In the years before Dubai's property boom, tourists would flock to the headquarters of the then National Bank of Dubai, photographing the reflection of the Dubai Creek over its glass facade.

The building is still a highlight of the city's skyline, but few know of the Pearl Museum on the 15th floor. It contains one of the world's largest and finest collections of saltwater pearls from the Gulf. It was donated by Sultan Al Owais, a descendant of a family of pearl merchants.

A former chairman of the National Bank of Dubai, now Emirates NBD after a 2010 merger, the late Al Owais was a distinguished poet and philanthropist.

His collection contains maps, diving paraphernalia and equipment used by pearl merchants such as weighing scales made from precious stones, imported from as far as Yemen, and wooden boxes where traders would keep their wares when travelling on business. There are, of course, pearls – more than 50 kilos of them.

Ibrahim Sowaidan, head of group corporate affairs at the bank, is hesitant to talk about monetary value.

"We say it is priceless because how do you measure its value to our heritage?” he said.

When it comes to distinguishing the value of a pearl, a variety of factors plays a part. Size is important and so is colour, said Mr Sowaidan.

A silvery white as well as golden hue are prized colours and so is symmetry. Teardrop or pear-shaped pearls are also valued, while when it comes to a pearl's lustre, a sharp mirror-like reflection brings in higher prices.

Most of the jewellery in the collection follows either European or Indian fashions since prior to the discovery of oil, people preferred to sell the gemstones rather than wear them.
Source: The National