Jewelry

Wednesday, July 1, 2015

Color

Different varieties: purple is a rare variety from Maine. Blue stones from Brazil with colors rivalling Paraiba tourmaline are most in demand
A light green variety of apatite carries the trade name "asparagus stone"
The recent availability of the neon blue-green variety from Madagascar has gained popularity

 

 

Clarity

Eye clean larger stones are quite common

Cut

Cabochon or creative cut by lapidary artists

Treatment

Color: Most apatites are heat treated to enhance color

Care

Apatites are delicate - especially when subjected to heat, temperature changes, changes in air pressure (such as in an airplane)
Dampened soft fabrics with no abrasive or chemical additives, or a soft bristle toothbrush doused with water
Not recommended to use in rings

Aquamarine Gemstone

Color

Main colors: greenish blue to blue green
Light in tone and transparent
Some milky quality if lots of inclusions
Most collectible colors: aquamarines that have saturated, light blue colours are especially desirable, though a few beryl collectors prefer a slight greenish tinge


Clarity

They frequently possess a vitreous clarity not found in emeralds. For this reason, aquamarines may be fashioned as exceptional clean gems and carvings
Lower grade aquamarines can have a milky appearance if the crystal has a lot of inclusions
a potentially desirable "cat's eye" effect occurs when miniscule, hollow growth tubes form parallel to one another

Cut

Relatively large stones can be cut due to its hardness and relatively large crystals (up to hundreds of carats) without inclusions
Unusually cut gems are also popular, especially in gems that have been fashioned by an important lapidary artist.
Aquamarines and other beryls often lend themselves to sculptures because of their size

Treatment

Consider every aquamarine heat treated
Heat treatment causes them to loose their secondary greenish color and create a more "aquamarine blue" gem
It is generally impossible to gemologically determine whether an aquamarine has been treated or not

Care

Aquamarine can be worn in jewelry under normal use. Larger aquamarines should be worn with care, especially in settings such as rings that can be easily knocked
Cleaning: sudsy water and damp cloth

Most collectible:

Saturated, light blue colours
Gems that have been fashioned by an important lapidary artist or cut in unusual ways
Aquamarines from desirable localities, such as Santa Maria aquamarines from Itabira, in Brazil, are collectible in accordance to their legendary depth-of-colour

Ametrine Gemstone

Color

In ametrine, a unique form of quartz mined from a single locality in Bolivia, the colours are both yellow and purple in areas of zoning

Clarity

Ametrine, just like most crystalline quartzes is often eye-clean


Cut

Ametrine can also be cut to blend the two colors so that the resulting stone is a mix of yellow, purple, and peach tones throughout the stone
Ametrine is most typically faceted in a rectangular shape with a 50/50 pairing of the two colors
Sometimes a checkerboard pattern of facets is added to the top to increase light reflection
Ametrine is also popular among artistic cutters and carvers

Care

Because the bi-coloured ametrine comes from only one mine in the world, it is sometimes collected if the depth of colour and the division of colour is strong, or if it has been skillfully or cleverly carved.

Amethyst Gemstone

Color

Transparent to translucent lilac to purple through bluish purple
A reddish purple colour-shift that is sometimes visible in incandescent light
In ametrine, a unique form of quartz mined from a single locality in Bolivia, the colours are both yellow and purple in areas of zoning. Such gems are sometimes cut in a way that mixes the colours, and at other times to show the division of colours

Clarity

Some amethysts have liquid inclusions containing solids and gases (water bubbles)
Some minerals suchas rutile and hematite can be found in amthyst as well

Cut

Amethyst can be found in many sizes and therefore offered in many different kinds of cuts and carvings
Many famous lapidaries (cutters) work with amethysts to make unusual carvings or cuts, which are also highly prized.
Bi-coloured ametrine has been skillfully or cleverly carved to emphasize the bi colored nature of the stone

Treatment

Amethysts are heat treated to improve an overly dark purple color or to get rid of the smoky color
Many amethysts in the market are synthetic. It is virtually impossible to differentiate the two

Care

Care should be taken not to knock the gem during use, as small fissures or cracks may develop, especially along facet junctions. It can be cleaned with warm, sudsy water or a dampened cloth. Some amethysts may lighten in tone over time upon prolonged exposure to bright light.
Collectors of amethyst look for depth of the purple colour with red flashes if the gem is cut conventionally. Many famous lapidaries (cutters) work with amethysts to make unusual carvings or cuts, which are also highly prized. Because the bi-coloured ametrine comes from only one mine in the world, it is sometimes collected if the depth of colour and the division of colour is strong, or if it has been skillfully or cleverly carved.

Amber Gemstone

Color

May be seen in yellow, orange and brown colours and rarely as blue and green.
Impurities and organic substances cause colours in amber.
Green and blue ambers are so perceived due to strong fluorescence in some amber from the Dominican Republic

Clarity

Amber often possess gas bubbles which vary in size and quantity within each piece. In the space between the bubbles, the resin is clear
The bubble inclusions actually interfere with the passage of light through the amber, resulting in the dilution and variation of color and opaqueness. For example, there are so many bubbles in milky amber, when examined under the microscope, it resembles sea foam – thus causing the solid milky color.

Cut

Most amber is fashioned as cabochons or rounded or free-form beads, and are rarely faceted

Treatment

Heating in oil causes some cloudy amber to clarify, or to produce darker amber colours
Amber is sometimes dyed to add a darker tone to lighter materials
Two factors that affect the color of amber is air and the actual tree source

Care

While rings using amber are used, the user must take special care
Avoid rough handling, heat and chemicals for all amber
They are soft, occasionally brittle, and porous enough to be attacked by acids
Cleaning may be performed using a dampened cloth or a moistened soft bristle toothbrush
Strong colours in amber are considered collector items, as is any amber containing unusual insects. Entomologists seeking to understand a bygone world often collect these amber samples for further study.

Alexandrite Gemstone

Color

The colour of alexandrite appears different depending on the light it is viewed in
Daylight: Yellowish, brownish, greyish or bluish green
Incandescent light: Orangy or brownish red to purplish red
The best stones are sometimes loosely described as "an emerald by day and an amethyst at night"

Clarity

The alexandrite variety contains gems that vary from transparent to semi transparent
In terms of clarity, alexandrite is comparable to ruby.
Clean faceted stones in sizes above one carat are rare and above 2–3 carats are extremely rare
Common inclusions are silk like rutile needles

Cut

alexandrites are found in a variety of shapes and cutting styles. Ovals are cushions are the most common

Treatment

Alexandrite is generally never treated to enhance its color or diminuish the appearance of inclusions

Care

Alexandrite is extremely resilient for use in jewellery and can be worn daily under normal circumstances
Most alexandrite can be cleaned in an ultrasonic cleaner and certainly with a damp cloth and warm soapy water
Alexandrite is one of the world‘s most expensive gems, with prices similar to those fetched by fine ruby or emerald because of their rarity and their exotic, phenomenal qualities. A combination of alexandrite and "cat's eye" is the most desirable.
A premium is placed on gems that contain strong colour change qualities, since with alexandrites a predominantly "muddy" mix of greens, browns and reds tends to be the norm, resulting in a vague colour change.

Saturday, June 27, 2015

The 10 biggest diamonds in the world

“Sergio”, a black carbonado diamond from Brazil discovered in 1893, beats all its rivals for weight. These so-called black diamonds are rare and scientists are still in debate over their origins. There are some that believe these black diamonds come from outer space, having travelled to Earth as fragments of an ancient meteor. Sergio (Portuguese Carbonado do Sergio) is the largest carbonado and the largest rough diamond ever found. It weighs 3167 carats and was found in the State of Bahia in Brazil in 1895. Like other carbonados it is believed to be of meteoritic origin.


2. Cullinan Diamond
The Cullinan diamond is the largest non-carbonado and largest gem-quality diamond ever found, at 3106.75 carat (621.35 g, 1.37 lb) rough weight. About 10.5 cm (4.1 inches) long in its largest dimension, it was found on 26 January 1905, in the Premier No. 2 mine, near Pretoria, South Africa., and was named after the owner of the mine, Sir Thomas Cullinan. It was given as a gift to the King of the United Kingdom (Edward VII) and was taken to Amsterdam to be cut. Nine large stones and 96 stones were taken from the rough diamond, including the famous Star of Africa (Cullinan I) which is 530.2 carats and is now part of the Crown Jewels, inserted into the Sceptre with the Cross. The value of the Cullinan diamond has been estimated at $2 billion.


3. Excelsior Diamond
Found in 1893 in South Africa, this huge rock was cut into many smaller pieces. The largest gemstone cut from this famous diamond was only 69.68 carats, but many in the diamond industry believe that much larger diamonds could have been taken from the original stone. Intriguingly, another diamond of a similar weight (around 1,000 carats) could have been included in this list, but little is known about it: It’s a rare black diamond that has been called The Nameless. No-one seems to know where it came from or when it was discovered, so – for now – it remains a side-note. 




4. Star of Siera Leone
Star of Sierra Leone diamond was discovered by miners on February 14, 1972 in the Diminco alluvial mines in the Koidu area of Sierra Leone. It ranks as the third-largest gem-quality diamond and the largest alluvial diamond ever discovered.  This diamond has 968.9 carat (193.78 g)
On October 3, 1972, Sierra Leone's then-President, Siaka Stevens, announced that Harry Winston, the New York City jeweller, had purchased the Star of Sierra Leone for under $2.5 million.[2]  The stone was initially cut into an emerald shaped stone weighing 143.2 carats (28.64 g) but was later re-cut due to an internal flaw,[3] eventually resulting in 17 separate finished diamonds, of which 13 were deemed to be flawless. The largest single finished gem was a flawless pear-shaped diamond of 53.96 carats (10.792 g). Six of the diamonds cut from the original rough were later set by Harry Winston into the "Star of Sierra Leone" brooch.[4] A rare characteristic of the stone is its perfect chemical purity: it is ranked as a type IIa diamond, a category which includes less than 1% of all diamonds.


5. Incomparable Diamond
At 890 carats (just over 6 oz) this Congolese rough diamond was discovered by a young girl in 1989. The smart child noticed the diamond in a pile of rubble and passed it on to her uncle, who sold it to diamond dealers. Like many of the world’s diamonds, it ended up at one point in the Belgian city of Antwerp, famous for its diamond district. It took experts years to cut the rough diamond into smaller gems, but they managed to create a beautiful yellow-brown stone weighing 407.48 carats that had been cut into an unusual triangular shape. Strangely enough, this fantastic gemstone actually appeared on eBay in 2002, but went unsold. 

6. The Woyie River Diamond
The Woyie River Diamond was recovered on 6 January 1945 from the Woyie River near Koidu in eastern Sierra Leone.[1] The uncut stone weighed 770 carats (154 g),[2] and at that time it was the largest alluvial diamond ever found, and the third largest diamond discovered in Africa, after the Cullinan Diamond and the Excelsior Diamond. The alluvial Star of Sierra Leone, discovered at the Diminco mine in Sierra Leone in 1970, is larger at 968.9 carats (193.78 g) uncut. 

The uncut Woyie River Diamond had a broadly lozenge shape, measuring 71 × 53 × 32 millimetres (2.8 × 2.1 × 1.3 in), with one unusually flat cleavage plane. The rough diamond was brought to London, where it was viewed by Queen Mary in October 1947 and then exhibited at the British Industries Fair in May 1949. The stone was cut by diamond cutters Briefel and Lemer in London (who also cut the Williamson pink diamond) into 30 gems weighing 282.36 carats (56.472 g) in total, including 10 of over 20 carats (4.0 g) each. The largest of the gems is the Victory Diamond which is weighs 31.35 carats (6.270 g) and is Emerald cut (occasionally described as "step cut").

7. Golden Jubilee Diamond
The Golden Jubilee Diamond is the largest cut and faceted diamond in the world. It weighs 545.67 carats (109.13 g). It outweighs the Cullinan I by 15.37 carats (3.07 g). The Golden Jubilee Diamond was discovered in the Premier Mine, which is also the origin of the Cullinan diamond (1905) and other notables such as the Taylor-Burton (1966) and the Centenary (1986). The Cullinan I, also known as the Great Star of Africa, had held the title of the largest cut and faceted diamond since 1908. The diamond is valued at 4–12 million US dollars.
The Golden Jubilee Diamond was cut from a large brown diamond of 755.5 carats (151 g), found in the prolific blue ground of the Premier Mine in South Africa in 1985. First known as the "Unnamed Brown," the Golden Jubilee was given to Gabriel Tolkowsky by De Beers for the purpose of testing special tools and cutting methods that had been developed for use on the colourless D-colour Centenary. Because of its deep cracks and several inclusions, the Golden Julilee Diamond was cut in a specially designed underground room free from vibrations. The yellow-brown diamond was transformed through a fire rose cushion cut. Until 1990, the diamond remained largely unknown to the outside world, requiring two years to bring it to its current state. The unnamed diamond was brought to Thailand by the Thai Diamond Manufacturers Association to be exhibited in the Thai Board of Investment Exhibition in Laem Chabang and was selected to herald De Beer's centennial celebrations in 1988. The Golden Jubilee was purchased from De Beers by a group led by Henry Ho of Thailand in 1995.

9. The Vargas Diamond
The Vargas Diamond, discovered in Brazil on August 13, 1938 by Joaquim Venancio Tiago and Manoel Miguel Domingues, was 726.6 carats (145.32 g) when pulled out of the ground. Twenty-nine smaller diamonds were carved from the larger rough Vargas Diamond including the 48.26-carat (9.652 g) 
This one was named for GetĂșlio Dornelles Vargas, who was the President of Brazil at the time. The diamond eventually found its way to Amsterdam and was finally bought by someone not only famous in jewelry circles, but who has also become synonymous with the industry as a whole: American jeweler, Harry Winston. Twenty-nine smaller stones were cut from this rock, with the largest being a flawless 44.17 carat gem which had been re-cut by Winston himself. The Vargas has 726.6 carats.

The Jonker Diamond
This giant gem, found in South Africa in 1934, was found by a settler called Johannes Jacobus Jonker, hence its unusual moniker. It’s believed the rough diamond was eventually cut into 13 smaller gemstones, with the largest diamond, the Jonker I, still weighing in at an incredible 142.9 carats. Diamonds are valued by weight, color, clarity and various other factors. However, with a colorless flawless diamond valued at $26,125 per carat, the Jonker I could be worth as much as $3.7 million!