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

Wednesday, April 30, 2014

Primordial Matter

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 regenerate over time. The metals themselves were thought to undergo a maturation process. 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" 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.

Monday, April 28, 2014

Archiater Reprise

Antonio Neri's family arms.
Archiater was a title used in ancient times for the doctors of Roman Emperors. Later, this term was applied to the head physicians of rulers throughout Europe. Even today, the pope’s chief physician holds the official title of archiater. 

In 1612 Florence, Antonio Neri wrote the first book devoted to glass formulation. His benefactor was Don Antonio de’ Medici, an alchemist prince from the royal family. There is no doubt that Antonio Neri gained some of his expertise at the prince’s laboratory, but his start in the chemical arts is probably owed to his own father. In the late sixteenth century, his father Neri Neri was appointed to the position of personal physician to the grand duke of Tuscany, Ferdinando I. For Antonio’s childhood and teenage years his father was the most esteemed doctor in all of Tuscany. 

Today, the connection between medicine, alchemy and glassmaking might not be so obvious, but in the early seventeenth century all three professions required use of similar materials, equipment and techniques. Here is what I wrote about Neri Neri last year on 14 August:

In the late 1580s, approaching the age of fifty, Antonio Neri's father was appointed the personal physician to Grand Duke Ferdinando de' Medici. The son of a barber-surgeon, Neri di Jacopo Neri - or Neri Neri, as he was known - had parlayed a degree in medicine into a successful and prosperous career. His elevation to 'citizen' status, a decade earlier, gave him entree into the world of the patrician elite and his appointment as royal physician secured a place for his young family near the top of the Florentine social hierarchy.

The fact that Neri Neri gained citizenship at the age of forty and did so together with his father shows it was not a legacy, but perhaps their medical prowess that lead to the award. One requirement of citizenship was possession of a domicile within the city. The baptism register lists Antonio and all of his siblings as residents of San Pier Maggiore parish, long before the citizenship grant. However, it is in the 1580s that we see the first reference to Neri Neri's ownership of the palazzo at what is now 27 Borgo Pinti.

Baccio Valori was librarian, keeper of the royal herbal gardens and the godfather of Antonio Neri's older sister Lessandra. In 1587, Valori received a letter from Filippo Sassetti, sent from India. Filippo was a native Florentine, the nephew of Antonio Neri's godmother, Ginevra Sassetti. He attended university in Pisa with Valori and they became lifelong friends. In the letter, he notes that he has collected rare varieties of cinnamon in his travels along the Malibar coast. His intention was to rediscover the species thought to be a powerful cure of disease by the ancients. He planned to send a parcel of seeds of these and other medicinal plants. "If it pleases God, in the coming year, I will send this to you, so that you may see it all, together with our Messer Neri Neri, who graces my memories."

In the autumn of 1587, Grand Duke Francesco I de' Medici and his wife Bianca Cappello both became ill and died during a visit by the grand duke's younger brother Cardinal Ferdinando. Pernicious malaria was to blame and accounts by physicians on the scene described identical symptoms for husband and wife. The thirty-eight-year-old Cardinal Ferdinando relocated to Florence from Rome; he took charge and assumed power as the new grand duke of Tuscany. Shortly after, he appointed Neri Neri as his head physician.

Friday, April 25, 2014

Rosichiero Glass

The most famous recipe in Antonio Neri’s 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, and was not reliably duplicated until many years after Neri’s death, although pieces made in ancient times have been unearthed.  

Even though it is his 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.
None of these ingredients excepting copper is common in color glass production today; in fact, 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, but it is commonly 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 chemistry is no easier for us than it was for him. 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.

Wednesday, April 23, 2014

The Godparents III

Portrait of Alessandro Gondi as a child (1569)
(Later became godfather of Emilio & Allesandro Neri)
by Anguissola Sofonisba.
This is the third and final part of an examination of the godparents of seventeenth century glassmaker Antonio Neri and his brothers and sisters. In early modern Florence, the families of godparents formed tight alliances, helping each other with business opportunities and social contacts. The Neri family was no exception; their godparents formed a very well connected group. Margherita Ardinghelli appeared as godmother to Antonio's brother Jacopo Neri. Eight years later, her husband Braccio's first cousin, Monsignor Giovanni Alberti, appeared as younger sister Maria Neri’s godfather. Giovanni was also the son of a Florentine senator. He served as protonotary apostolic for Pope Gregory XIII and as bishop of Cortona under Pope Clement VIII. A godfather serving in the papal inner chambers was a good family contact indeed. Also appearing for Maria was Pierfilippo Perini, a physician. Other records indicate Perini was also a lawyer, apparently part of the Ricci household. The Registri lists Maria Neri's godmother as Alessandra di Girolamo Pepi. Among the prominent Florentine republicans was Alessandra's father, Girolamo. He was tortured by Alessandro de' Medici in the 1530s, upon the family's regaining control of Florence after the siege. 

Emilio's two godfathers were Alessandro Gondi (pictured) and Gondi's own father, Giovanbatista. At the time, they were 20 and 66 years-old respectively. The Gondi's ancient Florentine roots trace back to the rule of Charlemagne, who first established the heraldic nobility system in Florence in the year 800. The Gondi's were bankers and landholders in the Mugello region between Florence and Bologna, where the Medici family originated. A branch of the Gondi family became heavily involved in the French court under Catherine de' Medici. Giovanbatista had appeared two decades earlier, in 1564, as godfather for Bianca Cappello's first child Pellegrina. Bianca was the controversial Venetian lover of Grand Duke Francesco de' Medici who later became his wife and Grand Duchess. Giovanbatista's brother Piero was friends with Michelangelo. The artist once gave him the keys to the New Sacristy in the San Lorenzo Basilica in order to hide family belongings during the sack of Rome. In Antonio Neri's time, members of the Gondi family were intermarried with the Ardinghelli and Ricci families. They all supplied godparents to Antonio's siblings, the children of Neri Neri and Dianora. In addition to standing for Emilio Neri, Alessandro Gondi appears again four years later in 1587 as a godparent for Alessandro Neri, the eventual heir to the Neri family's fortunes. 

Lucrezia, the youngest Neri girl, has a single godparent listed in the register, Montiglio degli Albizi. The Albizi family boasted powerful bankers and politicians. This was another case where deep divisions over Medici rule drove a family apart and eventually into near extinction. Luca degli Albizi headed the pro-Medici faction in Florence in the latter half of the sixteenth century. This branch of the family thrived, living in a series of palazzi just a few steps to the west of the Neri's parish church, San Pier Maggiore, close to the Neri home. They resided alongside properties owned by the Altoviti and Valori families. Today, perhaps the best-recognized member of the Albizzi family was Eleonora degli Albizi the young consort of Cosimo I after the death of his first wife, also named Eleonora. Folklore has it that in 1566, Cosimo intended to retire from public life and marry Albizi quietly, after the birth of a girl, but his regent son, Francesco I, forbade it to due to the inheritance complications that would ensue. The story is that Cosimo's long-time personal secretary, Sforza Almeni, leaked word of the clandestine marriage to the family. For his betrayal, an enraged Cosimo murdered Almeni in cold blood.  Eleonora later gave birth to Don Giovanni de’ Medici, the uncle and friend of Don Antonio, Neri's sponsor. The specific Albizi family member we are interested in, Lucrezia's godfather, Montiglio degli Albizi, seems to have eluded history, although the first name ‘Montiglio’ is almost certainly a moniker for an immigrant to Florence from Italy's Piedmont region.

Like his older brother Francesco, Alessandro Neri boasted a godfather from a powerful banking family, this time the Ricci clan. Godfather Federico de' Ricci, was a very famous name indeed. Federico was named for his father's first cousin, who ran the influential Federigo de' Ricci and Partners public bank and helped to finance Cosimo I in the war for Siena. Together, the Ricci and Acciaiuoli families controlled the Tuscan treasury for the Medici. (Giovanni Acciaiuoli was Francesco Neri's godfather).  Alessandro Neri's godfather was closely related to the venerated holy-woman Catherine de' Ricci later canonized as Saint Catherine.  His second godfather, Alessandro Ginori, was a Benedictine monk at the Badia Fiorentina, taking the name of Don Gregorio. He descended from a long line of Florentine merchants, bankers and republican leaders. Four years after the baptism in 1591, the monastery elected Ginori as their abbot. Distinguished for great learning, his peers considered him one of the leading writers of his day. Five years later, he moved to the abbey of San Paolo d'Aragon in the territory of Bergamo, where he died in 1598. The same year saw the death of Neri Neri, Antonio's father.

Monday, April 21, 2014

Casino di San Marco Reprise

The Canio Mediceo di San Marco, Florence
Antonio Neri wrote the first book entirely devoted to making glass from raw materials. L’Arte Vetraria, or in plain English: 'The Art of Glassmaking' did not get written in a vacuum. When Neri put pen to paper for his book, he had been making glass for about a dozen years. He had the opportunity to learn his craft from some of the experts in the field. His first known experience in glassmaking was at the laboratory palace of Don Antonio de’ Medici, a prince from the ruling family of Tuscany. 

The Palace was called the Casino di San Marco. “Casino” not because it was a gambling hall (which it was not) but because of its informal organization like a small country house with the living quarters on the ground floor. It was built by Don Antonio’s father, the former Grand Duke, as a place where Nature’s secrets would be discovered and new inventions would be made. Neri worked at the Casino for a couple of years before moving to Pisa and then to Antwerp, all the while making glass. He returned to Florence to publish his book, and thanked Don Antonio for his long patronage. Here is what I wrote about the Casino last year on 12 August 2013:

Don Antonio de' Medici's Casino was as much a grand concept as it was a physical space. Completed to his father’s specifications in 1574, it evolved into a prince's palace par excellence. Within its walls, grand dinners were held, productions were staged and poetry was read. In 1605 Michelangelo Buonarroti the younger staged a play there titled "The Christmas of Hercules." In its chambers, music was performed, philosophy debated and diplomacy conducted. In its laboratories, alchemy was nurtured, and glass was formulated. It was a sort of grand royal conservatory, melding together art, letters, drama, music and science. From its courtyard, hunters set forth into the Tuscan hills in search of unicorns, and within its workshops, artisans explored the territory of new materials and natural secrets.

The Royal Foundry, as it was also called, became a place of pride for Grand Duke Ferdinando. It was a place that visiting dignitaries specifically asked to see and tour. Behind the doors of the Casino di San Marco, Antonio Neri and his associates worked their magic. This is probably where he first learned the secrets of Venetian style glass composition and undoubtedly much more. He assisted the prince in his research, formulated herbal remedies and helped in the production of luxury gifts for visiting dignitaries.
This was the way that I made chalcedony in the year 1601, in Florence at the Casino, in the glass furnace there. At that time, the task of scheduling furnace-work fell to the outstanding Mr. Niccolò Landi, my close friend and a man of rare talent in enamel work at the oil lamp. I made many pots of chalcedony in the furnace there. I never deviated from the method stated above, I always prepared the materials well and it always came out beautifully in all my proofs.-Antonio Neri 1612, p. 41.

Friday, April 18, 2014

The Godparents II

Opening lines of Piero della Stufa’s MS.
Translating Luca della Robbia from Latin to Italian.
In early seventeenth century Florence, the honor and responsibilities of being a child's godparent was a serious affair. There were the ceremonial aspects of taking part in the baptism, but that was just the beginning. A godparent pledged responsibility to the Church for overseeing the spiritual upbringing of their charge. Beyond the realm of religion, they later brought a child into the family’s web of social, business and political contacts. In the family of Neri Neri and Dianora Parenti, there were ten children. Their fourth child, Antonio, would go on to write the first book devoted to glassmaking formulas called L'Arte Vetraria. Each sibling with one, two or even three named godparents, made in total a list of eighteen family associates. These eighteen had families of their own, and soon the list becomes formidable. The genealogy is interesting; many of these families are intermarried, and a number of the godparents are related directly or have common family ties. However, even glossing over these specifics, a remarkable aspect of the list emerges that demands notice. This is the striking prominence of the names; almost all of the Neri godparents are known to history. They were lawyers, bankers, politicians, ambassadors, courtiers and high church officials.

Continuing where we left off, Francesco Neri was the third child. Francesco's only godparent was Giovanni Acciaiuoli. He was from one of the two influential banking families that managed the Tuscan treasury for Grand Duke Cosimo I. Giovanni had been one of five special administrators charged with the construction of the new seat of the Medici government, the Uffizi palace, on the banks of the Arno River. 

Antonio Neri's godparents were Francesco Lenzone  and Ginevra Sassetti. Lenzone was a Florentine lawyer and notary like Dianora's father. By 1590, he was ambassador to Spain for Ferdinando I. The wealthy Sassetti family was part of the early Medici banking empire. In the sixteenth century, the family continued as close allies of the Medici. They ran a trading operation within India through Pisa and Lisbon. Ginevra's nephew, Filippo Sassetti, was a correspondent with the circle of friends to which Antonio's father belonged. He sent medicinal samples back to Florence from his base in Goa India. 

Loyalist Jacopo di Alamanno Salviati (1537-1586) enlisted as the godparent of Jacopo, the Neri's second son so named. He was both friend and first cousin to Cosimo I. He was also the first cousin of Alessandro Ottaviano de' Medici, who at the time was Bishop of Pistoia and later rose to Archbishop of Florence. He would go on to become a Cardinal, and in 1605, his peers elected him pope, taking the name Leo XI.

Appearing in the register as godfather for Antonio's younger brother Vincenzio was Piero della Stufa, a church canon. The Della Stufa family has a long and venerable history in service to the Medici. Piero translated a book from Latin written a century earlier by famed sculptor Luca della Robbia. In 1570, the same year that Antonio's parents were married, he was named as will executor and administrator to the estate of mannerist sculptor Benvenuto Cellini. Other members of the Della Stufa family had come to the legal and financial aid of the colorful and somewhat volatile sculptor at various times in his life. Cellini himself wrote a book on goldsmithing and sculpture, in which he devotes a chapter to the art of enameling. He does not give specific recipes, but he does discuss transparent gold ruby enamel and the procedure for ‘striking’ the fabled color in the furnace. Striking is the special reheating process required to bring out the deep ruby red color. Neri would later discuss red enamel in letters to his friend Emanuel Ximenes and ultimately publish a short recipe for gold ruby glass in his own book. There is no indication if Neri was familiar with Cellini's 1568 publication, but this is entirely possible, especially in light of the family connection. 

Wednesday, April 16, 2014

The Godparents

Guido Reni (1575–1642)
St Joseph with the Infant Jesus (c. 1635)
It was not too long ago that the life of seventeenth century Florentine glassmaker Antonio Neri was regarded as a blank slate, a complete mystery. We now know that he was born into a patrician family, and probably enjoyed a very comfortable childhood. When Antonio was around age thirteen, his famous father, Neri Neri, was appointed personal physician to the newly crowned Grand Duke Ferdinando de’ Medici. His grandfather was a close friend to historian and poet Lodovico Domenichi. (In fact, Antonio’s second given name is Lodovico). 

Even with all the new material that has come to light, there is still much that is unknown about Antonio Neri, his family and their daily life. A window of sorts into that life can be opened by looking at some of the characters chosen as godparents for Antonio and his siblings, details that have been preserved in the city baptistery records.

The first-born child of Neri Neri and Dianora Parenti was Antonio’s older sister Lessandra. She claimed Baccio Valori as her godfather. The Valori family had a long, tragic history with the Medici. His father, grandfather and great-grandfather were all close Medici supporters, yet each ended up exiled, imprisoned, or executed after relationships soured. On one hand he was faithfully employed by the Medici, yet he reportedly spent a good deal of his time collecting letters and papers documenting his family’s close support of Girolamo Savonarola, the firebrand Dominican priest who lead Florence in the late 1490s, after the Medici had been temporarily expelled from the city.   

Lessandra’s godmother was Marietta Gaetani, also from a noble family, which included dukes, cardinals and popes. They played prominent roles in the politics of Pisa, Rome and Naples for several centuries. Marietta’s father owned the house from whose tower Galileo showed the moons of Jupiter to Grand Duke Cosimo II in 1610. 

Antonio’s oldest brother was Jacopo, named after his still living grandfather, barber-surgeon Jacopo Neri. His godmother, Margherita di Braccio Alberti, (née Margherita di Neri Ardinghelli) was the wife of a Florentine senator and the niece of a Cardinal.  

Of all the Neri godparents, Jacopo’s godfather was perhaps the most notable. Antonio Altoviti was the very controversial archbishop of Florence. It is an understatement to say that the relationship was tense between him and the first Grand Duke, Cosimo I de’ Medici. Nevertheless, he did eventually gain the trust of Cosimo’s inner circle; in 1567 Altoviti was involved in negotiations to bring Venetian glass workers to Tuscany, an agreement the grand duke very much wanted. 

  It is impossible to gain full appreciation of a man through a single anecdote, but we can get a flavor. In 1569, shortly after occupying his post for the first time, Altoviti introduced a new ritual to the Florentine Church. On Holy Thursday, the Bishop would wash the feet of twelve of the city’s poor residents rather than of twelve canons (as done previously) and he would give them generous alms. On 13 December 1573, Altoviti became godparent to Jacopo. But Jacopo would never learn what it was like to have the Archbishop as his spiritual guide. Two weeks after his birth, on the 28th of that month, Altoviti convened a special post-Christmas meeting of regional bishops. It was during this synod that he suddenly and unexpectedly died at the age of fifty-two. Within a few years, the boy would join him.

While these names do not tell us anything directly about the Neri family, they certainly provide us with insight into the people they befriended and trusted. In the next post we will take a look at a few more of the Neri children’s godparents.

Monday, April 14, 2014

Carries the Palm Reprise

Entry into Jerusalem, Pietro Lorenzetti 1320
For Western Christians, yesterday was "Palm Sunday," a feast day that falls on the Sunday before Easter and celebrates Jesus' entry into Jerusalem. His procession is said to have included his followers laying palm tree leaves before him along his path. The connection to seventeenth century priest and glassmaker Antonio Neri is this: In his book L'Arte Vetraria, Neri describes his very best green glass with a colloquial expression; that this recipe "carries the the palm" for all other greens. It seems like an ideal opportunity to reprise this post, which first appeared last year, on 25 October:  


Saint Justina of Padua with a palm frond,
Bartolo Montagna 1490s
In his book, L'Arte Vetraria, Antonio Neri presents a string of recipes for variations of green glass. Finally, in chapter 35, he presents his ultimate green, which he titles: "Another Green, Which 'Carries the Palm' for All Other Greens, Invented by Me." The phrase "carries the palm" alludes to the biblical story of Jesus entering Jerusalem, in which the people welcomed him by laying down cloth and palm branches on the ground in his path. Even before that, the palm branch served as a symbol of victory; in ancient Greece, palm fronds were awarded to victorious athletes. Later in history, Roman lawyers who won a case decorated their doors with palm leaves.


Copper Sulfate (vitriol of copper)
Cristallino was a mid-grade glass made with a soda based plant ash from the Levant called "rocchetta." For this recipe, Neri blends it with common glass, and adds red lead oxide to the mix, in effect forming an early version of what we now call lead crystal. He "cleans" the glass by using the well-established technique of flinging the molten glass into a large tub of clean water. This had the effect of "washing out" excess glass salt (flux). In addition, it provided the opportunity to sort through the fragments to remove any undissolved metallic lead. Lead that did not go into the glass had the tendency to collect at the bottom of the clay crucible. It could then eat a hole in the vessel, resulting in a glass-shop disaster, as he warns: 
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. Then add the color using the powder, made chemically by the dry distillation of vitriol of copper [chapter 31]. Also, add a little crocus of iron, but very little. The result will be a most marvelous beautiful green, the best that I ever made. It will seem just like an emerald of ancient oriental rock, and you can use it in every sort of job.
Crocus of iron is simply iron oxide or 'rust' as it is more commonly known. The vitriol of copper he refers to is copper sulfate. Neri forms it in a laborious process that involves cutting copper sheet into small, coin-sized pieces, mixing it with sulfur, heating in the furnace and then reprocessing it several times. The result is then added to water and the soluble part is further processed, filtered and evaporated. The final product is a pure blue crystalline material that has uses for our alchemist that go far beyond glassmaking, as he alludes to in the final sentence of the book:
Although I have placed here the way to make this powder with much clarity, do not presuppose that I have described a way to make something ordinary, but rather a true treasure of nature, and this for the delight of kind and curious spirits.

Friday, April 11, 2014

Glass Ornaments

Acrylic paint inside clear glass ornaments,
Artist: Alyssa Ruklic (2011?).
In early seventeenth century Florence, scientific investigation and artisanship went hand in hand. In the workshops sponsored by the Medici ruling family. Seemingly unrelated disciplines were practiced under one roof and sometimes even at adjacent workbenches. Skilled artists illustrated rare species of plants that were brought back from around the world by agents of the Grand Duke, these same plants then became the subject of beautiful pietre dure creations, but also the subject of pharmacological experiments in the search for effective medications. Pietre dure was a stone carving art in which scenic images were constructed entirely from inlaid stone and precious minerals. The result of clustering these diverse workshops together was a cross-pollination of ideas and solutions to technical problems that might never occur within a single discipline.

At the Casino di San Marco, the laboratory palace of Don Antonio de’ Medici, glassmaker Antonio Neri was an active participant in this exchange. He worked not only at glass formulation, but also as an alchemist and as something of a pharmacologist. Over his career he made glass for laboratory use and for artistic ends, he searched for ways to transmute metals and practiced his physician father’s skills in medicine. In L'Arte Vetraria, his book on glassmaking, chapter 114 beautifully illustrates the mixing of different arts that was taking place. Here he makes use of glass blowing, painter's pigments and isinglass; a type of glue made from the swim bladders of fish and used by gilders and furniture makers. The result is the creation of unique decorative ornaments. Which he describes as "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"

Have a ball of glass, or else glass of another shape, that is clear and beautiful. Take isinglass [fish glue], that has been infused in common water for 2 days. Put this hydrated isinglass into a bowl of clear water, and boil it until it all thoroughly softens. Make sure there is enough water to make the glue quite soft, and then remove it from the fire. When it is lukewarm put some in the glass ball, and swirl it around well. Turn the vessel, and in this manner bathe the entire inside of the glass with the glue. Then pour out the excess. Drain it and have the following colors ground and ready. Start with minium [red lead], pour it inside the ball of glass, sprinkling the color so that it runs in waves. Use a small spoon made of reed to cast the minium in more areas. Next, throw in the blue enamel. Sprinkle it with the reed spoon forming waves [of color] within the ball. In turn do the same with well ground verdigris [green], then with orpiment [yellow] also well ground, then with lake[organic pigment] well ground.


Always for each color, throw it in waves, in new areas. By means of the glue, which will bathe the paste within, all these colored powders will adhere to the glass. Now take well ground plaster of Paris, put some into the glass and quickly turn it all about, so that it will adhere to the entire glass from within [backing the colors]. Do this operation quickly while the moisture of the glue is fresh, therefore the powders will adhere well. Empty the excess plaster inside through the hole in the ball. It will appear tinted in various colors in a most beautiful sight, which resembles natural hard stone toy amusements. In the end, when the glue is fully dry, these colors affix themselves [to the glass] so they will never come loose. From the outside, the colors will always be beautiful. Affix these balls to wooden bases, or other painted materials, and keep them for their beauty on study shelves, and on desks, where they make a very beautiful sight.

Wednesday, April 9, 2014

Turquoise

Bes  image (ca. 1070–712 B.C.)  Egyptian Faience,
The Metropolitan Museum of Art (26.7.878).
It is estimated that turquoise is among the earliest gems ever mined. With colors that vary from pastel green to a bright sky blue, it has adorned Egyptian sarcophaguses of 5000 years ago, 3000-year-old Chinese art, Aztec death masks and the domes of Persian palaces. 

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

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

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

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

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

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

Monday, April 7, 2014

Salamander Reprise

I first wrote the following post last year on 19 August. Since recent discussion has included the goblins of the Saxon zaffer mines, it seems timely to take another look at the glassmaker's salamander. Glass work has always been a hot, sweaty, exhausting affair. It is not surprising that after a long day's labor one might honestly think they saw small animals scampering around in the fire. The legend, however, is an ancient one; Aristotle, in his History of Animals reported that salamanders were thought to possess the ability to put out fire with their bodies. They became part of the lore among glassmakers in Venice on Murano and were even spotted in Antonio Neri's Florence. Here is the original post:

If one can say that hot-glass workers have a mascot, it is without any doubt the salamander. Since ancient times, this lizard-like, poisonous skinned amphibian was ascribed to exist within fire, even to be born out of the flames. According to legend, its cold body allowed it to survive the heat. To see one in the flames of a furnace was considered good luck, but glassblowers who suddenly disappeared (to work elsewhere) were said to have been "eaten by the salamander." In his autobiography (1558-1567), Florentine artist Benvenuto Cellini offers this recollection:
When I was about five years old my father happened to be in a basement-chamber of our house, where they had been washing, and where a good fire of oak-logs was still burning; he had a viol in his hand, and was playing and singing alone beside the fire. The weather was very cold. Happening to look into the fire, he spied in the middle of those most burning flames a little creature like a lizard, which was sporting in the core of the intensest coals. Becoming instantly aware of what the thing was, he had my sister and me called, and pointing it out to us children, gave me a great box on the ears, which caused me to howl and weep with all my might. Then he pacified me good-humouredly, and spoke as follows: 'My dear little boy, I am not striking you for any wrong that you have done, but only to make you remember that that lizard which you see in the fire is a salamander, a creature which has never been seen before by anyone of whom we have credible information.' So saying he kissed me and gave me some pieces of money.


(Quotation from: J. Addington Symonds "Benvenuto Cellini's Autobiography" in Harvard Classics v. 31, Charles W. Elliot, ed. (New York: P. F. Collier & Son, 1910), p. 11 (book I, ch. V.))

Friday, April 4, 2014

Zaffer

Basilique Cathédrale Notre-Dame de Chartres,
located 80 km (50 mi) southwest of Paris,
(constructed between 1194 and 1250).
The first time that I really noticed glass was at four or five years old, at my grandmother’s house. 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 immediately 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 by their jewelry two thousands years ago. In all three cases, the deep rich blue of cobalt oxide glass was responsible. The source of Middle Eastern cobalt is unknown today, 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. Nevertheless, a strong market for the material developed 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.

Wednesday, April 2, 2014

Who Was Isaac Hollandus?

J. Hollandus,
Chymische Schriften,
(Vienna: 1773)
In early 1603, Glassmaker Antonio Neri traveled from Italy to Flanders, to visit his friend Emmanuel Ximenes. Neri would stay for seven years and in that time he worked on a number of glass related projects including the manufacture of artificial gems using lead crystal glass. An enduring mystery is that in his glass book L'Arte Vetraria, he gives credit to alchemist Isaac Hollandus for a "new chemical method never before used," yet no such recipe for artificial gems has ever been found in the writings of Hollandus.

Neri’s host Emmanuel Ximenes owned several titles by this somewhat obscure figure. Historians conjecture that there were actually two alchemists in the Hollandus family, Isaac and Johannes Isaac. Their relationship is not clear, although they are often assumed to be father and son. We know little about them; some authors date them as early as the fourteenth century. However, a preponderance of evidence point to about the time Neri lived. In his glass book, in the fifth part devoted to artificial gems, Neri writes:

Above all is this wonderful invention. A new way practiced by me, with the doctrine taken from Isaac Hollandus, in which paste jewels of so much grace, beauty and perfection are made, that they seem nearly impossible to describe and hard to believe.

In the 1679 German edition of L'Arte Vetraria, Johannes Kunckel implies that Isaac was dead before Neri came to Antwerp, writing "This is the manner to imitate precious stones, of Isaac Hollandus, (namely, from his posthumous writings) that I [Neri] learned in Flanders" (emphasis added). Yet, coinciding with Neri's visit, playwright Ben Jonson who had just returned to London from the war in Flanders, referenced the pair in his satirical work The Alchemist (1610). There he implies that the elder Hollandus was then dead but survived by "living Isaac." In 1644, the famous Flemish chemist Van Helmont identified Isaac Hollandus as a recent contemporary. In a 1716 treatise, Kunckel paid Hollandus a great compliment and at the same time took a swipe at Helmont saying "and the incomparable Hollandus had more of the fire-art in his little finger as Helmont in his whole body." In another reference, Sir Francis Bacon mentions Hollandus as "by far the greater part of the crowd of chemists."

One Hollandus title in Ximenes' Antwerp library was Opera Mineralia, first published in 1600. The subject of this volume is the philosopher's stone and its production. While there are no artificial gem recipes here per se, there are some intriguing connections between artificial gems and the philosopher's stone, both philosophical and practical. It was thought that the colors of metallic based glass pigments were an indication that the metals were "opened" and became susceptible to alchemical transmutation. Of special interest was the deep red ruby color made by adding gold to the glass melt. In the introduction to a 1797 French translation of Neri's book, artificial ruby or "vitrified gold," is equated to the bible's Electrum of Ezekiel —a red glow seen by the prophet in a vision.

By the mid-eighteenth century, Isaac Hollandus was lauded in industrial arts books as a genius of artificial gems. He may well have been, but the evidence does not support it. All of the specific recipes attributed to Hollandus seem to lead back to Neri's L'Arte Vetraria or its translations. A case can be made that Hollandus' reputation for artificial gems stems from a 1697 plagiarized version of Neri's book. A volume published in France by Haudicquer Blancourt that gives no credit to the priest. Blancourt used Christopher Merrett's English edition as his base and added to the recipes with his own embellishments. The chapter on artificial gems still lauds Hollandus, but its length was now doubled from the seventeen original recipes to thirty-five. The size of this one section jumped from thirteen to nearly two hundred pages, an increase in page-count larger than Neri's entire book. In 1699, Blancourt's version was then translated back into English, again without reference to Neri. There is no doubt that these two editions, with their expanded chapters on paste gems exerted a strong influence on later craftsmen. They may also be the source of the credit given to Hollandus' for paste gems in the eighteenth and nineteenth centuries.

A number of intriguing questions remain unanswered. Chief among them is the nature of Neri’s association with the Dutch alchemist(s). Was Hollandus or his son alive in the first decade of the seventeenth century and did Neri meet with either of them in person? We can only guess. The Hollandus men are notable, if not enigmatic, characters in the transition from alchemy to modern chemistry. Historians would very much like to know them better. Nevertheless, there can be no doubt of the strong impact Hollandus made on Neri. Isaac holds a singular honor as the one person named in Neri's book to whom he gives specific credit. As research on early modern science has progressed, the importance of communication between practitioners has emerged as a central theme. A meeting of the minds between Neri and Hollandus, if it ever occurred, would rank as a prime example of technology transfer with a definite impact.


For a comprehensive look at Hollandus see: Annelies van Gijsen, "Isaac Hollandus Revisited" in Chymia: science and nature in Medieval and early modern Europe, Miguel Lòpez-Pèrez, Dider Kahn; Mar Rey Bueno, eds., (Newcastle upon Tyne, UK: Cambridge Scholars, 2010), pp. 310–324.