Labradorescence

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.

Labradorescence

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

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.

Gemstone Testing tools

Gemstone Testing tools

by Ms Nandita Ray

It is tricky to test a gemstone. Some stones are soft, some are mounted while some can be coated, treated or easily scratched. One has to be very careful so as not to damage the stone in any way. With technology advancing rapidly, the tools used for testing are made to suit ones needs and pockets. Aiding the tools is a wide range of database, which lists the particular characteristics of gems.

Tools Required to Test Gemstones

There is an absolute and definite need to test gemstones, especially if they are expensive. Competition, economics, availability and demand have all worked towards the explosion of the gem market. The markets are flooded with gemstones of various hues, brand and breed. Therefore the need to test the authenticity of gemstones is imperative. Insurance too has a hand. They need the gem to be certified.

In the past, it was pretty easy for a trained gemologist to distinguish a flawless gem from a flawed one. There were no synthetic gems during those days. Today however, one has to determine whether a gem is real or not. Trained eyes cannot always avoid error, particularly, if the gem has been manufactured in the laboratory. It becomes a challenging task. Earlier on a magnifying glass was good enough. Presently however, a host of instruments are used, especially if one wants to be absolutely certain of the gem, its history and pedigree.

It is tricky to test a gemstone. Some stones are soft, some are mounted while some can be coated, treated or easily scratched. One has to be very careful so as not to damage the stone in any way. With technology advancing rapidly, the tools used for testing are made to suit ones needs and pockets. Aiding the tools is a wide range of database, which lists the particular characteristics of gems. This is valuable because the markets are deluged with zircons or the synthetic Moissanite, which are look alike diamonds and very difficult to differentiate from a real diamond.

Loupe

Loupe is actually a sophisticated magnifying glass. It magnifies the gemstone in detail. The internal flaws, surface blemishes, cracks and any other cover ups are easily seen. It is a powerful convex lens that produces a magnified image of the gemstone. The standard loupe that used is 10X, which magnifies the gem ten times its size. This standard is mandatory for testing gemstones in the USA.

Binocular Microscope

gemstone testing microscope image: www.ottofrei.com

Binocular Microscope is equipped to spread light from the bottom and from the sides. Its function is similar to the loupe. Presence of the lights and its superior optical strength provides excellent clarity. It usually has 10X magnification power though 200X can be got. Most common ones are 10X to 40X. There are stages of adjusting the iris diaphragm. It also provides coarse to fine focusing.

Refractometer

Refractometer measures the refractive index of the gemstone. This is needed in order to find out its composition and physical properties. It measures the extent to which the light that passes through the gemstone from the air is bent. It helps identify the gem by comparing the refractive index thus got with the established values. It assesses the purity of the gem by comparing it to the value of a natural gemstone. It also determines the amount of solute that has been added to the gemstone by comparing the refractive index thus obtained with the standard curve that is established. This is done by putting a drop of a liquid with a high RI, on a glass disc which is based on the tip of the Refractometer. Natural or white light is passed through this. The RI is reflected in the magnified gauge.

Dichroscope

Dichroscope is used for the quick identification of gemstones. It can effortlessly separate gemstones based on dichroism, which is the property of a gemstone to show two contrasting colors when turned in two different directions, under a light. This is used to distinguish two physically similar looking gemstones. The dichroscope is used to view the dissimilar color tones of the dichroic piece. It can easily differentiate a Ruby from a Tourmaline, which is dichroic while a Ruby is pleochroic. Some gemstones that are dichroic are Sapphire, Topaz and Zircon, to name a few.

Polariscope

Polariscope is used to determine if a gemstone is natural or not. It can differentiate diamonds from Moissanite. It also detects strains in diamonds. It can differentiate between gems that have double or single refraction i.e. birefringence. Double refraction is the breaking up of a ray of light into two rays, the ordinary ray and the extraordinary ray, when it passes through some materials like calcite also called Iceland spar. This effect can take place in gems that are anisotropic in structure i.e. having properties that differ according to the direction of measurement. The polariscope helps to track and see the path the rays of light are taking through the stone that is being tested. By measuring the optic characteristics of transparent to translucent gem material, the refractive index is found. Double refractive is only a property of solids. For transparent materials, the graph of index, unlike the wave length, is curved with a few general characteristics. A gem is held between two polarized plates and the light transmitted through it is studied and based on the readings the identification is made.

Some gemstones with double refraction are Quartz, Tourmaline, Ruby, Peridot, Sapphire, Zircon and Rulite to name a few. Diamonds are isotropic, meaning single refraction. Topaz, Mica and Perovskite have triple refraction.

Ultra Violet Light source: – some gemstones start emitting a fluorescent glow after being exposed to short or long ultra violet radiation. Many gems can be easily recognized by the Fluorescent color and the locale. Some fluorescent minerals are Agrellite, Tugtupite, dolomite, Fluorite and Benotoite.

Color Filter

Color Filter is also called a ‘Chelsea Filter’ or ‘Emerald filter’. This instrument helps in separating natural, synthetic and imitation gem material. It helps in establishing whether similar looking stones exhibiting the same colors are natural or not. It comes handy while dealing with some green, red or blue stones, like blue Spinel and blue Topaz. It detects dyes in gemstones also.

Spectroscope

Spectroscope is also used to separate natural gems from synthetic gemstones. This is used in specialized gem testing laboratories. The differences in the chemical composition are revealed by the absorption spectrum of the light transmitted through the gemstone that is being tested. The instrument breaks up the light that is being transmitted from a gemstone into its spectral colors. This helps in testing the various wavelengths that are being taken in i.e. being absorbed by the gemstone. This indicates the type of elements that are present in the stone, which are absorbing the wavelengths. It allows the gemologist to see which color of light is being absorbed and thus identify the gemstone.

Specific gravity Liquids

Specific gravity Liquids – this is important for identifying a number of gemstones. A carat scale also called hydrostatic balance is used.

X-Rays

X-Rays are sometimes conducted to separate natural pearls from cultured pearls.

Diamond Tester

Diamond Tester is used for testing diamonds. The unit is switched on and the diamond that is to be tested is touched by a pointed tip. A light will come on to indicate if the stone is a genuine diamond or not. It uses thermal conductivity to differentiate diamond from its many stimulants. When the tip is touched to the diamond, the meter will show green if it is a real diamond if not then it will remain in the red zone. This instrument can be used to test the minutest diamond, as small as 0.02 carats. It can also separate colored stones from one another. By merely touching the thermo electric probe to the gemstone, the relative heat conductivity of the material is exhibited on the dial.

These are the basic instruments. There are improved and sophisticated versions of these instruments available in the markets.

Gemstone Cutting

Gemstone Cutting

by Sheweta Dhanuka

Gem cutting is a long process that takes many months to convert simple rough into fascinating gemstone. It involves many steps. In order to acquaint the reader with the overall process of gem cutting, all the steps are explained one after the other. The steps elucidated are not in any fixed sequence.

Gemstones in the jewelry items enhance beauty of the women making her more attractive and splendid. Gem makes women beautiful and gem cutter makes gems beautiful. When woman is seen wearing the gemstone jewelries it is in it’s finest form but initially as rough any precious or semi precious stone is as simple and pale as a normal pebble. It achieves it magnificent look after it undergoes the gemstone processing. This process is known as Gem Cutting or Lapidary that involves cutting and polishing. An individual performing this art on the stone is known as gem cutter or lapidarist.

These amazing gemstones are created deep under the earth crust by the grace of Mother Nature. Innumerable chemical reactions take place in varied weather conditions like high temperature, pressure etc and then stones are retrieved after difficult mining. The material procured as the result of mining is referred as rough. The rough undergoes gem-cutting process in order to get transformed into small stones so that it becomes wearable and useful for other purpose.

Gem cutting is a long process that takes many months to convert simple rough into fascinating gemstone. It involves many steps. In order to acquaint the reader with the overall process of gem cutting, all the steps are explained one after the other. The steps elucidated are not in any fixed sequence. The reason being, it is not necessary that each single stone would go through all the mentioned steps like for example precious stone diamond is hardly ever seen in form of beads so for this gem drilling step makes no difference. Similarly, for gemstone comprising infinitesimal inclusions, two almost same steps like grinding, sanding gets clubbed into one.

Gem cutting process involves lapidary techniques that convert bleak rough into eye-catching gemstone. The well-defined gems then are used in distinctive ways viz. cabbing, faceting and carving. Be an adjunct with the above-mentioned techniques, the below text also mentions about the different shapes and mixing styles practiced in the gemstone industry.

Lapidary Techniques

These are the first and foremost techniques of this crucial process where rough is lightly hammered to confiscate unwanted part like brittle and fractured area of the stone. It is performed in eight different stages starting from sawing, grinding, sanding, lapping, polishing, drilling and tumbling.

Sawing

As the name specifies, in sawing a saw or cutter is used to convert rough into small stones. The saw is sharp circular blade made up of steel, copper or phosphor bronze alloy and its surface periphery comprises diamond clench. It is infused in the rough and then whirled at many thousand feet for every minute to make the gemstone. After heating in order to remove unwanted material from the stone, it is washed with either with water or oil. Washing helps stone and saw from getting overheated. This entire process requires lots of concentration and expertise, one single mistake can result in severe damage. Therefore, intense precautions are taken while sawing. It is brutal to hold the rough with naked hands while sawing; consequently the person covers hands and face with appropriate safety gadgets.

There are mainly two types of saws viz. circular and jig. According to the rough and the gemstones to be retrieved the saws are selected. Saws are available in different sizes.

Circular Saws

These are the most common saws used by gem cutters as it is suitable for the majority of roughs. The edge of the saw is plane and sharp. There are three different types of circular saws.

Slab Saw

Slab saw consists of 16-24 inches diameter. It is used for cutting thick rough into thin slab stones.

Trim Saw

Trim saw possesses 6-10 inches of diameter. It is used for cutting smaller roughs into small stones.

Faceter’s Trim Saw

This saw has minimum diameter that is of 4 inches, least amongst all. It is used for cutting the most valuable rough into small stones.

Jig Saws

As the name specifies, the edge of the saw is jig jag that is helpful in cutting curved lines in the rough. It is used along with a thin metal band or wire. This saw minimizes the wastage therefore is mostly used for costly stones like Ruby, Emerald, Alexandrite and so on.

Grinding

Once the rough is sawed into small stones then after each single stone is rubbed against either diamond – infused or silicon carbide wheels to bestow the preferred outward appearance. This is referred as preform. At this stage many times the surface of the stone is left with undesirable scratches. Subsequent to grinding the unwanted grits and mesh are removed by cleaning the preform with water or oil. It also acts as coolant as it averts the stones from excessive heat.

Sanding

In this stage the stone gets the flat and smooth surface. Through the use of excellent abrasives, the graze and scratches are removed from the stones that are left behind in the previous step. It is the crucial step for shaping the stone as from now the perfection in final appearance begins.

Lapping

This step of gem cutting process is quite similar to previous two steps that is grinding and sanding. The stones are stroked against one side of either gyratory or vibrating flat disk in order to give the flat surface. The disk is made up steel, cast iron and copper bronze alloy etc. It is known as Lap.

Polishing

It is the most important step as after this step the gemstones attain the mirror like appearance that helps in light reflection from its surface area. Different types of polishing agents are used for defining the overall look of the stone. Alumina, cerium oxide, tin oxide, lead, ferric oxide, chromium oxide and silicon oxide etc are few names of the polishing agents used by the gem cutters. Ferric oxide also known as jeweler’s rouge and silicon oxide called as tripoli are mostly used. According to the surface of the stone the polishing agent is selected for example flat surface stones are polished with tin oxide, lead, pellon or leather. For round surface felt, leather, cork or cloth is used.

Drilling

As the name specifies, in this step a small hole is created through the stone, such stones are known as beads. Only some semi precious stones are used for making the beads as precious stone and other semi precious stones like alexandrite etc are too expensive. Small revolving rod or else tube with a diamond or silicon carbide tip is inserted to drill the hole in the stone. Silicon Carbide consists of 9.5 Mohs while diamond is 10 Mohs on the hardness scale. The former is the synthetic compound of silicon and carbon. This manmade amalgam is used mostly for softer gemstones. Ultrasonic or vibrating drills are the most effective source for drilling the gems but are used exclusively for huge amount of beads, as it turns too costly for making small number.

Tumbling

It is the mode of giving the desirable attractive shape to the stone that are formed roughly in the lap of natural environment. Large numbers of unappealing shaped stone are turned in a tumbling barrel at a dawdling speed along with abrasive silicon carbide and water for days together. Stones are rinsed vigilantly between the grades there by attaining the smooth and polished look. There are two ways for tumbling the gemstones. One is rotating while other is vibrating.

Rotator Tumbler

These are the barrels hexagonal in shape that aids in the rotation of the gems. In rotator tumblers the gems are turned fully upside down. In order to know the progress of the gems inside the tumbler, it has to be brought to a standstill in regular time duration. Rotating tumbler is standard tumbling method and is cost effective too.

Vibratory Tumbler

These barrels are like a container in which the gems are in the stationary position but are vibrated from all sides. It is quite easy to monitor the progress of the gems inside this tumbler as compared to the rotator tumbler.

Faceting

The aim of faceting is to reveal the vividness and luminosity of a gem. It refers to the light refraction in the stone that is when light ray enters from one of the facet of the stone it is reflected back for the bottom facet. The viewer in rainbow colours views this light refraction. Proper faceting is very important for the transparent stones such as diamond, ruby, peridot, sapphire, topaz and many others. Well-created facets in the stone amplify its net value magnificently.

An individual creating the facet is known as facetor. He/she cuts and polishes the facet on the intact surface of stone using the faceting machine. The machine consists of a motor that holds the hand piece assembly by rotating the lap, water supply and adaptable hand piece along with index gears, protractor and mast/platform. There are two types of faceting machines – one is left that is known as mast- type and other is right faceting machine. The later is further having two varieties viz. hand piece and platform.

The flat surface of the gem is known as facet. Each facet on the stone is created in a proportioned pattern. First the facetor immerses the gemstone in the adhesive wax, epoxy or glue and sticks it on a metal dipstick. Later it is placed in the hand piece to get the position control. Then after cutting angle is adjusted vertically with the help of the protractor while rationally it is done through index gear. Finally then facets are created after grinding, sanding and polishing on the revolving lap. In the regular intervals water and other solutions are used as coolant and lubricant respectively. This cycle completes one side of stone. A jig is used to change the side on the dipstick. In the same way by repeating the steps opposite side is finished too. Normally flat facets are seen but with modern technology and innovative ideas of facetors, new-fangled concave facets, grooves and much such novel stuff are created.

Cabbing

It is also known as cabochon cutting, the simplest and most common lapidary form. Opaque and translucent stones are designed in this variety. Transparent stones with too many inclusions are also cut into cabochons to use it optimally. Cabochon at top are smoothly curved and polished while on bottom it is flat or round that could be polished or sanded as per the jeweler’s requirement. Turquoise, opal, bloodstone, lapis lazuli etc are mostly shaped into cabochon.

Cabbing procedure is almost same as faceting. Cabochons or cabs are cut through the process of dopping where the stone is attached to the dipstick with the help of either adhesive wax or glue. Later the stick along with the stone is rotated during all the lapidary techniques to have the smooth rounded surface all over the stone. Dopstick is made up of metal or wood. Separate cabbing machines are also available. These machines consist of quite a lot of wheels having diamond or silicon carbide gravel, twirled by one single arbor and motor. It also has a continuous water supply that acts as a coolant/lubricant to rinse off unwanted fragments and protects the stone from excessive heat.

Carving

It is a creative art in born in the carving artist. It is the most difficult art as the craftsmanship involves deep concentration, patience and imaginative skills. Apart from these talents he/she must also possess methodical knowledge about the lapidary techniques then only they could give astonishing look to their respective artwork. One who carves the costly gems is a skilled individual, turning the plain stone into captivating masterpiece having the functional or decorative use.

Semi precious stones are suitable for carving as precious stones are extremely valuable and pricy. There are many different types of carvings done on the gemstones. Some of the most common ones are :

Cameos

Stones and sea shells are referred as cameos. It is the carved portraits in any size of the stone. The portrait is carved above the surface of the gemstone. It seems striking because of the natural colored layers and remarkable carving. The wonderful blend of God’s creation and human art in one single frame looks amazing. Semi precious stone Agate is most commonly used for making this carving item however; some fine artist also brings other stones into play. Italy and Germany are the main source of premium cameos carved from shell and agate stone respectively across the globe.

Intaglios

This art conception is quite similar to that of cameos. It is carved on gemstones and seashells as well. The difference between the two is of carved portraits. Intaglios are the portraits that are carved down into the surface of the stone while the portraits are raised above the stone surface in cameos. The beauty of the carving emerges due the different coloured layers displayed in the stones through the natural formation. Italy and Germany again are the preeminent foundation of eye-catching art pieces of this form of carved item.

Sculpture

These are the carved forms of living things, it may be any animal, bird or even the human face or body. This is solely created and procured to decorate unusual corners of the dream home. It is mentioned especially for dream home because sculptures are relatively classy and pricey when compared with other carved forms.

It is priced high due to three reasons. First, creating a sculpture requires extreme expertise and artistic skills, as all the organs of the living creature should be well defined. There is no scope for minute errors or slight change else the final look of the art piece differs from the look of the living being. Artists take months to do fine detailing of their masterwork. Second reason is the cost of the raw material. The main raw material for carving sculpture is the stone. The price of the stone itself is very high. Further, the cost increases with the increase in the size of the stone. Moreover, for creating any size of carving the stone turns out to be more costly than the wood or clay. If it is carved on the single stone then the price is increased more. Finally the third reason, additional use of other coloured stones or diamonds to give it more natural look makes the price touch the sky.

Stand Alone Carving

These are the carving pieces that are not used for making jewelry items. They are created for decorative purpose or for some practical use such as ash trays, jewelry boxes, pen stands, key chains, paper weights and so on. These fine-looking objects are always in demand by the gemstone lovers.

Beads

These are engraved as small spheres first and later drilled to make beads that could be string together in a string to make the diverse jewelry items like necklace, earrings and hand bracelets etc. In order to make spheres, the lapidarist saws cubes or dodecahedrons from the rough. The cubes then are shaped into round by grounding it between the rotating concave cutters. The stone revolves around the concave cutter irrespective of the direction and attains the desired spherical shape. The spheres formed, then undergo the lapidary process of grinding, sanding and polishing. Finally, these are drilled to form the beads.

Once the beads are formed, it is taken over to bead mills for grinding and sanding in order to make high quantity commercial beads together at the same time. As a final point, these are polished through tumbling. Bead mill consists of two laps viz. one grooved while other flat. The spheres turned into beads are rolled between these laps to obtain the perfect pet shape.

Mixing Styles

The universe is crammed in with immense talent. People across the world use their groundbreaking ideas in each and every field like computer, fashion and so on. Similarly, gemstone industry too has billions of artisans who create attention-grabbing art pieces using their pioneer thoughts be it for jewelry items, functional items or decorative pieces. Artists mix different coloured stones in one single art work in a distinctive technique. Few such inimitable examples of mixing styles are inlays, mosaics and intarsia.

Inlays

Inlays are created by mixing gemstones with materials like metal, wood and other stones. The gemstone is cut in the favored shape, glued with the adhesive wax and then fixed into a void nook of other materials as mentioned. This style only uses opaque stones as the beauty of these lies in its façade that is only the outer appearance visible to the viewer. Semi precious stones commonly used as black onyx, turquoise, jade and so on. Transparent stone requires some ray of light that refracts along different facets, sparkles and looks fabulous. Therefore, transparent stones are not suitable as in an inlay once the stone is fixed it has no scope of any light rays.

Intarsia and Mosaics

This is the unique style of mixing that involves innovative and creative designing skills. Both these art pieces are crafted by joining together the coloured stones small in size like pebbles on a flat base material like stone, wood and metal etc. All the stones are top cut and polished in a way that it looks like a picture. It could also be set in some appealing pattern that grabs the attention of the viewer at the first glance.

Then main difference between these two at forms is same as that of cameos and intaglios. Mosaic is produced on the top of plane base of stone whereas intarsia is fashioned into the surface of the foundation material viz. stone, wood or metal. The later is also called as Florentine mosaic or Pietre Dure. The name Pietre Dure suggests, the finest pattern of this skilled artwork is brought into being from the land of artists called as Italy.

Shapes

As cited, in the ingenious world both the artist and the end user are passionate about new and unusual designs. The regular shapes like round and square still exist and shall subsists forever but the demand for something new is increasing at a very rapid pace. Thus, everyday new shapes are created as per the demand of the coloured stones enthusiasts.

Round

This is the standard shape quite common in faceted stones as well as cabochons. It is mostly used as a center stone in necklace or ring fingers. The beauty of this shape increases with the increase in size of the stone.

Oval

oval shape gemstone cutting

Oval is the most universal shape in the jewelry items as it compliments all other shapes very well. It adds an exclusive look to the designs. In cabochons, this shape is idyllic and the exquisiteness of the stone is highlighted very well. All opaque stones get very well cut in this shape. It goes well even for faceted stones.

Square

It is yet another regular shape but less common than the previous two. It is suitable only for those designs that are created with respect to the square cut gems. This shape does not match well with other shapes rather has its own sole significance.

Rectangle

This shape is little unusual for regular jewelry designs, same as square. However, it could be seen in cabochons as well as in faceted stones. Big size single stone cut into rectangle shape hung, as a pendant in a thick black or multi-coloured thread looks quite trendy and is ideal for the casual wear.

Emerald

It is initially cut as rectangle then the four corners are sliced away to give an emerald cut. This is relatively a new shape being like by young generation. Precious stone Emerald in this shape is in style amongst the elite families of the society. The attractiveness of this shape too increases with the increase in the size of the stone.

Marquis

It is a new creative shape, thin at the edges and thick in between of the stone body. The top and bottom of the stone are curved pointed points. Transparent stones are more suitable for this shape than the opaque gems. Female finger rings with gemstones cut in marquis shape are gaining popularity in every corner of the globe. It is also referred as Navettes.

Shield

This shape is proportioned at the sides of the stone but the ends are cut in diverse directions. It is available in different magnitude and varied sides. This is relatively less known and atypical shape.

Cushion

It is shaped similar to the cushions of the sofa or divan in the drawing room. It is more or less like either square or rectangle with its sides smoothly curved. This shape is more used for transparent stones.

Tear Drop

This shape is like a drop of water or tear thus named so. It is pointed at the top and curved as semi circle at the bottom. This is a bizarre shape therefore need to be clubbed along with other shapes to intact the design for any jewelry item. It is also called as pear shape.

Geometrical Shapes

Geometrical design jewelries are new-fangled choice of selection amongst the younger generation who seek fun and frolic in their trendy style. These designs are created using all different shapes of the geometry like triangle, hexagon, octagon, rhomboids, parallelograms and many more. The most remarkable part of these deigns is that it makes fabulous pendants for males. Normally, females dominate jewelries but as for geometrical jewelries it is mostly for males.

Fancy Shapes

fancy shape gemstone cutting image:GemsDB.com

These shapes are fashioned into jewelries that define the sophisticated and elegant aspect of women. The shapes are customized as per the requirement of the user. Few to name are leaf cut shape, princess cut, animals, alphabets, symbols and so on. Leaf cut shape is actually the shape of a new leaf of any tree; gold or silver sleek wires highlight the veins in the leaf. This cut is mostly made in light coloured stone such as peridot, amazonite etc. The absolute gaze of the shape is very charismatic and it represents the skilled craftsmanship of the artist. Similarly, the alphabets are shaped in different varieties of calligraphy. The fancy shapes has indefinite boundaries, it all dependence on ones ideas and thoughts.

This is long journey that the gemstone covers from being found in the lap of Mother Nature to the end possessor. The entire process is intricate and requires attention to the minute details. The hard work and creativity invested gives birth to the beauty.

More Resources
Step by step Gem cutting guide
Gem cutting company
Gemstone cutting terms

Chelsea Filter

Chelsea Filter

by Ritika Changrani

Also known as Emerald filter, Chelsea filter is used to identify natural, synthetic and imitated gemstones. Developed by the British Gemmologists Anderson and Payne, this filter was initially developed only for the separation of natural emerald from green beryl. Now it is being used to identify various gemstones.

Chelsea Filter – Gemstone Testing Tool

chelsea filter

Chelsea filters are designed to absorb all lights except red and yellow green which are transmitted through the filter. This causes different gemstones to exhibit different colors when observed through the Chelsea filter. Emeralds, when seen through the filter, appear red or pink in colour, while ruby appears brilliant red. Synthetic blue spinals appear yellowish orange or pink while the gems which are imitations appear green or greenish grey. Cobalt glass imitations of sapphire appear deep red.

How to use a Chelsea Filter

Hold the Chelsea filter close to the eye – may be at a distance of an inch or two from your eye. Provide strong light to the gemstone by lighting with a torch or bulb. Hold the torch or bulb such that the light falls directly down on the stone. When viewed from the filter, the stone may appear to change its colour. Never hold the Chelsea filter close to the stone since it may produce wrong results.

How does a Chelsea Filter Work?

Chelsea Filter works based on the characteristics of the gemstone. The Chelsea filter detects the presence of chromium and cobalt in the gemstone. Chromium, if present in the gemstone, produces red and green colour as in ruby and emerald, and the presence of cobalt gives a blue colour. It is the amount of chromium or cobalt present which gives a dark or light colour.

When white light is passed through a gemstone, it absorbs colours of some wavelength and lets other colours free. The other colours which are not absorbed by the Chelsea filter mix up and give the colour appearance to the eyes. Depending on the appearance of the colour when viewed through the Chelsea filter, it is easy to detect the type of gemstone it is. For example, when white light is passed through the Emerald, emerald absorbs all the yellow-green wavelengths. Chelsea colour filter can filter all the colours except yellow-green and deep red wavelengths. Since yellow-green wavelength is already absorbed, only the red colour passes through the Chelsea filter.

One has to make sure that there is enough light on the stone, else the reaction may not be visible to the eye.

Gemstones identified by Chelsea Filter

Red Stones

Red stones that contain chromium are Burma ruby, synthetic ruby and red spinel. Ruby and spinel when viewed through the Chelsea filter appear red. Demantoid Garnet when examined through the Chelsea filter in presence of light appears pinkish. Though Thai ruby and pyrope garnet contain chromium, there is no colour change observed due to the presence of iron in those stones, which prevents colour change. Red stones like garnets and paste do not contain chromium and hence there is no colour change. When viewed through the Chelsea filter, they appear dark red or black in colour.

Therefore when you are examining a group of red stones, you can easily separate different kinds of gemstones. Those which impart brilliant red are synthetic rubies. Stones which glow slightly red are natural rubies and spinals. Thai and Demantoid garnet may turn pinkish or slightly red. The stones which remain dark red or black are paste and other garnets.

Green Stones

Beryl is a green coloured stone which is coloured by chromium. The different types of beryl are emerald and aquamarine. Natural emeralds have a smaller amount of chromium, while synthetic emeralds have larger amount. Hence the change in natural emeralds is to dull or a little bright red. Synthetic emeralds change their colour to bright red. Some synthetic emeralds produce a dull red colour due to the presence of iron. Some natural emeralds like South African and Indian emeralds do not produce any red glow when viewed through the Chelsea filter. Chelsea filter can just give an idea that the gemstone may or may not be an emerald but the test is not a proof of detecting an emerald.

Some stones can be confused with the emerald. They are Demantoid garnet, green garnets or savolite and tourmaline. All these stones when tested using the Chelsea filter, appear to glow red and are often mistaken to be emeralds.

Green gemstones can be distinguished from each other by some of their characteristics. Emeralds produce an oily luster when seen through a Chelsea filter. Green garnets appear brighter than emeralds. Green zircon appears pinkish in colour and exhibits double refraction. Tourmaline is also a stone which exhibits double refraction. When green zircon and tourmaline are viewed through a 10X lens, the back faces of the stones appear to be doubled. Aquamarine has iron content due to which the colour produced is dull. The colour change in aquamarine is from blue-green to muddy grey-green. Green garnet, green zircon and chalcedony show very little colour change and appear pink or red. Pastes, green sapphire and peridot appear remain dark-green. Alexandrite appears red when seen through the Chelsea filter.

Blue stones

Blue stones contain cobalt which can be detected by the Chelsea filter. The colour change of blue stones when viewed though the Chelsea filter is red in highly doped stones and orange brown or green in light blue stones. The colour change to red when viewed though the Chelsea filter is an indication that the gem stone is synthetic. Sapphires show no colour change and remain dark blue or black.

How to take Care of a Chelsea filter

  • It is recommended not to touch the Chelsea filter as it may leave marks on the glass. A soft dry cloth must be used to remove the dust.
  • Never put the Chelsea filter in water or any liquid.
  • The Chelsea filter must not be allowed to get heated either in direct sunlight or on a radiator.
  • When not in use, the Chelsea filter must be kept closed.

Chelsea filter is an important tool in the field of gemology which can be used to test various stones. Although, the test is not cent percent reliable since the composition of every gemstone is not the same even in the similar type of stones, it is used by a number of gem testers for testing the gemstones.

More Info: Gem Testing Tools