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GEMSTONE CUTS |
| BAGUETTE |
A rectangular-shaped stone with rows of step-like facets. If the Baguette's two long sides taper inward, it is called a Tapered Baguette. Baguettes in long, thin cut rectangles are often used as enhancements to a larger centre stone, or on a watch bezel. |
| BRILLIANT-CUT |
Brilliant cuts are scientifically found to reflect the most light from within the stone, and often are considered to have the most brilliance of all cuts. A round brilliant-cut diamond has 58 facets. Other brilliant cuts include the heart, oval, marquise and pear shaped. |
| CABOCHON |
A cabochon is a stone cut in a facet-less style of cutting that produces a smooth surface. They can be in many shapes, from round with high domes to squares. |
| FACETS |
A Facet is the small polished surface of a muti-faceted Gemstone. This style of cutting gives the stone many small faces at varying angles to one another. The placement, angle and shape of each facet are carefully planned and executed to show the stone's inherent beauty, fire, color, and brilliance to the fullest advantage. |
| GIRDLE |
The girdle is the widest perimeter of a gemstone and the dividing line between the crown and the pavilion. Ideally the width of the girdle should be even and proportional to the cut of the stone. It can be either polished or un-polished. |
| STEP-CUT |
Is a cut with rows of facets that resemble the steps of a staircase. The Emerald Cut and the Baguette are examples of the step cut. |
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GEMSTONE SETTINGS |
| BEZEL SETTING |
Bezel Settings hold the gemstone by surrounding it with a band of metal, slightly shaped over the top of the girdle, thus securing the gem. They are often used in mens' jewellery, and for softer or more fragile gemstones and have been used to hold gemstones in rings since approximately the 10th Century and are sometimes referred to as collet settings or rub-over settings. |
| CHANNEL SETTING |
A Channel Setting is where the gems (often Diamonds, Rubies or Sapphires) rest in a channel and are only secured by a slight rim which runs the length of the channel. This style can only be used for gemstones that are faceted to precise dimensions (precision cut), as they all need to be of identical size in order to sit firmly in the channel and the gemstones are normally round cut, square cut or baguette cut. |
| CLAW SETTING |
Claw Settings, or Prong Settings are the easiest method of setting a gemstone and is probably the most popular setting. A small amount of metal is used to make up claw settings, allowing the optimum amount of light to pass through the stone, maximising its brilliance, and also easy access to the stone for cleaning. Claw settings are made up of prongs, which are used when bent over the stone to secure in place. There are usually four or six "claws" of metal that reach around the gem's girdle to hold it in place. Although the pieces of metal on show can be carved or be made into creative shapes, they are usually rounded to prevent catching. |
| PAVÉ SETTING |
Pavé Setting is used to describe a setting where gems are set very close together and are only separated by tiny prongs or metal beads. Typically the stones are so close together that one bead can capture two stones, while in the corners individual beads frame the setting. More elaborate styles of pavé feature stones that are farther apart and require individual beads, plus ornamental beads to fill spaces between the stones. The word pavé comes from the French word for paved, like a road is paved with bricks. |
| TENSION SETTING |
A Tension Setting holds the gemstone in place entirely by pressure rather than prongs, a bezel or other mounting. The metal setting is actually spring-loaded to exert pressure onto the gemstone, and tiny etchings/grooves are added to the metal in order to create a shelf for the gemstone's edges to rest. The gemstone appears to be suspended in the air with nothing holding it in place. Because tension settings place such pressure on the stone, only four types of gemstone can be placed in a tension setting safely (diamonds, rubies, moissanite, and sapphires) and a gemstone that either has significant inclusions or is too soft will fracture under the intense pressure of the setting.
A tension setting actually holds the stone in place by compression (a pressing force) and not tension (a pulling force). |
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GEMSTONES |
| AMETHYST |
Amethyst is the purple variety of quartz (SiO2), containing an impurity of iron, which gives the violet color to the mineral. In popular belief, Amethyst offers protection against drunkenness, the name derives from Greek 'amethystos' meaning 'not intoxicated', which is why wine goblets were often carved from it.
In Greek mythology, Dionysus, the god of intoxication, and of wine, was pursuing a maiden named Amethystos, who refused his affections. Amethystos prayed to the gods to remain chaste, a prayer which the goddess Artemis answered, transforming her into a white stone. Humbled by Amethystos's desire to remain chaste, Dionysus poured wine over the stone as an offering, dyeing the crystals purple.
Medieval European soldiers wore Amethyst amulets as protection in battle - the reason for this being that Amethysts are believed to heal people and keep them cool-headed. It was also thought to put the wearer in a chaste frame of mind and symbolise trust and piety, thus Amethysts came to occupy a very prominent position in the ornaments of the Catholic clergy over the centuries. It was the stone of bishops and cardinals and was used on prelates' crosses and rings.
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Colour | Purple
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Refractive Index | 1.54 - 1.55
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Luster | Vitreous
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SG | 2.63 - 2.65
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Hardness | 7
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Double Refraction | .009
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| AQUAMARINE |
Aquamarine is the blue to blue-green variety of beryl (beryllium aluminium cyclosilicate) (Be3Al2(SiO3)6, containing an impurity of iron (Fe2+) which gives the blue colour to the mineral. The name derives from the Latin 'aqua marina' meaning 'water of the sea' and it was said to calm waves and keep sailors safe at sea.
In Medieval times, the stone was thought to reawaken the love of married couples. It was also believed to render soldiers invincible. It was also believed to be an antidote for poison.
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Colour | Blue
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Refractive Index | 1.57 - 1.58
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Luster | Vitreous
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SG | 2.6 - 2.8
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Hardness | 7.5 - 8.0
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Double Refraction | .006
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| EMERALD |
Emerald is the green variety of beryl (beryllium aluminium cyclosilicate) (Be3Al2(SiO3)6 colored by trace amounts of chromium (Cr3+) and sometimes vanadium.
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Colour | Green
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Refractive Index | 1.57 - 1.58
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Luster | Vitreous
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SG | 2.6 - 2.8
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Hardness | 7.5 - 8.0
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Double Refraction | .006
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| JASPER |
Jasper is an opaque form of Chalcedony, which is a microcrystalline variety of the mineral Quartz.(SiO2) with mineral impurities dictating the colors of the stone. It can occur in many different colors such as red, green, yellow or rarely, blue. Red-brown Jasper is typically colored by the presence of iron. Jasper is mentioned in the bible and is a well known stone since antiquity, and was once regarded as a very valuable stone.
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Colour | Brown, yellow, orange, red, or green. May also refer to any form of opaque
Chalcedony in all colors, and may be multicolored or banded.
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Refractive Index | 1.53 - 1.54
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Luster | Vitreous
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SG | 2.61
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Hardness | 7
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Double Refraction |
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| PERIDOT |
Peridot is the gem variety of the mineral Olivine. It's chemical composition is (Mg, Fe)2SiO4, with Mg in greater quantities than Fe.
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Colour | Green, Yellow
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Refractive Index | 2.63 - 2.65
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Luster | Vitreous
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SG | 1.54 - 1.55
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Hardness | 6.5 - 7.0
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Double Refraction | .009
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| TURQUOISE |
Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It has been prized since ancient times and used as a decorative stone and gem. Archaeological excavations revealed that the rulers of ancient Egypt adorned themselves with turquoise jewellery, and Chinese artisans were carving it more than 3,000 years ago.
Turquoise is the national gem of Tibet, and has long been considered a stone that guarantees health, good fortune, and protection from evil. Turquoise's name comes from the French expression pierre tourques, or "Turkish stone". The name, which originated in the thirteenth century, reflects the fact that it probably first arrived in Europe from Turkish sources.
In the USA Turquoise was a ceremonial gem and a medium of exchange for Native American tribes in the southwestern US. They also used it in their jewellery and amulets. The Apaches believed that turquoise attached to a bow or firearm increased a hunter's or warrior's accuracy.
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Colour | Blue, Green, Multicolored
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Refractive Index | 1.61 - 1.65
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Luster | Waxy
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SG | 2.6 - 2.8
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Hardness | 5 - 6
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Double Refraction | .04
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GIRDLE |
see GEMSTONE CUTS |
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GLASS TECHNIQUES |
| HANDBLOWN GLASS |
The Glassblowing technique which was invented by the Phoenicians around 50 B.C.
The tip of the blowpipe is first preheated then dipped into molten glass in a furnace. The glass is 'gathered' on to the blowpipe. The glass is then rolled on a marver, traditionally a slab of marble, but is more commonly a fairly thick flat sheet of steel today. This forms a cool skin on the exterior of the molten glass and shapes it. Then air is blown through the pipe to create a bubble. Then, one can gather over that bubble again to create a larger piece.
A variety of tools including molds are then used to shape the glass. As the glass cools it begins to stiffen and must be continuously reheated to allow shaping and reshaping. The glassblower uses a smaller furnace, a "glory hole" for the re-heats.
When the piece is finished, it is placed in an kiln for annealing. This is the process of slowly cooling the glass to room emperature to stabilize its delicate crystalline structure. Rapid temperature changes will cause the glass to crack.
Patterns and color can be applied by rolling the molten glass in powdered color or larger pieces of colored glass called frit. Complex patterns can be created through the use of rods of colored glass known as canes, or with murrine (rods cut in cross-sections to reveal patterns). |
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GLASS TYPES |
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The main constituent of practically all glass is sand which by itself can be fused to produce glass at temperature of about 1700°C. Adding other minerals and chemicals to sand can considerably reduce the melting temperature and provide different chemical and physical properties. |
| BOROSILICATE GLASS |
Borosilicate glass is a heat-resisting glass, better known in the UK as Pyrex™. It is made mainly of 70-80% silica (SiO2) and 7-13% boric oxide (B2O3) with smaller amounts of the alkalis (sodium oxide (Na2O) and potassium oxide (K2O)) and aluminium oxide Al2O3). This type of glass has a relatively low alkali content and consequently has good chemical durability and thermal shock resistance (it doesn't break when changing temperature quickly). As a result it is widely used in the chemical industry, for laboratory apparatus, for ampoules and other pharmaceutical containers, for various high intensity lighting applications and as glass fibres for textile and plastic reinforcement. |
| DICHROIC GLASS |
Dichroic glass is glass containing multiple micro-layers of metal oxides which cause visible light to be split up into distinct beams of different colours or to absorb light with different polarizations by different amounts. The earliest known example of an object made with Dichroic glass is The Lycurgus Cup, a 4th century AD cup probably made in Rome and now exhibited in the British Museum. |
| LEAD GLASS |
Commonly known as lead crystal, lead glass is used to make a wide variety of decorative glass objects.
It is made by replacing the calcium oxide in Soda-Lime Glass with lead oxide and most of or all of the sodium oxide with potassium oxide. The traditional English full lead crystal contains at least 30% lead oxide (PbO) but any glass containing at least 24% lead oxide can be described as lead crystal. Glass containing less than 24% lead oxide, is known simply as crystal glass. The lead is locked into the chemical structure of the glass so there is no risk to human health.
Lead glass has a high refractive index making it sparkle brightly and a relatively soft surface so that it is easy to decorate by grinding, cutting and engraving which highlights the crystal's brilliance making it popular for glasses, decanters and other decorative objects. |
| SODA-LIME GLASS |
By adding limestone to the Water Glass components, chemicals like calcium oxide (CaO) and magnesium oxide (MgO) are added which result in a pure inert colourless glass freely able to transmit light. Other chemicals are added to produce different properties and colours of glass. Most Soda-Lime Glass has a composition of 70% - 74% silica (SiO2), 12% - 16% sodium oxide (Na2O), 5% - 11% calcium oxide (CaO), 1% - 3% magnesium oxide (MgO) and 1% - 3% aluminium oxide (Al2O3). |
| WATER GLASS |
The addition of sodium carbonate (Na2CO3), known as soda ash, to sand will produce a mixture of 75% silica (SiO2) and 25% of sodium oxide (Na2O). This will reduce the temperature of fusion of the glass to about 800°C. However, a glass of this composition is water-soluble hence its name. |
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GRAIN |
see WEIGHTS & MEASURES |
GUILLOCHÉ |
see VITREOUS ENAMEL |
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VITREOUS ENAMEL |
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Vitreous Enamel is a glassy substance (powdered glass with colorants) fused normally onto metal using heat (see basse taille, cloisonné, hamplevé, guilloche, and plique à jour). Several layers of enamel may be fired in succession. The enamels may be translucent or opaque. |
| BASSE TAILLE |
Basse taille is a type of enamelling in which translucent enamel (powdered glass with colorants) is applied over a metal surface that has been textured by etching, engraving, stamping or chiselling by hand. This results in the metal background and the pattern over it being seen through the translucent enamel. |
| CHAMPLEVÉ |
(meaning sunken enamel) Champlevé is a method of applying enamel (powdered glass with colorants) to metal in which the design is first outlined on the metal surface by cutting lines into the surface by engraving, etching or otherwise grooved . The engraved grooves are then filled with enamel, then fired to a glassy sheen, and polished |
| CLOISONNÉ |
Cloisonné is a method of applying enamel (powdered glass with colorants) to metal or porcelain in which the design is first outlined on the surface using a metal wire. The space between the wires is filled with enamel and then fired to a glassy sheen. Technically the chamber formed by the wire enclosure is known as a cloison |
| GUILLOCHÉ |
Guilloché refers to the process of preparing the metal surface for this type of enamelling
in which translucent enamel (powdered glass with colorants) is applied over a metal surface that has been textured
by engraving, stamping or chiselling using an engine-turning lathe. This results in the metal background and the pattern
over it which is extremely regular and precise, predominantly in radiating patterns of sunburst and rosette design or
linear patterns such as moiré silk and wave design, being seen through the translucent enamel. |
| PLIQUE À JOUR |
Plique à jour is a back-less enamel that is a bit like stained glass. In plique à jour,
the enamel work is translucent (light shows through it) since the backing of the enamel is absent. Cells of enamel are surrounded by delicate wire. Plique à jour is made by shaping cloisonné wire on a thin sheet of metal (or mica) that will not bond to the enamel. Enamel (powdered glass with colorants) is fired into the wire cells. After the enamel has melted and cooled, the backing (metal or mica) is peeled away or may be etched away and the translucent enamel is left suspended in a supporting framework of cloisonné wire. |