Ms. Tan, the curator, said: “It demonstrates that the Chinese potters were already experimenting with imported cobalt blue from Iraq, which they applied as underglaze painted decoration, some 500 years earlier than the famous blue and white porcelain of the 14th century.” At the time of the dhow’s discovery, cobalt-blue pigments had been found only in the Middle East, not yet in China, said Alan Chong, director of the Asian Civilisations Museum.

Aside from the rare ceramics, the haul also contained gold and silver objects, some of which Mr. Raby of the Smithsonian described as “of the very best quality you can see, clearly of imperial quality,” adding, “so we believe these were possible diplomatic gifts.”

The form and decorative motifs of an octagonal gold cup — musicians and dancers with long hair and billowing robes — suggest Central Asian metal wares. Mr. Raby said it was believed to be the largest known such gold cup from Tang China, even upstaging, he added, one of the great treasures of Tang gold and silver work: the so-called Hejiacun Hoard, found in what had been one of the southern suburbs of the Tang capital of Xi’an.

The rarity of the cup and its unusual style have puzzled researchers, Mr. Raby said: Why was it aboard the dhow and who owned it? But he said the dhow’s entire cargo raises myriad questions.

A replica of a Hejiacun cup can be seen at the ArtScience Museum in a parallel show, “Traveling the Silk Road: Ancient Pathway to the Modern World,” which is at the American Museum of Natural History in New York and is running through March 27. It takes viewers back to the heyday of the Silk Road, when Genghis Khan and his descendants restored order in the 13th century along the loose networks of trade routes that had become too dangerous for merchants. The museum is also showing “Genghis Khan: The Exhibition” until April 10.