David Warren has travelled hundreds of thousands of miles hunting down the objects of his desire. Over the past three decades he has descended into emerald mines in Colombia. He has brokered multi-million dollar deals with some of the most elusive, and wealthiest, people in the world. He has uncovered the true value of treasures of antiquity long dismissed as junk.
Oh, and he has found a really handy use for Microsoft Excel. He has employed the spreadsheet application to create his personal "Pearl Index", a meticulous log of every last detail of every pearl he has seen, bought, sold or longed for. To date, this list runs to 200 items.
Warren is the international director of Christie's Jewellery and head of jewellery, Middle East. But to colleagues in the auction house's Dubai and London offices, between which he splits his time when not roaming the world in search of acquisitions, he is Mr Pearl: part dusty academic, part big-game hunter, steadily tracking his prey. "Pearls," he says, "are my passion."
Next Wednesday evening, Warren will be in Dubai presiding over Christie's auction of "Important Jewels". Its 98 lots have an estimated worth of $13.5 million. Each one has been selected by Warren over the past six months, during which time, he says, he must have seen 10,000 items that were either the wrong piece, the wrong price, or both.
Those that made the final cut include an exquisite aquamarine and ruby ring, strings of diamonds and an array of pendants, rings and bracelets, each bespoke and arrestingly beautiful. For Warren, none hold the appeal of Lot 79, listed in the catalogue as "An Important Natural Pearl".
It is important for its provenance: it was once part of the collection of Valda Virginia Vaughan Scott, daughter of an English diplomat and member of the prestigious Alessi family. It is important for its cultural resonance in this region proudly bound to its pearl-diving past. It is important for its quality. And, at 239.7 grains (a whisper away from 60 carats), it is important for its sheer size.
Warren says: "It's a fabulous piece. I've known about this pearl and had it on my list for some time. I follow who owns what, what pearls are where, what's possibly up for sale, what's in museums and what's in private collections out of sight.
"Last year this particular pearl was exhibited in Qatar's Islamic museum. So it was back at the forefront of people's minds."
That, along with the fact that the pearl market has risen rapidly in the past five years, helped Warren convince the owner that now would be a good time to sell.
According to Warren a key factor in the success of any item up for auction in Dubai is that it is unique. With its baroque drop-shape, rainbow sheen, circular-cut diamond mount and diamond chain, Lot 79 is certainly that. But then, as Warren points out, "every natural pearl is a freak of nature."
It is part of the apparently unending appeal that pearls hold for this 53-year-old Glaswegian, who discovered a love of auctions as a teenager accompanying his antique dealer mother to sale rooms.
He decided to try his hand at trading and what began as a hobby - buying goods with his pocket money and selling them on for an increasingly tidy profit - morphed into a job on leaving school. Warren dropped out of college after a year as his antique and collectable trading was earning him enough to pay his rent as well as buy a car and a motorbike. His success caught the eye of a local auction house in Glasgow where he was offered a job. When the firm was taken over by Christie's they kept him on and within two years he was posted to London, where his love affair with jewellery began in earnest: first with emeralds, then Indian Mogul pieces and, ultimately, pearls.
Christie's doesn't deal in cultured pearls. They have a resale value, Warren explains, but not substantial enough to be of real interest to the auction house.
His passion is natural saltwater pearls whose lustre tends to exceed that of their freshwater cousins.
Warren says: "A lot of the best pearls in the world were fished from the Arabian Gulf, though sadly the pearl beds were all but destroyed when industrial scale fishing meant they could be trawled."
There are several major collectors in the area for whom a guaranteed Arabian provenance would prove appealing, but there is no way of scientifically proving which pearl bed any individual pearl comes from.
Natural pearls come in two categories: blister pearls, which grow attached to the mollusc and must be cut loose, leaving one side flat and lacking in shine, and precious pearls, which float freely in their shell home and have a more even shape as a result.
As Warren points out, "Pearls have been around forever. They were the first gemstones man knew of and understood because they were just there, found when fishing for food, unlike diamonds or rubies or whatever that have to be dug out of rocks, cut and polished."
Greeks believed that pearls were the result of lightning hitting the ocean. The Romans thought them the tears of the gods. The truth is more prosaic. They form when a foreign body - a grain of sand, a tiny sea creature - gets into a live mollusc and the animal coats the irritant with nacre, the substance which it uses to build its shell. It's the layers of nacre which form the pearl's "skin." That skin should be even and smooth, without blemish or blister and, ideally, white with a faint blush of pink.
Sadly, a pearl's skin is no more impervious to the ageing process than that of the beauties who wear it. It may take a tad longer - three, maybe four hundred years - but ultimately the pearl's porous skin will dry out, crack and discolour.
Warren says, "The oldest pearl necklace in the world is the Susa Necklace. It was actually found in the Middle East and dates back to antiquity. It's in the Louvre and I made a pilgrimage there to see it.
"I'm afraid to say it was a bit of an anticlimax. It's three rows of pearls interspersed with gold beads, but some of the pearls just looked like black lumps of charcoal. Pearls, unlike diamonds, aren't forever."
As for the size, providing the shape and skin are of quality, then the bigger the better. The pearl up for auction next week is among the largest in the world.
But Warren admits: "Because the nature of a pearl is so individual the same is true of valuation. It's not like diamonds where you can check up the Rapaport [Diamond Price List] and anyone, anywhere in the world can say, 'that's the price.'
"Every single pearl is different. Every single valuation comes down to a bit of educated guesswork. The only thing you can do is use your best judgement and your own reference library that you've built up in your mind ... or, in my case, the list. Sometimes when it comes to the day itself the key factor is emotion."
Two years ago a natural pearl necklace given to Umm Kulthum, the Arab singer, by Sheikh Khalifa bin Zayed, President of the UAE, sold for $1,385,000 (Dh 5,082,950), more than 10 times its pre-sale estimate. The exquisite quality of the piece and its provenance contrived to create a bidding frenzy that no one could have predicted.
Whatever price Lot 79 fetches on Wednesday, Warren will update the relevant line on his "Pearl Index". And when he does he will scroll over his spreadsheet and settle wishfully on the pearls that continue to elude him: The Dudley Pearl, 209 grains, a perfect drop, perfect white with a hint of blush, the Peregrina Pearl, owned by Elizabeth Taylor and three significant pearls owned by Princess Michael of Kent.
For Mr Pearl, the business of "Important Jewels" won't end when the final lot is sold on Wednesday evening. Far from it. There will always be more quarry to be tracked, hunted, bagged and, indeed, indexed.