Formed in December 2005, the company offers connoisseurs the rarest and most desirable diamonds and the highest-quality diamond jewellery, backed by the Sotheby's brand name.

Wong makes regular trips to Steinmetz's offices in New York, Geneva and Antwerp, where she surveys the full range of diamonds on offer and selects the stones she likes best, regardless of the price.

If most people who source diamonds are limited by a business or personal budget, she isn't.

'The beauty of the joint venture is that I can choose the best stones without worrying about that constraint,' she said. 'We have a chance to pick very special stones.'

These also include a sizeable amount of the rarest fancy coloured diamonds. Through Wong's hands have passed the then largest graded vivid blue (27.64 carats), the largest graded vivid pink (59.60 carats) and the largest graded vivid green (2.05 carats) diamonds.

Unlike other jewellery companies that design first and then source the diamonds, Sotheby's Diamonds starts with the diamond. Wong may examine hundreds of diamonds before finding what she wants. The process may take weeks or months.

Diamonds are always the focal point of each piece of jewellery, which can range in price from US$50,000 to a staggering US$50 million. The polished diamonds are typically from 5-10 carats in size, but some can be as large as 100 carats.

The company's exclusive client base is largely drawn from people who already have a relationship with Sotheby's through its auctions. 'We do not advertise. Ours is an operation that focuses on a very exclusive customer base,' Wong explained.

Creative director James de Givenchy, nephew of fashion designer Hubert de Givenchy, is in charge of jewellery design at Sotheby's Diamonds but he and Wong work closely together.

His striking contemporary creations combine diamonds with rubber, steel, wood, ebony or colourful semi-precious stones in ways that highlight the contrasts between them.

For traditionalists, classic diamond jewellery set in precious metal such as gold or platinum is also available.

'In terms of pieces, we sell more of the contemporary styles because they tend to have smaller diamonds, and therefore carry a lower price point. But in terms of very high value diamonds, we either choose to keep the diamonds unmounted or the classic styles are predominant,' Wong said.

Wong said Sotheby's Diamonds' emphasis on top quality stones coincided with a major consumer trend that had emerged in the past 10 years.

'Stone quality is becoming more important to clients not only in Asia but in Europe and America as well,' she added. 'People care about the diamonds they are buying and the brand name of the jewellery.'

From her very first days at Sotheby's when she began learning about diamonds from the company's in-house experts, the allure of diamonds has not waned for Wong.

'I love gems, and diamonds are very special to me,' she said. 'The whole industry fascinates me - the cutting, how people transform a piece of rough into a diamond, and then into a piece of jewellery.'

She carries a mental inventory of diamonds in her head, which she draws upon when matching stones or looking for that special combination, as she did recently by finding a vivid pink diamond with an outline that perfectly complemented a vivid blue diamond, which were paired together in a ring.

'The more you see, the choosier your eye becomes. The colour, the fire, the brilliance - everything has to come together at the same time,' she said.