The thirst for artistic exchange among the elites of different cultures often brings about an intermingling of technology and art from several regions. One particular example of this kind of exchange is the intricately designed hand warmers Muslim artists made for the European market. The idea of a circular metal heater seems to have originated in China, where small round fire pots with hinged tops were filled with burning embers and hung from the ceiling. Using a similar design, Muslim craftsmen made spherical incense burners, piercing the round body of each burner and decorating it with silver and gold inlaid designs. After merchants exported them to Europe, they discovered that the people in the cold climates of Europe were using the incense burners as hand warmers. Seeing a market for a new item, Muslim artisans inserted a brass pan inside each burner...