It was being sent in at the deep end," she recalled. "I was 19 and I was responsible for every single diamond the company had." Teaming up with school friends from Lagos who had moved into investment banking, West set up her own business in London to trade the precious stone. Metal tongs in hand, West explained the secrets of some of her stock. "Diamonds have fire," said West. "That stone is too flat but it’s got a lot of life in it, it was cut about 100 years ago,” she said, pointing to one tiny rock. "This one cost just over £100,000 ($141,000, 126,000 euros), it’s got a low colour but it has been cut perfectly so it reflects light in such an amazing way." Fewer than 50 clients, 12 of whom are investors, have access to West’s knowledge. "I can find a diamond and call them and say ‘we have to buy this diamond, trust me’ and they follow me," she said. Her multinational client base — introduced by word of mouth — includes Swiss, Russians, Ghanaians, Nigerians and "a handful of French". Helped by a 10-woman team, West creates all of her company’s products, which come with a lifetime guarantee. Her most ambitious creation was a custom-made necklace worth around #2 million. She plans to open a workshop in Nigeria, "where I’ll train girls in the art of making jewellery". West gives little away but also said she is creating "a revolutionary tool" that will help people in her business. "That tool should be part of every diamond dealer and every shop".

Thelma West, a 32-year-old Nigerian is the only woman in the male-dominated world of diamond business Nigerian Thelma West is a rare ...