The pearl, one of the three birthstones for June, along with alexandrite and moonstone, comes in a large variety of colours. Although the most familiar pearl colours are white, cream and black, this beautiful gemstone’s colour palette extends to many different hues.
Pearl Origin and Formation
Pearls are organic gemstones formed within the soft tissue of living shelled molluscs such as mussels and oysters.
The name pearl comes from the Latin “perna”, meaning leg, thought to be due to the ham-leg shape of the bivalve mollusc. It is also noteworthy that the scientific name for the family of pear-bearing oysters is Margaritiferidae which comes from the Old Persian word for pearl, which, in turn, is the source of the English name Margaret.
The finest quality natural pearls have been valued since olden times. They have been used as gemstones and objects of beauty for thousands of years, with the oldest recorded reference being the 7500-year-old Umm Al Quwain Pearl found in a grave in UAE.
Pearls build up in concentric layers around a microscopic irritant and are composed of nacre, which in turn consists of calcium carbonate (aragonite) and conchiolin which is a complex protein forming mollusc shells.
Before pearls were cultured by man, they were harvested from the Persian Gulf, Sri Lankan waters, and freshwater sources in Europe and China. Later, pearls were discovered in South America. When natural pearls were almost depleted in the early 20th century, people developed ways to culture pearls, first in China and Japan, then all around the world.
Natural gems also referred to as wild pearls, are very rare, expensive and typically small. Nowadays, natural sea pearls can be found in Japan, Central and South America, Australia, the Persian Gulf, the Gulf of Manaar, Madagascar, Myanmar (Burma), the Philippines and the South Pacific Islands. Natural river pearls are found in Asia, Europe and North America.
Cultured saltwater pearls come from Indonesia, the Philippines, Australia, China, Japan, French Polynesia and the South Pacific Islands, while cultured freshwater pearl sources include China and Japan.
Pearl Quality Factors
Pearls are unique gemstones. They can be plucked from the shell fully formed, with no need to be cut or polished. However, there are some quality factors such as nacre quality, lustre, surface quality, colour, size, shape and matching that determine the overall value of pearls.
Pearl nacre quality is one of the most important value factors. Its thickness determines the beauty and durability of the gem. If the nucleus is visible under the nacre, you can assume that the nacre is thin. This also translates into a dull and chalky appearance. A pearl without a thick, well-layered nacre will not look as attractive as other pearls and will not last long.
Lustre is probably the most important pearl value factor, and it is closely related to the nacre quality. Lustre is the glow that comes from within the gemstone. It is produced by light entering the pearl and reflecting at the viewer through the layers of nacre.
Lustre is a quality characteristic that measures how bright and shiny a pearl appears. In other words, it gives a pearl its unique beauty. The higher the lustre, the more valuable the pearl.
The quality of lustre depends on how even and smooth the layers of nacre are, and it is graded on the following scale:
- Excellent – reflections appear bright and sharp;
- Very Good – reflections appear bright and nearly sharp;
- Good – reflections are bright but not sharp, and slightly hazy around the edges;
- Fair – reflections are weak and blurred;
- Poor – reflections are dim and diffused.
Surface quality is a characteristic that measures how clean, smooth and free from blemishes a pearl appears. Like other coloured gemstones, pearls rarely achieve perfection.
The type of surface imperfections determines how noticeable the blemishes are and if they affect the durability of the pearl. For example, abrasions are scratches or scuffs that affect the lustre or colour of the stone. Bumps look like tiny bubbles on the surface of the pearl, while wrinkles are the areas where the nacre is not smooth.
Pearls come in a variety of colours and shades, such as white, cream, pink, silver, golden, blue, grey, green, bronze and black.
The colour of pearls is determined by the colour of the lip of the oyster and pigments within conchiolin, an organic substance that holds and glues aragonite together. We also get various shades depending on the thickness of the nacre. The thicker it is, the more vivid colour a pearl shows.
Pearl colour has three main components: body colour, overtone and orient. Body colour is the dominant overall colour of the gem. Overtone is one or more translucent colours (secondary colours) that lie over the body colour, and orient is a shimmer of iridescent rainbow colours. It is worth mentioning that all pearls show body colour, but only some display overtone or orient, or both.
The value of certain pearl colours is determined by the supply and demand. The more easily visible and saturated the pearl colour, the better. For example, white South Sea pearls with a fine pink overtone are rarer than pearls with a silver overtone, meaning they are more expensive.
All other factors being equal, larger pearls are rarer and more valuable. For example, cultured pearls can range in size from tiny 1.00mm beads up to 21.0mm.
The price of pearls increases with each millimetre size up. This is because larger pearls are much harder to find and cultivate, as it takes longer to produce them.
The ideal pearl is perfectly round, making it the rarest and most valuable cultured pearl shape. However, a well-formed pear, oval and irregularly shaped (baroque) cultured pearls are also prized by collectors.
Whatever the shape, the most important consideration is that the pearl features an evenly symmetrical shape.
Matching is a quality factor that is applied to jewellery featuring two or more pearls. It measures how beautifully pearls in necklaces, earrings, bracelets and sets are matched. Pearl matching is based on the main quality factors – size, shape, nacre quality, surface quality, lustre, body colour and overtone. While body colour, overtone, pearl shapes and sizes can be mixed to achieve unique effects in a design, other quality factors should be matched.
Pearl Care and Cleaning
Pearl is a relatively soft organic gemstone, 2.5 to 4.5 on the Mohs hardness scale, meaning it requires special treatment. It can be easily damaged by accidental hits, harsh chemicals and even your perfume.
Remember to remove your pearl jewellery before household cleaning, as this gem is sensitive to chemicals such as ammonia, alcohol and other acids. Similarly, chemicals from makeup, hairspray, perfume and body creams can change the colour of the gemstone or make it look dull. Putting your jewellery on should always be the last step.
It is highly recommended to wipe your pearls with a clean soft cloth after every wear. This will allow preventing the buildup of oils and dirt.
To clean your pearls at home, use mild dishwashing soap and mineral or distilled water. Tap water often contains chlorine which can damage pearls. Do not soak the pearls in the solution. Just dip the cloth in it and wipe the gems. Next, take a clean wet cloth and rub it over the jewellery to rinse away the soap and dry it with a soft and lint-free cloth. Do not use brushes, ultrasonic or steam cleaners. These can damage the nacre.
When storing pearl jewellery, keep it separated from other harder gemstones to protect it from being scratched. As a general rule, you should store your pearls in a space with good air circulation. Take out and wear them regularly, as leaving your pearls in storage for a long time will dehydrate and make them dull.
|Category||Carbonate mineral, protein|
|Colours||White, cream, silver, grey, blue, pink, green, brown and black|
|Hardness||2.5 - 4.5 on the Mohs scale|
|Refractive Index||1.52 - 1.69|
|Specific Gravity||2.60 - 2.85|
|Fluorescence||White pearls - light blue to light yellow, golden pearls - yellow-green, greenish brown to dark brown, black pearls - commonly pink to orange-red|
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