NO PEARL is cheap, but these ones are priceless.
Still in their shell, they are among the first spherical pearls ever cultured.
They were produced 250 years ago by the Swedish naturalist Carl von Linne, also known as Linnaeus, who was the first to discover a way to make a perfectly round pearl.
He inserted a T-shaped piece of silver wire into a freshwater mussel, allowing a tiny irritant granule to be held away from the shell so the nacre could build up around it.
So precious are the twin pearls, with the silver wires still in place, they had to be escorted to Sydney in a special suitcase by Kathie Way, a representative of the Linnean Society of London.
"They are literally irreplaceable," she said yesterday.
Ms Way, a collection manager at the Natural History Museum in London, also brought some fossilised pearls that are millions of years old for inclusion in an exhibition at the Australian Museum opening in April.
More than half a million pearls in 800 pieces of artwork, jewellery and historical artefacts will be on display.
Not all of Linnaeus's creations were a success, and some of his duds are included in the dozen or so of his pearls Ms Way delivered.
He let the mussels grow for about six years before opening them, she said. "You can imagine him wondering what was there, and it turned out to be a horrid little brown blob."
Linnaeus received his Swedish title of nobility, von, because of his invention's economic potential. He sold his patent to a local merchant for the equivalent of about $3000 in 1762, but the man made no attempt to establish a Swedish pearl industry. "It was a terrible shame," said Ms Way.
Linnaeus's pearl-culturing method was only rediscovered in the early 1900s by a researcher examining his manuscripts in London.
Pearl culturing was perfected by the Japanese a century ago. Highly skilled technicians insert a bead and a graft of nacre-producing tissue from a pearl oyster into a pocket they cut into a clam's reproductive organ.