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Thursday, October 13, 2011

Cubic Zirconia In Jewelry

 Cubic zirconia have become an affordable and acceptable substitute for diamonds. If you are looking to make a fashion statement, rather than an investment...considers cz's.

Courtesy of �w�edia Cubic zirconia (or CZ), is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard, optically flawless and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4).

Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important competitor for diamonds since 1976. Its main competition as a synthetic gemstone is the more recently cultivated material, synthetic moissanite.

TECHNICAL ASPECTS

As its name would imply, cubic zirconia is crystallographically isometric and, as diamond is also isometric, this is an important attribute of a would-be diamond simulant. During synthesis zirconium oxide would otherwise form monoclinic crystals, its stable form under normal atmospheric conditions. The stabilizer is required for cubic crystal formation; it may be typically either yttrium or calcium oxide, the amount and stabilizer used depending on the many recipes of individual manufacturers. Therefore the physical and optical properties of synthesized CZ vary, all values being ranges.

It is a dense substance, with a specific gravity between 5.6–6.0 — at least 1.6 times as dense as diamond. Cubic zirconia is relatively hard, at about 8 on the Mohs scale— much harder than most natural gems.[1] Its refractive index is high at 2.15–2.18 (B-G interval, compared to 2.42 for diamonds) and its luster is subadamantine. Its dispersion is very high at 0.058–0.066, exceeding that of diamond (0.044). Cubic zirconia has no cleavage and exhibits a conchoidal fracture. Because of its high hardness, it is generally considered brittle.

Under shortwave UV cubic zirconia typically luminesces a yellow, greenish yellow or "beige". Under longwave UV the effect is greatly diminished, with a whitish glow sometimes being seen. Colored stones may show a strong, complex rare earth absorption spectrum.

HISTORY

Discovered in 1892, the yellowish monoclinic mineral baddeleyite is a natural form of zirconium oxide. It has little economic importance because of its rarity.

The extremely high melting point of zirconia (2750°C) posed a hurdle to controlled single-crystal growth, as no existing crucible could hold it in its molten state. However, stabilization of zirconium oxide had been realized early on, with the synthetic product stabilized zirconia introduced in 1930. Although cubic, it was in the form of a polycrystalline ceramic: it was made use of as a refractory material, highly resistant to chemical and thermal (up to 2540°C) attack.

Seven years later, German mineralogists M. V. Stackelberg and K. Chudoba discovered naturally occurring cubic zirconia in the form of microscopic grains included in metamict zircon. Thought to be a byproduct of the metamictization process, the two scientists did not think the mineral important enough to formally name. The discovery was confirmed through x-ray diffraction, proving the existence of a natural counterpart to the synthetic product.

As with the majority of grown diamond look-alikes, the conceptual birth of single-crystal cubic zirconia began in the minds of scientists seeking a new and versatile material for use in lasers and other optical applications. Its evolution would eclipse earlier synthetics, such as synthetic strontium titanate, synthetic rutile, YAG (Yttrium Aluminium Garnet) and GGG (Gadolinium Gallium Garnet).

Some of the earliest research into controlled single-crystal growth of cubic zirconia occurred in 1960s France, much work being done by Y. Roulin and R. Collongues. This technique involved molten zirconia being contained within a thin shell of still-solid zirconia, with crystal growth from the melt: The process was named cold crucible, an allusion to the system of water cooling used. Though promising, these pursuits yielded only small crystals.

Later, Soviet scientists under V. V. Osiko at the Lebedev Physical Institute in Moscow perfected the technique, which was then named skull crucible (an allusion either to the shape of the water-cooled container or to the occasional form of crystals grown). They named the jewel Fianit, but the name was not used outside of the USSR. Their breakthrough was published in 1973, and commercial production began in 1976. By 1980 annual global production had reached 50 million carats (10 tonnes).

SYNTHESIS The Soviet-perfected skull crucible is still used today, with little variation. Water-filled copper pipes provide a cup-shaped scaffold in which the zirconia feed powder is packed, the whole contraption being wrapped with radio frequency induction coils running perpendicular to the copper pipes. A stabilizer is mixed with the feed powder, being typically calcium oxide.

The RF induction coils function in a manner similar to the primary winding in a transformer. The zirconia acts as the "secondary winding" of a transformer which in effect is "shorted" out and thus gets hot. This heating method requires the introduction of small pieces of zirconium metal. The metal is placed near the outside of the charge and is melted by the RF coils and heats the surrounding zirconia powder from the outside inwards. The cooling water-filled pipes embracing the outer surface maintain a thin "skin" (1-2 mm) of unmelted feed, creating a self-contained apparatus. After several hours the heat is reduced in a controlled and gradual manner, resulting in the formation of flawless columnar crystals. Prolonged annealing at 1400°C is then carried out to remove any strain. The annealed crystals, which are typically 5 cm long by 2.5 cm wide (although they may be grown much larger), are then cut into gemstones.


INNOVATIONS

n recent years manufacturers have sought ways of distinguishing their product by supposedly "improving" cubic zirconia. Coating finished CZs in a film of diamond-like carbon (DLC) or Amorphous Diamond is one such innovation, a process using chemical vapor deposition. The resulting material is purportedly harder, more lustrous and more like diamond overall: The coating is thought to quench the excess fire of CZ, while improving its refractive index, thus bringing it more in line with diamond. Additionally, because of the high percentage of diamond bonds in the amorphous diamond coating, the finished simulant will show a positive diamond signature under Raman spectroscopy.

Another technique first applied to quartz and topaz has also been adapted to cubic zirconia: Vacuum-sputtering an extremely thin layer of metal oxide (typically gold) onto the finished stones creates an iridescent effect. This material is marketed as "mystic" by many dealers. Unlike DLC, the surreal effect is not permanent, as abrasion easily removes the oxide layer.

CUBIC ZIRCONIA VS DIAMOND

There are a few key features of cubic zirconia which distinguish it from diamond, some observable only under the microscope or loupe, for example:[citation needed]

* Dispersion: With a dispersive power greater than diamond (0.060 vs. 0.044) the more prismatic fire of cubic zirconia can be seen by even an untrained eye.[citation needed]

* Hardness: Cubic zirconia has a rating of approximately 8 on the Mohs hardness scale vs. a rating of 10 for diamonds.[2]

* Specific gravity: Cubic zirconia crystals are heavyweights in comparison to diamonds; a cubic zirconia will weigh about 1.7 times more than a diamond of equivalent size.

* Flaws: Contemporary production of cubic zirconia is virtually flawless,[citation needed] whereas most diamonds have some sort of defect, be it a feather, included crystal, or perhaps a remnant of an original crystal face (e.g. trigons).

* Refractive index: Cubic zirconia has a refractive index of 2.176, compared to a diamond's 2.417.

* Cut: Some cubic zirconias use different facet shapes than are typically used for diamonds. This difference would be visible under close inspection with a loupe.

* Color (or more precisely, the lack thereof): Only the rarest of diamonds are truly colorless, most having a tinge of yellow or brown to some extent. By comparison, cubic zirconia can be made in most cases entirely colorless: equivalent to a perfect "D" on diamond's color grading scale.

* Thermal conductivity: Cubic zirconias are thermal insulators while diamonds are among the most efficient thermal conductors, exceeding copper. This makes telling the difference between diamond and cubic zirconia quite easy for those with the right instruments.

Monday, August 1, 2011

Can You Afford Jewelry?

What is happening to gold and silver jewelry!?!
In the past 10  years gold has gone from around $300 an ounce to $1600 an ounce and silver from about $3 an ounce to $40 an ounce. At the same time, real wages have fallen for most people and credit has become a more precious "commodity".
Of course there are many reasons for those changes and we need not discuss them here. But, we are all affected when it comes to jewelry.
At Foremost a gold pendant selling for $100 five or six years ago was affordable by a large portion of the population. Today, that same piece sells at about twice as much and is beyond what most people want to pay. Silver was affordable by almost everyone and is now beyond the reach of many. Still, we all want to use jewelry to accessorize, so what to do?
Many gold and silver jewelry makers have reduced the number of items they make to only the more expensive pieces, cutting out the products that used to sell to the "average" customer. Others have simply downsized or have gone out of business completely. Still others have evolved by creating jewelry out of different, less expensive materials. Glass, paper, wood , plastic, rubber and leather come to mind. Though these materials and others have been used, in the past, they are rapidly replacing more traditional gold and silver jewelry. Also, in tough economic times, jewelry tends to become larger and jewelry and clothing more colorful. This more easily accomplished with different materials, especially stones, glass and cloth.
Foremost Jewelry & Gifts is now in the process of eliminating approximately 20% of the products it carried in gold and silver. This is due to the reconfiguring of our suppliers products. Once the contraction is complete, Foremost will add additional items not carried in the past. During this period it is important that we keep in touch with our potential customers because of supply disruptions, cancellations and delays. We are here for our customers and appreciate their understanding and patience.
It is said, however, that as one door closes, another opens. I have recently launched The Fashion Garden, a site that offers the average person "Affordable Fashions For Less".
Presently, The Fashion Garden offers new, fashionable jewelry of paper and glass with a lot of colorful stones. To go with this fabulous new look in affordable jewelry, I am displaying cotton skirts, cotton shoulder bags and wool and silk scarves. And, there is much more to come, both in jewelry and other accessories.
Gold and silver has become very expensive to stock, "in house". Even worse, many of those making gold items do not stock or even make a piece until it is ordered. This can delay delivery for weeks. Everything in "The Garden" is in stock and ready to ship the next business day.
For the past 15 years, gold and silver jewelry have been the mainstay of my business. I look forward to staying in that business, but I am excited about the new fashion trends and what they will mean to all of us.
If you have some idea's or insights. Suggestions or comments, please let me know, either on this blog or at "Thoughts. The Fashion Garden".
Thanks! I hope to hear from you, soon.

Don

Sunday, January 2, 2011

Pearls In Jewelry

Pearls in Jewelry

The value of the pearls in jewelry is determined by a combination of the luster, color, size, lack of surface flaw and symmetry that are appropriate for the type of pearl under consideration. Among those attributes, luster is the most important differentiator of pearl quality according to jewelers.

All factors being equal, however, the larger the pearl the more valuable it is. Large, perfectly round pearls are rare and highly valued. Teardrop-shaped pearls are often used in pendants.

Shapes

Pearls come in eight basic shapes: round, semi-round, button, drop, pear, oval, baroque, and circled. Perfectly round pearls are the rarest and most valuable shape. Semi-rounds are also used in necklaces or in pieces where the shape of the pearl can be disguised to look like it is a perfectly round pearl. Button pearls are like a slightly flattened round pearl and can also make a necklace, but are more often used in single pendants or earrings where the back half of the pearl is covered, making it look like a larger, round pearl.
Woman with a Pearl Necklace, by Jan Vermeer van Delft, 1665

Drop and pear shaped pearls are sometimes referred to as teardrop pearls and are most often seen in earrings, pendants, or as a center pearl in a necklace. Baroque pearls have a different appeal to them than more standard shapes because they are often highly irregular and make unique and interesting shapes. They are also commonly seen in necklaces. Circled pearls are characterized by concentric ridges, or rings, around the body of the pearl.

In general, cultured pearls are less valuable than natural pearls, and imitation pearls are less valuable than cultured pearls. One way that jewelers can determine whether a pearl is cultured or natural is to have a gem lab perform an x-ray of the pearl. If the x-ray reveals a nucleus, the pearl is likely a bead-nucleated saltwater pearl. If no nucleus is present, but irregular and small dark inner spots indicating a cavity are visible, combined with concentric rings of organic substance, the pearl is likely a cultured freshwater. Cultured freshwater pearls can often be confused for natural pearls which present as homogeneous pictures which continuously darken toward the surface of the pearl. Natural pearls will often show larger cavities where organic matter has dried out and decomposed.

Some imitation pearls are simply made of mother-of-pearl, coral or conch shell, while others are made from glass and are coated with a solution containing fish scales called essence d'Orient. Although imitation pearls look the part, they do not have the same weight or smoothness as real pearls, and their luster will also dim greatly.

Lengths of Pearl Necklaces

There is a special vocabulary used to describe the length of pearl necklaces. While most other necklaces are simply referred to by their physical measurement, pearl necklaces are named by how low they hang when worn around the neck. A collar, measuring 10 to 13 inches or 25 to 33 cm in length, sits directly against the throat and does not hang down the neck at all; collars are often made up of multiple strands of pearls. Pearl chokers, measuring 14 to 16 inches or 35 to 41 cm in length, nestle just at the base of the neck. A strand called a princess length, measuring 17 to 19 inches or 43 to 48 cm in length, comes down to or just below the collarbone. A matinee length, measuring 20 to 24 inches or 50 to 60 cm in length, falls just above the breasts. An opera length, measuring 28 to 35 inches or 70 to 90 cm in length, will be long enough to reach the breastbone or sternum of the wearer; and longer still, a pearl rope, measuring more than 45 inches or 115 cm in length, is any length that falls down farther than an opera.

Necklaces can also be classified as uniform, or graduated. In a uniform strand of pearls, all pearls are classified as the same size, but actually fall in a range. A uniform strand of akoya pearls, for example, will measure within 0.5 mm. So a strand will never be 7 mm, but will be 6.5-7 mm. Freshwater pearls, Tahitian pearls, and South Sea pearls all measure to a full millimeter when considered uniform.

A graduated strand of pearls most often has at least 3 mm of differentiation from the ends to the center of the necklace. Popularized in the United States during the 1950s by the GIs bringing strands of cultured akoya pearls home from Japan, a 3.5 momme, 3 mm to 7 mm graduated strand was much more affordable than a uniform strand because most of the pearls were small.

Colors of Pearl Jewelry

Earrings and necklaces can also be classified on the grade of the color of the pearl. While white, and more recently black, saltwater pearls are by far the most popular, other color tints can be found on pearls from the oceans. Pink, blue, champagne, green and even purple saltwater pearls can be encountered, but to collect enough pearls to form a complete string of the same size and same shade can take years.

Fresh Water Pearl Farming

In 1914, pearl farmers began growing cultured freshwater pearls using the pearl mussels native to Lake Biwa. This lake, the largest and most ancient in Japan, lies near the city of Kyoto. The extensive and successful use of the Biwa Pearl Mussel is reflected in the name Biwa pearls, a phrase which was at one time nearly synonymous with freshwater pearls in general. Since the time of peak production in 1971, when Biwa pearl farmers produced six tons of cultured pearls, pollution has caused the virtual extinction of the industry. Japanese pearl farmers recently cultured a hybrid pearl mussel – a cross between Biwa Pearl Mussels and a closely related species from China, Hyriopsis cumingi, in Lake Kasumigaura. This industry has also nearly ceased production, due to pollution.

Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China. China has since become the world's largest producer of freshwater pearls, producing more than 1,500 metric tons per year.

Led by pearl pioneer John Latendresse and his wife Chessy, the United States began farming cultured freshwater pearls in the mid 1960's. National Geographic Magazine introduced the American cultured pearl as a commercial product in their August 1985 issue. The Tennessee pearl farm has emerged as a tourist destination in recent years, but commercial production of freshwater pearls has ceased.