The ancient Romans believed that pearls were the frozen tears of their gods, while the ancient Greeks thought that lightning strikes on the sea created these sought-after gems. In somewhat more modern times, that is to around AD 700, European scholars believed that pearls were solidified dewdrops, captured by clams. These are romantic images, but an extensive exhibition about one of mankind's most desired objects reveals a very different tale. Pearls, a Natural History is on display at the ROM until January 9, 2005, and it is worth the time it takes to really absorb what it has to offer.

This is not a show you walk through. This is a show where you really have to take a close look at the many objects to appreciate not only the beauty of what is on display, but also what it takes to create a pearl in all its many varieties. There is a misconception that pearls come only in white. This show very quickly dispels this notion.

Imagine looking at a 50-million-year-old pearl found encased in fossilized mud in England that still has all of its luster, or at a 100-million-year-old fossil of a now extinct mollusc shell called an ammonite from Madagascar that shimmers in multiple colours as if just found. It is such wonders that really makes one grasp the marvel of the only gem in existence that is created by a living being and needs no special polishing or cutting to show off its splendor.

Of course, it is interesting to see the classic beauty of the pearl necklace that Joe DiMaggio gave to Marilyn Monroe on their honeymoon in 1954, or a 19th Russian icon of Our Lady of Kayan that is covered in pearls, diamonds, rubies, sapphires and silver gilt. It also gives one a little thrill to look at pieces of jewelry once worn by Marie Antoinette, Queen Victoria, and Audrey Hepburn. In fact, this exhibit has so much jewelry and clothing, both excruciatingly beautiful and excessively gaudy, that it really drives home how obsessed we are with this unusual gem.

To think that it is created by a variety of soft-bodied creatures, which live in hard shells in salt and fresh water, simply emphasizes the marvel of nature even further in our minds.

For thousands of years humans have coveted pearls. It is said that the Romans so desired pearls, they became one of the reason for Julius Caesar's invasion of Britain. We do not think of Britain as a place where pearls can be found. Yet, from the evidence of that 50-million-year-old fossil, we know that the island could easily have offered a shorter route to Caesar's desire to obtain pearls than the Indian Ocean.

Prior to the discovery of the Americas by Columbus, most pearls came from the area that encompasses the eastern Mediterranean and the Indian Ocean. Then Columbus, on his third voyage, found pearls off the Venezuelan and Panamanian coasts in huge quantities. But, as with so many other things found by the conquerors of the New World, within 150 years the source of the pearls became almost extinct. So, the Indian Ocean reclaimed its former market, and then in the 1920s Japan came to the forefront with the production of cultured pearls. It was, however, a Swede, who discovered how to create spherical pearls through placing an irritant inside freshwater molluscs. Carolus Linnaeus (Carl von Linné), who developed the modern system of scientific nomenclature, discovered the method in 1740. Yet, it would not be until the early 20th century that this way of creating pearls was reinvented by Kokichi Mikimoto in Japan.

Should anyone feel inclined to look down on such pearls, this exhibit makes it patently clear that there is no difference between a pearl produced in the wild, and one in which man gave a bit of a helping hand. As long as 1,600 years ago, the Chinese produced a type of cultured pearl by placing tiny Buddha images in freshwater mussels to create Buddha blister pearls. In this case no round orbs were created. Instead, the mussel formed nacre (mother-of-pearl) around the Buddha image, which then became attached to its shell, hence the name blister pearl. There are other forms of blister pearls on display in this show, many of them of amazing shape, and created without man's helping hand.

Earlier I stated that some of the items on display are gaudy, at least to me. Looking at the manner in which Russians of a former age used pearls, one can perhaps comprehend why the ill-fated Russian Revolution occurred that gave us the horrors of the Soviet Union. While peasants starved and lived a feudal existence at a time when Europe had long ago overthrown feudalism, the Russian Orthodox Church, and the Russian aristocracy hoarded pearls in huge quantities and made a show of them. The icon of Our Lady of Kayan is a perfect example of excess, as is a Russian Orthodox priest's undergarment, decorated with thousands of small pearls, and also an altar cloth. A typical Russian cap, in this case worn by an aristocrat, is covered completely with pearls and other jewels.

For North Americans it will be revealing to learn that the largest find of pearls ever, including pearl jewelry, was discovered not in the area of the Indian Ocean, but in Ohio. There archeologists discovered in 1891 the burial mounts of the now extinct Hopewell Indians. The mounts date from 200 BC to AD 500. Several examples of this jewelry is on view in the show.

One of the three ROM curators — the exhibit actually originates with New York's American Museum of Natural History and Chicago's Field Museum — is David Zanatta. He is a malacologist (one who studies molluscs). He is involved in a very important project, the conservation of Ontario's pearly mussels, which is supported by Canada's Department of Fisheries and Oceans. I was amazed to learn that the creek flowing in view of my kitchen window is a home to pearly mussels. In fact, Southern Ontario is home to three quarters of Canada's mussel species, with the Thames, Grand and Sydenham Rivers being the most important. But, our mussels are an endangered lot, and they have now been placed on the federal government's list of Species at Risk.

There is a whole section in the display devoted to Ontario's mussels. A freshwater tank displays some of Ontario's more common mussel species, and the associated stream fish that host larval mussels. There are range maps to familiarize people with Ontario's major mussel areas, and the display also explains a bit about the conservation and recovery strategies being followed by scientists such as Zanatta. At present there are eight freshwater mussel species at risk in Ontario.

Fact: A pearl is formed when an organic irritant is trapped in the shell encasing the mollusc, which irritates its soft tissue. The irritant is coated with calcium carbonate from the mantle of the mollusc. Generally it is a tiny parasite that becomes the centre of a pearl. Sometimes, but rarely, the irritant is a grain of sand.

Myth: You can find a pearl in a dish of oysters

Fact: Pearl oysters and edible oysters are only distantly related. Hence, it is rare to find a pearl in a dish of oysters. Pearls created by edible oysters are dull and resemble marbles. This is because edible oysters do not produce nacre.

Myth: Pearls are only made in oysters

Fact: Pearls are produced by oysters, mussels, clams, land snails, and conches. In theory, any mollusc that creates a shell can produce a pearl, by they vary in quality and beauty.

Myth: You should sleep with your pearls on to increase their lustre.

Fact: Acidic oils and skin perspiration can actually discolour pearls and damage their lustre. It is recommended that pearls be wiped after being worn. Some experts suggest washing pearls occasionally in very mild, soapy water. Others, however, insist that moistening the string that holds the pearls will attract micro organisms that can potentially damage the pearls.

Myth: You can tell a real pearl from a fake one by rubbing it against your teeth.

Fact: That happens not to be a myth. Pearls are produced through a biological process that will often produce minor imperfections on the surface of the pearl. Each pearl has microscopic layers produced by the mollusc, which sometimes do not coat the entire pearl, thereby creating surface irregularities. Gently rubbing the pearl across your teeth will determine a pearl's authenticity: an artificial pearl will feel smooth and slippery, while an authentic pearl will feel gritty.

[Pearls - A Natural History runs at the ROM in Toronto until January 9, 2005]