Lignum nephriticum

Lignum nephriticum (Latin for "kidney wood") is a traditional diuretic that was derived from the wood of two tree species, the narra (Pterocarpus indicus) and the Mexican kidneywood (Eysenhardtia polystacha). The wood is capable of turning the color of water it comes in contact with into beautiful opalescent hues that change depending on light and angle, the earliest known record of the phenomenon of fluorescence. Due to this strange property, it became well known in Europe from the 16th to the early 18th-century Europe. Cups made from lignum nephriticum were given as gifts to royalty. Water drunk from such cups, as well as imported powders and extracts from lignum nephriticum, were thought to have great medicinal properties.