The Royal Gold Cup or Saint Agnes Cup is a solid gold covered cup lavishly decorated with enamel and pearls. It was made for the French royal family at the end of the 14th century, and later belonged to several English monarchs before spending nearly 300 years in Spain. It has been in the British Museum since 1892, where it is normally on display in Room 40, and is generally agreed to be the outstanding surviving example of late medieval French plate. It has been described as "the one surviving royal magnificence of the International Gothic age". According to Thomas Hoving, former director of the Metropolitan Museum of Art in New York, "of all the princely jewels and gold that have come down to us, this is the most spectacular—and that includes the great royal treasures."

Vitreous enamel, also called porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C. The powder melts, flows, and then hardens to a smooth, durable vitreous coating. The word vitreous comes from the Latin vitreus, meaning "glassy".