* This discovery was originally made around 100 CE by the Romans and rediscovered in the early 1300s CE in Italy. Incidentally, these Italian glassmaking kilns sometimes caused fires—a particular danger when most buildings were made of wood—and so the government of Venice banished all glassmakers to a nearby island. While this was intended as a safety measure, concentrating all glassmakers together led to an explosion of talent and shared expertise, which allowed glassmaking to advance quickly, leading to the rediscovery of the “burn seaweed and add its ashes to make clear glass” trick. Even clearer glass can be made by a 10 percent to 30 percent concentration of lead oxide, which produces a glass (known as “crystal glass”) that’s very refractive and pretty but can also give you lead poisoning. The association of the upper classes of Europe and North America with gout around the 1800s CE has been traced to them drinking out of their fancy lead glasses.