The Dance of Lead Crystal Reprise

Roemer type drinking glass c. 1677,
George Ravenscroft.

The entire fourth part of Antonio Neri's book L'Arte Vetraria is devoted to the preparation of lead glass, a forerunner of what is now commonly known as lead crystal. This section is unique in the book in that it contains the only instance of the author giving direct advice to glass artists themselves:

"To work lead glass into various drinking glasses or other vessels, or even to draw cane for beadmaking, it is necessary to raise the punty [out of the melt], and to make a gather of glass by turning. Take it out, let it cool somewhat and then work it on a well-cleaned marble [marver]. The marble should be somewhat cool, and well bathed with water before use."

He goes on to describe what might be termed a kind of dance with the glass. As with a human partner, gentle patience is required in learning the boundaries of what can and cannot be done. Ultimately, an artist must come to understand the material's behavior and personality in order to result in a great partnership. For the artist who makes unrealistic demands, glass can be a heartbreaker.  

"This sort of glass, lead glass, is so runny that were it not cooled, and taken up by turning [the punty] to wind a gather, it would be impossible to work. It is so runny that it would not even hold onto the punty, because it is as loose as soup. This arises out of [the fact that] the lead calx causes it to become very fluid."

"Namely, gather the glass little by little, allow it to cool, and work it over marble frequently bathed in water. Furthermore, make sure to keep the pot of glass rather calm, and in a place in the furnace where it will not see too much heat, otherwise it will not be possible to work this glass at all."

It is true that the formulation of modern lead crystal is a relatively recent development. This is a composition of crushed silica (sand or quartz), potash (potassium carbonates) and lead oxide substituting for calcium to stabilize the composition. It is also true that lead has been added to glass since its invention a few thousand years ago. It is not clear that this addition was always intentional, but a Babylonian tablet of 1700 BCE gives a recipe for pottery glaze that explicitly contains lead. At some point, a discovery showed that small amounts of lead and pigment smeared on glass and fired made stained glass paintings possible. The earliest examples of colored stained [1] glass windows date to first century Pompeii and Herculaneum.  In medieval Europe, leading up to Antonio Neri's time, lead glass was used in mosaic tesserae and in artificial gems.

Finally, it is worth noting that Neri's childhood church in Florence, Cestello (now called Santa Maria Maddalena dei Pazzi), was then run by Cistercian monks. It was the Cistercian luminary St. Bernard of Clairvaux who, in the twelfth century, built the first church with large windows, urging, "The soul shall seek the light by following the light."

This post first appeared here 15 November 2013.
[1] See comments, edited 11 November 2014.

Witch’s Brew of Glass

Glass pumpkin evocative of chalcedony glass
Courtesy of  Smithsonian Museum store.

In honor of Halloween, we will take a detailed look at chalcedony glass; this is one of, if not the most colorful types of glass ever made. In the seventeenth century, it was one of the most dangerous for glassmakers and artists, containing a veritable “witch’s brew” of toxic materials. In his 1612 book, L’Arte Vetraria, glassmaker Antonio Neri presents three recipes of which he is clearly very proud. Each of the three is attended by a complex list of ingredients. He describes the end result this way:

It will be adorned with so many graceful and beautiful areas of undulations, and enhanced with the play of diverse, lively, flaming colors, that truly it will seem nature cannot attain so great a height or grand a prize. [1]

In the same passage, Neri explains the importance of purifying each ingredient and eliminating all contamination. In so doing, he provides a fascinating insight into the thinking of an alchemist. He writes:

There is no doubt that in this art, when the ingredients are well prepared, they permeate the glass with dazzling lively colors. Impurities will ordinarily impede the entry of the tinctures into the glass, and prevent their intimate unification. However, when you open the colors of the metals well, and separate them from their impurities and sediment, their beauty will always by far surpass those that are common and ordinarily made in the furnace. [2]

To Neri’s mind, the metals used as pigments must undergo a process of “opening.” Once this was done, each metal’s characteristic color or “tincture” was free to permeate the glass, provided it was free of impurities. Today we might say that by reducing each metal into an extremely fine powder, the individual atoms more easily disperse in the glass. Neri’s “opening” process usually involved dissolving a pure metal in an acid and then slowly evaporating the liquid, resulting in a fine powder. Most color arises because, once in the glass,  the metal atoms block some parts of the spectrum, but not others. The result is that each metal gives rise to its own hue and only because it is dispersed in the oxygen rich environment of the glass matrix. 

 The striking point here is how the alchemist’s model was a perfectly adequate description for the times, in the same way that the atomic model works for us. Unfortunately, there was less awareness of the negative health consequences in some of these preparations. The evaporation of powerful acids could (and can) certainly cause acute respiratory and tissue irritation. However there were far more insidious dangers lurking in Neri’s chalcedony recipes.

In his first prescription, he dissolves silver, mercury, cobalt, manganese, copper and iron. [3] Some of these have been prepared with sulfur which also ends up in the mix. He evaporates it to a powder and adds it to well seasoned, good quality clear glass along with pulverized chimney soot. He notes “When you stir [the molten glass] thoroughly it gives off a definite blue smoke.” Specifically hazardous in this recipe is the formation of mercury fumes, which are extremely toxic to breathe. 

He advises that in the furnace the glass appears “as red as fire,” but that “master craftsman always pinches off the glass for the job with nippers, and reheats it, in order to make waves, undulations and interplays of the most beautiful colors.” The reheating process is known to modern glassmakers as “striking,” a maneuver that brings out surprising color in some glass formulations. He suggests that this chalcedony can be used to form drinking glasses to more shapely cups, saltshakers, flower vases and similar vessels.

In his second and more sophisticated preparation Neri dissolves the materials in groups, in six separate flasks, only then combining them. He also adds new materials: lead, zinc, “blue painters enamel,” antimony and red varnish. The final recipe for chalcedony introduces new purification procedures and increases the number of separate flasks to nine. Additional ingredients include metal sulfides, ultramarine, tin, arsenic (read: death's calling card) and crimson paint. 

It is tempting to dismiss a few of these ingredients, like red varnish, or pulverized chimney soot; organic materials that would readily decompose in the heat of the furnace. However, Neri is known to have been a careful experimenter and these additions may well have had an effect on the melt, even if not in terms of color. Of the third recipe, which Neri developed in Antwerp, he wrote: 

Many Portuguese gentlemen in the practice of appraising jewels said that nature could do no better. This was the most beautiful chalcedony that I have ever made in my life. While it may be quite laborious and take a long time to produce, the result is fit for a king. I presented His Excellency, the Prince of Orange, with two vessels of this chalcedony, which delighted him greatly. [4]

[1] Neri 1612, p. 34.
[2] Ibid.
[3] Manganese and cobalt were unknown as distinct metals, but were used in their oxide forms, mined as minerals.
[4] Neri 1612, p. 48. The prince of orange was Philip William.

Alessandro Neri

Ecce Homo by Titian, circa 1570-1576

Antonio Neri was the son of a royal physician and the grandson of a well respected barber-surgeon. At the turn of the seventeenth century he pursued a career as a priest in the Catholic Church, but with the rare distinction of alchemy as his specialty. He is best remembered for his book on glassmaking, but he also wrote on the subjects of chemistry and medicine; an area of study that his family had embraced and would continue to practice  for several generations. 

According to Florentine genealogy records, Antonio's mother died in 1594, at the age of 42. She had given birth to ten children; Alessandro was the youngest, born in 1587. The same year as her death, the family would loose, Antonio's grandfather Jacopo, the barber surgeon. He had moved the family back to Florence after the turbulent 1520s; the years of what would be the final attempt to re-establish a self governing republic.  In 1598, just as Antonio finished seminary his father died leaving his ten children orphaned. A year later fifteen year old Emilio died on Christmas day.  Details of how the family survived this series of calamities may never be known, but in the end it was the youngest child, Alessandro who inherited the family house and fortune. Only eleven years old at the time of his father's death, an administrator was appointed by the court to oversee his and his siblings interests until they were of age. By all indications, the Neri children were well cared for; the list of godparents reads like a who's-who of the Florentine elite, including wealthy bankers, lawyers, senators and curia officials at the Vatican.

Alessandro would become the royal physician’s main heir. We might expect this honor to fall to the eldest son, and how the youngest of the seven brothers could end up in this position is a matter ripe for conjecture. Antonio and perhaps Francesco were in the clergy and therefore ineligible. We can surmise that the first of the sons named Jacopo died in infancy and if the second Jacopo survived he along with Vincenzio were somehow also out of consideration. One compelling scenario passes the family inheritance to fifteen-year-old Emilio, who would also die within a year leaving the mantle to Alessandro. Not yet of legal age, the family assets would have been held in trust, perhaps by his mother’s brother, notary Agostino Parenti.

Future research will likely uncover more details about the family after Antonio's death in 1614, however, a nice outline is already in place. In 1620, Alessandro inherited a second house from his uncle Agostino. It was located outside the city walls in a wealthy neighborhood, just to the southeast of Florence. It was along the old road called Via del Ponte a Ema.

In a 1630 court case in Rome, Orazio Morandi, abbot general of the Vallombrosans gave testimony. One  incidental remark he made indicates he was a Neri family friend; he told prosecutors that when he lived in Florence he often saw fellow astrologer Simon Carlo Rondinelli at the home of Alessandro de’ Neri. [1]

Although the exact date is not clear, Alessandro would marry Caterina di Becci and have three children; Neri, Dianora and Filippo. We can speculate, the first two were named after their grandparents, and the third after Saint Philip, canonized in 1622. Dianora was married to Ottaviano Buonaccorsi and had a son named Alessandro.

The bloodline would continue for another generation through Alessandro's son Neri, who would enroll in the medical program at Pisa and become a physician in his own right, taking a degree in 1646, where his diploma is still on file. [2] He in turn would marry Margherita Scalandroni who gave birth to Ottaviano. Alessandro, Francesco and Caterina.

At the end of the seventeenth century, historian Giovanni Cinelli wrote about our glassmaker’s nephew, who at the time had been practicing medicine for twenty years:

Succeeding M. Neri Neri, is a grandson [Neri di Alessandro], alive today, [1677] a man of good taste, who is delighted by pictures and sculpture, who has imitated his grandfather Neri, by [collecting] many paintings and gallant statues by talented artists. Two small bronze horses by Giambologna, many works of [Simone] Pignoni and others, among which are two marvelous holdings; a waist-up Ecce Homo by Titian and a Satyr of beautiful ancient bronze which is wonderfully captivating; it is of the Greek manner and expresses an attitude of prompt movement that recalls liveliness, the muscles are very well prepared. Finally, a statue of Cupid flanked in marble in the best Greek style. [3]

The elder Alessandro’s daughter, Dianora, would marry Ottaviano di Camillo Buonaccorsi, who gave birth to seven children. Her son named Francesco would marry into the Medici Family, coupling with Aurelia de’ Medici, daughter of Luigi di Francesco.

In 1768, historian Domenico Maria Manni wrote about the family. [4] In a short pamphlet about ancient Christian tombstones, he reports on the lineage of his patron, Girolamo Neri, a Camaldolese abbot. It traces the family back through two centuries, back to our doctor Neri Neri and to Antonio the glassmaker. Manni connects Girolamo to the family through the elder Antonio, the brother of Jacopo Neri, the barber surgeon.

Although further work is needed, all indications are that our glassmaker’s branch of the family died out by the end of the eighteenth century. [5] The family arms do not appear in use again, nor is there any evidence of a Neri tracing his heritage to the noble family of physicians. It seems finality is provided by Manni. He references a court judgment which awarded inheritance of the property of the extinct branch to Girolamo Neri’s kin. 


[1] Dooley 2002, p. 32. Dooley states that Alessandro is not related to Antonio Neri, but I feel otherwise; the name, timing, and circumstances are a perfect fit. His conclusion may be based on the scant family history available to him. Cf. ASR 1630.
[2] Mazzatinti 1917, p. 44, n. 549.
[3] Cinelli 1677. 
[4] Domenico Maria Manni, a member of the Messina scientific society known as the Accademia Pericolante. Manni was a prolific historian, although has on occasion been accused of careless work. For instance, he misidentifies Antonio’s mother as ‘Dianora di Ser Agostino di Ser Francesco Parenti’ Manni 1763, p. i-vi.
[5] Mecatti 1754, p. 77; Manni 1763, p. v.

The Inquisition Reprise

Insignia of the Inquisition, 1574.

The mandate of the Catholic Church's inquisition was to stamp out heresy. Although empowered to impose sanctions that included torture and execution, such extreme measures were not imposed casually. Nevertheless, the Holy Office of the Inquisition  was not an organization with which to trifle. In 1600, just over a decade before Neri's book was printed, former Dominican friar Giordano Bruno was convicted of heresy and burned at the stake in Rome's Campo de' Fiori market, albeit after nearly a decade of confinement and numerous opportunities to recant. Shortly before that, the inquisition ordered Neapolitan polymath Giambattista della Porta to disband his group of scientific investigators and to cease all publication without special written permission from the Church, an order with which he readily complied. Famous French essayist Michel de Montaigne complained of having books confiscated upon entering Rome, although in Florence he was welcomed with open arms by Francesco de' Medici at the Casino di San Marco, where Antonio Neri would later work.

There was special attention paid to books, because they carried the potential to 'corrupt' large numbers of people over a wide geographic area. Heresy was considered a disease of the mind, the devil's work, and books were seen to be a potential source to spread the infection, especially books from the Protestant quarters of Europe, but also from the 'misguided' notions of early scientific investigators.

The last page of Neri’s L'Arte Vetraria is devoted to the official permissions that were necessary to print and sell the book. Here we read that Pie[t]ro Niccolini, Vicar of Florence (a man destined to become the archbishop) ordered Canon Filippo del Migliore of the Florentine archdiocese to review the manuscript. Upon doing so, he found nothing that "contrasts with Christian conscience." Next, it was passed to the Holy Office of the Inquisition, where the head inquisitor of Florence, Fra Cornelio Priatoni from Manza, assigned that the manuscript be reviewed by Agostino Vigiani, Regent of Servants. Final approval came from Florentine Senator Niccolò dell’ Antella.

Within a few years, Cornelio Priatoni would  be embroiled in the investigation of Galileo. In fact, the reviewers of Neri's glass book reads like a cast of characters from the initial investigation of the famous astronomer. The Galileo case would also include Ferdinando Ximenes, the brother of Antonio Neri's good friend Emmanuel. Ferdinando was prior of Santa Maria Novella where the inquisition was based. In fact, Emmanuel's uncle, after whom he was named, also worked in the Holy Office of the Inquisition in Florence and would later give testimony in the Galileo affair.

Writing that could be perceived to defy the Church's teaching was a serious concern for authors in Italy, even those under the protection of the liberal Medici family. Although not overtly heretical, Neri's other manuscripts could have easily fallen into this category. Thankfully for our alchemist and glassmaker, upon reading Neri's book, Vigiani stated "I have not found anything repugnant to the Christian conscience and good customs, but [a book] full of things and natural secrets, no less useful than curious." 

This post originally appeared here in a slightly different form on 13 November 2013.

Pirates!

Sea fight with Barbary corsairs, c. 1581
Lorenzo Castro.

In the early seventeenth century, moving goods and travelers around the world was big business; it was an excellent way to find adventure, make a fortune or even become famous. On the other hand it was also an excellent way to lose one's freedom, loose a fortune or lose one's life. International trade affected Florentine glassmaker Antonio Neri in at least two major ways; first as a consumer of exotic materials and second as a traveler. Land routes were plagued by highway robbers, corrupt officials and a host of other problems that included keeping perishables viable over long journeys, keeping pack animals in good health and navigating unreliable roads. Transport by sea promised a potentially quick journey, but at the risk of bad weather, water damage and the dreaded scourge of pirates.

In early 1604, Neri traveled to Antwerp to visit his friend Emmanuel Ximenes, who as it happens was himself an international banker; he provided the financial backing for trade expeditions to the Far East, Brazil and Africa. His extended family ran what today would be recognized as a vertically integrated corporation. The control of raw materials, to the supply chain, through to finished products was under the common management of the family. It is an open question if the Ximenes family supplied Neri with materials for his work in Florence, but it is undoubtedly the case for his seven year long visit to Flanders. 

With Ximenes extensive shipping connections one might well ask why Neri did not take a boat from the Medici’s port of Livorno near Pisa, sail to one of the Spanish or Portuguese ports, where Ximenes had family and then on to Antwerp which was, after all a Spanish domain. It would be faster and one might think safer, weighed against the very real perils of violence, highway robbery and a host of other dangers when traveling by land. 

The sea route, however, was in fact far more problematic and dangerous. The Mediterranean was teeming with pirates and privateers. Privateers were state sponsored raiding parties, who commandeered the trade ships of their enemies and split their bounty with the government, often stranding the crew or selling them into slavery; it was a very lucrative enterprise, even if often short lived. Pirates, on the other hand, were independent operators, commonly they were former navy men who had lost their commission or otherwise ran afoul of their sovereigns. Basic equipment for any pirate was a chest of flags of the various nations. For any ship encountering another vessel on the high seas running under the same flag, the very first order of business was to ascertain if it was a friend as presented or a foe in disguise. An elaborate series of secret signals would follow. To complicate matters, the signals were sometimes compromised or changed without notice.  For the Spanish treasure ships returning from South America, evading pirates in the Caribbean at the start of a journey was matched by similar perils the last few days before making port in Spain. Tuscan and Venetian ships were in conflict with the Ottomans, but did conduct trade with them through intermediaries. The Dutch were undercutting Spanish deals in the Far East, while the Spanish paid cash bounties for any ship caught trading south of the equator. Meanwhile, the English were at war with the Spanish, trading with the Ottomans, but amicable with the grand duke and Tuscany.

The Barbary Coast in Tunisia was a popular haven for pirates. Infamous at the time was Captain Jack Ward, [1] an Englishman who found shelter with the Ottomans through the local governor [2] to whom he paid ten percent of his bounty. Ward with his crew had converted to Islam and caused no end of grief to all European shipping. This included traders from Spain, the Netherlands, Britain, France, Tuscany and Venice. Ward had amassed a fleet of his own based on the African coast near Italy in Tunis. From here he conducted operations as far north as Ireland, running them under the Tuscan flag as well as numerous others.

Despite all these issues, for Neri, the biggest impediment by far to traveling by sea or by land was that he was heading into a confrontational hurricane. Antwerp was the calm at the center of a bloody war that thrashed and destroyed the surrounding countryside. The Dutch fleet had blocked the city port on the Scheldt River and opposing armies clashed in a great ring around the Low Countries. This is what Emmanuel Ximenes was alluding to in his letter of December 1602 when he said “the lack of peace in these countries prevents me from recommending them for you to come or not” [3] The northern Netherlands were in the midst of a war for independence against Spain and the Holy Roman Empire.  These two superpowers of Europe were governed by the same tightly-knit Habsburg family, who at the time controlled what are now Portugal, Spain, Southern Italy and Flanders on one side of the family; Germany, Austria, Hungary and Transylvania, on the other. At the same time, the region had become a haven for formerly Jewish "New Christians" (like the Ximenes family) after their expulsion from Spain. [4] The city was blocked from sea trade by their Dutch neighbors to the north and armed confrontations with imperial troops from the south demolished surrounding towns. The conflict threatened to spill into the city for which Neri was bound.

The other way that international trade affected Neri was through the materials so necessary to glassmaking, to medicine and to his other alchemical activities. As our priest makes clear in his book, the quality of ingredients must always be tested and assayed before purchase or use. Unscrupulous merchants could and did mix or dilute expensive materials with inexpensive fillers and made unreported substitutions. The level of mistrust over imported ingredients can be better appreciated through an understanding of just how chaotic life was on the high seas. Even generally honest traders might turn to deceptive or otherwise questionable business practices when faced with the staggering losses of an entire ship and its contents. 

As the first decade of the seventeenth century unfolded, the pirating of trade ships turned into a well-organized and quite profitable occupation. Operations blanketed the entire Mediterranean and the eastern Atlantic from the Canary Islands to Ireland, which as we have seen complicated Neri’s travel arrangements in the region. Captain John (Jack) Ward was based in the Algerian and Tunisian Barbary Coast and commanded a formidable armada. Dutch born Zymen Danseker (Simon the Dancer) specialized in raiding Spanish and Portuguese trade ships. Much to Spain’s dismay, the Dutch set up outposts in India, Africa, Asia and the Americas circumventing the Habsburg’s previous monopoly.

As pirating became endemic, friction started to build between competing interests. The British and the Florentines clashed often in the Mediterranean. The grand duke employed English mercenaries to harass Turkish (Ottoman) vessels. The Ottomans were valued trading partners to the London based Levant Company. The Ottomans, upon seeing a ship manned with Englishmen, did not know whether to extend a welcome or to prepare for a fight.  Meanwhile, from his Barbary base of operations, Captain Ward continued to take British ships, strand crews and reap the rewards. All the while, he seemed to enjoy an indifferent if not outright amicable relationship with Grand Duke Ferdinando. This “understanding” developed after the sound thrashing Ward received, in 1607, at the hands of the Knights of Malta and the Knights of Saint Stephen. Once a pecking order was established with Florence, Ward did very well for himself. In June of 1608, the following description was given at court in London and then repeated to the Venetian senate through their ambassador. 

John [Jack] Ward, commonly called Captain Ward, is about 55 years of age. Very short, with little hair and that quite white; bald in front; swarthy face and beard. Speaks little and almost always swearing. Drunk from morn till night. Most prodigal and plucky. Sleeps a great deal and often on board when in port. The habits of a thorough "salt." A fool and an idiot out of his trade. [5]

This "idiot" outlived many of his detractors, evading capture and sleeping late until the ripe old age of seventy. For a man of his occupation this was a remarkable accomplishment. Reports claim he succumbed not to the sword of a British officer, but to the ravages of the plague in 1622.

[1] Jack (alias John, Birdy) Ward (c.1553–1622),Also known as Siemen Danziger, Zymen Danseker, Simon de Danser, Danziker, Dansker, Danser and later after conversion to Islam, Yusef Re’is or Reis.
[2] Uthman Bey.
[3] Ximenes 1601–11, 5 Decembre 1602.
[4] For an excellent synopsis of the historical events leading up to the 80 years war see Christman 2005.
[5] Brown 1904, (no.268 ), 23 June 1608; see also (no. 2), 6 June 1607; (no. 7), 11 June 1607; (no. 33), 21 July 1607; (no 34), 25 July 1607; (no. 112), 15 Nov 1607; (no 319), 4 September 1608.

San Giovanni

"Florence - Church of San Giovanni, the Baptistry",
Photo: Giacomo Brogi (1822-1881).

Dear readers, I will be traveling all day, so I beg your indulgence in putting up with the repeat of a post which first appeared here last November. Regular service will resume with Friday's column.

The San Giovanni Baptistery stands in the heart of Florence, directly in front of the city's most famous structure, Santa Maria del Fiore Cathedral, also known as The Duomo. The church and its dome are so large that they dwarf the baptistery by comparison. Nevertheless, a simple look inside its cavernous, octagonal space easily shatters this illusion. In Antonio Neri's time, this place was a civic hub; a space where masons and tailors rubbed shoulders with nobles and princes. One of the oldest structures in the region, it was also one of most cherished, clad in polychrome marble, with imposing bronze doors intricately sculpted by masters. Michelangelo dubbed them "the gates of heaven." It was here, in this ancient basilica that the future of Tuscany could be seen plainly, in the eyes of its youth. New generations of Florentines were welcomed into the world by their neighbors, anointed and christened, as they had been for centuries. The current structure dates to the eleventh century, but it replaces octagonal baptisteries built on the same spot as early as the fourth century, originally surrounded by a cemetery.

Antonio Neri was baptized here, as were all his brothers and sisters, his parents, some grandparents and quite possibly some much earlier relatives. His sponsor, Prince Don Antonio and his Medici ancestors were also given rights at San Giovanni, in the same octagonal marble bath at its center. The unusual font was a sister to the one still standing in the identically named baptistery in Pisa. Along each side, there was a dry-well. By standing in it, a priest could perform the ceremony and avoid jostling by the crowd. Legend tells that one of the stations showed the repair made after poet Dante Alighieri took an axe to a well in order to free a child who had become entangled and was at risk to drown. The font was replaced later in the same year of Antonio Neri’s birth, 1576, on orders of the Grand Duke, in preparation for a royal baptism.

The ancient mosaic tile floor, although repaired many times, still shows its original signs of the zodiac and other early Christian iconography. As a newborn infant, tightly wrapped in swaddling, Antonio Neri would have been carried across that floor, busy with families and children, and then gently handed to the priest, perhaps by his father, already a famous physician. Joining them would be his grandfather the barber surgeon, his other grandfather the lawyer to Michelangelo, his godparents, other family, friends and perhaps a wet nurse. His mother stayed at home with her close friends to recuperate from the ordeal of birth, and to prepare for a neighborhood celebration. Even in the dead of winter, if his eyes were open, the sparkling glass mosaics covering the entire domed ceiling of San Giovanni could not have failed to catch the wandering eyes of this future glassmaker.

Black is Beautiful Reprise

Black glass cameo vase, c. 1900
Thomas Webb.

Antonio Neri was a technical adept, a student of alchemical history and a glassmaker extraordinaire. He was also a gear in the Medici innovation machine. The glass recipes he developed were likely put to work in the glass shops sponsored by the ruling family in Florence, Pisa and elsewhere. Making advances in technology gave the region a competitive advantage; encouraging the arts cemented a reputation for creativity that endures to this day throughout Tuscany.


Black is one color that has given glassmakers difficulty ever since the material's invention over four thousand years ago. It is easily approximated for large, heavy objects, but to achieve a true solid black in blown vessels, or thin layers is a challenge even for current technology.

Obsidian is a naturally occurring volcanic glass that was prized in antiquity, most often occurring in black or very dark brown. In prehistoric times, it was coveted for cutting tools and arrowheads. As technology advanced, it was ground and polished for mirrors. Later, obsidian became popular in ornamental objects ranging from dinner plates to jewelry. The production of obsidian, gemstones and other natural materials through artistry was a quest that kept glassmakers busy.

In many ways, making black glass shows the other side of challenges in making colorless crystal; instead of a formulation that will transmit virtually all the light falling on it, the aim is to produce a glass that will absorb virtually all the light. In his book, L' Arte Vetraria, Neri presents three recipes for "velvet black" glass (# 51-53), and three recipes for black enamel (#100-102).

His first black glass is made with the discarded broken pieces of "glass of many colors." To this, he adds 'zaffer,' a cobalt ore used to produce deep dark blue, and manganese, which produces a magenta color. He advises that it will be good for bead making cane and other work. For his second black glass, he starts with high quality frit to which he adds lead and tin oxides. This forms an opaque, white lead crystal, which he tints with calcined "steel" (probably bronze) and pulverized iron flake. He claims that after twelve hours "the glass will be a most beautiful velvety black." Neri's ultimate black glass is his simplest. He starts with his 'rocchetta' frit, and adds the dried, pulverized dregs left in red wine casks, advising us to go slowly since it froths up. He allows it to cook on the fire for four full days, and finally "washes" the glass by flinging a ladle-full at a time into clean cold water. He then re-melts it; "You will have a black fit for any job and more marvelous than all the other blacks of which I have written."

* This post first appeared here on 8 November 2014.