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 31, 2020

The Duke's Mouthwash

Ferdinando de’ Medici (1549-1609),
Scipione Pulzone (1544 - 1598), Private collection.
Antonio Neri's father, Neri Neri, was royal physician to the family of Grand Duke Ferdinando de' Medici. As such, he regularly interacted with other members of court, ranging from the archbishop of Florence, to his colleagues in medicine, including the royal apothecary (speziale), Stefano Rosselli. Rosselli shared more than a professional relationship with Neri Neri. They both admired the work of an ancient Greek physician named Dioscorides; Rosselli was something of an authority on his methods. In addition, he ran the 'Speziale al Giglio' shop, once owned by Tommaso del Giglio, who's chapel Neri Neri took over at Cestello church. Rosselli's son, Francesco, and Neri Neri were among the four chosen to revise and update the famed 

On 21 September 1589, Rosselli started to compile his own book of recipes to pass down to his two sons, Francesco and Vincenzo, who would go on to continue the pharmacy.[2] The book begins with a poison remedy credited to none other than Cosimo de' Medici. Recipe no. 9 is the grand duke’s antispasmodic oil, presented by Niccolò Sisti, with whom Antonio Neri would later work at the glass house in Pisa. No. 20 is the duke's oil for deafness, also presented by Sisti. No. 41 is a poison antidote revealed to Francesco de' Medici by the Archduke of Austria. It was tested on a prisoner at the Bargello prison, a "volunteer" who was intentionally poisoned as part of the experiment, then revived with the antidote in the presence of Stefano Rosselli and Baccio Baldini, the long time physician to Cosimo I. Supposedly, the prisoner's reward for surviving was early release.

Recipe No. 30 carries perhaps a bit less risk; it is titled "Acqua da gengie di messer Nerj Nerj" (Mouth wash of Neri Neri):
Take a quarter of a bushel of mastic buds,a quarter of a bushel of myrtle buds, a quarter of a bushel of red roses, three ounces of alum, a half ounce of salt and a quarter ounce of hard rose honey. Mash the herbs with a mortar and pestle and put them in nine pounds of Greek wine for twenty-four hours, then boil in a bain-marie and reduce to two-thirds. In this, we bathe the gums: it makes them dry and firm.
Rose Honey
Greek Wine

The date that Stefano Rosselli started his book of secrets is interesting because it is the same day that Neri Neri, with the grand duke's two other physicians, Cini and Da Barga, were busy making medicinal wine based on Dioscorides' ancient recipes. Perhaps they all met that day at Rosselli's shop, for his advice. 

[1] Neri, Benadù, Rosselli, Galletti 1597.
[2] Rosselli 1996; an Italian transcription and French translation of Rosselli's recipes, with a very entertaining introduction.

* This post first appeared here on 4 November 2013 in a shorter form.

Wednesday, July 29, 2020

Rosichiero Glass

Sunset over Venice
(click image to enlarge)
The most famous glass recipe in Antonio Neri’s 1612 book, L'Arte Vetraria, is “#129 Transparent Red.” The reason for its notoriety is, of course, the pure gold used as a pigment. Gold-ruby, or “rubino” is a devilishly difficult color to produce in glass and was not reliably duplicated until many years after Neri’s death, although pieces made in ancient times have been unearthed.  

Even though gold rubino is Neri's most well known recipe and certainly his most famous red glass, this recipe does not exist in isolation. In fact, it fits in the middle of a group of eleven recipes (120–130) devoted to transparent, or at least translucent red glass, enamel and related preparations. 

120 Transparent Red in Glass.
121 Red Like Blood.
122 Balas Color.
123 To extract the Spirit of Saturn, Which Serves Many Uses in Enamels and Glasses.
124 Rosichiero to Enamel Gold.
125 Rosichiero for Gold by Another Method.
126 How to Fix Sulfur for the Above Described Work.
127 A Glass as Red as Blood, Which Can Serve as Rosichiero.
128 A Proven Way to Make Rosichiero.
129 Transparent Red.
130 The Way to Fix Sulfur for Rosichiero to Enamel Gold.

A particular shade that was popular at the time was known in Italian as "rosichiero." Our glassmaker presents four different recipes and two more on “fixing” sulfur, which some of the preparations require. Most dictionaries cite Neri as the first to use of the word 'rosichiero' in print, but we know it was a common term of art among glassmakers much earlier. The French equivalent is "rouge clair." The Spanish edition of L'Arte Vetraria notes that in that language the term is “rosicler,” which is still used today to describe the intense rosy twilight color of a nice sunset.

The red glasses of this group all call for the addition of copper as a colorant and copper has remained a popular pigment up to the present. For instance, red traffic lights that are made of glass are typically tinted with copper. But that is not the entire story; some of Neri's rosichieros also include the addition of sulfur and some require hematite or iron oxide, red lead oxide, manganese oxide, or wine tartar. In his recipe #125 for rosichiero, he starts with four pounds of high quality cristallo glass. To this adds equal parts of tin and lead oxides, mixed together: 
[A]dd this calx little by little, ½ oz at a time, let it incorporate, and watch for when the glass becomes an ash gray color, at which point it will be good. Do not add too much calx because if you overload it, the glass will become white in color, which is not good.When it turns the said gray color, do not add more calx but leave it to clarify. Then have 2 oz fine minium [red lead oxide], add this to the glass, and let it incorporate well, and clarify. When it clarifies well, throw into water, return it to the crucible and leave it for 8 hours [in the furnace]. 

Have ½ oz of calcined copper, that is to say red copper and ½ oz of raw white [wine] tartar. Throw these materials in, and stir them well. Now add a dram of hematite, which the sword makers use for burnishing, and 1 dram of fixed sulfur. Stir and incorporate these powders, and watch. If it is over-colored, give it a little manganese to dilute it. If it is clear of color, add more of the fixed sulfur, hematite, a little red copper and a little white wine tartar at your discretion so it becomes the desired color.
Many of these ingredients are no longer common in color glass production today; in fact, free sulfur is usually considered an undesirable contaminant. Hematite is a naturally occurring mineral form of iron oxide. It is so named because if abraded in water it tints the water red, appearing to bleed. Hematite is not currently used as a red pigment in glass because of its temperature sensitivity, but it is used in some pottery glazes. 

From a chemistry standpoint, a good guess is that sulfur added to the glass would react with the copper and iron to produce various sulfide compounds. How those compounds affect the color and texture of the glass is an open question. Here is where we get into uncharted territory; four hundred years after Neri’s book was first published, predicting colors based on specific chemistry is not as easy for us as it might seem. The science of color in general remains a difficult nut to crack. However, the fact that there is still much that we do not understand does not prevent us from enjoying the brilliant reds inspired by a good sunset.

* For the technically minded, the University of Oslo has a wonderful presentation on the state of color physics. For the non-technical, take a look – a series of fascinating images that spans the sense of sight and beyond. There is a link address in the "picture credits" for this post.

** This post first appeared here on 24 April 2014.

Monday, July 27, 2020

Arminia Vivarini

Nef Ewer, Late 16th century, Murano Italy.
Courtesy Milwaukee Art Museum
On the afternoon of Friday, 22 March 1521, The Venetian Senate - then called the ‘Pregadi’ - reconvened after lunch. Senator Marino Sanuto (the Younger) recorded in his now famous diary that among the afternoon business was the granting of a ten year exclusive license to Arminia, the daughter of painter ‘Alvise da Muran’ (Luigi Vivarini). She was granted this privilege to produce the ornamental glass galley ships she had recently devised. [1,2] Once called 'Navicella' (little ships) these ewers, probably most used to serve wine, are now known as ‘nefs’. A pour spout was situated at the ship's bow, and often a handle astern. These objects soon became iconic symbols of the island-nation’s long dominance in trade, and regularly appeared on sideboards and elaborate dinner table settings, not only in the lagoon, but in Florence, Rome and far beyond.

In their Objects of Virtue: Art in Renaissance Italy, Syson and Thornton write,
“It was not only the use of coloured canes in complex patterns embedded into clear glass that typified Venetian glass from the 1520s, but also the manipulation of cristallo into ever more fantastic forms. Novelties were first displayed at the Ascension Day Fair, which, like visits to the glasshouses in Murano itself, was firmly on the tourist map by about 1500. The Venetian diarist Marino Sanuto mentions the work displayed at three booths at the fair in 1525, those of Barovier, Serena and Ballarin workshops ‘among other things, a galley and a very beautiful ship were to be seen.’”
Syson and Thornton continue, “Leandro Alberti singled out just this kind of glass in his famous description of the marvels of Murano in his Description of All Italy of 1550: ‘I saw there (among other things made of glass) a scaled-down model of a galley, one braccia long and with all its rigging and equipment, so perfectly in scale that it seemed impossible to model such things accurately in such a medium.” [3]

Scholar and science investigator, Georgius Agricola, described a vessel in the form of a ship in his De re metallica published in Basel in 1556,
“The glass-makers make diverse things, such as goblets, cups [...] and ships, all of which excellent and wonderful works I have seen when I spent two whole years in Venice some time ago. Especially at the time of the Feast of the Ascension they were on sale at M[u]rano, where are located the most celebrated glass-works. These I saw on other occasions, and when, for a certain reason, I visited Andrea Naugerio in his house which he had there, and conversed with him and Francisco Asulano.” [4]

Arminia Vivarini’s father was a painter of some renown, but her family is also among the earliest recorded glassmakers on Murano. Her third-great grandfather, named Vivarino, arrived from Padua, just ahead of the plague in 1346. [5] The family seems to have been involved in the craft on the island from then on. She clearly had access to a furnace, perhaps one owned by an uncle or a cousin. In any event, she exemplified the qualities of the very best glass artisans throughout history: a clear design sense coupled with technical expertise and the opportunity to put them both into practice.

Her very existence also forces us to more closely examine the well worn narrative that hot-shops were exclusively male domains, from which women were strictly excluded. In such a highly competitive arena, it is perfectly reasonable that a family would promote its best talent, regardless of gender. In many ways, we owe homage to Vivarini for her success with this style of novelty glass object; it started the genre that continues in popularity today, five centuries later, with works of art prized by collectors and in museums around the world. [6]

[1] Arminia  (Armenia, Ermonia) Vivarini (1490-1569). See Luigi Zecchin: Vetro e Vetrai di Murano, 3 vols. (Venezia: Arsenale, 1987-9) v.3, p. 194.
[2] Marino Sanudo: I diarii di Marino Sanuto (1466-1536)  v.30. Eds., F. Stefani, G. Berchet, N. Barozzi (Venezia: Fratelli Visentini, 1891) col. 45. Also see Zecchin 1987-9, v.2, p.276.
[3] Luke Syson, Dora Thornton: Objects of Virtue: Art in Renaissance Italy (Los Angeles: J. Paul Getty Museum, 2001), p. 197.
[4]  Georgius Agricola (Georg Bauer): De Re Metallica: Tr. from the 1st Latin Ed. of 1556… trns: Herbert Hoover, Lou Henry Hoover. (Princeton: Mining Magazine, 1912), p. 592 (Book XII.)
[5] op. Cit. Zecchin 1987-9, v.3, p194-5.
[6] Thanks to Sophie Small‏ @sophieesmall for inspiring the subject of this post.

Friday, July 24, 2020

Reticello Glass

Reticello by Aaron Tate (detail),
Photo by David Lindes.
In fine art of the early twentieth century, ‘cubist’ painters and sculptors caused a sensation by pioneering a style that was fluid and emotional yet rigorously geometric. Earlier still, eighteenth century Baroque musicians thrilled audiences with ‘counterpoint’; music that was melodic and harmonious yet structured with an almost mathematical precision. The recurrence of similar themes in widely differing arts is perhaps not so surprising. When successful, these are themes that resonate deeply within us; they amplify what is common to our nature and remind us that we are in the world together. 

In sixteenth century Venice, a form of glasswork emerged that anticipated these juxtapositions to similar popular acclaim. In fact, the technique of ‘reticello’ went on to become an enduring trademark of Murano technical skill and artistry. To this day, well executed pieces of reticello glass are coveted by collectors and displayed with great pride. 

The form is characterized by a transparent glass base which is embedded with a network of crisscrossing threads of opaque glass, forming a lattice of diamond shaped pockets. Classically, white 'latimo' glass was used in a clear 'cristallo' base.The overall effect is reminiscent of fine lace or of fishing net, both of which are strongly evocative in Venetian culture. When executed in the classical technique of the island’s glassblowers, each diamond in the pattern contains a single bubble of trapped air, perfectly centered and uniformly sized. 

In general, the latticework theme in art traces to much earlier times. It is common in Hellenistic and Islamic art. To an extent it is a natural consequence of mosaic making. However the application of the pattern in glassblowing requires a completely different approach and a complex series of steps. First a ‘filigrana’ bubble is formed. To accomplish this, a series of pencil thin glass rods called ‘canes’ are laid side by side, touching each-other, in a pan ('piera' in Venetian, 'pietra'=stone in Italian) and partially fused together in the furnace.[1] Each cane is made of transparent glass with a core of opaque glass (a thread) running its entire length. Glass artist Emilio Santini writes:
On Murano, the "piera" is coated with a thin layer of clay from the laguna marshes. This is rich in salt and does not stick too much on the glass even if overheated. Then they preheat the, piera (called a 'plate' in the US) to dry the clay. While it is still hot but not scorching they lay down the canes so they are partially warmed before they go in the furnace. Remember that they are not annealed [and could easily shatter from thermal shock]. Then two little square metal pieces are placed at the two ends to hold the cane in place. These are called fereti (V) ferretti (I) . Some of these same terms are also used in the US by skillful glass blowers.[2]

On the end of an iron blowpipe, the fused mat of glass rods is wrapped around into a hollow cylinder. Next the open end is gently worked closed. This forms a sealed bubble of glass that can be manipulated by standard glassblowing techniques. Soft from the heat of the furnace, the glass can be given a twist so the parallel threads form a loose spiral. This piece is stored in a ‘garage’ kiln while a second bubble is formed in the same way but with the spiral running in the opposite direction. The first bubble is opened wide at one end, removed from its iron rod and placed in a cradle on the floor which holds it upright. The second bubble is carefully lowered into the open end of the first bubble. The glass artist stands above, with the second bubble inside the first and blows, inflating the inner glass until it comes in contact with the outer bubble. Watch master Dante Maroni at work in this video

Because both glass bubbles are formed with canes, they have a ribbed texture both inside and outside. When the two glass bubbles contact each other, the high-points of the ribs meet first, which is where the threads of the two bubbles cross. The valleys of the ribs are where one cane is fused to the next; these areas cross between the bubbles at the center of each diamond in the pattern. The two bubbles fuse together trapping air in the valleys. As the glass is worked and heated these regions form small, perfectly round air bubbles trapped inside the glass. You can see this for yourself by taking two or three fingers of each hand and crossing them against each other. Imagine the threads of opaque glass running down the center of each finger. The air bubbles are trapped where you can see light between your fingers.
Reticello ("fillacello") style flamework pendant,
by Adam Reetz 2015.

The distinctive diamond pattern of reticello has been successfully achieved with other glassmaking techniques. In flameworking, glass is manipulated using only a torch and handtools. The torch is fixed to a bench where the artist either stands or sits. In general, this is a more accessible technique because it does not require a glass furnace. Here, the reticello pattern is accomplished by starting with glass tubing. The crisscross pattern is ‘painted’ onto the outside of the tubing, one line at a time; with very thin rods of glass known as “stringers.” In one version, evenly spaced straight parallel lines are drawn along the length of the tube. The tube is then reheated in the flame and twisted. Next, a second set of lines are drawn twisting in the other direction, forming the diamonds. The ends of the tube are drawn down and one end can be mounted to a rod or tube of glass and further manipulated in the flame. 

In a testament to the continued popularity of reticello, a new colorful variation of the flamework technique has emerged within the past decade, among American flameworkers. [3] This has been playfully dubbed “fillacello.” After painting the fishnet pattern on tubing, and further working the glass, the individual diamonds are “filled” with various colors using stringers. The resulting effect recalls mosaics and the ancient inspirations of reticello.

[1] The iron tool used to move the 'piera' of filigrana cane in and out of the furnace is called a 'pasorale' (V), 'pastorale' (I) = pastoral, named after the staff carried by the pope. It consists of a straight rod with a U-shaped fork in the end. Thanks to Emilio Santini for his kind assistance with Muranese terminology and knowledge of hotshop technique.
[2] Private correspondence, March 2015. Here is a video of the reticello technique as executed by American glass artist Dante Maroni.
[3] My research point to the first examples of this technique emerging on the west coat of the United States around 2005-07. (Further information on its origin would be greatly appreciated).

Wednesday, July 22, 2020

Filigrana Glass

Mezza Filigrana footed vase, circa 1950s,
by Dino Martens (for Aureliano Toso).
Filigrana is a classical glassmaking technique developed in the sixteenth century on the Venetian island of Murano. In the broadest sense, a piece of filigrana -- let's say a vessel -- is composed of transparent glass with very fine vertical threads of color running through it. Traditionally, these threads were opaque white lattimo (milk) glass, running through a colorless high quality product known as cristallo. Because of this, the technique was originally known as “latticino,” a term still in use, but now falling out of favor and being replaced by filigrana (filigree), a name that does not imply any particular color. 

Over the centuries, this and closely related techniques became a kind of trademark for the Murano glass industry. Parallel threads in a loose spiral winding around a vessel from top to bottom form what is perhaps the most basic application of the method. This is known as mezza filigrana (half filigree). The reason for the “half” becomes apparent when we consider its far more famous cousin reticello. With this technique, two sets of threads are used winding in opposite directions to form a fishnet pattern of  diamonds. The name recalls reticella, a traditional Venetian lace. When the work is done properly, tiny air bubbles are trapped inside the glass, one in the center of each diamond of the fishnet pattern.

Even more exotic variations have been developed, which we will discuss another time. First, let's explore how the glass artisan is able to achieve these fine threads in the glass, so perfectly spaced. I should hasten to say that I am not a glassblower and this description is not an instructional, but simply a window into some of the fabulous artistry that takes place in a glass shop. These techniques take hundreds or thousands of hours of practice to master. Even a shallow understanding of the steps that go into a piece of filigrana lead to a far richer appreciation than simply being able to identify it by name.

 “Cane” is a general term for long straight rods of glass. They have many uses in glass artistry and the method by which they are made can be surprising the first time you see it done. It is the same method as was practiced a thousand years ago. A gob of molten glass is removed from the furnace on the end of an iron rod. A second rod is attached by another artisan, with the lump of molten glass between the two rods. They start to pull in opposite directions, slowly at first. They swing and manipulate the hot glass as it cools, forming a mass of relatively uniform diameter. They continue to walk away from each other, the glass pulling thinner as they go. Practiced artisans can end up with a uniform pencil thin straight rod of glass that extends for many meters. It is laid on spaced wooden slats on the floor, allowed to cool and then snapped at regular intervals to form smaller rods.

In the case of filigrana cane, the artisan starts with a smaller gob of opaque glass; let us say lattimo (white). This gob is then dipped into clear glass, which encases it in a heavy transparent layer. When the cane is pulled, the result is a clear rod with a filament of opaque white glass running down the center. Short lengths of cane are laid side by side in a pan. The pan is heated so that adjacent rods start to fuse together into a mat. The glass artist will again take a gather of glass from the furnace around the end of an iron blowpipe and flatten it into a disk, leaving the blowhole unobstructed. The disk, known as a "collar"[2] is touched to the mat of canes at one end and rolled so that the canes wrap around and form a cylinder. The open end of the cylinder is then closed down, in effect forming a bubble on the end of the pipe. The glassblower can then treat this as if it were a bubble formed straight out of the furnace, but of course, this bubble has the threads of lattimo glass running through it. The bubble is then manipulated into a finished piece. [2]

Miniature flameworked vessels (aprox. 3cm tall)
in the style of filigrana, by Emilio Santini. 
Outside of the hot shop, there are methods that use only a torch to duplicate the appearance of filigrana and reticello on a smaller scale. This involves starting with glass tubing and "painting" the threads on using thin "stringers" of glass. It is a completely different technique which requires an entirely different set of skills. In the right hands, the results can be strikingly similar. Now that we have the basics down, we can discuss the more spectacular variations that have been developed, which we will talk about next time.

[1] "Colletto"(Italian) "Coeto" (Venetian), means narrow neck or little neck.
[2] The following Youtube video shows American glass artist William Gudenrath, assisted by Harry Siemens pulling filigrana cane and executing a reticello vase at the Corning Museum of Glass.

Monday, July 20, 2020

Incalmo Glass

Incalmo vessels by Tapio Wirkkala for Venini.
In this post, we will explore one of the classical techniques of glass art. Along with filigrana, latticino, reticello and pezzato, incalmo is a classical Venetian technique well established in the art, even if poorly understood by many outsiders.

‘Incalmo’, in Venetian dialect literally means “graft” as in joining two plants. That is a pretty good description of how this effect is achieved; think of a vase whose bottom-half is one color and top is another. The glass artist blows two separate bubbles of glass, opens them and joins them together to form a single bubble. It is a difficult operation because the two open lips must be exactly the same size to join properly. The process can be continued to add more colors; virtuoso pieces may include several sections, each a different color. In addition, the position of the iron rod that the artist uses to hold the bubble can be changed while the piece is under construction, leading to asymmetrical effects.
16th century incalmo plate,
unknown artist.
The above description is the classical way of achieving incalmo, but modern materials and equipment allow artists to achieve a similar effect with considerably less skill. For instance, precise diameter glass tubing is now available in a wide variety of colors. This can be cut into rings with a saw, then stacked in a kiln and fused together. From there, this “prefabricated incalmo tube can be worked by traditional methods. Whether or not this meets the definition of true incalmo depends entirely on whether one focuses on the method or on the end result.

9-10th century incalmo vase,
Syria or Iraq.
The name ‘incalmo’, was applied to glass in the first half of the twentieth century by the Venini factory on Murano, in Venice. [1] However, both the word and the method are much older. The Venini artisans revived the technique to great acclaim, but Venetian examples date from the sixteenth century and Islamic examples from ninth century Syria have also survived. It is not hard to imagine that this joining technique was experimented with shortly after glassblowing became common around the first century BCE. However, what is truly amazing is that any of these early examples survived to be sold to customers without breaking in the cooling process. The reason for this is a technical issue that we have not discussed yet.

All glass expands a little when it is heated and shrinks when it cools. Different formulations of glass generally expand by differing amounts. When a single piece incorporates more than one type of glass, and the thermal expansions differ significantly, the result is disaster. After the piece is finished it is placed in a kiln where it slowly cools back to room temperature. Because of the mismatch, one area wants to shrink more than the adjacent area and the glass cracks along the join. The expansion and contraction is microscopic, but it is enough to ruin hours and hours of work, leading to much gnashing of teeth the morning after, when the finished work is inspected. 

The Venini glass masters had the benefit of this knowledge, but for earlier artisans, trial and error must have played a big role in determining which formulas were compatible. Different colors mean different metallic additives and to match expansion other ingredients would need to be adjusted. Today, manufacturers produce glass in a series based on expansion; artists can be relatively sure that two different colors from the same series can be “grafted” and not self-destruct when cooled.

[1] I have not absolutely confirmed this, but authoritative secondary references credit Venini, and I can find no mention to "incalmo" as a glass technique prior to the twentieth century.

Friday, July 17, 2020

Primordial Matter

16th century Mining practices, 
from Agricola, De Re Metallica
In the early seventeenth century, Florentine priest Antonio Neri wrote the first printed book devoted to formulating glass from raw materials. His work is called L'Arte Vetraria, which translates to "the art of glassmaking." The book became quite famous and this is what he is remembered for today, yet he considered himself first and foremost an alchemist. In previous posts, we have explored the commonalities between glassmaking, medicine and the apothecary's trade. Another field closely connected to alchemy was mining. 

In the seventeenth century, the earth was considered a living entity; metals were found to occur in "veins" which were thought to grow and once mined, regenerated over time. The metals themselves were thought to undergo a maturation process. The thinking was that primordial material left over from the creation of the world exerted its influence deep in the ground. Nurtured by the earth, under the influence of the suns rays, a process took place that eventually turned base metals into the more noble silver and gold. As far as Neri was concerned, alchemy was the art of imitating and enhancing natural processes that were already at work. In his manuscript Discorso, he writes:
I feel that the more perfect the art the most simple it is; so the authors [of alchemy] most unanimously agree that the ‘primordial material’ [prima materia] of the [philosopher’s] stone is something vile [base] and not bought with money, but easy to find. Moreover, the manner of work must imitate nature, which in order to produce gold makes use of the singular or simple material, which is the seed of gold, of a single vessel, which is the ‘womb of the earth’ [seno della terra] and of a single natural and vital fire, which is the sun.*
Elsewhere in the manuscript, Neri discusses several specific mines. He discusses the use of "vitriol" water that flowed in certain mines and how it could be used to transmute iron into copper. He discusses an unidentified mine "some distance from Leiden" (possibly in Limburg) and another in Slovakia in the town of Smolnik. It is reasonable to think that Neri visited these places himself. A third location, which he purposely keeps under wraps, is where he obtained "immature" gold that he was able to "multiply" through alchemical manipulation. With a certain disappointment, he writes "To this day I have never found another mine like it, and therefore suitable for this purpose." Clearly, he spent a significant portion of his time looking. He advises:
The gold mines are not all in the same condition, which is well understood for those of silver and all the other [metals]. Some are already perfect, in which nature has done what it could do and reduced the gold to its maturity, while other [mines] are still imperfect and in their infancy*
In his work for Medici prince Don Antonio in Florence, Neri's assistant/disciple was Agnolo della Casa. Della Casa took copious notes of Neri's experiments, and literally filled thousands of pages in notebooks that are today held by the National Library in Florence. Much of this material dealt with the transmutation of metals, and as we have seen Neri was not only concerned with materials, but with their specific place of origin. His first manuscript was titled "Treasure of the World, By Priest Antonio Neri – which [covers] the whole of alchemy with various illustrations, not only of the furnaces, vessels and chemical instruments but with other illustrations concerning the mining of all the metals." For he and his colleagues, mining and alchemy shared theoretical connections but also familial ones. Della Casa had a relative named Filippo Talducci della Casa (1543- c.1615), who was a celebrated alchemist and mining engineer, working in Prague and Krakow for the Holy Roman Emperor. Last but not least, there was also a practical connection. Mining provided many of the raw materials used in Antonio Neri’s glassmaking activities.  

* For a full discussion of Neri’s Discorso, see M. G. Grazzini, “Discorso sopra la Chimica: The Paracelsian Philosophy of Antonio Neri”, Nuncius 27, pp. 411-467.

** This post first appeared here 30 April 2014.

Wednesday, July 15, 2020

Washing Molten Glass

Washing, sorting and carrying cullet
Denis Diderot 1772
One of the continuing frustrations with the study of glassmaker Antonio Neri, is that there is no known example of his glass to be found anywhere. It is very possible that pieces do survive, but so far, none has been tied to him or his recipes. At first it might seem to be a straightforward task of analyzing the composition of likely candidates and comparing the results to his formulas. Unfortunately, this plan does not hold water. Even if a recipe for glass was followed exactly, the result will have a different composition from the starting materials. One reason is that before the hot glass was crafted by artisans, a new batch was typically "washed" by flinging ladle-fulls of molten glass into great vats of cold, clean water. In this process, excess flux is dissolved in the water and left behind. In his 1612 book L'Arte Vetraria Neri wrote:
After a while, when the glass is well fused, take it out of the crucibles and throw it into large earthenware pans or clean sturdy wooden tubs filled with fresh water. This step of throwing the glass into water has the effect of causing the water to remove a kind of salt called Alkali salt [glass gall], which ruins the cristallo and makes it dark and cloudy. So while it is still being worked let the glass spit out this salt, a substance quite foul, then return it to clean crucibles. Carry out this flinging into water repeatedly as necessary. In order to separate the cristallo from all its [alkali] salt, this should be repeated to the satisfaction of the furnace conciatore [glassmaker].
This step, he assures us, is absolutely necessary for the finest glass, but also helps improve the most common glass:
If you throw it into water at least one time, what you will have will be beautiful and clear. The same is true for common glass, which once brought to perfection you should return to the crucibles for use. It will be bright, fine and quite satisfactory to work in those jobs that require it. […] when a more than ordinary fine glass is desired it is necessary. Beyond becoming very white[clear], it calcines and clarifies nicely with few impurities.
This technique becomes even more critical for Neri's lead crystal, in fact, any glassmaker who ignored this step for a leaded glass did so at risk of a major disaster.
In a few hours everything will have clarified, now purify it by throwing it in water. Inspect the glass carefully before returning it to the crucible. All lead precipitating out of the glass must be removed with diligence, throwing it away, so that it does not make the bottom of the crucible break out, as can happen. Return the glass that was thrown in water to the crucible and leave it to clarify for a day.
In addition to washing the glass, sometimes the top layer of a melt was skimmed off and discarded because it contained contaminants that floated to the surface. To complicate matters further, molten glass can stratify in the crucible, meaning the composition might vary from top to bottom and from the center of the pot to the edges. 

Scientists and historians have collaborated to see what can be learned from period samples of glass. When attention is focused on the composition of a single type of glass, like Venetian style cristallo for example, one might expect a wide variation. The opposite turns out to be true. Even with all of these factors conspiring to change the glass composition, remarkably the analysis shows it is quite difficult to tell apart glass that was known to be made in Florence from that of Antwerp or Venice. Recent efforts have centered on identifying minuscule amounts of trace materials in the old glass that were unique to the raw ingredients of a specific region. Meanwhile, Antonio Neri's glass continues to elude us, even though it might be sitting on the shelves of museums around the world, right in front of our eyes.

* This post first appeared here on 9 May 2014.

Monday, July 13, 2020

Pebbles from Pavia

A Bridge on the River Ticino, near Polleggio,
William Pars (1742‑1782).
In the sixteenth and seventeenth century, a type of glass known as 'cristallo' was the absolute pinnacle of the art. Its recipe was invented in Venice and guarded there as a state secret. Its name derived from the mineral it was designed to mimic: rock crystal. As clear as water, rock crystal was valued since ancient times for carving into cups, vessels and other objects of art. Today we know it as a form of quartz, but in Roman times it was thought to be a type of frozen or coagulated water.

In the early 1600s, when Antonio Neri started making glass in Florence, the grand duke's craftsmen were routinely carving this hard and brittle rock crystal into complex thin shapes, a process that took great skill and effort. Due to the expense involved in producing a piece, this art was the exclusive province of extremely wealthy individuals. Thus, objects made from rock crystal were considered markers of status. The recipe for cristallo glass was a very great secret indeed, but its real value lay in the specific materials used. Even if the recipe found its way out of Murano, which it inevitably did, the Venetian's tight trade network ensured a monopoly on many of the ingredients. It is said that even the furnace crucibles for cristallo were made from a specific clay gathered in Constantinople.

Cristallo was not only exceptionally clear, but for the artist it had working properties like no other glass. Thin, complex shapes were possible in cristallo that could never be duplicated in common glass. The secret for making cristallo came to Florence in the late 1560's, only a few years before the birth of Antonio Neri, who would learn the techniques and go on to publish the recipe for the first time anywhere.

 After protracted overtures, which involved diplomats, spies and the archbishop of Florence, Grand Duke Cosimo I managed to negotiate with the Venetian Doge and Senate for a Muranese master and two assistants to come to Florence and teach the way to make cristallo. It is likely that the raw materials were all purchased through the Venetians, at least initially. By the time Neri wrote his book, L'Arte Vetraria, in 1612, the Florentines were already finding alternate sources. In Venice, the ingredients of cristallo were prescribed and controlled by strict laws. The Florentines did not have this constraint and were free to experiment.

In the second recipe of Neri's book, he spills the beans on where the Venetians procured the single most important ingredient for cristallo, the pure quartz stones which account for the material's clarity. Notice in the following excerpt that Neri mistakenly thinks that the white river stones are a form of marble and also notice the alchemical language he uses to describe the process in which the stone is "transmuted" into glass.
When you want to a make cristallo that is beautiful and fully perfect, see that you have the very whitest tarso. At Murano they use pebbles from Ticino [Pavia], a stone abundant in the Ticino River. Tarso, then is a species of very white hard marble [quartz]. 
In Tuscany, it is found at the foot of Mount Veruca in Pisa, at Seravezza, at Massa near Carrara, and in the Arno River both above and below Florence. In other places as well, common stone is often recognized, which is seen to have the same qualities as tarso; it is very white and does not have dark veins, or the yellowish appearance of rust, but is spotless and pure. Take note that any stones that will spark with a piece of steel or strike plate, are apt to vitrify and will make glass and cristallo. All those stones that do not make sparks with a piece of steel or striker as above will never vitrify. This serves as advice for being able to distinguish stones that have the ability to transmute their form, from those that cannot be transmuted. 
Start with this same tarso, as fair and as white as possible. Grind it finely into powder in stone mortars. Do not use bronze or any other metal for this purpose or the stone will take in the color of the metal, which then would tinge the glass or cristallo, and make it imperfect. The pestle must be iron by necessity but at least the other materials will not have the possibility of causing any effect. Pulverize the tarso well and sift with a fine sieve. It is important that the tarso is ground as finely as flour, so that it will all pass through a fine sieve.
* This post first appeared here on 30 May 2014. 

Friday, July 10, 2020

Scraping the Barrel

4th century BCE philosopher Diogenes
(supposedly lived in a wine barrel)
by Gaetano Gandolfi (1792)
To seventeenth century glassmaker Antonio Neri, "tartar" was a well-known byproduct of the winemaking process. If we chill wine or grape juice to below 50 degrees (10 deg. C.) crystals of tartar start to form and once they do, then tend not to dissolve back, even at room temperatures. Today, these crystals are commonly found in a powdered form, in kitchen cupboards as "cream of tartar." Bakers and cooks use it to stabilize whipped egg whites, and it has a number of other applications. 

Neri used tartar in his glass to add sparkle, a trick known to Venetian glassmakers as early as the 1400s. It was obtained from the dregs at the bottom of wine barrels. To understand how this works, it is useful to know that Florentines, Venetians and most southern Europeans made glass from crushed up quartz pebbles or sand mixed with a specific flux known as "glass salt." This salt was rich in sodium carbonates, which greatly reduced the melting point of the quartz. It allowed artisans to work the material at the temperatures easily achieved in their furnaces. Tartar turns out to be very similar, except that it is rich in potassium rather than sodium. 

Potassium atoms are larger and heavier than sodium atoms and when light passes through a piece of potassium-fluxed glass, it bends and refracts more. This effect is not as pronounced as when adding the even heavier lead to form fine crystal, but it still adds noticeable sparkle to finished pieces. Using all tartar as a flux has the undesirable effect of reducing the workability of the hot glass. Outside the furnace, it becomes stiff quicker and artists have less time to create fancy shapes and forms. The solution to this dilemma is to use a mix of sodium and potassium fluxes together, which is exactly what Neri did. 

In his 1612 book L'Arte Vetraria, he shows how to prepare tartar and then adds it to a number of his glass recipes saying, "The tartar is the secret way to produce more salt and to make cristallo which is whiter and of rare beauty." Here is Neri’s prescription:

To make Purified Tartar Salt you should obtain tartar, which is also called gruma, from barrels of red wine in which it forms large lumps, however do not use powder. Roast it in earthenware pots amongst hot coals until it becomes calcined black and all its sliminess is roasted away. It then will begin to whiten, but do not let it become white, because if you do the salt will be no good.  
Calcine tartar this way: put it in large earthenware pans full of hot common water, or better yet in glazed earthenware pans then made to boil on a slow fire. You should do it in such a way that in two hours the level of the water will slowly decrease to one-quarter, at this point lift it from the fire and leave it to cool and to clarify. Now decant off the liquid, which will be strong lye and refill the pans containing the remains of the tartar with new common water. In the way stated above, boil as before and repeat the procedure until saltiness no longer charges the water. 
At this point, the [decanted] water is impregnated with all the salt. Filter the lye clear and put it in glass chamber pots to evaporate in the ash of the stove over a slow fire. In the bottom, white salt will remain. Dissolve this salt in new hot common water and leave it in the pans, letting it settle for two days. Then filter it and return it to chamber pots to evaporate over a slow fire. In the bottom, a much whiter salt will be left than the previous time. Now dissolve this salt in fresh hot common water and leave it to settle for two days. Evaporate, filter and repeat everything as before. Overall, repeat this procedure four times to dissolve, filter and evaporate the salt of tartar. This will make the salt whiter than snow and purified from the vast majority of its sediment.
When mixed with sifted polverino, or rocchetta, with its doses of tarso [quartz] or sand, this salt will make a frit that in crucibles will produce the most beautiful crystallino and common glass, which one cannot make without the accompaniment of tartar salt. Without it [tartar], good fine crystallino can be made, nevertheless with it, it will be the absolute most beautiful.

*This post first appeared here on 16 May 2014.

Wednesday, July 8, 2020


Antique Apothecary jars,
cobalt blue glass.
As best as I can remember, the first time that I really noticed glass was at four or five years old, at my grandmother's house in Queens, New York. The sunlight filtering through a low window caught my eye with a brilliant blue glint through a small cobalt glass bottle.  My grandmother held it up to the light for me and I was enchanted; transported into a realm of exquisite pure color.

Little did I know that the spell cast on me at such a young age had been cast on Egyptian pharaohs of the eighteenth dynasty and on Persian princesses, two thousands years ago, by their cobalt glass jewelry. In all three cases, the deep rich blue of cobalt oxide glass was responsible. Today, the source of ancient Middle Eastern cobalt is unknown, possibly West Africa, but more recently, in the Renaissance; it was mined in Hungary, in Bohemia and in German Saxony, where it was called "zaffer," after its sapphire color.

Legend tells that sixteenth century silver miners in Germany amassed a hoard of smaltite thinking it was silver ore. When they tried to smelt it, the arsenic which cobalt ores always have, evolved highly toxic fumes that made them sick. Discouraged and maligned, they said the product of their labors was cursed by goblins; they named it "kobald" (cobalt) after the evil spirits. The theme of 'evil spirits' (toxic fumes) was common in mining circles. A mythology persisted from ancient times up until the eighteenth century that divided the spirits into two groups; mischievous, and malevolent. The mischievous spirits played tricks on the miner's perception and equipment, the malevolent spirits could stop a man dead in his tracks, literally. 

Regardless of the difficulties both terestrial and otherwise, a strong market developed for the newly found "kobald" among artists for paint, potters for glazes, and glassmakers. The Saxon miners gained a reputation for producing the finest zaffer.

In his glassmaking book L'Arte Vetraria, Antonio Neri describes his method for purifying and preparing zaffer for use in glass. It is a recipe that would stand the test of time, still quoted by authors into the nineteenth and twentieth century.

To Prepare Zaffer, Which Serves for Many Colors in the Art of Glassmaking

You should get zaffer in large pieces and put it in earthenware oven-pans holding it in the furnace chamber for half a day. Then put it into iron ladles to inflame it in the furnace. Heat it well, then take and sprinkle it with strong vinegar. When cold, grind it finely over a porphyry stone into glazed earthen pots with hot water. Then wash more water over it always leaving the zaffer to settle in the bottom.

Now gently decant, to carry away the sediment and impurities of the zaffer. The good part and pigment of the zaffer will remain in the bottom. The pigment remains are now prepared and purified to be far better than it was at first, which will make clear and limpid pigment. This zaffer should be dried and kept in sealed vessels for use, which will be much improved over the original.

Until the mid 1700s zaffer had been associated with silver and copper mines, and was commonly thought to be a derivative of copper. It was Swedish chemist Georg Brandt who finally isolated the new metal, and gave it the name which honors the miners and the subterranean spirits which still can cast a spell on us through its deep pure blue color in glass.

* This post first appeared here in a slightly different form on 4 April 2014.

Monday, July 6, 2020

Flexible Glass

Roman Emperor Tiberius - Glass paste cameo
 c 20CE by "Herophilos, Son of Dioskurides"
In the first century CE, references appear in the literature for a malleable form of glass --that is to say flexible-- the method for which is reported as lost. This 'vitrum flexile' was a material that supposedly could be worked with a hammer like metal; not brittle but plastic, yet retaining the other favorable properties of glass. In the ancient world, historians Strabo (c. 63 BCE–24 CE), Pliny (c. 23–79 CE), Petronius (c. 27–66 CE) and others recount the story of a hapless artisan who brought his great discovery to Roman emperor Tiberius. Fearing the devaluation of his wealth, the emperor had the glassmaker executed on the spot and his workshop destroyed. The implication being that the inestimable value of a malleable glass would crash the markets for gold and silver. [1]

Since then, the legend has resurfaced in various forms, notably at periods in history of technological upheaval; times when innovative knowledge threatened to 'disrupt' the established order. One incarnation has the sophy of Persia gifting a set of malleable drinking glasses to the king of Spain, Philip III, around 1610. Just then, new trade deals with the Middle East rattled the European economy and Venetian glass craftsmen fanned out through Europe, disrupting local glass furnaces and guilds with their superior techniques. [2] Another version tells of a French sculptor bringing his malleable glass-work to Cardinal Richelieu (1585-1642), of Dumas' Three Musketeers fame. According to the story, that particular artisan’s reward was life in prison. The tale takes place in a tumultuous political period in French history and appears in print at the dawn of the so-called industrial revolution. [3]

Chronologically, this last story aligns nicely with the publication, in southern France, of a Latin book of alchemical recipes by royal physician Pierre-Jean Fabre (1588-1658). Contained in his volume is a prescription for a malleable form of glass, presumably the fabled vitrum flexile. Fabre's book was titled Palladium Spagyricum, 1624. [4] Spagyricum is a reference to spagyrics, the specific brand of chemistry practiced by sixteenth century alchemist-physician Paracelsus. Palladium translates to 'protector' or 'savior'. As an aside, it is interesting to note that Fabre developed an elaborate philosophy which integrated chemistry as a 'sacrament' to Catholic theology, but that is a story for another day.

In 1685, Fabre's recipes were nicely translated into English and tucked into the end of a book otherwise devoted to the art of drawing, by William Salmon [5]. Here is the full recipe "To Make Malleable Glass" as rendered in Salmon's book:

I.        Take oyl of Luna, twenty drachms: oyl of Mercury, or its water seven times rectified, one pound: mix them together and distill them.
II.      Repeat this distillation till the oleum Lunae rises with the water of Mercury in distillation. 
III.     Distill this water again until it is fixed, and converted into a fixed oyl, and this repeat four times. 
IV.     In the fourth time the oyl of Luna is fixed with the oyl of Mercury, so that they render glass malleable; for so great is the viscosity in your oyls, that it removes the brittleness of the glass, and so leaves it of a malleable temper. 
V.      The reason is, because that the radical moisture of the glass is multiplied by the radical moisture of the metals. Which is plentiful and turgent or swelling in the oyls of Luna and Mercury. 
VI.     And if [in] this oyl made volatile, diamonds should be dissolved, and then digested into a fixt oyl, it would transmute all glass into diamonds, only by projecting this oyl onto melted glass. 
VII.   There are also other precious stones comprehended within this oyl, when it is made volatile, and digested, and fixed again by digestion continually for the space of a year. 
VIII.  Also this oyl can turn glass into precious stones of any kind whatsoever, if therein (being made volatile) precious stones of the same kind have been dissolved, and digested with it into a fixed oyl. 
IX.     For as metals are included in their fixed oyls: so are precious stones in theirs, as Raymundus Lullius doth witness in many places; the which thing we shall teach you in the following chapter. 
 Elsewhere in the book, it is explained that 'oyl of Luna' is silver dissolved in acid, and 'oyl of Mercury' is a sublimation of mercury and saltpeter. [6] From a purely technical standpoint, the formula would have been regarded credible by 17th century and earlier practitioners in that both mercury and silver were successfully used as additives to glass and they do integrate into the matrix. Notably, Antonio Neri used both of them in his chalcedony glass. In Neri's case he was using these metals to produce color, although he does not attribute specific tints to the ingredients. Under some circumstances, silver is known to produce an attractive blue. It should also be noted that Renaissance glassmakers used similar silver-mercury formulas to produce the reflective layer on finished glass mirrors, in a process that resembled gilding. They formed what was known as "mercury glass." It is not beyond the pale to speculate that experiments would have been conducted by alchemists to add such concoctions directly to the glass melt. In the end, though, there is no indication that these additives would produce a malleable glass. Last, we should note that prolonged exposure to mercury vapor causes irreversable neurological and organ damage. It undoubetly contributed to the demise of alchemists, gilders, milliners and many others who worked with it throughout history. 

As far as I am aware, this is the first example of a specific recipe for malleable glass uncovered in the literature. If nothing else, it is an important marker for further research into the history of glassmaking.

[1] Strabo: Geography, v. 8; Pliny: Naturalis Historia XXXVI.lxvi.195; Petronius: Satyricon 50.7; Also recounted by Casius Dio (c.150–235 CE): Historia Romana 57.21.7; Isidore of Seville (c. 560–636 CE): Etymologiae XVI.16.6, ‘De vitro’; Suetonius; Ibn Abd Alhokin; John of Sailsbury.
[2] Knolles, Grimstone, Johnson: Richard Knolles' The General Historie of the Turkes (London: Adam Islip, 1621).
[3] Neri 1697 (Introduction). A French translation of Florentine glassmaker Antonio Neri’s 1612 book L’Arte Vetraria [The art of making glass] by Jean Haudicquer de Blancourt. Also see my earlier post here .
[4] Pierre-Jean Fabre: Palladium spagyricum Petri Ioannis Fabri doctoris medici Monspeliensis ... (Toulouse: Bosc, 1624), p. 276. Later translated into several English editions, see note [5].
[5] William Salmon: Polygraphice: Or the Arts of Drawing, Engraving, Etching, Limming, Painting … (London: T. Passenger & T. Sawbridge, 1685), pp. 598, 599.
[6] To more adventurous readers: DO NOT TRY THIS AT HOME, or anywhere else, ever. Vaporized mercury is a powerful neurotoxin. Small amounts can cause permanent brain damage and multiple organ failure. Furthermore, this recipe uses powerful acids and nitrates, which are extremely dangerous even in a controlled laboratory setting. Even if you have little regard for your own health and safety, consider those around you; this includes loved ones, family, children, pets, neighbors and the emergency workers who will inevitably be left to clean up your mess.

Friday, July 3, 2020

Glass of 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 the practice of 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 next 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”
[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.” . Also see Halle du Verre regional glass museum website .
[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.