameter of less than 0.02mm, through the diamond to reach the inclusion. The inclusion may be burnt out by a laser beam or removed with acid. The hole may then be filled with a glass or an epoxy resin filling to prevent the entry of dirt.

Detection: Many lasered diamonds are drilled through the crown. These may be seen with a 10x lens by careful inspection through the side of the stone.

Laser drilled diamond

Laser treatment in Diamond

5. Heat treatment :

Heating is the most common treatment available. It can cause the colour of a stone to lighten, darken, or change completely. It can bring about an improvement in clarity and brightness.

It is common for many heat treatments to be done on pre-formed stones, i.e. stones that have already been shaped or cut, and from which all unwanted material has been removed.

Heat treatment is very common in a wide variety of stones. For example:

1. Amber is heat-treated to darken the colour or to induce disc-like fractures known as sun-spangles.

Heat treatment in Amber

2. Brownish zoisite is heated to produce the colour of blue tanzanite

After heating brown color converted in blue

3. Greenish blue aquamarine is heated to produce blue aquamarine. A yellow colour component, caused by iron Fe3+(Ferric) ions, together with the blue colour caused by iron Fe2+, gives the greenish-blue colour of untreated aquamarine. By heating the material more of the blue causing ions are created as the yellow causing ions are reduced.

greenish blue aquamine is heated to remove secondary color

5. a Heat treatment without additivies in Corundum (ruby/sapphire)

Heat treatment is used extensively to alter the appearance of nearly all gem corundum.

Depending on the required effect, heating is carried out in either oxidizing or reducing (non-

oxidizing) atmospheres. For example, the blue sapphire with an excess of Fe2+ (Ferrous iron)

has a very dark colour. By heating these stones in an oxidizing atmosphere, i.e. in the

presence of oxygen, the Fe2+ changes to Fe3+ and the colour becomes paler.

Detection: Detection of heat treatment is possible because processes used to enhanced colour

and remove silk involve very high temperatures. Such heating modifies the appearance of the

internal and external features of corundum.

Surface features: pitting and pockmark may remain on the facets and girdle; however, most

corundum is treated in the rough state.

Crystal inclusion may appear pale, with rounded outlines; original crystal form is lost. Disc-like

stress fractures develop around inclusions.

Natural Sapphire before and after heating

Natural Ruby before and after heating

Sri lanka sapphire before and after heating

discoid like inclusions in heated sapphire

discoid in heated sapphire

HPHT Treatment in Sapphire

5(b). Heat treatment with additives in Corundum (ruby/sapphire)

· Glass (Lead) filling

External: Open cavities (usually on pavilion), filled with glass for a better looking stone (seals cavities, adds weight). Internal: Traces of glassy residue in fractures after heating may be found as a by-product of the particular heating process used. (Stable).

ruby before and after heat treatment with addatives (lead glass etc)

Glass filled ruby / sapphire after cutting & polishing

Detection: Magnification. Differences in luster between glass infilling and stone plus possible bubbles in filling and blue orange flashes.

Air bubbles in glass filled ruby

Lead glass ruby under gemological microscope

Surface Diffusion:

Corundum is also surface diffused to improve its colour. In this process, colour and asterism can be induced in the outer part of a ruby or sapphire.
Surface diffusion is achieved by coating the stones with aluminium oxide and the appropriate compounds and subjects the stones to very high temperature for several days. The blue colour is produced by the diffusion of iron and titanium, red by chromium, yellow by nickel. Asterism requires the introduction of excess titanium.
The depth of diffusion penetration is small--- a fraction of a millimetre because the process is limited and works extremely slowly, even at the very high temperatures that are required.

Detection: Immerse stone (Ideally in di-iodomethane / methlene iodide). Colour is concentrated in a thin surface layer.

Surface Diffused Sapphire

Surface diffused sapphire.

Beryllium treatment or Bulk Diffusion:

A recent process involving the heat treatment of corundum in the presence of beryllium has been developed. This causes diffusion of colour through most, all of the stone.