Appraising the Value of Gems

by Mathew Abraham

Gems are appraised mainly to determine their fair market value (FMV) or for insurance purposes. Qualified gemologists undergo specialized training to be certified as accredited appraisers of gems. If a gem has been certified by a Master Gemologist Appraiser, his/her valuation is accepted as final.

The Need for Having Gems Appraised

The techniques for manufacturing imitation costume (or artificial) jewelry have been developed to a level where it is almost impossible for an average person to differentiate between them and the originals. Add to this the fact that some jewelry retailers ridiculously inflate the price of genuine precious stones and you can see why it is necessary to have your gems appraised and certified at the time of purchase. After spending a tidy amount on a gem you have just acquired, the last thing you would want is to find that your friend has purchased an identical stone for a much lower price, or that your stone is of inferior quality! There is no ready market for the resale of gems so you need to get professional advice and analyze the various gems and their characteristics before deciding what to buy. Whether it is for your collection, an investment for resale, or as a gift, get your gems appraised for insurance purposes as well as for knowing their fair market value.

Grading and Appraising Gems

There are a standard set of rules to be observed in the purchase of any gem, followed by separate rules for each variety of gems. While the system for grading and valuing diamonds is well established and dependable because of steady market conditions and stable supply and demand, the same cannot be said for most other gems, especially when supply and demand are unpredictable. While most gemologists can prepare a grading or identification repot on a stone, only an appraiser can give its exact value. Most appraisers include a grading report also. Some jewelers subject inferior quality colored gems to enhancement – like heat treatment, irradiation or oiling – to get a better price for them and a good appraiser will be quick to notice such embellishments. Some stones have a high value because of the history or folklore attached to them. Stones coming naturally in identical pairs or suites fetch a comparatively better value than a single stone of the same quality.

What does an Appraiser do?

The term ‘appraising’ refers to the process of evaluating a product on the basis of specific criteria and for specific purposes. Gems are appraised mainly to determine their fair market value (FMV) or for insurance purposes. Qualified gemologists undergo specialized training to be certified as accredited appraisers of gems. If a gem has been certified by a Master Gemologist Appraiser, his/her valuation is accepted as final. These appraisers need to have their credentials revalidated every five years. They need to update themselves with the latest developments in the field of gemology. Appraisers may specialize in evaluating different kinds of gems and jewelry. They are even given special courses in market research and analysis for gems.

Appraisers make a detailed study of the various characteristics of gems. The chemical composition is analyzed to determine if it is essentially a chemical element, a simple chemical compound, or a complex compound of chemicals and elements. The crystal structure is analyzed to determine whether they are crystalline, non-crystalline or organic. The crystal structure can be cubic, hexagonal, tetragonal, orthorhombic, monoclinic or triclinic. Gems are studied for their optical effect. Besides assessing the color, they are analyzed for factors like optic character, refractive index, birefringence, dispersion, fluorescence, phosphorescence and clarity of color. Some gems display rare special optical effects called ‘phenomena’, which enhance the attractiveness and value of the stone. These gems are studied for chatoyancy, asterism, iridescence and aventurescence. Each gem is assessed for specific gravity or relative density. Durability of the stone is assessed to determine hardness and toughness. Thermal conductivity is assessed as the ability to conduct heat varies from stone to stone.

A variety of appliances and accessories are used in the process of appraising a gem. These include binocular microscopes, refractometers, polariscopes, Chelsea filter, aka emerald filter, spectroscope, ultraviolet light source, special specific gravity testing liquids, X-ray photographs, etc.

The Final Analysis

Generally gems are categorized as Precious stones – diamonds, rubies, emeralds, sapphires, opals and pearls – and Semi-Precious stones – most other colored gems. But this classification is rather ambiguous as inferior quality ‘precious stones’ are much cheaper than top quality ‘semi-precious stones’. Even the general differentiation between diamonds and ‘colored stones’ is inappropriate, as some diamonds are colored and some ‘colored’ stones have no color. Some unusual gems are further classified as Museum Grade stones and Rare or Collector stones.

The basic principle of the 5 Cs is applied for all gems – Cost should be determined by Carat, Cut, Clarity and Color.

The price per carat does not rise proportionately but exponentially. This is because large gems are difficult to come by. While larger carat weights naturally attract higher prices, the stones should be of a size suitable for ornaments to have value.

A gem must be strikingly beautiful in appearance to have real value. Sparkle and color are the primary considerations and should be evident even from several yards away. Cut and clarity determine the impact of sparkle and color. The pattern of cutting differs for diamonds and colored stones, as the optical properties of the latter are variable. Different types of cuts include heart, octagon, pear, marquise, round brilliant, oval, square, trilliant, round cabochon, princess, antique cushion, baguette, emerald cut, and briolette. Good diamonds should be dazzling with their white fire and good colored stones should maintain the richness of their color in daylight as well as indoor conditions. A really good gem will stand out anywhere, anytime!

Some persons claim they can asses a stone with just one careful look. They may or may not be correct in their assessment, but, when you consider the professional competence of a certified appraiser, it is much better to be certain than to take a risk when investing your valuable money in gems. Certified gems are far more valuable whether they are for resale or for a collection. It is a good practice to have precious stones appraised and revalued periodically, so that you can always rest assured that you know the exact value of your collection.

How gemstone hardness measured

by Binashaji

Diamonds measure 10 on the MOHS scale and Aquamarine measures 7 whereas Pearls can measure between 3 and 4 on the MOHS scale. MOHS is a term oft used in Gemstone Jewelry, but what exactly does MOHS mean and signify?

The MOHS scale was formulated in the 1800’s by a German mineralogist (Geologist) named Friedrich Mohs. As a Geologist, he spent over a decade studying and experimenting with various minerals and gemstones. Friedrich Mohs created an easy to remember scale by which one could easily discover if a mineral was delicate or hard. The resultant MOHS scale makes it possible to gauge the scratch ability of a mineral or gemstone. He took 10 minerals and gave each one a number from 1 to10 depending on its hardness as compared to the minerals above and below it. The MOHS scale is given below:

The symbol for MOHS is HM.

Although Friedrich Mohs designed this model for minerals in general, it is not used scientifically in laboratories because it is not an exact measurement. The MOHS scale is only a comparative scale. The degree of the hardness is only to check if a gem can be scratched by another gem that is above or below it. For eg. Garnets and Amethyst are both rated as 7 on the MOHS scale and it means that both can scratch each other if they are handled without care or placed with each other. But if a Garnet is placed with a stone like opal which is 6 HM then the opal can be scratched by the Garnet. Alternatively if the Garnet is placed with a Ruby (hardness of 9) then the Garnet can get damaged but not the Ruby. So if new , unknown gem is discovered and its hardness is not known , it can be rubbed against various known gems. Depending on which material leaves scratches on it, it hardness on the MOHS scale can be arrived at with relative ease.

The MOHS scale only determines the ability of the gemstone to resist scratches. It is not a measurement of the strength of the stone. A high MOHS rating does not necessarily mean the material is strong. For example a Diamond is 10 HM, which means that it measures 10 on the MOHS scale. Diamonds are the only substance with a rating of 10 on the MOHS Scale. They are the hardest gemstones known to man and Diamond bits are used to cut glass, metal and other diamonds also. Although Diamonds cannot be scratched easily, they are brittle. A light blow and a diamond can crack and break.

There are several other exact scientific methods to arrive at the exact hardness of any material. It is not possible to decide that a stone which has a hardness of 3 is exactly half as hard as a stone which measures 6 on the MOHS scale. For eg. Corals measure 3.5 and an Amethyst is 7on the MOHS scale. But accurate scientific tests have shown that the hardness of the Amethyst is more than 20 times the coral. The numbers accorded to the stones on the MOHS scale are only for comparison and they are not proportionate with each other.

But the MOHS scale has been a boon to the Jewellery industry and specially for the Gemstone buyers. This easy to remember scale makes it very easy to maintain and care for Gemstone Jewellery. This scale helps even a layman understand about how Jewellery should be maintained and stored. Storing Aquamarines with Pearls can be disastrous. The Aquamarine will scratch the delicate pearls leaving ungainly scratches which can be felt if a finger is rubbed gently across the Pearls. These scratches will even show up when light falls on the earrings or necklace, ruining the classiness of the Pearls.

When buying Jewellery, just ask your Jeweler what is the MOHS rating of the gemstone. It is much easier to store and maintain Jewellery when you have an idea about the MOHS rating of piece you have bought. Corals, Pearls, Amber all are delicate and need to be used with care. As a rule, if your gem does not measure at least 7 on the MOHS scale, it is a delicate stone and can be damaged very easily. So extra care should be taken while wearing these ornaments.

The MOHS rating can help determine the usage of the Jewellery too! For everyday wear, Diamonds are the best – their hardness is 10 and they do not get scratched easily. Rubies, Emeralds also are great for people with active lifestyles since they measure 9 on the MOHS scale and have a greater resistance.

If you love wearing Gemstone Jewellery, get to know the MOHS scale to help you understand and care for your precious pieces. Although the scale is not an accurate measure and can only be used for comparisons, it is great to care for your precious ones !

Factors affecting quality of pearls

by Bina shaji kurup

An important factor in deciding the quality of the Pearl is its Luster. A high luster is visible in the reflections on the surface of the pearl – a clearer reflection signifies a better luster and such pearls seem to have a warm glow. The luster of the pearl is dependant on the thickness of the nacre coating on the pearl – it is normally understood that the longer a pearl is left inside the mollusk, the thicker is the nacre layer.

How does one decide if a pair of pearl earrings or a necklace is worth its price? As with all gemstones, pearls too have certain factors, which decide their quality and price. Since pearls are natural creations and do not require cutting or polishing, it is rare to find uniform pearls unlike gemstones which can be cut and polished into uniform sizes. This is the beauty of the pearl, each pearl is unique and sometimes particular shades, sizes, and shapes can become scarce. Natural factors like water pollution, diseases, temperatures etc, all affect the availability of this delicate gem. Of late, with the advent of the pearl farms, the conditions are kept controlled giving better results and improved quality pearls. Some of the factors affecting the price and determining the quality of pearls are given.

An important factor in deciding the quality of the Pearl is its Luster. A high luster is visible in the reflections on the surface of the pearl – a clearer reflection signifies a better luster and such pearls seem to have a warm glow. The luster of the pearl is dependant on the thickness of the nacre coating on the pearl – it is normally understood that the longer a pearl is left inside the mollusk, the thicker is the nacre layer. A good quality pearl will glow warmly and reflect images clearly. Pearls with thin nacre are not of good quality and will not have the glow of thick nacre pearls.

Associated with the luster is the Surface of the pearl. Most pearls have some small blemishes or marks on the surface or they may slightly dented – this is more visible in larger pearls, although jewelers normally make sure the pearl is polished and sometimes treated to ensure its surface looks smooth and flawless. The pearl is a creation of nature and some flaws are normal in most pearls. But deep cracks or holes or overgrowths on the pearl or too many dents and blemishes should be avoided as they ruin the elegance of the pearl. A naturally flawless surface is extremely rare and such pearls are not made into jewellery, they are kept as they come from the oyster – without drilling holes or converting them into pieces of jewellery.

Origin of the pearls is important while deciding on the quality and price. Natural pearls, which are rare, command a higher price and the saltwater cultured pearls are the next on the price range. Freshwater cultured pearls are the cheapest and are available to suit all budgets – from economical to expensive.

The shape of the pearl is another factor in deciding the quality of the pearls. A round shape is highly valuable. This is because finding a perfectly rounded pearl is fairly rare – the Black Tahiti pearls are some of the rare examples of round pearls. White round pearls are normally rare. It is easier to find pearls in other shapes, the oval shape being less expensive and more readily available. Rice Pearl strands are eye-catching and are available in several designs. Thus the shape of the pearl although important in deciding the cost, is not important while purchasing a strand or pair of earrings since all shapes of pearls are equally enticing.

Large pearls above 14mm size are rare and most freshwater cultured pearls (pearls grown on cultured pearl farms) range from 1mm to 12mm. The larger pearls are normally saltwater pearls like Tahitian and South Sea pearls in sizes from 12mm to 20mm (which are rare and most prized). Most Freshwater pearls are small ranging 1mm to 9mm. The diameter of the Pearl is measured in millimeters to get the exact size. Although large pearls are expensive, if they do not have a good luster or are flawed, it is safer to avoid buying them. Instead buying smaller sized pearls with a good luster is advisable.

Silvery white, a gentle tinge of gold or pink, hues of black and blue – pearls are found in myriad colors. The color factor while deciding on a strand or a pair of earrings is a purely personal choice – some prefer the light shades of white, pink or gold whereas some love the look of the gray or black Tahitians. The colors most sought after are the whites with a tinge of rose in them and the colors most avoided are shades of green and brown. Ensure that you ask your jeweler if the pearls have undergone color enhancement, which has become a custom. Pearls that have not undergone color enhancement are rare.

While buying strands or pearl necklaces, the size, shape and color of the pearls is very important.
A necklace that does not have matching pearls can look shabby and cheap. In fact, expensive necklaces are those which have matching pearls – the size of the pearls is irrespective. A necklace could have the pearls of the same size, shape, color or they could be of varying sizes with the same shape and color. It is important that the strand looks uniform and has a certain balance in the pearls used. Uniformity and balance is the key to acquiring an elegant pearl necklace.

Buying pearls with these qualities will make your purchase worth the price you pay for your elegant pair of earrings or the special bracelet or necklace.

How Pearls are graded

by Bina Shaji Kurup

A good pearl has several qualities and based on these qualities pearls are graded. There are two systems of grading pearls, which are accepted worldwide. One system is the ‘Tahitian’ system developed by the Polynesian government. This system is used to grade Black Tahiti pearls and other Saltwater pearls like the South Sea pearls. The other is the ‘AAA-A’ system, which is used to grade cultured Freshwater pearls.

The Tahitian System adopted mainly to grade Saltwater pearls grades pearls on a scale of “A” to “D”. “A” signifies pearls of the highest quality and “D” are the lowest quality pearls which can be used to make jewellery. Any pearl lower than “D” grade is not used to make jewellery and is not exported out of the country. Lower than “D” grade pearls are used to make pearl powder and are sold only in Tahiti. The Tahitian system of grading pearls works as follows:

“A” quality pearls have a brilliant luster, reflecting images and colors clearly. They will have a clear surface with only 10% blemishes or flaws on the surface. These flaws are usually not visible since the hole is drilled over these flaws. Mainly these pearls are round in shape and their color is deep with overtones of Pink, Peacock Blue, Gold etc. These pearls are round in shape with a thick nacre coating, which is evident in the luster of the pearl. The pearls belonging to grade “A” are large pearls – more than 14mm in size. Grade “A” pearls are rare which makes them the most expensive pearls.

“B” quality pearls have a good luster and approximately one-third of the surface is flawed lightly. Their shape is round or semi-round and the flaws are often invisible from a distance and show up only on closer examination of the pearls. These pearls are between 12mm to 14mm in size with overtones of Gray, Pink, Gold etc.

“C” quality pearls are lustrous and pearls having less than 60% minor imperfections come under this category. These pearls are normally semi-round and have a variation of more than 5% in their diameter. Although there is a difference between the “B” and “C” grade of pearls, an untrained eye cannot really pinpoint the difference. The size or luster may vary and the shape will not be as round as “B” grade pearls. The pearls in this category are smaller and their color may not be as pronounced as the “B” grade pearls.

“D” quality is accorded to pearls if they have flaws like deep dents or cracks on the surface. Even pearls with high luster are graded D if more than two thirds of the surface is flawed.

Pearls below “D” quality or with flaws covering more than 65% of their surface are not used for making jewellery. To understand the differences in luster and surface of the pearl, try comparing pearls of different grades, it is possible to get a better understanding of how pearls are graded!

Black Tahitian pearls are renowned the world over and their color makes them unique. The beauty of these pearls is in their overtones. A plain black pearl costs much less than a similar pearl, which has overtones of Green, Pink, Gold Purple etc. (but brown shades are not considered to be a good buy) The exception to this rule is the large size pearls – exceeding 18mm, which are rare and are categorized as “A” grade irrespective of their color. Pearls with a mix of more than two colors are considered to be of a higher quality and command a higher price. Multicolor strands are famous in Tahiti and are absolutely eye-catching.

The other system for grading pearls is the “AAA -A” system. Used mainly for grading freshwater and Akoya pearls, sometimes even saltwater pearls are graded under this system. In this classification, the pearls are graded as being “AAA” (the highest grade), “AA” being medium quality and “A” being accorded to pearls, which do not meet the requirements of either “AA” or “AAA” grades. As with the Tahitian system, the pearls are graded as per their size, shape, color, surface, nacre thickness and luster.

“AAA” grade pearls are the ones with the highest luster, least blemishes on the surface and have a rounder shape (although perfect spheres are unusual in Freshwater pearls). These pearls have a thick nacre coating and are normally white with Pink or Gray overtones. Pearl strands cannot be of a higher grade than “AAA” grade and are expensive. Necklaces are also rare in this grade and most pearls are sold as strands or as individual pieces or as rings and pendants. These grades of pearls are the largest in size exceeding 8mm (sizes of 10mm or more amongst freshwater pearls are very rare)

“AA” pearls have a good luster and their surface is slightly flawed but hidden by mounting or drilling the flawed area, whereby only the flawless surface is visible. Their shape may be less round than the “AAA” grade pearls but not of a semi-round shape or a baroque shape. Rolling a pearl along a straight surface determines its shape – a straight line signifies a round shape, a zig-zag line signifies the shape is semi-round and a semi- baroque shape will rotate on one side only. The semi-baroque shape is further divided into drop, button, pear and oval – all four shapes are nearly similar with small differences. “AA” grade pearls are found in shades of White, off-white or cream with pink, silver and green overtones. They are available in sizes of 5mm to 8mm and have medium nacre thickness.

“A” grade pearls are available in many shapes and their natural shapes gives them a look that is unique yet elegant. These pearls have a flawed surface of more than 25%, but it is not visible from a distance. These pearls make an economical buy and are available in a variety of designs, a spectrum of colors and shapes like Rice or Seed pearls, Oval or pear shaped, Button and Baroque shapes. These are normally smaller size pearls between 1mm to 4mm in size. The nacre coating in these pearls is not as thick as pearls of “AA” and “AAA” grade pearls. But in no way does the lack of luster or size or shape reduce the beauty of these pearls.

Pearl jewellery, especially Necklaces and Strands of pearls are made of several pearls and not all of them may meet the same classification, some may be of an “AA” quality whereas some maybe of “A” quality. Also mounting or drilling the pearls at the point of the blemish cleverly hides blemishes and a dishonest jeweler can pass of “A” grade pearls as “AA” pearls and sell them at a higher price. The Lustre of the pearl cannot be hidden and that would be the best test to determine whether a pearl necklace is of “A” grade or “AA” grade. It makes sense to check each pearl for luster and flaws before buying an expensive piece. If a strand of pearls is graded “AAA”, most of the pearls, if not all, must be of “AAA” quality.

The main difference in both grading systems is that under the Tahitian system, pearls are graded only as A, B, C or D. Under the second system, it is possible for sellers to give grades, which are higher or lower than the specified grades like AA+ for pieces that do not meet the specifications but are in between two classifications. This gives the sellers a little more flexibility.

Some sellers may tell you that the pearls sold by them are of “AAAA” quality, which is better than the “AAA” grade and not usually accepted as a grading measure. In such a scenario, remember some rules about “AAAA” pearls. “AAA” and “AAAA” pearls are different mainly in terms of their shape. “AAAA” pearls are the perfectly rounded pearls, which are very rare – especially in Freshwater cultured pearls. Since their availability is limited, these pearls are mainly used to make solitaire pieces like pendants and rings. A necklace or strand of pearls in the “AAAA” grade is almost impossible to find. They have a flawless surface and are normally smaller in size.

Pearls are delicate gems measuring 2.5 to 4 on the MOHS scale. Even our tooth enamel can leave scratches on its beautiful surface. Always buys pearls with a thick coating of nacre – which will protect it from cracking (in case it falls), discoloration and age.

Store your pearls separately away from other jewellery and remember the golden rule of wearing jewellery – ” always put it on last and remove it first”. This means that only after applying make-up, dressing up, spraying on perfume etc and finishing every aspect of getting ready should you wear your jewellery to protect it against any chemicals contained in sprays or cosmetics. Similarly, remove your pearls first and keep them safely to ensure they do not get damaged. Pearls do not need to be washed; just a mild rub with a dry cloth will remove accumulated oils and dirt and restore their luster. At regular intervals, return your pearls to your jeweler for re-stringing. A little care will go a long way in making sure your pearls remain lustrous and elegant for a long time.

Always buy from a reputed jeweler whether you are buying it from a store or via the Internet. Investing in a good quality strand or necklace can be a joy for years and will never go out of fashion.

International Colored Gemstone Association – ICA

by Ashish Dimri

International colored Gemstone Association has its headquarters in Newyork city; U.S.A. It also has additional bureaus in Idar- Oberstein and Israel. It has over 400 members in 41 countries worldwide.

International colored Gemstone association (I.C.A.) and its role in gemstone industry

International Colored Gemstone Association is a non-profit association of international gem traders, gemmologists and people associated in various capacities with this trade. International Colored Gemstone Association has its headquarters in New York City; U.S.A. It also has additional bureaus in Idar- Oberstein and Israel. It has nearly 500 members in 42 countries worldwide. International Colored Gemstones Association (I.C.A.) has members belonging to different fields for example miners, gemstone cutters, jewellery manufacturers, and service providers. It was formed in 1984 when it was felt that there was no association to look after interests of gem trade.

Its association’s membership represents seventy-five percent of the purchasing power of the international market for colored stones. The main objective of I.C.A. is to unite various segments of colored gem trade. Previously, gem trade had no association to work united. This association made a way for all who work in this lucrative trade. This excellent association stands for excellence and knowledge. Any person who is associated with gemstone industry enjoys patronage and ample guidance from it. In other words, I.C.A. is living ocean of wisdom for the gem trade industry. International Colored Gemstone Association conducts so many functions from conducting tours, congresses and seminars to publishing newsletter to educate its members about latest happenings in the colored gem trade. For example from time to time, it organizes special tours to prominent gem producing countries like Belgium, Colombia, and Brazil for its members. The main purpose of these tours is to inform the various facets of this trade to new and veteran members.

Some of the prominent activities performed by International Colored Gemstone Industry are

Congress

International Colored Gemstone Association often organizes congresses on different issues like promotion and production of gemstones. The main purpose of these congresses is to play link between various segments of gem industry. Here everybody gets an opportunity to discuss various problems and all get a chance to foster business. Mentoring Tours- I.C.A. In addition, plays role of a mentor by organizing tours to various gem producing countries where participants get a rare opportunity to visit places such as advanced laboratories where they are familiarized with modern scientific methods used in trade. They also attend meetings with veteran members of colored gem trade who share business secrets with them. They also visit mining areas to get a first hand knowledge of raw gems.

Marketing Program

ICA has recently launched a marketing program through which gemstone and jewellery manufacturers and retailers try to steer and increase demand for colored gemstones in the consumer market. It hopes to gain a lot of experience and profit through this magnificent program.

Exhibitions

It also organizes exhibitions of exotic gems and jewellery in international museums. These exhibitions provide ample chance to the visitors to learn about rare gemstones and jewellery. These exhibitions help to develop interest in history of gem trade. From exhibits belonging to past like mogul jewellery to modern age rare collection, one can get to watch these things at these exhibitions.

Formal Meetings

It regularly organizes meetings between its representatives and prominent jewelers and gem manufacturers. This is a better way to evolve new and better marketing and publicity strategies for gem trade.

Educational Seminars

It regularly organizes a series of educational and discussion seminars that intend to increase colored gemstone perception amongst the local trade. These seminars range from gem export, gem enhancement methods, and new technology. These seminars are helpful as they point out numerous problems and provide their solutions. These educational seminars provide a right platform to share one’s experiences with others.

Information provider

Being a collective body of gemmologists, gem cutters, jewelers, and gem enthusiasts; I.C.A. is coffer of valuable information. It informs on supply, demand, innovation and challenges in the colored gemstones business of the 21st century through its publications, forums and tours for all those interested in gem trade.

Committees

I.C.A. has set-up many committees to look after various aspects of gem trade. Its various committees oversees many activities associated with trade for example, it gathers data on various issues and provide certification to put in place protocols and standards to be used by the mine operators. There are committees which look after trade policies and technical matters.

Magazine

In past, I.C.A. used to publish a two-decade-old IC.A. Gazette providing information about various happenings of the gemstones industry. Now it has revamped it and introduced a new colored magazine, InColor. This magazine contains a cover story, a news section, and two regular feature articles. This new magazine is a mine of information for those associated with the trade. InColor, regularly informs new happenings and future programmes in it.

International Watchdog

International Colored Gemstone Association acts as an international watchdog to protect rights of its members. It understands international gem market is evolving day by day and as a result, spurious elements are bringing disrepute to this excellent industry. It informs the prospective buyers and sellers to conform to the standards set by it while doing transaction. As it is an international association therefore its influence is wide spread. Those who need help can contact I.C.A. regarding any complaint.

Promoter of interests

I.C.A tries hard to promote business interests of its members. It acts as a facilitator of their business interests. It actively promotes cooperation between various segments of gem trade. In other words it is a dynamic promoter of cooperation on trade and technical matters.

Advisory role

From time to time, it advises its members on various trade policies, planning and related programs. Gemmologists and others associated with gem trade can benefit vast amount of knowledge through valuable advices given by I.C.A.

Friend, Philosopher, and Guide

It acts as a true friend, philosopher, and guide to its members. It always tries to foster solidarity among various segments of colored stone trade. One could be a gem cutter or jeweler but they feel sense of oneness because of this international association. Being a non-profit association, International Colored Gemstone Association wants prosperity and constant benefits for this lucrative trade and people associated in it. Apart from its commercial activities, it also organizes recreational programmes for its members.

Pleochroism in gemstones

by Yuman Hussain

Scientific explanation of pleochronism which is an ability of the stone to absorb different wavelengths of light displaying brilliant colors when viewed from different directions.

What is Pleochroism

Have you ever wondered about the color of a gemstone? How and from where different colors originate in a stone? Well, it is through a phenomenon known as Pleochroism, a term with many might not be familiar with.

Pleochroism is derived from a combination of Greek words-‘pleion’ meaning more and ‘chros’ means color. However it does not mean multi-colored but a change of color in a stone due to movement of light through it. Pleochroism is a general term referred to the processes of dichroism and trichorism. Dichroism is found in uniaxial crystals with single optic axis and trichorism is found in biaxial crystals with two optic axis. When ordinary light falls on uniaxial crystal any given wavelength of light is absorbed except along the optic axis displaying one color in its direction and different color at other angles. These dichronic stones show two colors or shades and trichronic stones with two optic axis shows sometimes three or more shades or colors. The main cause of Pleochroism is due to absorption of particular wavelengths of light. This selective absorption leads to transmitted light, which appears as colored. Two conditions are must for this phenomenon including thickness and crystallographic structure. Secondly the chemical properties of the stone should be strong enough to see the effect.

Highly visible in doubly refracting colored stones Pleochroism is defined as an optical phenomenon in which light is focused on stone splitting in two different components – ordinary ray and extraordinary ray polarized at perpendicular angle to each other. When different wavelength of light is traveling at different speed following different directions within a stone it gets absorbed producing different colors when it leaves the stone. It makes the stone as if made up of different colors. It is basically an ability of the stone to absorb different wavelengths of light displaying colors when viewed from different directions. These colors depend upon the optical path viewed .This phenomenon can be understood through following example. If all the light except green and blue is absorbed in a crystal then it reflects green color. If a stone absorbs all light except yellow than it will display yellow color. If the stone is observed when turned from first direction to the other then color will change from green to yellow.

All stones do not show Pleochroism. For example isometric stones such as diamond, garnet, spinel and halite do not show change in color as they have same structure having same light absorbing capacities preventing light waves vibrating in different directions. Almost all transparent minerals show Pleochroism. Most of the dichronic stones are hexagonal, Trigonal or tetragonal with one structural direction along the major symmetry axis whereas trichronic stones are orthorhombic, monoclinic or triclinic with three axis of symmetry or direction that can absorb light.

Sometimes in order to display color or to make it more attractive stones are cut in such a way to show Pleochroism or to hide it. An important tool for mineral identification it is required to examine the stones displaying different pleochronic color schemes. When we use plane-polarized light under microscope a pleochroic stone changes its color. Many stones are pleochronic but sometimes color change is so negligent that it require optical instrument for detection. Some gemstones show stunning color displays. Often color change is restricted to shade changes for example from light purple to dark purple or violet. Pleochroism is strong when color change is distinct and it is said to be weak when there is only minor color change in a stone. An individual transparent crystal can show the display of Pleochroism.

Pleochroism is observed:
– If there is change in actual color that is, if a stone is seen blue or red from different positions.
– If there is change in the intensity of color that is if a stone becomes light to dark in shade.

Tourmaline is a dichronic substance reflecting two colors in which ordinary ray is absorbed and extraordinary ray is transmitted. Cordierite crystal show trichorism when light passes through parallel to three crystal axis violet, yellow or blue light is absorbed. When crystal is cut the axis edges show mixed colors of blue, yellow, violet and yellow, violet and blue. Tanzanite is also another popular diachronic stone in which there is selective absorption of different lights displaying brilliant colors ranging from blue to purple when seen from different light sources. Blue Aquamarine sometimes might show a slight color change from pink to green if viewed from different directions. Fluorpatite is a diachronic yellow mineral which turns blue when it is viewed along its axis. There are some other stones which show best examples of Pleochroism. These are:

• Andalusite which show change in color yellow green to red brown.
• Zoisite which show colors from pink to yellow.
• Kunzite which show colors from pale pink to dark pink.
• Iolite which show colors from blue to purple.
• Corundum which shows color from violet to orange.
• Alexandrite which colors from red purple to orange to dark green.
• Peridot which shows colors from yellow green to green.
• Beryl which shows color violet to being colorless.
• Elbanite which shows pale color to dark color.
• Carletonite which shows blue color to being colorless.

A spherical shell of color, pleochroic halo is present around radioactive impurity in a stone. This ring or halo said to represent a site where crystal structure has got changed by the absorption of energy of radioactive alpha particles .As energy has got absorbed it produces an intense color centre on the inclusion with in a stone. These pleochroic halos are common in zircon, monazite, xenotime and apatite. The rings are distanced and identified according to the range of alpha particles with in a stone.

The beauty of a stone is enhanced when it display different colors from different angles. So next time while buying a gemstone do not forget to look at the kind of light displayed at the stone.

Asterism in Gems

by Nasrina Parvin Khan

“Asterism” is an exclusive light effect (which we called special optical phenomenon) of some crystal. When light pass through these crystals, its exhibit a star-shaped figure, which called “asterism”.

Asterism

Asterism” is a term, which is most commonly used in gemology. It refers a kind of special optic phenomenon that has been seen in several gems.

Special optic phenomena refer uncommon and excellent optic properties exhibit by some rare gemstone. The phenomena are particular property of transmitting or reflecting light. The structure or inclusions of a mineral in gems is the reason of this property. The beauty and value of gems depend on their optical properties.

“Asterism”-one of the important optical phenomena has been seen in sapphires, rubies, rose quartz and some other gems. The term “Asterism” came from the Greek word “aster”, which means star. From the name we can guess “asterism” is star-shaped light effect across the surface of gems.

Special optical phenomenon

“Asterism” is an exclusive light effect (which we called special optical phenomenon) of some crystal. When light pass through these crystals, its exhibit a star-shaped figure, which called “asterism”. This figure is produced by reflected or transmitted light.

Asterism in Gems

Gems, which show an illuminated star, just bellow the surface of crystal called star gems. The most popular star gems are star ruby and star sapphire. Other gems, which also possess the special optic phenomenon “asterism”, are rose quartz, garnet, spinel, Chrysoberyl and Diopside. There are a few specimen of rock crystal, which has the phenomenon.

The star in the star gems may have four to twelve rays depending on the crystal system of the gems. But the six- rayed star effect is most common. Usually, six-rayed star show by the star rubies and star sapphires. Sometimes these star gems exhibit the twelve-rayed star effect. But the twelve-rayed star effect in corundum is occasional. Rose quartz exhibits six-rayed star. Some garnets and spinel commonly have the star effect with four rays, but these star gems can show six-rayed star effect if cut in a distinct way. Some crystals like Chrysoberyl and Diopside only exhibit four-rayed star effect.

“Asterism” is caused by the dense inclusions of tiny fibres of foreign minerals in gems. Generally, these inclusions are the reason of the reflection of light and form a wavy star like formation, which moves around when the mineral is rotated. All the inclusions in the gems are formed via exsolution.

The inclusions must be long, very thin needle like which called as rutile. “Asterism” is produced when needles intersect each other in multiple groups. Small needles of rutile (titanium oxide), sometimes called “silk” are oriented inside the minerals in the direction of the crystal growth system. There is a relationship between the gem’s growth and the number of rays produced by the reflected light.

There must be three or more chatoyant bands inside the gems to produce “asterism”. The arrangement of needles in a hexagonal pattern produced six-rayed “asterism”.

Exsolved inclusions form a pattern in the host mineral. The pattern may vary from mineral to mineral, but in case of specific mineral the pattern remain same. In case of corundum, we can see rutile is exsolved in three directions crossing at 60 degree or 120 degree in the basal and produce six or twelve-rayed star. When the rutiles crossed at 90 degree, it produces a four-rayed star. Star gems are translucent to opaque .The rays of star should cross at the top of these gems and be distinct.

Star Sapphire

The sharpness and the size of “asterism” in gems, which identified as phenomenon, depend on the quality and quantity of rutile needles. Small to smaller size of rutile needles help “asterism” to be sharper. When the needles are visible with open eyes as inclusions, the gems turned into a low translucent stone and lack “asterism”.

Large quantities of rutile needles in a crystal produce phenomenal “aster”. If the quantities of rutiles are small, “Asterism” is visible in only a small area. These gems are not recognized as phenomenal gems .The clarity of these gems can be improve by dissolving some rutile needles with heat treatment. Heat treatment allows various elements to be incorporated into crystal. Then rutile needles form by very gradual cooling system and induce “asterism”.

Inclusions are not present in all star gems. Some specimens leave holes or empty areas in the host. Reflection creates from fibres or fibrous cavity in the crystal.

Types of asterism

There are two types of “asterism”, like Epiasterism and Diasterism. Epiasterism is creates by the reflection of light on parallel-arranged inclusions inside the crystal. Diasterism is creates by the transmitting light through the stone, mostly seen in rose quartz. To see this effect a lighted background is essential.

To display the star effect in best way a gem is cut as cabochon with the girdle parallel to the needles. The domed stones are round or oval shaped.

The special optical phenomenon “asterism” is most visible in direct, single pointed light source, like an incandescent bulb, fibre optic light, and penlight or in sunlight.

The distinctiveness of the star and degree of strait ness of each ray help to judge the quality and value of star gems.

More Resources:
Asterism in gemology
Asterism pictures
Asterism in quartz

Labradorescence

by Nasrina Parvin Khan

Labradorescence is an exclusive optical phenomenon that has solely shown by the feldspar gem Labradorite in this earth.

Iridescence flashes of colors, which appear on the surface of the labradorite feldspar is known as Labradorescence. Labradorescence is an exclusive optical phenomenon that has solely shown by the feldspar gem Labradorite in this earth. This phenomenon like, Adularescence of moonstone with more attractive bluish color. The iridescent display on the surface of the gem especially directional oriented.

Image courtesy Mineralminers.com

Labradorite

Labradorite changes color with its every position, which is usually available in glittering pastels and deep gold colors. The bright and beautiful display of Labradorescence can be change with movement of the stone. The “shiller” would be vanishing temporarily when the stone turned to a different angle. But it comes back again with movement of the gem in another direction.

One or more colors can be seen on the surface of the gem by this special optical phenomenon. A bluish sheen with a colored flash exhibits by this phenomenon. But the bluish flash of Labradorescence is more common. Sometimes greenish, purplish, gold and yellowish reddish bronzy flashes can be seen. Red-orange or peach-orange and white or off-white hues also seldom appear, when the stone is moved under a source of light.

Bright metallic looking spectral colors create on the surface of the Labradorite with the movement of the stone. This colors compares with the wings of tropical butterflies.

Labradorite is also known as “Black Rainbow” in India for its astonishing rainbow colored reflection. Large quantities of translucent white Labradorite can be found in this country. This stone is also called “firestone” because of its rainbow colored sheen.

Labradorescence phenomenon

The structural pattern of Labradorite is the reason of the phenomenon “Labradorescence”. Iridescent effect in Labradorite caused by repeated, microscopic thin layer (lameller) twinning inclusions made-up of black magnetite or ilmenite and generally showing some fracturing. Due to this structure interference and diffraction of light occurs, when it passes through the stone and reflects from the parallel surfaces.

The “shiller” of Labradorite visible at certain angles. No effect is seen when the angles of light faces no thin layer. Some faces of the gem show the silvery or bluish “shiller” this effect will display in cabochon cut gem (tall, domed shaped gem is called cabochon).the colors to be seen on the surface of the gem is also depends on the thickness and uniformity of the layers.

The special optical phenomenon “Labradorescence” named after the mineral “Labradorite”, which distinctly posses the phenomenon.

On the other hand the name “Labradorite” derives from the Labrador Peninsula (now part of Newfoundland and Quebec Provinces, Canada), where it was first discovered by a Moravian missionary on the Isle of Paul in 1770. This sodium rich feldspar is also found in Australia, Madagascar, Russia, Mexico, China, India, the Scandinavian Peninsula and the United States etc.

The brightest and most uniform color flashes, without “dead” areas determine the values of the gem. The most valuable deposit of Labradorite is Spectrolite. This particular colorful deposit of Labradorite was discovered in Finland. It shows not only bluish, but also green, gold and rarely red or violet sheen and has been given the name “Spectrolite” for its similarity to the color spectrum. “Spectrolite” is the national stone of Finland. It is said to be that it reflects the colors of the nature of Finland.

The background color of the Labradorite is unattractive just like dark smoky gray. The gemstone best esteemed when viewed from different angle and the magical effect of “Labradorescence” observed. Different colors may display or a range of all colors can be visible at the same time due to this phenomenon and added an attraction.

More Resources
Labradorite

Color Change phenomenon in Gems

by NASRINA PARVIN KHAN

Gems change their color according to the nature of the light they are seen. Alexandrite appears gr4een in daylight or fluorescent light (blue in rich) and in incandescent light (orange to red rich light) it appears as red.

Color change is a distinct optical phenomenon. It helps the gems to change their color distinctly under different lighting conditions, such as incandescent light to natural light. Alexandrite is the best example for showing color change effect. For this reason usually it referred as “Alexandrite effect”. This phenomenon is also found in sapphires and garnets occasionally.

Color change effect first discovered in the chromium colored variety of Chrysoberyl called Alexandrite. Alexandrite is the gem which shows true color change effect. On the other hand others gemstones are called as Alexandrite like.

Gems change their color according to the nature of the light they are seen. Alexandrite appears gr4een in daylight or fluorescent light (blue in rich) and in incandescent light (orange to red rich light) it appears as red.

Chemical composition of the stone is responsible for this property of the color change effect. Presence of chromium+++ ion as a major impurity in the stones works as coloring agent. This composition is the cause of spectacular color change effecting gems. Rarely vanadium can also play a part.

Due to their chemistry color change gems do not absorb colors, such as red and green. So, these colors reflected from the gem and we see the colors.

In daylight, there is little to absorb blue because of daylight’s richness in blue. So, the gem reflects blue and appears as green colored stone in daytime or under fluorescent lighting source. Similarly in incandescent light due to its richness in red, there is little to absorb red for the gem and we get the red stone.

Usually the ranges of changing color are from green to yellow, brownish red to purple, yellow green to bluish green.

The strength of color change is depending on the difference in the areas of transmission and absorption in the yellow. The greater difference shows the stronger color change.

When color change gems viewed in light made up of all wavelengths, the gems transmit blue and red usually look purple or purple gray.

Alexandrite is a true color change gem. It appears green to blue green in daylight and purple to purplish red in incandescent light. Cr+++ ion in its composition is responsible for this effect, which also gives the rich hues in ruby and emerald.

Alexandrite first found in Tokovaya deposits, Russia and named after the Russian Tzar Alexander II at his coming of age ceremony. It accepted as the national stone of Russia because of its red and green colors, which were also the colors of the old Russian Imperial.

Alexandrite is also found in Sri Lanka, Zimbabwe, Burma, Tanzania, Madagascar, India, and Brazil etc.

Except Alexandrite, there were garnets and sapphires which also posses the phenomenon of changing of color occasionally.

A color change garnet is known as “Alexandrite garnet” in the field of gemology. It changes color from smoky grayish blue (in day light) to vibrant raspberry red (in incandescent light) in case of color change garnet vanadium plays a major role for its color shift. A little amount of chromium with a high concentration of vanadium in its composition is responsible for the color change phenomenon.

Color change garnets are rare and comparatively small. It is found in Madagascar and East Africa.

Occurrence of color change sapphires are extra ordinarily rare. They tend to change their color from yellowish green to slightly bluish green in daylight and bluish purple to bluish violet in incandescent light. Chromium and vanadium in its composition play the roles to posses the uncommon phenomenon. It is found mainly in the Umba River Valley of Tanzania.

Rarely we can found a color change natural stone, which shows a complete color change. The completeness of the change of color is generally revealed by the percentage. For example we can say that a specific stone shows an 80 % color change.

Color change phenomenon is also depends on the thickness of the stone with the light. More color change is visible with the thicker stone.

Color change factor justify the value and beauty of the stone. The particular colors noted in the stone are very important for these. More visible color change adds more value for the stone.