Secret Laboratory

The Studiolo of Francesco de' Medici,

Palazzo Vecchio, Florence.

In all likelihood, Antonio Neri started his glassmaking career around 1601 in the laboratory palace of Medici prince Don Antonio. The Casino di San Marco is located on the north side of Florence, not far from where the old city walls once stood. It was purpose-built as a laboratory by Don Antonio’s father, Grand Duke Francesco and stands on the former location of the sculptural school that Michelangelo attended as a boy. The Casino is a remarkable structure in the history of science, however, our subject today is not the laboratory but one of its primary inspirations, located across town in the Palazzo Vecchio; The Studiolo of Francesco de’ Medici.

Books of secrets, like Neri’s L’Arte Vetraria exposed methods to transform nature. Cabinets of curiosities, on the other hand, celebrated the finished products as well as nature’s ready-made treasures. These so-called cabinets were a sort of physical counterpart to books of secrets. Starting as small collections of exotic objects, princes and nobles strove to out-do each other and the largest examples encompassed entire rooms. In the early 1570s, at around age thirty, Francesco de’ Medici initiated a special project; he constructed a secret room in the Palazzo Vecchio. [1] Accessible through a concealed staircase in his bedroom, this small, but opulent, study chamber was devoted to natural curiosities and secrets. The “Studiolo” contained his collection of rare gems, exotic seashells, animal horns, chemicals, potions, scientific instruments and other strange and wonderful treasures collected from around the world. 

From floor to barrel-vaulted ceiling, paintings and niched sculptures covered the chamber walls. Celebrated artist Giorgio Vasari designed and constructed the secret room in partnership with Vincenzo Borghini, a Benedictine priest and close Medici advisor. [2]  In all, thirty-two of the city’s artists contributed to the project, although most had no idea where their work was destined to hang. Francesco organized paintings such that each wall was themed by one of the four Aristotelian elements: air, earth, water and fire. Behind nineteen of the lower paintings, cabinets housed the treasures of Francesco’s collection. From within the Studiolo two other secret passages were accessible from behind concealed panels. One leads to a smaller private treasury once used by Francesco’s father, Cosimo and another leads down a stairs to an unmarked outside door on the street. [3]

Part study and part museum, Francesco used the Studiolo to escape public life and explore the secrets of nature. This menagerie and ones like it were an outgrowth of the wunderkammer or “cabinet of curiosities.” Early in their evolution, they took the form of single pieces of furniture for the display of collections. Monarchs and nobles throughout Europe boasted collections of ever-increasing size and diversity. In a way, the Casino di San Marco was the next evolutionary step; from a cabinet of curiosities, to a study room, to an entire facility devoted to nature’s secrets. 

The paintings in Francesco’s Studiolo depict various religious, mythological, historical and industrial scenes. [4] Some of them show various royal workshops documenting activities as diverse as goldsmithing and wool dying. A 1571 painting by Giovanni Stradano [5] is entitled the Alchemy Studio. It shows Francesco I in the Uffizi surrounded by laboratory equipment and workers. 

[1] Constructed between 1567 and 1675, cf. Feinberg 2002, Edwards 2007.
[2] Giorgio Vasari (1511–1574), Vincenzo Borghini (1515–1580).
[3] Via della Nina.
[4] Feinberg 2002.
[5] Giovanni Stradano, also called Jan van der Straet (1523–1605).

Fall From Grace

In 1790, two centuries after the life of glassmaker Antonio Neri, his name appeared in an unlikely place: in the annotations of a Swedish manuscript that was translated into Italian by one of Florence's leading scientists.[1] On second thought, perhaps its appearance is more unexpected than unlikely. Torbern Bergman was the celebrated Swedish chemist responsible for the manuscript and the translator was Felice Fontana, the founding director of Florence's Natural History Museum (La Specola). Fontana took the opportunity to annotate Bergman’s History of Chemistry in the Middle Ages with a list of Renaissance era materials collected in the Grand Ducal library in Florence (now the BNCF). Figuring prominently among the documents was alchemist Antonio Neri.

Below is an excerpt from one such letter, penned by Don Stefano Giraldi, the prior of San Pancrazio Church in Florence, addressed to "Your Excellency." In the passage notable characters are Don Antonio de' Medici, Neri's long-time benefactor — the prince who ran the Casino di San Marco laboratory where the priest first made glass. Also, Francesco Orlando Lorenzi (Count Lorenz, active 1793) was third count of Lorenzana and the minister of France at the Florentine court in the time of Louis XV.

Among those who abused the credulity of the Prince D[on] Antonio by leading him to understand they knew how to make gold, the most famous was Florentine Priest Antonio Neri, who, if he could not make gold, did know how to make many other beautiful and useful things, and has secured eternal fame with his work on the Art of Glassmaking, which also found prestige in the Tuscan language…  

Of other works of Preist Neri, I do not know if they have been published or even if the manuscripts have been found. Uniquely, Father Maestro Arrighi, [Augustinian] Serviette and Alchemist, in 1735 bought books that Count Lorenz had sent to France. Among them was a large manuscript in quattro by Antonio Neri. He told me that it contained a method of making the philosopher's stone and that there was a preamble  in which Neri confessed to have copied this method from a manuscript found in an old library. He  tried [the recipe] several times and always  failed.  To raise hope for others to enjoy much treasure, he had copied the method by characters in a cipher he invented and burned the old original. P[reist] Arrighi never let me see the manuscript, which was four fingers high as he assured me that the bookseller had sold it to him for the price of 5 lire; and no doubt, there will be other things besides the process of the philosopher's stone, which occupied[only a]  few page.

This flaw in Priest Neri to pass himself off as the possessor of the philosopher’s stone detracted much from his esteem. Nearby, his countrymen were wise and enlightened, and therefore he never attained the good image he should have had in his country, his mercy was the real merit of so many other good things; indeed always absent [making] gold, though he wanted to give the impression that he could, he incurred various dangers, and was forced to spend some time wandering.[2]

This gem of a letter has many interesting facets. First, it establishes that 150 years after Neri’s death, his name was still on the lips of royal courtiers and his manuscripts commanded a dear price from booksellers. It also establishes a route that his unpublished work took in leaving Italy, through France. 

The letter also provides us with insight to the changing narrative about alchemy. Neri was being distanced from the less palatable aspects of his work. "[I]f he could not make gold, [he] did know how to make many other beautiful and useful things, and has secured eternal fame with his work on the Art of Glassmaking." His sponsor Don Antonio’s portrayal as gullible about the possibility of transmutation kept the prince's reputation intact, even if somewhat diminished. (Popular history seems to have little conscience when it comes to making those who came before seem stupid.) Both Neri and Don Antonio were dedicated experimenters and they knew the proof of transmutation lay in actually making gold and they tried relentlessly. The narrative presented in the letter makes an appealing, face-saving story line, but we need only cast a sideways glance for it to start crumbling. According to the writer,  Florentines were too sophisticated to be drawn into alchemical gold-making schemes, yet a little later we find out Neri was forced to "wander" Europe, chased out of Florence by those demanding the secret of transmutation. Which was it?

The work of Neri's countryman and contemporary Galileo had established the natural sciences as Tuscany’s great patrimony. In the mid eighteenth century, when the letter was written, experimenters were as eager as ever to separate themselves from the charlatans and mountebanks who sold miracle cures and fueled impossible dreams. By then, it was agreed by researchers that transmutation was not possible, but even in the nineteenth century, there was no theoretical foundation to back up this supposition, which made it a sore point. Because of the acclaimed glass book, Neri earned a place in the pantheon of Italy's 'great men', but at a cost. His now 'embarrassing' work on transmutation caused the rest of his legacy to be largely written out of the history books.

[1] Bergman, Tofani 1790. (Fontana was writing under the pseudonym Giuseppe Tofani.)
[2] Ibid, pp. 99 - 101.
* This post first appeared here 24 December 2014.

Sal Ammoniac

Ammoniac crystals, Fan-yagnobskoe coal mine, Tadjikistan,

Photo (c) A. A. Evseev.

Here we will examine "sal ammoniac," a common alchemical ingredient used by Antonio Neri in many of his early seventeenth century preparations. In its pure form, it is a colorless crystalline material and is known to chemists as ammonium chloride. It does occur as a (rare) natural mineral, but it was also manufactured as early as the thirteenth century, as noted by alchemist Albertus Magnus in his De alchymia.[1] Neither he nor Neri provides a recipe for sal ammoniac, but other sources indicate that it was made by allowing urine to putrefy with common salt. French investigators documented another method used in Egypt in the eighteenth century. This scheme involved burning the dung of animals who fed on spring grasses and then sublimating the ammoniac out of the resulting soot. Sublimation occurs when a heated material goes directly from a solid to a gaseous state without ever becoming liquid. Sal ammoniac has this property; when heated it turns to a gas and upon cooling, turns back to a solid.
The usefulness of sal ammoniac in alchemy stems from the fact that when dissolved in water, which it does easily, it immediately dissociates into equal parts of ammonia and hydrochloric acid, which in turn will dissolve some metals, including tin, zinc, iron and (reluctantly) lead. Its most famous use was as an additive to the stronger acid aqua fortis (nitric acid). Together the two formed aqua regis which was strong enough to dissolve gold. At the time that Neri was working, the only known way to dissolve the most 'noble' of metals (gold) was with the 'king' of acids (aqua regis). Neri puts this knowledge to use in his recipe for ruby-red colored glass made with pure gold. His description is light on details, but he does clearly direct the reader to dissolve the precious metal in aqua regis, then gently evaporate away the acid to obtain the red pigment.

Elsewhere in Neri's glassmaking book, L'Arte Vetraria,[2] he uses sal ammoniac in the production of "alemagna blue" paint and in the tinting of natural rock crystal. 

Another of Neri's creations requiring sal ammoniac was Chalcedony glass. It had swirls of every color the glassmaker could produce. He achieved this feat by making extensive use of aqua regis to dissolve a long list of metals. He then gently evaporated off the acid, leaving ultrafine powdered metals, which he added as pigments to the glass melt. 

With this powder, I made a chalcedony in a glass furnace in Antwerp that was then run by a most courteous gentleman; Mr. Filippo Gridolfi. This chalcedony gave rise to work so nice and graceful, that it emulated true oriental agate, and in beauty and delightful colors by far exceeded it.

Today, chemical factories produce vast quantities of the materials used by Neri in his glassmaking exploits and in far higher purities. Having unlimited quantities of every conceivable chemical compound at our fingertips makes it difficult to appreciate the physical labor involved by seventeenth century alchemists, both in the preparation of the glass and in the production of the individual ingredients. The chalcedony glass recipe cited above must have taken workers many, many hours to produce and must have cost a small fortune. 

[1] Magnus 1958.
[2] Neri 1612.
[3] Glauber and others used the term 'sal ammoniac' to describe a related chemical (NH4)2SO4. When mixed with aqua fortis this forms a nitric-sulfuric acid solution, which does not form aqua regis, and does not dissolve gold.

*This post first appeared here 22 August 2014.

Roasting the Frit

Diderot & d'Alembert, L'Encyclopédie (1772)
Raking Out Roasted Frit

Making glass from raw materials involves several steps. In his 1612 book on glassmaking, L'Arte Vetraria, Antonio Neri breaks the process down into parts so that, "given a bit of experience and practice, as long as you do not purposely foul-up, it will be impossible to fail." Pure white sand, or preferably quartz river stones which Neri calls "tarso" is broken up and pulverized into a fine powder. The initial work can be done by heating the stones in a furnace, then dropping them into a vat of clean cold water, where they will fracture due to the thermal shock. The process was often repeated multiple times. From there, the pieces are pulverized in a stone mortar and pestle. Stone, because metal tools would contaminate the quartz, and in the end tint the glass. Finally, a powder is obtained by grinding with a stone tool on a flat granite "porphyry stone." This powdered quartz is the main ingredient of glass.

The second critical ingredient is the flux, what Neri calls "glass salt" or "soda." This can be obtained from mineral sources, but European glassmakers in the seventeenth century extracted all their salt from certain plants. The powdered quartz was mixed with the salt and a third ingredient, which is critical, lime. Lime is simply calcium oxide used by builders to make cement. It is nothing more than pulverized seashells roasted to a high temperature. Neri advises using two pounds of lime for every hundred pounds of salt. He specifies that it should be added to all his frit recipes, but it is not clear that he understood its critical importance; without lime, the glass would be subject to attack by mere water, eventually decomposing. This mixture of soda, lime and silica when heated in a kiln would chemically react forming "frit." The combined materials were raked around in a kiln for a long period (many hours) and finally formed nut sized pieces. It was cooled and heaped into piles in dry cellars where it was aged for a time. This is where some chemical "magic" in glassmaking takes place. The glass salt or soda dramatically lowers the melting temperature of the quartz, all the way down to a point that was easily achieved in a wood fired furnace. When a batch of glass was made, the aged frit was then melted in furnace crucibles and skimmed to remove excess salt, which floated on the surface; it could foul the glass, and smelled terrible. The melted glass, now ready to work, was sometimes colored and finally made into objects by gaffers. 

Neri obtained his glass salt from products shipped by traders from the Levant (eastern Mediterranean). It was supplied as the dried, partially charred remains of special plants that grow in arid seaside conditions; 'Kali' and 'Soda'. Shipping them this way cut down on weight and volume, and prevented rotting. These plants contain large amounts of sodium carbonates. This is a white powder, chemically identical to what we know as "washing soda." He advises, 

In buying either of these make sure it is richly salted. This may be determined by touching it with the tongue in order to taste its saltiness; but the surest way of all is to do a test in a crucible and to see if it contains much sand or stones, a thing common in this art and very well known by glass conciatori.

He crushes any large pieces of the product in a stone mortar, and sifts the result through a fine screen, ensuring that most of what remains is salt.  

As the common proverb of the art of glassmaking says: a fine sieve and dry wood bring honor to the furnace. Then with any of these sodas, 100 pounds of soda ordinarily requires 85 to 90 pounds of tarso.

Neri sets up large cauldrons of clean water over brickwork stoves, adds the plant product and boils the water. He strains the insoluble parts out and reduces the liquid by evaporation until crystals of the salt start to form on the surface. He skims these off and continues the process. Finally he carefully dries the product. Our glassmaker describes several variations of this process, including one in which he takes extreme measures to ensure the purity of the salt and clarity of the finished glass. In all, this is a task that could easily take several weeks to perform for the amount of frit to fill a single pot for the gaffer to work.

Not content with the established materials, our glassmaker experimented extensively with other plants: 

[U]se the husks and stalks of fava beans after the farmhands have thrashed and shelled them. With the rules and diligence prescribed for the Levantine polverino salt, extract the salt from this ash, which will be marvelous, and from which a frit can be made using well-sifted white tarso, as is described throughout this work. A very noble frit will result, which in the crucible will make a crystal of all beauty. The same may be made from the ashes of cabbages, or a thorn bush that bears small fruit, called the blackberry, even from millet, rush, marsh reeds, and from many other plants that will relinquish their salt. *

*These other plants produce potassium carbonate salts with similar properties to sodium carbonate.

** This post first appeared here 9 December 2013.

Glass Pearls

Johannes Vermeer

"Girl with a pearl earring" (1665-6)

Natural pearls, found inside various seashells, have been prized and worn as jewelry since antiquity. The pearl is formed as a secretion of the mollusk; it is the animal's response to an irritant, perhaps a sharp grain of sand, which has become lodged in its tissue. The secretion, called "nacre" is the same material from which the mollusk builds and enlarges its shell. Natural pearls are rare; large, well formed ones are even more so. A famous legend claims that Cleopatra used pearls to win a bet with Marc Antony: that she could spend ten million sesterces on a single meal. She literally drank pearls that had been ground up and dissolved in wine. Because of the difficulty in obtaining pearls, and their high demand among the wealthy, it is not surprising that like artificial gems, artificial pearls have enjoyed a brisk trade throughout history.

In Antonio Neri's era, the early seventeenth century, a number of recipes used glue, egg whites or other organic materials to simulate pearls. These had the obvious disadvantage of being susceptible to degradation by moisture and physical handling. Another alternative was to simulate pearls with glass, and on this count, Neri does not disappoint. Recipe number sixty in his 1612 book L'Arte Vetraria gives his prescription for artificial pearls. Here it is in its entirety:

In fused and clarified cristallo, add three or four portions of tartar from wine dregs. You must thoroughly calcine this tartar to a white color. Stir it thoroughly into the glass, and continue to add more tartar, also well calcined until it is white. Add four to six more portions, always stirring the glass thoroughly, continuing thus until the cristallo takes on a pearl color. In this recipe, I cannot give exact rules, because it is a matter of experience, which is gained through experimentation. Once obtained, you must work the color quickly, because it will dissipate. I have practiced and experimented with this method many times.

"Cristallo" is the exceptionally clear glass the Venetians developed, perfected and were renowned for throughout Europe. "Tartar" is a crystalline growth that forms on the inside of wine casks, what we now know as "cream of tartar." Occasionally, one might spot crystals at the bottom of bottles of wine. They are a rich source of potassium. Neri, the Venetians and others had used tartar as a glass flux over a period of centuries. Here, however, he is not using it as a flux, but as a colorant to give the glass the pearl's shimmering appearance. His claim to making many batches of this glass implies large numbers of artificial pearls were in circulation. Our glassmaker presents a second recipe, which does not make any mention of pearls, but oddly may have much more to do with the evolution of reproducing these treasures of the sea. Recipe number 114 is entitled "The Way to Tint Glass Balls, and Others Vessels of Clear Glass, From the Inside, In All Kinds of Colors, So They Will Imitate Natural Stones." Here, Neri spreads fish-glue on the inside surface of a blown globe of clear glass, followed by various pigments.

Even in his time, artificial pearls found their way into royal courts and onto the canvasses of master painters. The fashion-setting monarchs of France and Britain Catherine de' Medici and Elizabeth I were famous for their extravagant love of pearls. Elizabeth famously purchased faux pearls from Venetian glassmakers to adorn her garments. She commissioned many portraits donning her pearl studded creations. Referring to the famous painting by Johannes Vermeer, Lloyd Schwartz recently observed, "[T]he scholarship on Girl with a Pearl Earring reveals that the pearl isn't really a pearl […] the famous pearl is probably just glass painted to look like a pearl."* It is interesting to note that Vermeer's famous painting was executed in 1665-6, within five years after three reprints of Neri’s book, two in Italian one in English, and only a couple of years before a Latin edition printed in Vermeer's own country.

Around 1680, a Parisian maker of rosary beads invented a type of artificial pearl consisting of a small hollow glass bead, painted on the inside with the iridescent discharge of fish scales mixed with glue. He then filled the beads with wax. Jacquin had apparently rediscovered the shimmering pearly residue of a specific fish. His innovation fueled a new industry; he called the precious pigment "essence d'orient." But the material had already been employed in eastern France in 1656 and according to other reports as early as the reign of Henry IV of France (1572–1610), which closely coincides with Antonio Neri's own lifetime. By 1716, scientists were investigating essence d'orient under a microscope. Rene Antoine Ferchault de Reaumur reported tiny, perfectly formed rectangular plates that reflect the light to cause the shimmering.**

Perhaps more interesting than who discovered what, is the exchange of ideas and the overlap of interest between an Italian alchemist, a British queen, a Dutch painter, a French jeweler and a biologist.


* Also see Anthony Bailey, A View of Delft: Vermeer Then and Now (London: Chatto & Windus, 2001), p. 123, 124.
** For an English summary see The Edinburgh Philosophical Journal October 1839-April 1840 (Edinburgh: Adam & Charles Black, 1840), v. 28, p. 114, 115.

Neri the Scholar

Francesco Bartolozzi, Laurentian Library in the 18th cent.

(click to enlarge).

Whether one's chosen field was medicine, law, religion or alchemy, in the late fifteenth and early sixteenth century, books played as important a role in education as they do today. The schooling of Florentine priest and glassmaker Antonio Neri was no exception. The details of his training at seminary remain elusive, but there is no mistaking that his introduction to alchemy occurred well before his ordination as Catholic Priest around 1598. [1] Since his father was the celebrated physician to Grand Duke Ferdinando, there is a good chance that Antonio had access to wide variety of Medici resources, not the least of which was the famed Laurentian Library, designed by Michelangelo and run by Neri family friend Baccio Valore. [2]  

But we need not look as far as the Laurentian, which was only a ten-minute walk from the Neri household. Closer to home, in fact inside his home, there was the extensive library of his own father. At the turn of the century, it contained 477 volumes, spanning poetry, philosophy, the Greek classics, medicine, pharmacology, surgery, religion, even grammar. [3] We know this thanks to an inventory taken at the time of the physician’s death, leaving a list of titles that has survived the ages, even if the volumes themselves have long been dispersed or lost. At the time, outside of the royal family, it was probably one of the largest collections of books in private hands in Florence. Neri’s father had himself been in charge of the revision of the Ricettario Fiorentino, [4] the gold standard of doctors and apothecaries throughout Europe for medicinal prescriptions, published in 1597 and again without revision in 1623.

Antonio Neri is known best as an artisan who worked with his hands. No evidence has been found to place him at a specific monastery or university classroom. Nevertheless, what emerges from the details that we do have is a picture of a man who was steeped in a literary, scholastic tradition from an early age. His Mother’s father, Ser Francesco, held a degree in law as did her grandfather and great-grandfather. [5] Antonio’s father held a degree in medicine from the “Studio Fiorentino,” the forerunner of what today is the University of Florence.[6]  In addition, it would be reasonable to assume the household library included titles once owned by his grandfather Jacopo, a noted barber-surgeon who was known among the literati. It has been speculated that Jacopo’s best friend in the world [7] was poet Lodovico Domenichi, who wrote of his friend in a sonnet:

Marvel about you the people do,
Over how, one might say, almost stupidly,
So many lecturers and scholars admire you. [8]

Domenichi who had been appointed court historian by Grand Duke Cosimo I de’ Medici, goes on in the sonnet to name a list of mutual friends that includes poets, playwrights and intellectuals of the day.

In a similar way —that is through legal records—we know the contents and titles of the alchemical library of Neri’s sponsor, Don Antonio de’ Medici at the time of his death in 1621. These included several manuscripts by Neri himself, as well as his book on glassmaking. [9] However, one title did escape the attention of the bean-counters; sixty years after Don Antonio’s death, at the death of his son, Giulio, a handwritten book of recipes by Neri was found along with a box of elixirs. “Among them there was a booklet, entitled: Material of all the compounds of Priest Antonio Neri; there is a red dustcover, which says “experiments.” [10]

In his twenties, after a couple of years of making glass in Florence, Neri moved to Pisa where he assisted at the Medici’s furnace run by Niccolò Sisti. Pisa was home to a thriving university, with ample study possibilities, and Neri was proving himself a life-long researcher. From Pisa, in early 1604 he embarked on a seven-year long residence in Antwerp, where he stayed with his friend Emmanuel Ximenes. Ximenes was one of the wealthiest men in Flanders and maintained an extensive library in his palace. He owned many volumes devoted to the chemical arts. [11] In fact, his collection of books was probably the largest in the entire region. [12] Here too, the full list of books is preserved in an inventory compiled after the death in 1617 of Emmanuel’s wife, Isabella da Vega. 

Upon Antonio’s return to Italy, he published his glassmaking recipes in L’Arte Vetraria and then appears to have focused his attention on chemistry and medicine. In the last manuscript he is known to have written, within a year of his death, he writes of a recipe copied “from an old book, here in Pisa” in 1613. 


[1] In his manuscript Tesoro del Mondo devoted to “all of alchemy” (Neri 1598-1600) Neri self-identifies as a priest.
[2] Bartolomeo di Filippo di Niccolò Valori [il giovane] (1535–1606). He was keeper of the Laurentian, steward of the Medici herbal (simples) garden and an early director of the Accademia delle Arti del Disegno. He was a personal friend to Antonio Neri’s father and godfather to his first child (Antonio’s older sister) Lessandra.
[3] Bec 1984, pp. 299–310.
[4] Neri, Benadù, Rosselli, Galletti 1597, 1623.
[5] Ser Francesco di Ser Niccolò di Ser Antonio Parenti (1519 - ?)
[6] Fathers medical degree ref.
[7] . Garavelli 2004, p. 82, n. 186.
[8] Domenichi 1555, Stanza 7.
[9] Covoni 1892.
[10] Ibid p. 193.
[11] Duverger 1984.
[12] Dupré, Lüthy 2011, p. 272; Göttler, Dupré 2009.
* this post first appeared here on 31 Dec 2014.

Glass Beads

Six-layer glass chevron trade beads

(photo attr. unknown)

One of the oldest applications of glass, perhaps the oldest, is the production of beads. That development took place about 5000 years ago, but in the history of beadmaking, glass is a relatively recent innovation. Before glass was developed, beads were made from clay, metal, wood, horn, bone, shell and stone. Examples are included in some of the oldest human artifacts ever found, as old as 100,000 years, and that number has increased regularly with new discoveries. Moving closer to the present, in 1612 the first printed book on glassmaking was published in Italy and it contains numerous references to beads made of ordinary glass, Venetian style cristallo and what we would now call lead crystal. [2] 

In his 1612 book, L’Arte Vetraria, Antonio Neri describes preparing batches of 300 to 400 pounds of a blue-green colored glass destined for beadmakers [3]. The molten glass was drawn out into thin rods and cooled for use by workers who formed beads by winding the glass around a metal rod over an oil lamp. 

I demonstrated this method of making aquamarine in Florence in the year 1602, at the Casino, and I made many batches of it for beadmaking cane, which always resulted in a most beautiful color. Take note, than in Murano for beadmaking cane they take half crystal frit and half rocchetta frit, and nevertheless still get a nice aquamarine; but in pure crystal it is the most beautiful.

Elsewhere, we learn that Neri supervised the production of beadmaking cane, not only in Florence, but also in Pisa. At that time, glass beads were manufactured for use both within Europe and for use around the world as a trade currency. Locally, beads found use in devotional objects in the form of rosaries, where they were called ‘conterie’ and ‘paternostri’ (literally 'our fathers'). Outside of Europe, in Africa, the Americas, the Far East, and in China, glass beads were used in trade for sugar, spices and other goods. On the darker side of history, they were used to buy men, women and children for the slave trade.

The question of Neri’s involvement in the production of trade beads naturally arises, but it is a question not so easily answered. He makes no direct mention of the intended use of the beads made from his glass, but there are clues. On one hand, the Medici family, for whom Neri worked in Florence and Pisa regularly engaged in trade expeditions, on the other hand Neri himself was a Catholic Priest, with some obligation to the Church. His work could as easily have been destined for foreign shores as for the hands of the laity.

Neri’s good friend, Emmanuel Ximenes came from a family of traders, or “bankers” as they were called at the time. They financed expeditions to Africa, India and the Americas. Glass beads were not the only goods used in trade, but they were relatively inexpensive to manufacture and made a convenient ballast material for ships. Empty vessels needed something heavy in the cargo hold to keep the boat from riding too high in the water. Often rocks or sand was used, but barrelfuls of glass beads served the double purpose of a near universally accepted currency. It is easy to imagine Neri’s friendship with the wealthy banker facilitating trade deals, but no evidence has come to light that anything like this took place. 

Antonio Neri visited his friend Emmanuel Ximenes at his palace in Antwerp and stayed for about seven years. It might seem like an ideal opportunity for bead production, except that the port at Antwerp had been blockaded by their Dutch neighbors to the north for several years. They were fighting a bloody war for independence from Spain and any trade that did occur had to be routed to other ports. Emmanuel’s brother Duarte had a large shipment of sugar confiscated in this period and went to considerable trouble to have it returned. [4] This does not rule out a role for Neri in trade beads, but it does make it less likely than when he was living in Italy.

There is also no evidence that I am aware of that the Ximenes were involved in the slave trade. It is true that Emmanuel was a Knight of Saint Stephen, which essentially served as the Tuscan Navy. They regularly intercepted Ottoman pirate and military ships and when caught, the crew was generally pressed into slavery. However, this was not a profit driven activity and by the time Neri and Ximenes met, the later was well beyond the age of active service. 

[1] Old beads: http://www.sciencedaily.com/releases/2009/05/090505163021.htm
[2] Neri 1612, chs. 22, 26, 29, 36, 46, 47, 62, 64, 65.
[3] Ibid, ch. 22.
[4] For a full description of the 1602 Sugar Confiscation, see Roitman 2009, pp. 207–229.
* This post first appeared here 17 Dec 2014.