Difference between revisions of "Pearl"

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[[image:Baroda Pearls.jpg|thumb|250px|left|The Baroda Pearls<br />Photo courtesy of Christie's Images LTD. 2007]]
 
[[image:Baroda Pearls.jpg|thumb|250px|left|The Baroda Pearls<br />Photo courtesy of Christie's Images LTD. 2007]]
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The Baroda pearls were sold in auction at Christie's New York for USD 7,096,000 an all time auction record (April 25th, 2007).
 
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==Famous pearls==
 
 
===The Baroda Pearls===
 
 
The Baroda pearls were sold in auction at Christie's New York for USD 7,096,000 an all time auction record (April 25th, 2007).
 
  
 
==Formation==
 
==Formation==

Revision as of 04:34, 26 April 2007

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This section is currently under construction, do not edit until this message is gone
--Doos 04:15, 12 April 2007 (PDT)

Pearl
Chemical composition Calcium carbonate, conchiolin and water
Crystal system Amorphous
Hardness 2.5-3.5
Refractive index 1.52-1.69
Specific gravity 2.68-2.86
Lustre Pearly
The Baroda Pearls
Photo courtesy of Christie's Images LTD. 2007


The Baroda pearls were sold in auction at Christie's New York for USD 7,096,000 an all time auction record (April 25th, 2007).

Formation

Pearls are, usually, created by certain types of mollusks, which we shall refer to as oysters, when an inorganic or organic material is embedded between the mantle and the inner shell of the oyster.

The mantle is the outer organ of the oyster which covers most of the shell. The outer cells of this mantle (called the epithelium) are responsible for the secretion of nacre and conchiolin (AKA mother-of-pearl).

Mother of pearl with drillholes caused by living organisms
Photo courtesy of parels-ael.nl

Natural pearl formation is very rare and usually happens when a parasite or other living organism drills its way through the shell of the oyster, where it will then encounter the mantle. The mantle is irritated by this parasite and tries to defend itself by encapsulating the irritant with epithelium cells, forming a sac of cells covering this parasite. These cells will then secret layers of nacre and conchiolin on the parasite.
Conchiolin is an organic substance made by the epithelium cells that act as a glue between different layers of nacre (a calcium carbonate).

Mostly this process takes place in the mantle of the oyster and free pearls of all shapes are formed. When an irritant is attached to the inner shell, then epithelium cells will deposit conchiolin and nacre on the irritant and it will form a blister on the inside of the oysters' shell. To no surprise the latter type of pearls are named blister pearls.

There are other irritants that may induce pearl formation, but the story that they originate from sand grains is a myth. Although it could be possible that a grain of sand gets trapped between the mantle and the shell, it is very unlikely. Oysters live in sandy environments and they simply "spit" any dirt out.

Formation of natural pearls


In the image on the left the formation of a natural pearl is illustrated.

1. An irritant is trapped between the mantle and the innershell of the oyster.
2. The epithelium cells start to divide and try to encapsule the irritant.
3. The irritant is now fully enclosed with epithelium cells and has moved inside the mantle. This creates a sac of epithelium cells around the irritant. Such a sac is named a pearl sac.

From the outside in, the pearl sac (the cells) secrete nacre and conchiolin unto the irritant and the pearl starts to grow. The pearl sac expands through cell division as the pearl grows.

In this illustration a "free" pearl is formed. When the irritant attaches itself to the shell, then there will be no formation of a pearl sac and the epithelium cells just deposite nacre and conchiolin on the irritant and the inner shell, creating a blister.

A pearl sac is essential in the formation or free pearls, for both natural as cultured pearls.


Types of oysters

There are many oysters that can form pearls, either living in fresh or saltwater. The species that produce pearls of commercial value are listed below.

  • Pinctada Martensii (Akoya pearls)
  • Pinctada Maxima (South Sea pearls)
  • Pinctada Margaritifera (Black or Tahiti pearls)
  • Pteria Sterna (Sea of Cortez pearls®)
  • Pinctada Mazatlanica (Mexican pearls)
  • Pteria Penguin (Blister pearls - Mabe)
  • Haliotidae Haliotis (Abalone)
  • Hyriopsis Cummingii (freshwater "Zebra mussel")
  • Cristaria Plicata (freshwater "Cockscomb mussel")

There are also other creatures that can produce pearls without nacre. Some people do not regard these as real pearls (due to the lack of nacre), but the formation is strongly related to that of oysters and the "pearls" they produce are very rare.

  • Strombus Gigas (Conch pearls), a sea snail
  • Melo Melo pearls, a sea snail
  • Quahog ("Hard clam")

Cultivation

Since the middle ages people have been trying to influence the creation of pearls by oysters and mussels. This is named "cultivation" and the pearls that are created in such a way (with some influence by man) are termed "cultured pearls". Often, but not always, the entire product is of natural origin (from mollusks) and by law are considered as natural pearls.

Early cultivation

Although most cultured pearls on todays market are created entirely by mollusks, that was not always the case. In the 13th century [Webster, 1990] the Chinese made blister pearls in the form of Bhuda statues by placing a metal Budha against the innershell of a freshwater mussel and keeping it in place with a metal wire that was connected through an artificial drillhole.

Carl von Linné (better known as Linnaeus) was able to create the first free cultured pearls in the 18th century, but the final product was not in total created from mollusks. He drilled a hole in a freshwater mussel and inserted a silver wire with a piece of limestone into the mussel, making sure the limestone was free from the innershell to prevent it from becomming a blister pearl. While he was the first to create some sort of free pearl, the results were not as good as the cultured pearls that are created today.

Modern cultivation

In the late 19th and early 20th century several people were independently researching how to cultivate better round pearls.
One of the most agile and best known of these entrepeneurs was Japanese Kokichi Mikimoto (1858-1954) who was able to create cultured blister pearls in 1893 and was granted a patent for it 2 years later.
Around the same time William Saville-Kent (1842-1908), an English scientist, conducted parallel research on Thursday Island (Torres Straits, Queensland, Australia). Saville-Kent gave evidence of his cultured blister pearls in 1891, 2 years earlier than Mikimoto did [Harrison, 2005].
Both Mikimoto and Saville-Kent were from there on in search of a method to create detached cultured pearls.

The Mise-Nishikawa controversy

In 1907 Japanese Tatsuhei Mise and Tokichi Nishikawa both applied for a patent to create such detached pearls and the method they used is known as the "Mise-Nishikawa method". This method is still used today.

While it took Mikimoto decades of research to create his first detached cultured pearls in 1908, Mise and Nishikawa patented a better method independently of eachother in 1907 with none to little research.
Mise was a carpenter with no training in pearl cultivation and Nishikawa a young graduate from the university of Tokyo. In 1901 Nishikawa and Mise's stepfather (a senior inspector for the Japanese bureau of fisheries) were sent to Thursday Island to inspect the Japanese fleet. It is believed that around this time Saville-Kent was experimenting with mantle tissue and nuclei to create round cultured pearls with some success.

On the islands in the Torres Straits some 2000 Japanese were involved in the pearl and fishery industry and it is very plausable that Nishikawa and Mise's stepfather have been informed about Saville-Kent's work at Thursday Island. As both Mise and Nishikawa had almost instant success in their efforts to create round cultured pearls instead of decades of research, one can only wonder if they indeed were the inventors of their method [Harrison, 2005].

Harvesting

Grading

Sources