Palo Azul or lignum nephriticum (Latin for "kidney wood") derives from two species of tree, the Narra (Pterocarpus indicus) and the Mexican kidneywood (Eysenhardtia polystachya).
In the Nahuatl language Palo Azul was known as the coatli, coatl, or cuatl (snake water) or tlapalezpatli (blood-tincture medicine). It was traditionally used by the Aztecs as a diuretic.
The wood is capable of turning the colour of water into beautiful opalescent hues that change depending on the angle of light and is one of the earliest known records of the phenomenon of fluorescence. Due to this unique property, it became popular in Europe from the 16th to the early 18th-century. Drinking cups made from Palo Azul were given as gifts to royalty. Water mixed with lignum nephriticum extract were drunk from the cups and thought to contain excellent medicinal properties.
