The Discovery of Luminescence: "The Bolognian Stone"

For the University of Bologna hosting an International Conference on Bioluminescence and Chemiluminescence has a very special significance. Indeed, it is in our fair City that modern scientific research on these phenomena has its earliest roots. 

The oldest known written observations on bioluminescent phenomena in nature were made in China, dating roughly from 1500 to 1000 B.C. regarding fireflies and glow-worms; however, no effort was directed at understanding and applying knowledge of such phenomena until the full flowering of alchemy in Europe during the 16th and 17th centuries. By that time, the philosophical and intellectual groundwork that permitted a rational and materialistic approach to the study of natural phenomena had been laid and, in the spirit of times, this approach was applied to finding or making the Philosopher's Stone, that which would be capable of turning "ignoble metals" into gold.

Conditions were thus ripe for excitement when, in 1602, one Vincenzo Casciarolo, a cobbler by trade and dilettante alchemist, discovered the "Bolognian Phosphorus" on Monte Paderno just outside of Bologna. It was this natural stone, subsequently referred to also as the "Bolognian Stone" or "Litheophosphorus", that became the first object of scientific study of luminescent phenomena. 

The most complete text on the subject of Vincenzo Casciarolo and his stone, "Litheosphorus Sive De Lapide Bononiensi" (Fig.2), was written in 1640 by the scholar and professor of Philosophy at the University of Bologna Fortunius Licetus (1577-1657), of which the following is an excerpt in translation from the original Latin text:

"About thirty-six years ago, a stone of this type was found in the countryside near Bologna by an honest man of humble circumstances who was given to assiduous pursuit of activity in the science of chemistry; he was called Vincenzo Casciarolo, and he was of Bolognian origin. As asserted by the Excellent Petrus Poterius Andegauensis, the illustrious chemist now among the Bolognians, in his "Pharmacopea Spagirica", Casciarolo who abandoned his work as a cobbler to pursue transformation of humbler materials into gold, took the stone that he called "solar" to Scipione Begatello, an expert in the art of transformation in that time. [Casciarolo] sustained that the stone was most suitable for the production of gold by virtue of its notable weight and content of sulphur. After submitting the stone to much preparation, it was not the Pluto of Aristophanes that resulted; instead, it was the Luciferous Stone, which woud not itself produce gold, but which would absorb the golden light of the sun, like a new Prometheus stealing a Celestial Treasure. Casciarolo communicated this wonderful and unexplained event not only to Begatello, but also to the Illustrious Antonio Magino, the excellent Professor of Mathematics in this Archiginnasio [of the University of Bologna].
Magino gave preparations of the stone as a gift of a wonderful and unheard-of substance to several men of letters and to many others as well. I myself, in the company of the Illustrious Carolo Antonio Mangino, Bolognian philosopher, have seen many stones made of this substance, whether in their natural or calcinated form, whole or fragmented, alone or in mixture with albumin. With diligent observation, again and again I have seen the conception of the light of the Sun, the glowing in the darkness, and the spontaneous extinction. I went with the Illustrious Ovidio Montalbano, noble interpreter of the mathematical arts in our Palladium
[University of Bologna], and with Carolo Antonio Mangino, Philosopher, to Monte Paderno, the place of origin of the stone, and the surrounding valleys, and I collected many stones of this substance made, most suitable for producing light" (Fig.3).

The rudimental alchemistic approaches of the cobbler Casciarolo led, by a process of heating and calcination of the stone, to the discovery of its mysterious and magical ability to "accumulate" light when exposed to the sun and to emit it in the darkness (Fig.4). 

The recipe and method of preparation of the Bolognian Stone were kept secret only briefly, the first detailed description on the methods being published in 1625 by Pierre Potier (Poterius), physician to the King of France, in his "Pharmacopea Spagirica", a treatise on inorganic remedies based on the teachings of Paracelsus. Potier lived for some time in Bologna, and he was able to give an acceptable interpretation of the discovery. 

Potier's version of the recipe is quoted by E.N. Harvey in his famous book "A History of Luminescence":

"According to the light-bearing quality sought for, it is calcinated in two ways. The first is to reduce the stone to a very fine meal, then to calcinate it in a crucible with a very strong fire. The second is to reduce it to meal and, in the place of thalerum, work it into cakes either with plain water or the white of an egg. After they have dried out they are put in layers with coal in a blast furnace and, after a very hot fire has been made, they are calcinated for four or five hours. When the oven has cooled off the cakes are taken out. If not cooked sufficiently the procedure is repeated as before. Sometimes this is done three times. The best calcination results when choice stones, shining, pure, and diaphanous are used. From this powder various animals are formed in little boxes (pyxidiculum) which shine wonderfully in the dark. The lixivium is prepared in the same way and once it is dry it produces a sulphurous, fetid, sharp, and biting salt".

Casciarolo showed his "lapis solaris" to many learned men of the time, and there was widespread interest in Italy despite the fact that attempts to use it as the "Philosopher's Stone" were unsuccessful. Galileo Galilei (1564-1642) participated in scientific debate regarding the stone, and he also presented it to Giulio Cesare La Galla (1576-1624), professor of Philosophy of the Collegio Romano who first reported this phenomenon in the book "De Phenomenis in Orbe Lunae" (Venice, 1612). La Galla asserted that the untreated stone was not able to emit light, but that it acquired this property only after calcination. He explained this phenomenon, as related to him by Galileo, as a certain quantity of fire and light to which the stone was exposed being trapped in the stone and then slowly released from it, comparing its absorption to that of water by a sponge.

Subsequently, Ovidio Montalbani (1601-1671), professor of Astronomy and Mathematics at the University of Bologna, published a brief report, "De Illuminabili Lapide Bononiensi Epistola" (1634), in which he gave a dissertion on the various colors of light that could be obtained from the stone, and was the first to suggest that the light resulted from a kind of burning. As mentioned above, the most important and comprehensive contribution to the subject was given by Fortunius Licetus (1577-1657) in his lengthy (280 pages) treatise of 1640, "Litheosphorus Sive De Lapide Bononiensi". His approach was detailed and very enthusiastic, so much so that publication of the book led to a famous controversy between himself and Galileo Galilei: whereas Licetus sustained that the faint light of a crescent moon was produced by phosphorescence similar to that of the Bolognian Stone, Galileo believed that it was a reflection of sunlight from the Earth to the Moon. The debate extended throughout Europe, aided by the fact that the Bolognian Stone was included in Pierre Potier's widely used "Pharmacopea Spagirica" (1425), where it was mentioned for its presumptive depilatory properties. Potier wrote: 

"So far, the known use of this stone has been only external. From it is made the lixivium for the psilothrum, which could be probably be applied to the beard and for removing hair if did not have such an offensive odor....."

This use of the stone was noted by French and German physicians and pharmacologists until the 18th century. 

Another important European contributor to the study of the stone was given by Athanasius Kircher of Fulda (1601-1680) who, during his sojourn in Rome, wrote two books on the subject, "Magnes Sive De Arte Magnetica" (1435) and "Ars Magna Lucis Et Umbrae" (1646). To Kircher, the ability of phosphorus to attract light was similar to that of a magnet for iron, and his studies led him to believe that the material was made porous by calcination, thereby holding the subtle vapors of air suffused with light in its pores. 

John Evelyn (1620-1706) was one of the first Englishmen to learn of the stone during his visit to Bologna in 1645. Although he apparently observed the luminescence, confirming that it occurred with various colors of light, he did not take any samples back to England because, as was reported in the "Philosophical Transactions of the Royal Society" in 1666, the recipe for the preparation of the stone had apparently been lost. The most important contribution of the mid-17th century to understanding of the phenomenon came from Nicola Zucchi (1586-1670), a professor of Mathematics at the University of Rome. In 1652 he reported in his book "Optica Philosophia" that the more intense the light to which the Bolognian Stone was exposed, the more strongly it luminesced, and also that the color of the light emitted by the stone was the same regardless of whether it was exposed to white light or that passed through red, yellow or green glass. From this he concluded that the light is not merely absorbed as such but:

"rather it excites and unites with spiritous substances contained in the stone and, when the illumination has ceased, these substances gradually dissipate and become unsuitable for exhibiting a visible glow"

Although his experiment was very important, it was not repeated until almost a century later when, in 1728, a group of scientists in Bologna led by Francesco Maria Zanotti renewed the study of phosphorus, arriving, however, at an interpretation that was entirely different from the one commonly held at the time. In his experiments with the Bolognian Stone Zanotti showed that it did not soak up the light like a sponge but that the light coming from the stone was its own. He wrote: 

"In my experiment I used two pieces of phosphorous, putting one in red light, one in blue, after refracting a ray of the sun in a dark room, as Physicists do to obtain the seven colors of the light. These two stones glowed softly with the same [color of] light...."

They essentially repeated Zucchi's experiment, aided by Count Luigi Ferdinando Marsigli, Bolognian naturalist and mathematician.

In 1691, Marsigli wrote "Del fosforo minerale e sia della pietra Bolognese" and dedicated it to his English colleague Robert Boyle, who unfortunately died before he was able to read it; because of Boyle untimely death, the work was put aside and not published until 1698. Several decades later, Count Camillo Galvani wrote in his tract "Sulla pietra fosforica del bolognese" (1780): 

"The Bolognian Stone was considered one of the most surprising natural phenomena and learned men of the time sought an explanation for it. Some including Giovanni Enrico Cohansen (Lumen Novum Phosphoris Accensun, Amsterdam, 1717), were of the opinion that it shone of its own light, but most of the ancient as well as modern authors have believed that it shone by drawing light to itself and then reflecting it. Our Bartolomeo Beccari, who was also of this opinion, wrote in his tract of 1746, "De Quam Plurimis Phosphoris": 
'In eo tandem genere, quod postremo loco posuimus, principatum sibi jure vindicat lapis Bononiensis. Namque, & admirabilem hanc facultatem externi luminis ad se attrahendi, ante plane inauditam primus physicis patefecit, & eorum industriam ad similem vim in aliis etiam corporibus investigandam excitavit. Diu tamen irriti fuerunt corum conatus; & nisi casus eos juvisset, fortasse unicum adhuc in hoc genere lapidem nostrum haberemus' "

Many other prominent men searched for the Bolognian Stone or visited Monte Paderno, among them Goethe in 1786. 

Today we have a vastly more comprehensive understanding of the Bolognian Stone and its ability to luminesce. We know it is made of barite (barium sulphate) in the form of heavy silvery concretions with fibrous radial formations that widen toward the periphery of the stone. 

The phenonenon discovered by Casciarolo was the first recorded observation of inorganic phosphorescence. In these earlien times, the scientific dimensions of studies were often tinged with a magical quality that has, perhaps unfortunately, now largely disappeared. Even in the popular mind, this discovery was perceived as wondrous and momentous, and awareness of the stone was so common that in Bologna it was even employed in satire, as a metaphor for the splendor of the reigning Prince. A popular sonnet with this theme is shown in Fig.5.

I have had the good fortune of being born and raised in Bologna, and I still remember when, as a young student charmed by magical aspect of studying minerals and chemicals, I ventured along the path taken by Casciarolo, over the Calanques of the Colli bolognesi (Bolognian Hills) to Monte (Mount) Paderno, less than three miles from the center of Bologna. I can still remember the excitement I felt when I found my first Bolognian Stone, a piece about the size of an orange, which still has a place of honor in my collection (Fig.6). 

When my friend and colleague Anthony Campbell of the University of Cardiff (Wales), who has a passionate interest in Natural History, recently came to Bologna to give a series of lectures I was more than happy to accomodate his request that I accompany him to the same area around Monte Paderno to look for the Bolognian Stone. Although we were not successful in this regard, we did found or perhaps, refound, the enthusiasm and excitement of our earliest days of scientific exploration. It was great fun!

Almost four hundred years have passed since the discovery of the Bologna Stone. Since then, the earlier occult studies, filtered by illuministic rigor, have given way to a modern scientific approach that has produced a vastly greater knowledge of luminescent phenomena, including recent acquisitions in the fields of bioluminescence and in genetic manipulation.

Nonetheless, the phenomenon of luminescence remains a fascinating field of study that still has a magical quality, at least for those of us who remain young at heart. We of the University of Bologna are proud of its history; indeed, in its more than nine hundred years of existence many other chapters have been written in the history of science. 

We would like to extend an invitation to all who are interested in these fascinating stories to visit the University and the city of Bologna.

Aldo Roda, Bologna 1998

Fig.1 - Bologna (XVI sec.)


Fig.2 - A portrait of Fortunius Licetus and the title-
page of his book "Litheosphorus Sive De Lapide
Bononiensi" (1640).
The original volume can be found in the Historical
Section of the University Library of Bologna, Italy.


Fig.3 - Pages 12 and 13 of the original volume
"Litheosphorus Sive De Lapide Bononiensi" by
Fortunius Licetus (1640).
The original volume can be found in the Historical
Section of the University Library of Bologna, Italy.


Fig.4 - Drawing of the fumace used by Vincenzo
Casciarolo to calcinate the Bolognian Stone. Taken
from the book  "Il Fosforo o vero la Pietra Bolognese"
by Marc'Antonio Cellio (1680).
The original volume can be found in the Historical
Section of the University Library of Bologna, Italy.


Fig.5 - Title-page of the book "Il Fosforo o vero la
Pietra Bolognese" by Marc'Antonio Cellio (1680)
and a sonnet dedicated to the Prince Marc'Antonio
The original volume can be found in the Historical
Section of the University Library of Bologna, Italy.


Fig.6 - A piece of Bolognian Stone, barium sulphate
(barite), with a maximum diameter of about 12 cm,
found on Monte Paderno, Bologna. Private collection
of Aldo Roda.


Fig.7 - The illustration is taken from the book
"Il Fosforo o vero la Pietra Bolognese" by
Marc'Antonio Cellio (1680) and represents an
allegory of a "magic-alchemic" phenomenon: the
emission of light (phosphorescence) achieved by
calcination of the Bolognian Stone.
The original volume can be found in the Historical
Section of the University Library of Bologna, Italy.

I would like to thank the Italian Ministry of Cultural Heritage for permission to publish the figures 2-5© and 7© presented in the text. The author also extends his thanks to miss Janice Capan for her assistance in the translation of the Archaic Italian in this text.

Reproduced by permission from "Bioluminescence & Chemiluminescence: Perspectives for the 21st Century", A Roda, M Pazzagli, L.J Kricka & PE Stanley (Eds), ISBN: 0 471 98733 6, Copyright John Wiley & Sons Ltd.


Museum of Mineralogy "L.Bombicci, University of Bologna
Pieces of Bologna Stone, barium sulphate (barite)