Amylin's is the most reliable retailer of pearls of all colours and sizes. It's been touting its wears since 1993 in the most unlikely location – a pearl- and jewel-filled room in a tower block near Jing'an Temple. Buy freshwater pearls (from ¥100), prized black Zhejiang pearls (from ¥1500) and saltwater pearls (from ¥200).
The staff speak English and will string your selection for you. They sell jade and jewellery too.