The Holy Roman Emperor Ferdinand III once received a gift from Athanasius Kircher, a German Jesuit scholar, sometime in the middle of the 17th century. It was a wooden cup but unlike any the Emperor already possessed. When clear spring water was poured into the cup and left for a while, the water turned brilliant blue. But when the water was poured back into a glass bowl, the blue hue disappeared.
This remarkable cup was made from a type of wood called lignum nephriticum. Because of its almost miraculous optical properties, this wood became very popular throughout Europe in the 16th, 17th, and the early part of the 18th centuries, and were the subject of investigations by the most celebrated physicists of that period. Cups made from this wood were deemed fit gifts for emperors and princes, and water drunk from these cups was said to work marvelous cures.
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A cup of Philippine lignum nephriticum, Pterocarpus indicus, and flask containing its fluorescent solution. Image credit: William Edwin Safford