The Florescence of Lignum Nephriticum

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.

A cup of Philippine lignum nephriticum, Pterocarpus indicus, and flask containing its fluorescent solution. Image credit: William Edwin Safford

The wood was first described by the Spanish physician and botanist Nicolás Monardes. In 1565 he wrote the following account in his work Historia medicinal de las cosas que se traen de nuestras Indias Occidentales:

They also bring from New Spain a wood resembling that of a pear tree, dense and without knots, which they have been using for many years in these parts for diseases of the kidneys and of the liver. The first person I saw use it was a pilot, 25 years ago, who was afflicted with urinary and kidney trouble, and who after using it recovered his health and was very well. Since then I have seen much of it brought from New Spain and used for these and kindred maladies.

It is used in the following manner: They take the wood and make of it chips as thin as possible and not very large and put them into clear spring water, which must be very good and pure, and they leave them in the water all the time that it lasts for drinking. A half hour after the wood is put in, the water begins to assume a very pale blue color, and the longer it stays the bluer it turns, though the wood is of a white color. Of this water they drink repeatedly and with it they dilute their wine, and It causes very wonderful and manifest effects without any alteration nor any other requisite than good order and regimen. The water has no more taste than if nothing had been put into it, for the wood does not change it at all. Its complexion is hot and dry in the first degree.

In 1570, Francisco Hernández de Toledo, the court physician of King Philip II of Spain, led what is considered the first scientific expedition to the Americas. When he returned to Spain in 1577, he gave testimony of the medicinal properties of lignum nephriticum, as described by Monardes. However, he expressed uncertainty as to its origin, stating that while he was told the source plant was a shrub, he had personally also witnessed specimens that reached the size of very large trees.

In 1646, Athanasius Kircher, a German Jesuit scholar known for his great learning and his contributions to science, published an account of his experiments on lignum nephriticum. He conducted his experiments on a cup given to him as a gift from Jesuit missionaries in Mexico, the same cup he later gifted to Holy Roman Emperor Ferdinand III. He commented that while previous authors only described the color of the water mixed with lignum nephriticum as blue, his own experiments actually showed that the wood turned the water into all kinds of colors, depending on the light. He wrote:

The wood of the tree thus described, when made into a cup, tinges water when poured into it at first a deep blue, the color of a Bugloss flower; and the longer the water stands in it the deeper the color it assumes. If then the water is poured into a glass globe and held against the light, no vestige of the blue color will be seen, but it will appear to observers like pure clean spring water, limpid and clear. But if you move this glass phial toward a more shady place the liquid will assume a most delightful greenness, and if to a still more shady place, a reddish color; and thus it will change color in a marvelous way according to the nature of its background. In the dark, however, or in an opaque vase, it will once more assume its blue color.

Four years after the publication of Kircher's work Swiss botanist Johann Bauhin in his great work Historia plantarum universalis, describes a second cup made of lignum nephriticiom, which he had received from a colleague. Bauhin also received shavings from the same wood along with the cup. Bauhin observed that when water was poured into the cup with the wood shavings, the water shortly turned into “a wonderful blue and yellow color, and when held up against the light beautifully resembled the varying color of the opal, giving forth reflections, as in that gem, of fiery yellow, bright red, glowing purple, and sea green most wonderful to behold.”

The first scientific study of lignum nephriticiom and its remarkable properties was made by Robert Boyle in 1663. Boyle gave for the first time a precise and scientific description of the phenomenon, now known as fluorescence which this rare wood so exquisitely presents. He pointed out that the “tincture afforded by the wood must proceed from subtiler parts of it drawn forth by the water” and also shows that the color effects disappeared on the addition of small quantities of acids, but reappeared on neutralization with alkalis. By Boyle’s time, however, lignum nephriticum became exceedingly rare and by the end of the 18th century, the wood had completely disappeared.

It wasn’t until 1915, when lignum nephriticiom was rediscovered by the American botanist William Edwin Safford. He deduced that lignum nephriticum actually came from two species of trees that became confused as one. He identified the original traditional remedy described by Monardes as Mexican kidneywood (Eysenhardtia polystachya), a native of Mexico, while the cups which became famous in Europe were originally carved from narra wood (Pterocarpus indicus) by the inhabitants of southern Luzon from the Philippines. It was imported into Mexico through the Manila-Acapulco Galleon trade and from there, introduced to Europe.

A mature Pterocarpus indicus as seen in Hok Tau in the northeastern New Territories, Hong Kong. Photo: Geographer/Wikimedia Commons

Eysenhardtia polystachya. Photo: Juan Carlos Fonseca Mata/Wikimedia Commons

Lignum nephriticiom’s ability to impart color to water is caused by a phenomenon called fluorescence, where certain substances or chemicals absorb light or other electromagnetic radiation, and then emit it back in a different frequency. The wood of lignum nephriticiom contains a rare compound, which when it comes in contact with alkaline water, undergoes a fast, irreversible reaction giving rise to a strongly blue-emitting compound called matlaline. Safford wrote in a report published by the Smithsonian Institution:

The fluorescing power of the wood is so great that an extract of one part of the wood in one hundred-thousand parts of water or alcohol, after having been made alkaline, showed a distinct fluorescence in diffused daylight, and when diluted to a ratio of one to one million a fluorescence could still be detected in the rays of a fluorescence lamp. In very attenuate solutions the fluorescence is bluish; in more concentrated solutions it is distinctly yellowish green.

Eysenhardtia polystachya is still highly valued in Mexico for the medicinal properties of its wood, to which is ascribed an almost miraculous ability to cure kidney and bladder ailments. The deciduous shrub can grow up to 5 meters tall and is widespread in its natural range.

Pterocarpus indicus, in contrast, is a relatively large tree growing 30 to 40 meters tall and trunk 2 meters thick. The tree is found predominantly in southeastern Asia, northern Australasia, and the western Pacific Ocean islands. The timber of the Pterocarpus indicus is used to make high grade furniture, its flower is used as a honey source while leaf infusions are used as shampoos. The leaves of the plant are also used in traditional medicine to treat a variety of health problems, such as inflammation, and kidney trouble. Pterocarpus indicus is the national tree of the Philippines.

References:
# Annual report of the Board of Regents of the Smithsonian Institution
# A. Ulises Acuna et al, Structure and Formation of the Fluorescent Compound of Lignum nephriticum, Organic Letters
# Lignum nephriticum, Wikipedia
# Otto Stapf, Lignum nephriticum. (Eysenhardtia amorphoides, H.B.K.), Bulletin of Miscellaneous Information (Royal Botanic Gardens, Kew)