Dear Readers,

As you may have seen elsewhere, in mid February my wife and I suffered the loss of our home in a fire, in the hills of central Massachusetts. The good news is that we got out safely and had no animals in our care at the time. The fire crews were able to contain the fire from spreading, in what turned into a 3-alarm, 5-hour-long ordeal in subzero temperatures; they did amazing work, and no one was injured. The bad news is that all of my physical historical materials and research of 30 years have gone up in smoke. As a result I have decided to suspend this blog for the time being. It will remain online as a resource for those interested in the history of glass and glassmaking in the seventeenth century and beyond. I do intend to resume writing when I can, but for now my time and energy are required in getting us back on our feet.

Friends are providing temporary shelter for us nearby and our intention is to rebuild as soon as possible. To those who have reached out with a steady hand, to those who have opened their wallets, and offered advice in our time of need, we thank you from the bottom of our hearts. In what are already difficult times for all of us, you have made a huge difference in our lives.

Paul Engle
6 March, 2021

Friday, July 29, 2016

Purpurine

Fabergé c.1900. Purpurine cherries,
nephrite leaves, gold stalk, rock crystal pot.
Peter Carl Fabergé is known the world over for producing elaborate jeweled fantasy eggs for the Russian royal family in the late nineteenth and early twentieth centuries. [1] The artisans of his firm made use of a wide variety of exotic and precious materials in the execution of their commissions and later in items made available to the general public. Among the most exotic and sought after were objects made with an opaque bright red stone-like material known as ‘purpurine’. This was a glass based concoction whose composition was kept a tightly guarded secret. In fact, it was so tightly guarded that the formula was subsequently lost. Purpurine was typically cast into blocks which were then sawed and carved using traditional lapidary and gem carving techniques. The final appearance was of an unknown exotic mineral.


Red Glass Beads, 1st cent. BCE, Tissamaharama, Sri Lanka
The origin story of purpurine begins much earlier than Fabregé, in fact, not hundreds but thousands of years earlier. “The art of making this type of glass seems to have originated in India; glass beads of a similar material have been found in the Indus Valley and were dated to the late 2nd millennium BCE.” [2] In southern Sri Lanka deep red opaque glass beads have been found dating to the first millennium BCE; these turn out to be closely related to purpurine, through a long glassmaking tradition. [3] A version of the bright red glass was made in the Egyptian- Roman era. The first century CE historian Pliny the Elder noted that in Greek it was called ‘haematinon’ or blood-red ware. [4] He implied that this specialty glass, was routinely produced in Rome and indeed archaeologists have recovered numerous examples. The glass was used in a wide range of applications from dinner plates to pieces of elaborate mosaics. Eventually, though, the method of making haematinon was forgotten and remained so for several hundred years.


A small (1cm) Medusa's head in
opaque red glass c.1st. cent. CE.

The Renaissance era had been marked by a strong motivation to recover lost knowledge of the ancient world, but many challenges were beyond the technology of the time. However, attempts were made that eventually led to success.  In the second half of the 16th century, Pope Gregory XIII instituted the Vatican mosaic studio to decorate the new Saint Peter’s Basilica, begun by Pope Julius II in 1506. As an aside, this workshop continues today, repairing and conserving the ceilings of St. Peter’s. [5] Having quickly exhausted local talent in Rome, Gregory brought in Venetian masters to teach the art. With the mandate to make the mosaics appear as if painted, the studio developed many new formulations for the glass tesserae – the individual tiles used to form mosaics. It was in this environment that the deep red purpurine [Ital: porporino] was eventually rediscovered.


C. 1st cent. BCE/CE Roman bowl (patella cup) in
red opaque glass (haematinon).

It is still an open question whether the secret was discovered in Rome or brought there. There is evidence that the fabled red glass was being produced in Venice in the eighteenth century and possibly earlier.[6] One (Swedish) source credits Vatican studio employee Alessio Matteoli, in the 1700s, when he oversaw the development of many new colors. In the early 1800s, interest rekindled in the ancient material and by then, analytical methods were up to the task of finding their composition. German chemist, Martin Heinrich Klaproth, analyzed haematinon from the Villa Jovis, a first century palace built by Roman emperor Tiberius on the island of Capri in southern Italy. [7] He correctly found copper, but incorrectly assumed the material was glassy slag, a byproduct of the smelting process. Later, in 1844, Schubarth did further work indicating haematinon was, in fact, a true glass. [8] King Ludwig I of Bavaria intended to build a reconstruction of a Pompeian villa for educational purposes. He assigned Max Joseph von Pettenkofer to the task of rediscovering the method of manufacturing the antique “blood glass,” and the young chemist reported success in 1853. [9] His process fused standard alkali-lead glass with copper oxide and magnetite in the presence of small amounts of magnesium oxide and carbon, followed by very slow cooling of the resultant mass, which would then take on a deep red color.


Roman Mosaicist
Michelangelo Barberi, 1809.
Other sources name one of two students of the famous Roman mosaicist Michelangelo Barberi (1787–1867). Barberi had a long standing relationship with the Russian royal family and accepted Russian pupils at his studio in Rome, he even set up a mosaic shop in St. Petersburg at the request of Tsar Nicholas I. [10] In 1846, these two pupils of Barberi, brothers Giustiniano and Leopold Bonafede were called to St. Petersburg by the tsar to work for the royal court. Giustiniano (1825-66) had served as head chemist at the Vatican studio and both would attain that post for the tsar at the Russian Imperial Glassworks. It is Leopold (1833-78) who is now most often credited with the invention of purpurine as a recreation of the fabled haematinon. His formulation was based on a standard potash lead crystal.


Purpurine taza made at the Russian
Imperial Glassworks, c.1867.
(Shown at Paris Exposition)
The first documented uses in objects of art were five entries of the Imperial Glassworks at the Paris Exposition Universelle in 1867, for which the glassworks was awarded gold medal status. [11] “After Bonafede's death in 1878, purpurine continued to be made at the factory under the direction of the chief chemist, S. P. Petuchov.” [12]

In 1882, after considerable training and apprentice work, which began when he was a teenager, a 46-year-old Peter Carl Fabergé fully assumed control of his father’s small jewelry shop in St. Petersburg. Within a short time, he was supplying the royal family with his exquisite eggs and many other items made by a growing assemblage of master craftsmen. The first use of purpurine by the Fabergé shop occurs early in Carl’s tenure, perhaps as early as 1880. Initially, they use material supplied by Petuchov at the Imperial Glassworks. Over a period of years, though, the Fabergé shop developed its own recipe based on soda lead glass, more similar in composition to the ancient samples of haematinon.[13]  Other isolated examples of purpurine are known to exist made by competitive jewelers of the time, but no documented recipe has been found. [14] Apparently, Petuchov took the Imperial Glassworks formula for purpurine to his grave. As fame grew for Fabergé, their version is the one that became familiar to a growing clientele in Great Britain and in the United States. When the February Revolution of 1917 brought an end to the Romanov dynasty in Russia, Carl Fabergé fled the country, his company disbanded. In the west, the Fabergé name only multiplied in prestige among the elite and wealthy and items made with purpurine continue to command stratospheric prices.

Significant analytical work has been done on the ancient haematinon as well as purpurines of the Imperial Glassworks and of Fabergé. [3,5] The technical differences could easily be the subject of a separate treatment; suffice it to say that knowing the composition of a glass is not the same as knowing the recipe. (Just as knowing the composition of a cake does not mean that one can bake it.) The exact method for making the glass must have involved a long period in which snowflake-like crystals of cuprous oxide (Cu2O) would be encouraged to form, grow and spread throughout the glass forming a tightly interlocking network in the glass. One interesting point is that unlike many other opaque glasses, the ingredients of purpurine do not include a discrete opacifier; it is a clear glass base, which is so loaded with deep red cuprous oxide crystals that light does not pass through even small or thin pieces of the material. Another point is that this glass was not suitable for blowing on a blowpipe and therefore did not take forms typically expected for glass. Perhaps because of this, it has been largely overlooked.

The history of purpurine is a reminder of the fragility of human knowledge; it was discovered in ancient times, lost, rediscovered and lost again in modern times.


[1] Peter Carl Fabergé =Карл Густавович Фаберже. For more, see Abraham Kenneth Snowman, The Art of Carl Fabergé, Faber & Faber, 1974.(original ed 1953). Also see
 https://en.wikipedia.org/wiki/Peter_Carl_Faberg%C3%A9
[2] Gowlett, J.A.J.: High Definition Archaeology: Threads Through the Past, Routledge, 1997, pp. 276–277. Quoted in https://en.wikipedia.org/wiki/Purpurin_(glass)
[3] Rösch, Cordelia; Hock, Rainer; Schüssler, Ulrich; Yule, Paul; Hannibal, Anne. “Electron Microprobe Analysis and X-ray Diffraction Methods in Archaeometry: Investigations on Pre-Islamic Beads from the Sultanate of Oman” in: European Journal of Mineralogy, 9 (1997), 763–783. (Specifically, beads found at Tissamaharama, pp. 771,772). http://archiv.ub.uni-heidelberg.de/propylaeumdok/volltexte/2009/305
[4] Natural History, xxxvi, LXVII, 198.
[5] For more, see http://www.30giorni.it/articoli_id_10283_l3.htm
[6] RR Harding, S Hornytzkyj, A. R. Date. “The composition of an opaque red glass used by Fabergé”in the Journal of Gemmology, 1989. No.5, pp. 275-287.
[7] Klaproth M.H., Beiträge zur chemischen Kenntnis der Mineralkörper Vol. VI (1815), p. 136
[8] Schubarth. "Einige Notizen über rothes und blaues Glas." Journal für Praktische Chemie Vol. 3 (1844), pp. 300-316
[9] Pettenkofer, M. "Ueber einen antiken rothen Glasfluss (Haematinon) und über Aventurin-Glas." Abhandlungen der naturw.-techn. Commission der k. b. Akad. der Wissensch. I. Bd. München, literar.-artist. Anstalt, 1856. Also see https://en.wikipedia.org/wiki/Purpurin_(glass)
[10] Alessio Matteoli https://nononsensejewellery.wordpress.com/tag/purpurin-faberge/ , for more on Matteoli see http://www.aiellomosaics.com/about-mosaics/techniques-and-materials/roman-or-byzantineglass-or-marble-tilesmicromosaic-or-glass-enamels/ .  On Michelangelo Barberi, see Renata Battaglini Di Stasio, “Michelangelo Barberi” in Dizionario Biografico degli Italiani – v. 6 (1964)  http://www.treccani.it/enciclopedia/michelangelo-barberi_(Dizionario_Biografico)/
[11] Catalogue Special de la Section Russe a l'Exposition Universelle de Paris en 1867, p. 44, Classe 16, no.111.
[12] See http://art.thewalters.org/detail/77444/pair-of-tazzas/
[13] Op cit. RR Harding, S Hornytzkyj, A. R. Date, 1989.
[14] For more on competitive jeweler’s purpurine, see: Géza von Hapsburg: “Some of Fabergé’s Other Russian Competitors” in Fabergé, Imperial Craftsman and His World, London: Booth-Clibborn, 2000, pp. 323-325.
* This post first appeared here 8 Feb. 2016.

Wednesday, July 27, 2016

Decolorization of Glass

The green tint from iron contamination
is neutralized by magenta from manganese.
For Antonio Neri and his contemporary glassmakers, contaminants, especially metallic contaminants were the bane of producing a crystal clear product. Great care was taken to ensure the purity of each ingredient at each step of the glass making process. The greatest threat of all was iron. Even small amounts will impart a green tint and for Renaissance era glassmakers, nemesis iron was everywhere. It is a common impurity in quartz, the main ingredient of glass, showing up as yellow "rust stains" both in sand and stones. It turned up in the plant salts used for glass flux as a trace-element and finally it was in the tools. Iron was in the mortars and pestles, in the pots and kettles, in the frit rakes, in the ladles, the stirring rods and in the blowpipes. A mistake at any step could easily tint the batch, even at the final stages. Neri admonishes glass workers:
Make sure never to return the neck, where the rod attaches to the glass, into the crucible of cristallo, because there are always remains of the iron that will cause it to become dark ... 
Centuries before Neri, it was discovered that the antidote to iron contaminated glass was manganese or more specifically manganese oxide, a mineral mined throughout Italy. However, Neri cautions: 
… you must always use manganese of Piedmont the way it is made for Murano, because the manganese of Tuscany and Liguria has more rust, which always make the melt dark. 
This color correction technique was known as early as the late 14th century and by Neri’s time it was a widely practiced technique in the glassmaker’s toolbox. Manganese oxide was known as a pigment in antiquity; the Magnesia region in Thessaly, central Greece was an ancient source for the black mineral. Around the year 1450, a clear crystal-like glass suitable for working into thin elaborate forms was developed in Venice. The glass was called cristallo and Murano glassmaker Angelo Barovier is often given credit. He may well be responsible for bringing together several existing techniques—manganese color correction among them — but these techniques individually were all available and utilized by glassmakers at least fifty years earlier. Barovier’s innovation would become a tradition giving Murano the reputation for the finest glass made anywhere, carried on by countless glassmakers and ultimately by our Florentine priest more than a century and a half later.

Removing the green tint of iron contamination with manganese is a clever trick. The manganese imparts a magenta tint to glass. As the complementary color to green, it effectively "cancels out" the green tint. The trade-off is that the glass is slightly darkened, even if appearing as a neutral color to the eye. When light passes through glass tinted by iron, green light is unaffected, which is why it appears green. The other colors that make up white light, notably red and violet are dampened. In effect, the green is enhanced. Now, adding manganese to the glass dampens only green light and brings the spectrum back into closer balance. The overall effect is that all the colors of light are slightly dampened, but by the same amount. In Neri's case, minor contamination from iron would produce only a small green tinge and the problem was corrected with a small dose of manganese. The resulting grey would hardly be noticed, especially in the thin, delicate pieces so popular at the time. To the eye of all but the most experienced expert, this decolorized glass had perfect crystal clarity.

Decolorization of glass is an example of a technique that was developed through experimentation without a deep understanding of the physics involved. Theories of light and color and the way they are perceived by the human eye came much later. In fact, manganese itself was not isolated as a metal until 1774, yet it was used skillfully by glass artisans three or four hundred years earlier. 

This post first appeared here in a slightly shorter form as 'Manganese of Piedmont' on 14 October 2013.

Monday, July 25, 2016

Francesco and Bianca

19th century romantic depiction of
Bianca Cappello, Francesco de' Medici 
(with Don Antoni as a child.)
The story of 17th century glassmaker Antonio Neri weaves together closely with that of a Medici prince also named Antonio. The prince was six months younger, living quite a different life, yet holding many of the same interests. Don Antonio de' Medici was the eldest and only surviving son of the second grand duke of Tuscany. He became both Neri's employer and his benefactor. Don Antonio's own fascination with nature's secrets ran in his blood, a fascination that preceded him by at least four generations. His father Francesco and his grandfather Cosimo, both grand dukes of Tuscany, avidly pursued the vagaries of natural secrets. Cosimo had picked up the interest of alchemy from the notebooks of his own paternal grandmother, Caterina Sforza, as preserved by his father, Giovanni dalle Bande Nere. Don Antonio would carry on the family passion working in the laboratory built by his father on the north side of Florence, called the Casino di San Marco. Shortly after the prince settled in, priest Antonio Neri came to work in the Casino laboratory and there learned the craft of glass formulation. 

By the time Don Antonio dusted off the cobwebs at the Casino and restarted the laboratory there in his early twenties, he had already experienced more than his share of misfortune. At the age of eleven, his life was suddenly changed forever when he lost both parents. Among many other implications, it meant relinquishing his future as grand duke of Tuscany to his uncle Ferdinando. Cardinal Ferdinando de' Medici had been visiting his brother, Grand Duke Francesco and his wife Bianca when they both became violently ill and died within days of each other in the fall of 1587. It was no secret that the brothers had running quarrels on a variety of matters from the cardinal's allowance to the way Francesco was running Tuscany. It was also no secret that Cardinal Ferdinando strongly disapproved of his older brother's wife, Bianca Cappello. She had earlier been the duke's mistress; they married in secret shortly after Grand Duchess Giovanna died in pregnancy. 

As soon as Francesco and Bianca's deaths were made public, rumors began to fly that the cause was poison in their food and not pernicious malaria, as pronounced by Ferdinando's own two doctors, Cini and Da Barga. Related rumors claimed that Don Antonio was an illegitimate child, or adopted, or even the product of witchcraft, none of which hurt Ferdinando's case for succeeding his brother as grand duke. The narrative was that Ferdinando had made a ruthless power grab, assassinating his brother and sister-in-law; it was a narrative that spread and gained momentum over the years, fueled by careless researchers and Victorian era romanticism. In some nineteenth and twentieth century history books, it was reported as all but fact. The poisoning of Ferdinando and Bianca has been the subject of theatrical productions, novels, poetry, paintings and a musical composition. Admittedly, it does have all the elements of a great story: Marriage for love in the aristocracy, sex, murder, intrigue, politics and religion. Truth be told, given the Medici family’s actual history, the story is not all that far-fetched, but it turns out not to be true, at least as far as modern forensics technology can determine.

 Controversy erupted in 2007 when a team from the University of Florence reported that they had unearthed what they presumed to be the long-lost (but partial) remains of Grand Duchess Bianca. Testing revealed a significant level of arsenic, leading some to give assassination another look. Others pointed out that arsenic was commonly used as an embalming preservative in this period. Meanwhile, a team at the University of Pisa confirmed that there are malaria pathogens in what are not disputed to be Francesco's remains, interred at the Chapel of Princes in Florence. 

Ferdinando's two physicians, Giulio Cini and Giulio Angeli da Barga, who were on the scene in October of 1587, reported that symptoms were identical in both patients. Modern forensics pathologists agree that those symptoms are entirely consistent with pernicious malaria. Furthermore, it was recorded that a few days earlier, Francesco and Bianca had ventured into a swampy area on a walk near the estate where they met their end. In fact, Francesco had lost two younger brothers and his mother to malaria, and I can personally vouch that Tuscan mosquitoes are nasty little creatures. If not for an insect bite, Don Antonio might well have become the third grand duke. As it was, Ferdinando took the reigns of power and Antonio Neri's father was appointed to be the new grand duke's royal physician, with Cini and da Barga his assistants.

Friday, July 22, 2016

Don Giovanni in Flanders

Spanish attack on a Flemish village,
Attr:  Pieter Snayers. (click to enlarge)
In the winter of 1603-04, Glassmaker Antonio Neri embarked on what would become a seven-year-long visit to Antwerp, possibly the most productive period of his career. He was to stay with his Portuguese friend, Emmanuel Ximenes, one of the richest men in that city. But Neri was not the only Florentine courtier in Antwerp; Don Giovanni de' Medici, Florence's top military commander was already there, prosecuting a war. He was uncle and friend to Neri's sponsor Don Antonio, as well as an alchemist in his own right. There is no known record of a meeting, but it is not hard to imagine Giovanni as a dinner guest at the Ximenes household.


Neri had moved from the safety of the Tuscan hills into the very center of a bloody war for Dutch independence. The Dutch wanted freedom from Spain, which was allied with the Holy Roman Empire through a single ruling family: the Habsburgs. Within the previous thirty years, Antwerp had been burned and pillaged by Spanish soldiers that had gone unpaid by their employer. The carnage cemented a regional rebellion that would last for most of a century. The so-called "Low Countries" were divided by religious lines into the Protestant "North", and the Catholic "South". The northern territory, known as the Dutch Republic, had seceded from Hapsburg rule in 1581. As Neri started his journey in late 1603, the southern territory, Flanders, was caught in the middle between warring factions. The North had become a haven for protestant Calvinists and Lutherans who streamed in from surrounding countries. In the South, Catholic Antwerp was near the center of the conflict. The city was blocked from sea-trade by their Dutch neighbors. Armed confrontations with imperial Habsburg forces demolished surrounding towns; fighting threatened to spill into the city that Neri would call home for the better part of a decade.

The troops on both sides of this conflict were not monolithic armies, but patchworks of borrowed forces and paid mercenaries. On the imperial side, an early attempt to break the blockade had been under the command of Don Giovanni de' Medici on behalf of his half-brother, Tuscan Grand Duke Ferdinando. Florence owed its allegiance to the Habsburgs. Don Giovanni was anxious to secure Catholic Flanders for Spain and secure a military success for himself. However, in truth, the situation was more nuanced. The Medici were privately sympathetic to the Dutch cause. They were friendly with the French Bourbons as well as the English who were both secretly financing the Dutch resistance, neither of whom wanted to see a strong imperial presence in the Low Lands. Flemish Catholics themselves lost no love for their Spanish overlords, who had already destroyed Antwerp once. Furthermore, trade and commerce continued between the North and South even if sometimes rather covertly. In 1604, Don Giovanni was back to help prosecute the siege of Ostend, under Don Ambrogio Spinola. This was a conflict so bloody that it ultimately leveled that city and took the lives of thirty-five thousand men. Ostend was the last remaining stronghold of the Dutch on the North Sea coast between Sluys and Nieuport. It was only sixty miles (95km) west of Antwerp.

As bloody as it was, war in the seventeenth century followed the seasons. In the winter, Don Giovanni found time to submit a design for the Chapel of Princes in Florence. He also had Flemish marble cut for the project, and shipped back to Tuscany using, yes, Dutch traders in Amsterdam. During the lull in fighting, at the behest of Grand Duke Ferdinando he commissioned paintings of famous contemporary battle scenes by Flemish masters, which were also shipped back to Florence on Dutch ships. One set of seventeen pictures, fully paid for by the Ximenes family, was destined to hang in the new Medici villa 'La Ferdinanda' at Artemino in Prato. The interior decoration of the public spaces in this villa were being executed by artists Passignano and Poccetti, fresh from their recently completed collaborative masterpieces; the Neri Chapel and Cestello church on Borgo Pinti, financed by Antonio Neri's father. After some delay, the paintings finally shipped to the Tuscan port of Livorno, in April of 1604, just as Antonio Neri was settling into his new quarters on the most fashionable street in all of Antwerp; the Meir.

By June of 1605, fighting was on Antwerp’s doorstep, Don Giovanni de' Medici was dispatched to London. He saw the King (James I) several times, but the reception was somewhat less enthusiastic than he had hoped (at least according to reports sent home by the Venetian ambassador). Three weeks later Giovanni left for Paris with the promise of a British royal ship to bring him across from Dover to Calais. Finding no such escort, he commissioned a Dutch captain for the voyage.  

Don Giovanni's behavior, at first blush, seems quite odd; perhaps even treasonous. Commanding troops under the Spanish flag, he left the front lines at Antwerp. Using enemy (Dutch) transportation, he traveled first to the English and then the French royal court, both powers recently at war with Spain and both sympathetic to the Dutch. However, Giovanni was in constant contact with Grand Duke Ferdinando and undoubtedly acted on direct instructions. While technically subjects of the Spanish crown, the Tuscan duchy had close economic and strategic ties with all the countries involved and had every reason to pursue a diplomatic solution that would avoid another bloodbath in Antwerp. A few years earlier, Giovanni had successfully stalled the Spanish infantry from a potentially devastating invasion of France and had military experience in the Low Countries that spanned two decades. Historically, Giovanni's part in any diplomatic negotiations has not been established, but within two years, a temporary truce was reached that would eventually result in Dutch independence. In April of 1607, a temporary eight month ceasefire was negotiated, which was later extended to cover conflicts at sea. For all intents and purposes, the war was winding down.

Wednesday, July 20, 2016

An Art of Fire

Antonio Neri, MS Fergusin 67, 1598-1600,
ink and water color.
In L'Arte Vetraria, Antonio Neri describes glass as "a fruit of the art of fire." He apparently liked this evocative phrase enough that he borrowed the words from an earlier volume written in the first half of the sixteenth century by Vannoccio Biringuccio. Biringuccio's De la Pirotechnia was a sort of bible for metal workers, refiners and miners. The author was in charge of an iron mine near Siena and in the late 1520's he became something of a local hero for casting cannons to help Florence defend itself in the great siege.

Neri’s opening line reads:
“Without a doubt, glass is a true fruit of the art of fire, as it can so closely resemble all kinds of rocks and minerals, yet it is a compound, and made by art.”
And here is Biringuccio, half a century earlier in 1540:
“… it [glass] is one of the effects and real fruits of the art of fire, because every product found in the interior of the earth is either stone, metal, or one of the semi-minerals.  Glass is seen to resemble all of them, although in all respects it depends on art.”
In one sense, Neri is paying homage to his distinguished predecessor, but he is also lending a new meaning to Biringuccio's words. The mining expert's short chapter on glass is a survey and a great deal of it is spent on the debate of whether glass should be classified as a 'semi-mineral' because of its similarity to rocks and gems, or as a metal because of its molten properties in the furnace. Neri puts a different spin on the fruits of glassmaking. He is not as worried about classification as he is excited about the material's many uses. He composes a formidable list for us, one that ranges from drinking glasses, to optical lenses, to church windows, to laboratory equipment.

Neri uses Biringuccio's chapter as a format for his own introduction; they both cover much of the same ground, but with a telling difference in tone. Biringuccio is very much 'old school.' His main concerns are taxonomy of the material and the construction of the equipment. For him, the finished products of glassmaking are more ornamental curiosities. He trumpets that glass objects hold more beauty than their metal counterparts, but he warns that we should not give them too much love because they are fragile and therefore, like life itself, ephemeral. Neri, on the other hand, agrees that glass can be beautiful, but he is all about the chemistry and the innovative things that can be done with this versatile material.

The differences in emphasis between the two men nicely illustrate a shift that was taking place throughout society in general. For hundreds of years, the focus of scholars and craftsmen had been on rehabilitating ancient knowledge. Europeans very much saw themselves as recovering from the long slow decline of medieval times. To learn the secrets of a craft, one looked backward, not forward, and the farther back the better. Ancient texts were prized and coveted because they were seen to contain purer wisdom, uncorrupted by centuries in the dark. Both men discuss the ancient origins of glass, recounting that it is mentioned in the Bible and by scholars of the Roman Empire like Pliny. The difference is that Neri's gaze is turning; instead of looking back so much, his eyes are shifting to the present. Biringuccio's Pirotechnia and books like it created a platform from which Neri and his generation could then build on. 

There are many definitions possible for the beginning of modern science. One that is compelling from a broad, non-technical point of view is that modern science began when we spent less time looking backward for answers and more time learning from the world as it is.
This post first appeared here in a slightly different form on 7 October 2013.

Monday, July 18, 2016

Olearius on Glass

Adam Olearius
In the autumn of 1633, a trade mission heavily laden with gifts headed east from northern Germany. The great duke of Holstein was sending an ambassador to Moscow to request the czar’s permission for travel rights along the Volga  RiverHolstein was the northernmost tip of the Holy Roman Empire, in many ways more  closely tied to Scandinavia than to their Habsburg overlords. This expedition was part of an attempt to establish an inland silk-trade route between Europe and the Orient. Such a route would eliminate the circumnavigation of Africa, shortening the trip and reducing risk. After several years and initial high hopes, it became clear that the effort was doomed to failure. Czar Michael I of Russia was enthusiastic about the project, but at the southern end of the route, the king of Persia was not so receptive. Nevertheless, the expedition did become famous for a different reason: a written account of the adventures of the diplomats.

Upon the delegation’s return to Holstein, their secretary Adam Olearius (1599-1671) published a book that chronicled their travels. [1] As a mathematician, astronomer and general polymath, Olearius provides an uncommon perspective of the various cultures, practices and technologies encountered. Ultimately, he was appointed royal librarian and keeper of the duke’s cabinet of curiosities. The book proved so popular that more comprehensive editions soon followed, adding the contemporary accounts of another traveler, Johann Albrecht von Mandelslo. [2]

Glass is not the central theme of his adventures, yet this and related subjects are discussed in a number of different passages, giving us a unique insight into the material’s place in those societies.

In August of 1634, the group arrived in Moscow. Having been granted audience with the czar, Olearius describes the procession of the entourage and enumerates a long list of the gifts they brought. Among them was “a great looking-glass, being an ell and a quarter high and half an ell broad, in an ebony frame, with boughs and fruits carv'd thereon in silver, carried by two Muscovites.” [3] An ‘ell’ was the northern european equivalent of a cubit or about 25 inches, so the mirror measured about 12 inches wide by 30 inches tall, not enormous by current standards, but quite an achievement in the seventeenth century. Glass workers would have to blow a large cylindrical bubble, cut it open and lay it flat on a polished marble surface. To be usable, the sheet of glass would have to be made without waves or defects and it would have to be cooled slowly, over a period of many hours in order not to form cracks. Silvering the back was a whole other ordeal performed by an artisan schooled in alchemy.

Speaking of the chemical arts, gifts from the duke of Holstein to the czar of Russia also included “an ebony cabinet, garnish'd with gold, like a little apothecaries shop, with its boxes and vials of gold, enrich'd with precious stones, full of several excellent chymical extractions, carried by two Muscovites” [4]

While in Moscow, Olearius put on a demonstration of optics for some locals. “I shew’d them upon a wall of an obscure chamber, through a little hole I had made in the shutter of the window, by means of a piece of glass polish’d and cut for optics, all was done in the street, and men walking upon their heads: This wrought such an effect in them, that they could never after be otherwise persuaded than that I held a correspondence with the devil.” [5] Here he is describing a ‘camera obscura’ in which scenes from outside are projected upside-down onto the wall of a darkened room.

A couple of years later, after a return to Holstein to ratify a treaty with the czar, the delegation arrived in Persia. They were treated to a sumptuous meal by the king’s chancellor. “The walls were all set about with looking-glasses, to the number of above two hundred, of all sizes. So that when a man stood in the midst of the hall, he might see himself of all sides. We were told that in the king’s palace, in the apartment of his wives, there is also a hall done all about with looking-glasses, but far greater and much fairer than this.” [6]

“For the teaching of astronomy they have neither sphere nor globe, insomuch that they were not little astonished to see in my hands a thing which is so common in Europe. I asked them whether they had ever seen any such before. They told me they had not, but said that there was heretofore in Persia a very fair globe which they call ‘felek’, but that it was lost during the wars between them and the Turks. They haply meant that which Sapor, king of Persia, had caused to be made of glass, so large, that he could sit in the center of it, and observe the motions of the stars and must no doubt be like that of Archimedes, where of Claudian speaks in the Epigram which begins thus: Jupiter in parvo cum cerneret aehera vitro.” [7]

Olearius goes on to describe the Persian army in some detail, including this account of an early form of chemical warfare. “At the siege of Iran, in the year 1633, they had the invention of casting into the place with their arrows, small glasses full of poison, which so infected the air that the garrison was extremely incommodated thereby and made incapable of handling their arms for the defense of the place.” [8]

In 1637, near Tehran, Iran, he describes a royal tomb “adorn’d all about with glass of all sorts of colors, which are preserved by iron grates.” [9] And in the same area,

“At Kimas, in the province of Kilan, there was one of these mountebanks, who having found out the trick of setting cotton on fire by means of a crystal cut in half-round and held in the sun like a burning-glass, would have people persuaded that by operation, which he affirmed to be supernatural, that he was of the kindred of Mohammed. After our return to Holstein, I shew’d the Persians, whom Schach-Sefi [king of Persia] sent thither, that it was the easiest thing in the world to get fire from the sun, and I lighted paper in the very depth of winter by means of a crystal full of cold water, or a piece of ice, which I had made half round in a pewter dish. They were astonish’d at it, and said, that if I had done as much in Persia, I should have pass’d there for either a great saint, or a sorcerer.” [10]

As an addendum, in later editions of Olearius’ book, the recollections of Johan Albrecht de Mandelslo (1616–1644) were added. He accompanied an unrelated trade mission to Isfahan,Persia, and then split from his group to continue touring the region. He traveled through India, and then down the African coast. In 1639, the German traveler passed through Madagascar. He commented on the inferior quality of European glass trade-beads, compared to those of India, which he acquired earlier in the trip.

“The glass-bracelets, beads and agates, we had brought from the Indies [India] were incomparably beyond what they were laden with out of Europe; so that it was resolved ours should not be produced, till the others were sold. By this means, we bought every day four oxen for forty pair of glass bracelets, which the inhabitants call ‘rangus’; a sheep for two, and a calf for three ‘rangus’; and for a brass ring, ten or twelve inches about, a man might have an ox worth here six or seven pound.” [11]

Much has been made of the use of glass trade-beads by Europeans around the world.
In Madagascar and along the trade routes of the Indian Ocean, European traders were fairly late to the party. For a thousand years earlier, [12] beads had been used as the currency of choice among disparate cultures from Indonesia and China to India to Africa who did business with each other.[13] The above quote from Mandelslo’s diary provides a fascinating firsthand account of transactions with beads. The passage also hints at the superior quality of Indian glass beads. Today, glass beadmaking continues on an industrial scale there, and the glass bracelet industry still survives, notably in Firozabad, northern India.

[1] Adam Olearius: Beschreibung der muscowitischen und persischen Reise, (Schleswig: 1647).
[2] Adam Olearius, John Davies, Johann Albrecht von Mandelslo, Philipp Crusius, Otto Brüggemann: The Voyages and Travells of the Ambassadors Sent by Frederick Duke of Holstein, to the Great Duke of Muscovy, and the King of Persia... (London: John Starkey, and Thomas Basset, 1669).
[3] Ibid, p. 11.
[4] Ibid.
[5] Ibid, p. 58.
[6] Ibid, p. 212-213.
[7] Ibid, p.252. Jupiter in parvo quum cerneret æthera vitro [When Jove a heav’n of small glass did behold,] see Henry Vaughan: Silex scintillan, Hermetical physick, Thalia redivava, Translations, Pious thoughts and ejaculations. (Oxford: Clarendon Press, 1914) v. 2, p.635.
[8] Ibid, p. 271.
[9] Ibid, p 182.
[10] Ibid, p. 280-281.
[11] Ibid, p.204.
[12] For example warring states beads in China, see https://en.wikipedia.org/wiki/Ancient_Chinese_glass
[13] Carla Klehm has a nice post on the subject of trade beads used around the Indian Ocean; see “Trade Tales and Tiny Trails: Glass Beads in the Kalahari Desert” in The Appendix, Jan. 2014, v. 2, n. 1. http://theappendix.net/issues/2014/1/trade-tales-and-tiny-trails-glass-beads-in-the-kalahari-desert

Friday, July 15, 2016

The Neighbors

"Portrait of Giamologna"by Hendrick Goltzius
In Florence, directly across the street from the Palazzo Neri, where glassmaker Antonio Neri spent his youth (now the Marzichi-Lenzi), was the residence and workshop of famed sculptor Giambologna. This two-building compound was a 'gift' to the artist from the newly crowned Grand Duke Ferdinando de' Medici, in 1587. It was intended to settle debts incurred for the artist's work by the previous grand duke, Francesco. The dwelling, at 26 Borgo Pinti, was located on the same street that was formerly inhabited by the likes of Michelangelo, Perugino, Pontormo and Cellini.

Neri's father, the royal physician, had collected art. According to historian Giovanni Cinelli, in 1677, when Antonio Neri's nephew owned the property, among the pieces in the house were:

Two small bronze horses by Giambologna, many works of [Simone] Pignoni and others, among which are two marvelous holdings; a waist-up Ecce Homo by Titian and a Satyr of beautiful ancient bronze which is wonderfully captivating; it is of the Greek manner and expresses an attitude of prompt movement that recalls liveliness, the muscles are very well prepared. Finally, a statue of Cupid flanked in marble in the best Greek style.
Giambologna had a strong influence on Florentine art and his work was to be found throughout the city, from the courtyard of the Palazzo Vecchio, to the gardens of the Casino di San Marco, where Neri made glass. The sculptor was well known for the fine surface finishes he achieved on marble and for his ability to resolve the technical challenges of portraying multiple figures, especially those involving a complex intertwining of limbs and bodies. The Rape of the Sabine Women, completed when Neri was a boy, is considered his crowning achievement.

Giambologna was born in Douai, Flanders, now in France, as Jean Boulogne. He landed in Florence in 1553, after a period working in Rome for Pope Pius IV among others. The Medici never allowed him to leave Tuscany for fear that once out of their reach, he would be enticed to go to work for another of the European sovereigns, never to return. It is reasonable to speculate that before his own trip to Flanders in 1604, Antonio Neri offered to relay messages or other effects to the family of his seventy-five year old former neighbor. Neri spent seven years with his friend Emmanuel Ximenes in Antwerp. Before his return to Tuscany, in 1611, both Grand Duke Ferdinando and Giambologna had already gone to meet their maker.


Neri had left Florence in his twenties, and returned in his thirties to a very different city. He settled down to write the book for which he will forever be remembered, L'Arte Vetraria, the first printed book devoted to the formulation of glass.

This post first appeared here on 20 Sept. 2013.

Wednesday, July 13, 2016

Turquoise Glass

Turquoise glass stamp
of calif Mustadi  c.1170.
It is estimated that turquoise is among the earliest gems ever mined. With colors that vary from pastel green to a bright sky blue, it has adorned Egyptian sarcophaguses of 5000 years ago, 3000-year-old Chinese art, Aztec death masks and the domes of Persian palaces. 

When traders brought it to Europe from the Mideast, it became known as "turks" or "turquoise" after the old French for "Turkish." While it has never been mined in Turkey, the most highly valued Persian stones were imported there and used extensively for trade. Polished pieces were famously mounted on Turkish equestrian saddles, in the belief that the material conferred sure-footedness and protection from injury during a fall.

As one of the first gems to be collected and traded, turquoise was also one of the first to be imitated. Egyptian faience blue is an early forerunner of glass. It is more porous than glass, but it contains all the same ingredients and could be cast into forms that look just like solid turquoise. In the seventeenth century, the genuine mineral and its imitation continued to hold importance. In Antonio Neri's book L'Arte Vetraria, the subject is mentioned several times; he offers one recipe to restore faded stones by soaking them in almond oil. For turquoise colored enamels he presents two different shades. On the subject of glass, he notes that "Sky Blue, or more properly turquoise, is a principal color in the art of glassmaking" and "I have made this color often, because it is very necessary in beadmaking and is the most esteemed and prized color in the art."

To make his imitation turquoise glass, Neri starts with a batch of high quality transparent aquamarine blue, to which he adds a specially prepared variety of common salt. "Add it little by little, until the aquamarine color loses its transparency and diaphany becoming opaque."

Take the sea salt known as black salt or rather coarse salt, since the ordinary white salt that they make in Volterra would not be good. Put this salt in a frit kiln or oven to calcine, in order to release all moisture and turn white. Next, grind it well into a fine white powder. This salt now calcined should be stored for the use of making sky blue or rather turquoise color as described below.

Sea salt is mostly composed of sodium chloride, which is like table salt that we use for food. However, it can include significant additional minerals, as implied by Neri’s description of it as "black salt." Additional elements can include sulfur, potassium, manganese and more. Regrettably, he leaves us with no further clues to its identity, nor does he explain why the recipe would not work as well with the salt available from Volterra. He goes on to advise that the mix should be used quickly, because if left to sit in the furnace, the glass would start to revert to an ugly transparent color. The remedy for this is to add more salt. He finishes with some practical advice for glassmakers about adding salt to molten glass:

The furnace conciatore should take careful note here, when you add this salt, if it is not well calcined it always bursts. Therefore, you should be cautious and shield your eyes and vision, because there is a danger you could be hurt. Add the doses of salt little by little putting in a bit at a time pausing from one time to the next until you see the desired color. With this, I do not rely on either dose or weight, but only on my eyes. When I see that the glass reaches the desired level of color, I stop adding salt. This all comes with experience. 

* This post first appeared her in a slightly shorter form on 9 April, 2014.

Monday, July 11, 2016

Glass Headhunters

Berkshire Glass Works cane from 1878 – Charles Flint collection
These were novelty items made my glassworkers after hours.
(hollow, filled with the fine quality sand of the area)
Since early days, the technical aspects of making and manipulating hot glass have remained a closed and secretive business. Down through the ages, those with inside knowledge of this art have been highly valued and highly sought after. Even with the circulation of technical manuscripts and the ultimate publication of the technology in Antonio Neri’s 1612 book L’Arte Vetraria. The beating heart of the craft remained at the furnace among those with hands-on experience. [1] These artisans could and often did make the difference between success and failure in a business that was notorious for sending substantial fortunes up in smoke.  


In some places, strict laws forbade glass workers from leaving their employ and forbade outsiders from attempts to lure them away. Recruiting seasoned talent could be a delicate if not clandestine undertaking. This was as true in the ancient world as it was through the Renaissance and it also played a significant role in the 18th and 19th century for the nascent American glass industry.

Many have, heard of the legendary prohibition forbidding Renaissance Venetian glass workers from travel abroad. The fear was that they might divulge secrets of their craft to outsiders, thereby compromising the virtual monopoly on high quality luxury glassware made on the fabled island of Murano. Many also have heard that the penalty for violating these rules was death at the public gallows located between the columns at Saint Mark's square.  While there were laws on the books that listed possible penalties as severe as death, the records show that no glass worker was ever executed for leaving and many did leave. In fact, glass workers were sometimes part of state brokered deals to exchange technology.

These Venetian laws have also led many to the incorrect conclusion that the glassmakers were held captive and treated like prisoners. Nothing could be farther from the truth; glass workers were treated like rock-stars of their time. The daughters of glassmakers were allowed to marry into the nobility, a privilege granted to no other guild. [2]

Early American efforts to recruit experienced glass workers provide some amusing stories. In 1894, William G. Harding, a principal in the Berkshire Glass Works in Massachusetts wrote a detailed history of glassmaking in the region.  Harding’s research was meticulous, drawn from factory records, official legal filings and personal correspondence. Two stories in particular relate the great lengths pursued in recruiting experienced European glass workers to New England.


The first concerns Robert Hews, who despite repeated failures in starting a glassworks in the late 1700s, finally partnered in Boston with one Charles F. Kupfer newly arrived from the Duchy of Brunswick in Germany. Together they formed Boston Crown Works on Essex street.  Kupfer immediately returned to Germany to recruit workers, as harding records,
“Mr. Kupfer upon his arrival at his old home, found it no easy matter to get his blowers. The works belonged to the Duke of Brunswick, and it was a penal offense either for the men to leave, or for him to entice them away. He was obliged to conceal his designs and operate in the dark, but succeeded in escaping in the night with a set of workmen and sailed from a German port before being overtaken. After a long voyage they landed in Boston and met with a Royal reception. So much interest in the new enterprise had been awakened in the citizens of Boston, that they turned out en masse…” [3]


The other story of clandestine recruiting related by Harding concerns a venture started in Sand Lake, about 10 miles east of Albany, New York around 1806.
“They had to import their skilled workmen. Mr. William Richmond, a Scotchman, was the Superintendent of their works. He went abroad to procure workmen. Disguised as a mendicant [monk/priest], with a patch upon one eye and playing upon a bag-pipe, he wandered through the glass district of Dumbarton in Scotland and engaged his blowers to cross the Sea. With great difficulty they secreted their tools on Ship-board, for it was a penal offense for glass-workers to leave Scotland as well as Germany.” [4]


[1] Antonio Neri, L’Arte vetraria, distinta in libri sette, del R.[everendo] P.[rete/ padre] Antonio Neri fiorentino. Ne quali si scoprono, effetti maravigliosi, & insegnano segreti bellissimi, del vetro nel fuoco & altre cose curiose. All’Illvst.mo et eccell.mo Sig., Il Sig, Don Antonio Medici (Florence: Giunti 1612).
[2] A daugher of a glassmaker could marry into the nobility, which was a great honour for a family, but strategically, the son of a glassmaker had no such privilege, meaning that there were no inheritance rights for the family.
[3] Collections of the Berkshire Historical and Scientific Society, (Pittsfield: Sun Printing, 1894),  p. 37-39
[4] op cit. p. 39-40.

Friday, July 8, 2016

San Giusto alle Mura

Window of  Santa Maria del Fiore cathedral,
Florence, Italy.
In Florence, at the very end of the street on which Antonio Neri spent his youth, Borgo Pinti, was the residence and estate of the Archbishop. Beyond were the city walls and the enormous wooden doors of the Porta Pinti gate (115 foot, or 35 meters tall). Just on the other side of the gate, which in Neri’s time was normally closed and guarded, once stood the San Giusto alle Mura monastery, built in the thirteenth century. Despite the similar name, there is no connection between the Ingesuati monks of San Giusto and the modern order known as the Jesuits, which was not formed until 1534 and recognized by the Church in 1540.

The monks at San Giusto were famous for the stained glass windows they made; hence one of numerous theories that the street name 'Pinti' may be a contraction of 'dipinti 'or 'dipintori' (paintings or painters). Using their own glass furnaces, the Ingesuati monks provided windows for the Neri family's church Cestello and for Santa Maria del Fiore among other churches. They also ran an art school and were famous for making the color pigments used by painters, producing a coveted ultramarine blue. Their customers included the likes of Leonardo, Michelangelo, Botticelli, Del Sarto, Ghirlandaio and Filippo Lippi. 

Apparently, the Ingesuati's artistic devotion was not matched by their religious observance. In his Lives of the Artists, Giorgio Vasari recalls the less than complimentary sentiments of the monk's own in-house chaplain, a certain Servite monk named Fra Martino. He notes that the monks do not read Mass, and that they, "do nothing but say paternosters ['our Father...'], make glass windows, distill herbs for sweet waters, dig their gardens, and perform other works of similar kind, but do not study or cultivate letters."

Antonio Neri has a slightly more positive opinion about the value of stained glass windows. In the introduction to L'Arte Vetraria, he waxes poetic: 
Glass is also a great ornament to God's churches since, among other things, many beautiful windows are made, adorned with graceful paintings, in which the metallic colors are so intense and vivid that they seem like so many oriental gems. 
The windows that inspired these lines may well have been made by monks of San Giusto. As a child, Antonio Neri had seen the striking windows in Cestello and in the city cathedral. It would be nice to be able to connect him to the Ingesuati, but in 1529, long before his birth, their entire complex just outside the Pinti Gate was dismantled in defensive preparation for the siege of Florence. The Florentine military cleared away the structures near the outside of the city walls. The monks of San Giusto alle Mura moved to the much smaller Calza Convent on the oltrarno, on the opposite side of town near the Porta Romana gate. They did not rebuild the glassworks at the new location and it is doubtful that any of the glass workers would have still been alive by the time Antonio Neri came of age.

This post first appeared here in a slightly shorter form as "Glass Monks" on 30 September 2013.

Wednesday, July 6, 2016

Montpellier

Montpellier, France, in the seventeenth century.
(Attribution unknown)
Montpellier is an old city in southern France. It stands about halfway between Marseille and the Spanish border along the Mediterranean Sea (strategically located slightly inland to avoid pirates). First documented in the tenth century, it is one of very few French cities that developed without the influence of ancient Roman occupation; it is a pure product of the local region. It became a center of intellectual learning and attracted students from throughout Europe. Around it sprung a number of supporting arts not the least of which was glassmaking. Once famous for its fine glassware, today this centuries long heritage is all but forgotten, yet when we dig into the literature, we find a surprise connection to one of the oldest legends in the history of glass.

Since before the Renaissance, Montpellier was an established center for medical and legal education, a strong tradition that continues at the university there; today, it houses the oldest running medical school in the world. This prestigious institution "was founded perhaps by people trained in the Spanish medical schools; it is certain that, as early as 1137, there were excellent physicians at Montpellier University." [1] In 1529, Nostradamus entered to study for a doctorate in medicine, but shortly thereafter, he was expelled when it was discovered that he previously worked as an apothecary; a 'manual' skill that was banned by the school's rules of conduct.

Paradoxically, these impugned 'manual' arts account for some the region's more intriguing activity. Along with medicine, the area became known for the production of paint pigments, for glassmaking and finally for alchemy. All of these turn out to be closely related to each other, but perhaps not obviously so. Throughout the Renaissance, apothecaries were responsible for a wide range of distillations and extracts used by physicians to treat disease. They were also the de facto suppliers of pigments and other fine art supplies and even sourced some of the materials for glassmaking. Glassmakers often relied on painters to embellish their products, painters used ground glass in their pigments and apothecaries needed glassmakers to produce the flasks, beakers and other alchemical equipment required for their profession.

An anonymous Montpellier manuscript of the fourteenth century, called the Liber diversarum arcium [Book of Various Arts], offers us one of the most complete guides to the production of pigments to have survived from that period. [2] Another, later writing of the sixteenth century offers an extensive collection of glassmaking recipies brought to Montpellier from Venice. This one is titled Recette per fare vetri colorati et smalti d’ogni sorte havute in Murano 1536 [Recipes to make colored glasses and enamels of every kind as in Murano, 1536]. [3]

Local history points to the town of Claret just north of Montpellier as the seat of regional glassmaking. Beginning in 1290, the oak forests on the Causse de l'Orthus attracted glassmakers and their families. "So maybe the oaks got used for fuel. (A 'causse' is a geological term for a limestone plateau.) [also a material of glassmaking] At any rate, the glassmakers were ennobled by the King and formed a guild of premium glassmakers whose wares were sold all over Europe from the market at Sommières." [4]

In the early seventeenth century, Pierre-Jean Fabre (1588-1658) studied medicine at Montpellier where he discovered the works of Paracelsus, to which he became a devotee. [5] After securing a medical degree, he returned to the nearby town of his birth, Castelnaudary, to work as a doctor. Eventually, he was awarded the status of "Royal Physician" by Louis XIII, probably for his work on treating victims of the plague with chemical preparations. [6]

Fabre's first book, of a total canon numbering sixteen volumes, was on the subject of alchemy and medicine titled "Palladium spagyricum" 1624. [7] The book, written in Latin, contains advice on the transmutation of metals, turning water into "good wine" and elixirs to cure all disease. It contains one recipe that is of particular interest on the subject of glassmaking; a malleable form of glass, known in legend since the Roman Empire as Vitrum Flexile.

See my previous post to take a closer look at Fabre's specific recipe for a glass that is malleable at room temperature and trace a bit of the legend's history.

[1] Wikipedia, “University of Montpellier” https://en.wikipedia.org/wiki/University_of_Montpellier.
[2] Mark Clarke: Mediaeval Painters' Materials and Techniques: The Montpellier Liber diversarum arcium (London: Archetype Publications, 2011).
[3] Montpellier 1536, MS. H. 486: Recette per fare vetri colorati et smalti d’ogni sorte havute in Murano 1536, Bibliothèque de l'Ecole de Médecine de Montpellier, see also Zecchin 1987, v.1 p 247-276. Although the manuscript is dated 1536 it is probably copied from much earlier Venetian sources.
 [4] Ed Ward, Blog: City on a Hill, 1 Nov. 2010 post “Where the Glass-Blowers Were.” http://wardinfrance.blogspot.com/2010/11/where-glass-blowers-were.html . Also see Halle du Verre regional glass museum website http://www.cc-grandpicsaintloup.fr/-Halle-du-verre-.html .
[5] Paracelsus (1493-1541) was a Swiss born physician and alchemist who looked to nature rather than ancient texts for remedies to disease. He was widely condemned durring his lifetime but became very popular after his manuscripts were printed in the late sixteenth century.
[6] The definitive reference on Fabre is Bernard Joly: La rationalité de l'alchimie au XVIIe siècle (France: Vrin, 1992), pp. 35-50. A good English treatment can be found in Allen George Debus: The French Paracelsians: The Chemical Challenge to Medical and Scientific Tradition in Early Modern France (Cambridge: Cambridge University Press, 2002) pp, 75, 76.
[7] Pierre-Jean Fabre: Palladium spagyricum Petri Ioannis Fabri doctoris medici Monspeliensis ... (Toulouse: Bosc, 1624), p. 276. Later translated into several English editions, notably by William Salmon: Polygraphice: Or the Arts of Drawing, Engraving, Etching, Limming, Painting … (London: T. Passenger & T. Sawbridge, 1685), pp. 598, 599.