Cardinal del Monte Reprise

Portrait of Francesco Maria del Monte
Ottavio Leoni (1578–1630)

In the early seventeenth century, Cardinal Francesco Maria del Monte was the unofficial Florentine cultural ambassador in Rome. He regularly entertained visiting dignitaries and represented the Medici family's interests within the Vatican. He was an avid art collector, glass enthusiast and amateur alchemist.  He was a patron to the artist Caravaggio, to the astronomer Galileo and a dear friend to Neri's employer Don Antonio de' Medici.

There is a chance that he met Glassmaker Antonio Neri in person; in 1602 he visited the Casino di San Marco, where the glass foundry was located and he returned in 1608, although by then Neri was in Antwerp. The strong bond of affection between Don Antonio and Cardinal Del Monte is clear from their extensive correspondence and gifts to each other.  In addition to their passion for alchemy, the two shared a strong interest in glassmaking technology.

Del Monte collaborated with Niccolò Sisti, the grand duke's glass foundry master at Pisa, where Neri also worked for a time. Sisti often provided Del Monte with glassware for Medici customers within the College of Cardinals in Rome. Thanks to the cardinal's patronage, many glassmakers in Rome were brought to the appreciation of the papal court.  

There are indications in Neri's 1600 manuscript that he visited Rome. If so, it is hard to imagine him not seeking an audience with the cardinal, either at his villa on the Pincio,  overlooking the city or at the Palazzo Madama, now offices of the Italian Senate. The palazzo was Del Monte's main residence near the center of Rome, appointed in fabulous luxury and arranged to accommodate a constant flow of dignitaries from around the world. The villa, on the other hand, was where his alchemy laboratory was located. This was a more secluded retreat where the cardinal could entertain guests with more discretion.

Del Monte's will shows that at the palazzo he maintained an entire room, "gabinetto dei vetri" [cabinet of glasswork] that housed five hundred pieces of glassware. It cannot go without mention that he was also the proud owner of what has become one of most celebrated pieces of ancient glass, now referred to as the Portland Vase.

This post first appeared on 27 November, 2013.

Lake of Flowers

'The Miracle of the immobility of Santa Lucia'
Leandro Bassano, using Florentine lakes.

In the final part of Antonio Neri's 1612 book on glassmaking, [1] he presents several recipes that are devoted to pigments for painting. His intention for including them is for their application on glass objects, but these were the same materials used in general by fine artists in the early seventeenth century. 

In his recipe #110, the Florentine priest gives a wonderfully simple method to extract the color from common flowers. The term for these pigments is "lakes." Once obtained, the pigments were often used to dye a powdered carrier material in order to give them more body and behave like other paint. From there they might be mixed into egg-tempera, varnish or oil depending on the application. It is likely that Neri used similar pigments for the illustrations in his 1598 manuscript.[2] Here is his recipe in its entirety: 

A Way to Extract the Lake [3] and Color for Painting, from Orange Blossoms, Red Poppies, Blue Irises, Ordinary Violets, Red Violets, Carnations, Red Roses, Borage Flowers, Day Lilies, Irises, and From Flowers of Any Desired Color and the Greens of the Mallow, the Pimpernel and All the Plants. 

Take whichever flower you want, of any color you want, or even a [green] plant. If it will rub green from a leaf onto white paper staining it with color, then it will be good. The plants and flowers that do not show this effect are no-good. Put ordinary aqua vitae into a glass urinal, with a cappello [alembic cap] for its cover, making sure the said crystallo cap is as wide as possible. 

Into this cap, pack the leaves [or petals] of any flower or plant from which you want to release and extract the tincture. Now lute the mouth joint of the cap. Fit a receiver to its snout and lute that joint. Give it a moderated fire so that the volatile part [alcohol] of the aqua vitae rises into the alembic, and falls down into its volume upon the petals of the flowers, extracting the tincture. 

In time, drops will run down the snout of the cap into the receiver, colored and charged with the tincture. Once all of the volatile part of the aqua vitae passes and becomes colored, distill this colored volatile part of the aqua vitae in a glass vessel. [The alcohol] will pass white and will be useable three more times. The dye will remain in the bottom, which you should not allow to dry too much, but just moderately. Then you will have the very best tincture or lake for painting from an abundance of flowers and plants.

The "aqua vitae" he refers to is simply a distilled alcohol such as grappa. The important point here is that it is a potent solution of ethanol and water; a well-known modern equivalent would be vodka. The chemical apparatus he describes is about as simple as it got for alchemists. It has three parts; the first is a base consisting of (in this case) a urinal—an inexpensive and convenient glass container with a wide mouth. The second piece is what Neri calls a "cappello"; it is a special glass cap featuring a long tubular snout leading from the top, angled slightly downward. When the cap is affixed to the base with the materials inside and gently heated, vapor will condense in the cap and run down the snout for collection in the third piece, a "receiver" vessel. 

The material he uses to seal the pieces together was called "lute," a mixture of mud, cloth fibers, egg and some other materials that stick to the glass and withstand the heat of the fire. Its only purpose was to keep the glassware sealed until the procedure was complete. [4] 

In the mid nineteenth century, Mary Merrifield made an extensive survey of Italian manuscripts with recipes for artists. She included this comment about Neri's home town:

Florentine lake must have had considerable reputation in Venice, since Leandro Bassano contracted to employ it in his picture of the 'Combat of the Angles,' painted for the church of S. Giorgio Maggiore at Venice in 1597. [5]

Today, this painting is known as 'The Miracle of the immobility of Santa Lucia' and is shown at the top of this post.



[1] L'Arte Vetraria, Neri 1612.

[2] Discorso, Neri 1598-1600.

[3] Neri uses the word "lacca," the equivalent of "lacha" in other manuscripts. For a specific reference to Neri in this regard, see Merrifield 1849, v. 1, p. clxxxi.

[4] A word to the wise: high proof alcohol in a confined glass container near an open flame is a good way to cause a minor explosion and a fireball featuring glass shrapnel.

[5] Merrifield 1849, v.1, p. clxxxiii. She references Cicogna  1824–1858, v. 4, p. 349 for this information. 

Benedetto Vanda

View of Badia Fiesolana - Gaspar Van Wittel called 'Vanvitelli' (1652/3-1736)
(Click  to enlarge)

Early seventeenth century  Catholic priest Antonio Neri is remembered for his 1612 book on glassmaking recipes [1] and more recently as an alchemist quite competent in the field of chemical investigation.[2] A great deal has been learned about his life, but one of the enduring mysteries is the question of his religious order. The Archdiocese of Florence records for this period were largely destroyed in a fire and no definitive evidence has ever been found concerning his specific affiliation with the Church. [3]

There were dozens of practicing orders in and around Florence at the time and none of them present an obvious fit for a group that would be engaged in the education of a young alchemist. Contemporary records yield a handful of clues, each with its own set of merits and problems. Here we will take a closer look at just one of those possibilities. 

In 1614, at the age of thirty-eight, Neri apparently died rather suddenly, of a cause that is not known today. Folklore tells that he had previously promised to reveal the recipe of the philosopher's stone to his sponsor, Prince Don Antonio de' Medici. The 'stone' was conceived to be a substance with miraculous powers including the ability to transmute base metals into gold and to cure disease. The story tells that Don Antonio was delayed in coming to Neri's side and the secret died with the priest.

On the Prince's orders, interviews were conducted by fellow alchemist and disciple Agnolo della Casa.[4] In his notes, Della Casa remarks that a "relative of F. Benedetto Vanda, Carmelite of S[anta] M[aria] Maggiore, confessor of P[riest] Antonio Neri" was suspected by Don Antonio of stealing the secret of the philosopher's stone from Neri on his deathbed. [5] Setting aside for the moment the issue of a dying man's whispered secrets, this passage provides us with the name of Antonio's regular confessor, Benedetto Vanda. It establishes that Vanda was a Carmelite and it seems that Neri was attending Santa Maria Maggiore, [6] the Carmelite run church just west of the baptistery in Florence. [7]

Another earlier document names Vanda as Parocchiano (parish priest) of the abbey called Badia Fiesolana at San Domenico outside the city of Fiesole, located in the Tuscan hills just to the north of Florence. [8] Beyond these two references, Vanda seems to disappear into the mists of time. [9] While Priest Neri was free to pick anyone qualified to hear his confessions, a likely choice would have been a leader in his own congregation. Vanda's monastery lies three kilometers, less than two miles as the crow flies, across the hills from the villa in Serpiolle once owned by the Neri family and a similar distance to his childhood residence in Florence on Borgo Pinti. The route was an easy walk, even if uphill. [10]
Here the evidence takes a twist. While Vanda was the parish priest at Badia Fiesolana around the time of Neri's ordination, the monastery itself was run not by Carmelites, but by Canons Regular of the Lateran, [11] an Augustinian sect. The two orders are unrelated and report through different hierarchies. Why a Carmelite should be leading an Augustinian [12] institution is not clear. [13] However, the abbey was heavily patronized by the Medici family. They paid for extensive construction, renovation and expansion projects dating back to the fifteenth century. When the bishop of Fiesole moved to a new cathedral in 1439, the abbey was given to the Canons. If Neri did serve his initial training for the priesthood here, his novitiate, perhaps his career was already under Medici direction. In earlier times Cosimo the Elder and Giuliano de' Medici had private contemplation cells at the abbey. The Medici funded library there had been a long-time meeting place for humanist intellectuals, as was the Medici Villa half a kilometer away. Marsilio Ficino and others met there regularly. [14] Giovanni Pico della Mirandola, a student of Ficino and a friend to Savonarola, was sheltered by Lorenzo de' Medici in a nearby house. Pope Innocent VIII would have rather seen him tried for heresy, but the pope allowed the Medici to harbor him under special considerations.
The way of life of the Canons Lateran is a good fit for Neri. Their houses were self-governing. They followed the rule of Augustine of Hippo independent of the main Augustinian order. The Priests did not serve congregations. They acted independent of each other; they went into the world and did physical work with the laity. There is no ready evidence implicating the canons at San Domenico in the practice of alchemy, which makes them a less attractive possibility for Neri. However, their specific mandate was to relieve the suffering of the sick and the poor. This mission would have been satisfied with ease by producing medicinal remedies at Don Antonio’s Casino. 


[1] L'Arte Vetraria, Neri 1612.
[2] Rodwell 1870.
[3] Florentine Archdiocese records prior to 1650 were destroyed in a fire. See Zecchin 1987–89, vol. 1, p. 169, note 12.
[4] Casa 1614. Cf. Galluzzi 1982, pp. 53, 54.
[5] See Grazzini 1983, pp. 217, 218. 
[6] Not to be confused with San Pier Maggiore, Neri's childhood parish church.
[7] See Galluzzi 1982, p. 53; Casa 1614; cf. Grazzini 1983, pp. 217, 218.
[8] AOI 1587–1591, cf. Butters 1996, pp. 415, 416. 
[9] I have not been able to find any other reference to Benedetto Vanda, which may not be his birth name, but one chosen when he joined the Carmelites.
[10] The Badia Fiesolana [Abbey of Fiesole] is located in San Domenico, about halfway between Florence and nearby Fiesole.
[11] The Canons Regular of the Lateran (C. R. L.), their full title is Canons Regular of St. Augustine of the Congregation of the Most Holy Savior at the Lateran. They occupied the monastery from 1440 until 1778.
[12] Although ancient in origin, the Canons Regular of the Lateran adopted the rule of St. Augustine of Hippo.
[13] The two groups did share use of the liturgical 'Carmelite Rite' practiced at mass. 
[14] Canons lateran Matteo Bosso, see Mutini 1971; Timoteo Maffei see Moroni 1879. The canons hosted humanists Pico della Mirandola, Angelo Poliziano, Roberto Salviati, Demetrio Calcondila, Marsilio Ficino and Lorenzo de’ Medici.

Galileo and Glass Reprise

Portrait of Galileo Galilei, 1636 (detail),
by Justus Sustermans (1597-1681).

No known direct contact occurred between glassmaker Antonio Neri and the astronomer Galileo Galilei, but the two men lived simultaneously in Florence and then in Pisa. Their paths crossed many times, orbiting around each other like planets. 

As a youth, Galileo was taught at the Cestello monastery by court mathematician Ostilio Ricci. This was around 1580 when Galileo was sixteen, and Neri was a four year old toddler, living only a block away and attending the Cestello church with his family. Neri's father and grandfather had just been granted citizen status, already well known for their medical prowess. Galileo would go on to become good personal friends with Prince Don Antonio de' Medici, Neri's sponsor. Later, the astronomer would have telescope tubes made by Jacopo Ligozzi, a regular at the Casino di San Marco, where Neri worked as an alchemist and took his first steps into the craft of glassmaking. As Galileo started to experiment with lenses, Neri was leaving for Antwerp and would be absent for seven years. Meanwhile Galileo landed a job at the Florentine court as mathematics tutor to Grand Duke Ferdinando's son, Cosimo II. 

Both Galileo and Neri worked hard for their achievements. In the hindsight of history, innovations are often romanticized into shining moments of inspiration, forgetting the painstaking effort and dogged persistence required to bring those ideas to fruition. For his telescopes, Galileo encountered tremendous difficulty both in the production of suitable glass and in grinding that glass into usable lenses. His celestial observations included sunspots, lunar craters and the planet Jupiter with its moons, which he named "Medicea Sideria" after his Medici benefactors. As these revelations became known, there was a clamor of orders for telescopes from princes throughout Europe and Galileo struggled to keep up. He maintained a circle of trusted craftsmen on Murano in Venice, and elsewhere, but still, the majority of output was unusable.

Initially, he had reasonable success grinding and polishing broken pieces of mirrors. In early 1610, Galileo held a demonstration in Pisa for his former pupil, Grand Duke Cosimo II. A short time later, the grand duke ordered that a special batch of glass be made for Galileo by Niccolò Sisti, for whom Antonio Neri had worked just a few years earlier. At the time, Neri himself was still in Antwerp and would not return until the following year.

Neri returned to Tuscany and wrote his book on glassmaking,  L'Arte Vetraria, but then turned his attention to other pursuits. This, just as Galileo's quest for high quality glass to make his lenses took off in earnest. Neri’s final manuscript places him in Pisa working on alchemical recipes. There was no more optimal moment for the two men to meet; both were working in Pisa, both knew Niccolò Sisti, Neri had just published his book and the astronomer was becoming desperate for clear flawless glass. If such a meeting ever occurred, it has not been recorded, and shortly thereafter, in 1614, Neri died of an unspecified illness.

On 20 December of that same year, four days before Christmas, Tommaso Caccini, Neri's childhood next-door neighbor, delivered a scathing denouncement of Galileo from the pulpit of Santa Maria Novella church. While the sermon earned Caccini a reprimand, and was an embarrassment to his family, it did also serve as a start to Galileo's troubles with the inquisition.

While Antonio Neri may have never encountered the astronomer, shortly after the time of the priest’s death, the astronomer acquired Neri's book on glassmaking. One copy was sent to Rome, to Federico Cesi, founder of the Accademia dei Lincei, a scientific society to which Galileo belonged, and another copy was saved for the astronomer's personal library. Galileo continued his quest for flawless glass and in his correspondence he takes on the same obsession with purity of ingredients that Neri exhibits throughout his book.  

This post first appeared here on 18 Novenber 2013.

Neri's Cabinet #8: Sulfur

Alchemical Symbol for Sulfur

Bright yellow elemental sulfur or “brimstone” as it was often called, occupied a central place in the cabinets of seventeenth century alchemists. Antonio Neri used it in many of his preparations and specifically in pigments for glass. When sulfur is heated with thin sheets or shavings of metal, foul smelling chemical reactions can take place that reduce the metal to a powdered compound and some of these turn out to be effective glass colorants. Neri’s 1612 book, L’Arte Vetraria, offers a variety of recipes, which specifically prepare iron and copper using sulfur to form pigments. In reality, the resultant chemicals were mixtures of oxides and sulfur compounds. Since these also chemically interact with each other in the glass melt, many different effects are possible. Modern glass artists sometimes specifically use both oxide and sulfide pigmented glass side by side in the same piece; a striking effect can be the spontaneous formation of a third color along the boundary. As Neri says in the closing line of his 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.[1]

Keep in mind that the thinking of alchemist Neri was that the sulfur acted upon the metal, but did not necessarily combine with it. From his point of view, the exposure resulted in the metal’s infusion with new properties. The Aristotelian conception of the world was that everything under the sun contained various amounts of four elemental essences: air, water, fire and earth. Sulfur was seen to be dominated by the latter two, ‘fire’ because it burned easily and ‘earth’ because it occurs as a solid.

In the sixteenth century, a Swiss physician named Paracelsus developed an extension of the four-element system. After his death, his writings enjoyed a new popularity among chemical experimenters in the period that Neri came of age. Since his teenage years, the work of Paracelsus was a strong influence on both Neri and separately on his benefactor, Florentine prince Don Antonio de’ Medici. According to Paracelsus, sulfur was one of a triad of “principles” consisting of salt, sulfur and mercury. These three had philosophical as well as physical interpretations attached to them. Besides other applications, like in medicine, the three physical materials figured prominently in efforts to transmute one metal into another. 

In fact, sulfur in particular played a starring role in a very convincing demonstration that purported to turn iron into copper. Mining operations often utilized water to clean or separate ore from tailings. Other times, water was used to keep dust down, or simply flowed naturally through underground springs. When sulfur-bearing earth is exposed to air and moisture, the result can be the formation of dilute sulfuric acid. This “vitriol” was an irritant to the eyes and skin, and very unpopular with the miners. However, in at least one location, it seemed to have a miraculous property. When this “vitriolated water” flowed out of the mine, it seemed to transform bits of iron into copper. [2]

Chemically, copper had already been dissolved in the acid, forming a copper sulfate solution. But sulfuric acid shows a preference for iron. When the copper solution flowed over iron tools, it took up the iron and dropped the copper, depositing it in a thin layer. The effect appeared to be a transmutation of iron into copper. Further testing and scrutiny confirmed that pure iron, when exposed to the mine fluids resulted in real copper. Neri for one was well aware that the vitriolated water might have arrived containing copper, as he explains in his manuscript Discorso. [3] But apparently, it did not occur to him that the water leaving the scene might have contained the iron. If he had made the connection, the observation would have advanced the understanding of both ion-exchange chemistry and the principal of conservation of matter; these were two ideas that would not be explored seriously for another hundred years.

Well into the eighteenth century, the mine at Smolnik, (now in Slovakia), was a highly touted tourist destination for chemical experimenters. [4] For some, it was considered among the strongest evidence that transmutation could and did take place in the natural world. I like this demonstration so much because it works the same way as a parlor trick; while we are so intently focused on the metal changing before our eyes, Mother Nature quietly slips the copper in with one hand and takes the iron away with the other, no one the wiser.


[1] Neri 1612, p.114.
[2] See this post for a more detailed description  http://www.conciatore.org/2014/01/turning-iron-into-copper.html
[3] Grazzini 2102.
[4] The effect had previously been described Georgius Agricola, in book 5 [9] of Nature Fossilium. See edition, transl. from the first Latin edition of 1546 by Mark Chance Bandy, Jean A. Bandy (New York: Mineralogical Society of America, 1955), p. 188.

Bibliomaniac

Broadway Tower, Worcestershire. 
The home of Phillipps' Middle Hill Press

In 1612, Antonio Neri published his famous book on glassmaking, L'Arte Vetraria. [1] The venture was apparently bankrolled by Medici prince Don Antonio for whom Neri had worked as an alchemist and glassmaker in 1601 and possible a couple of years earlier. The printer was Giunti, the venerated Florentine family of typographers who set up their first press in Venice a century and a half earlier. In Neri's era, they operated as the de facto press for the grand dukes of Florence and they are still in business today.

Neri's book was noticed almost immediately; in a 1614 letter addressed to Galileo, Roman Prince Federico Cesi practically begged his astronomer friend to send a copy. [2] Cesi was the founder of the "Accademia dei Lincei" [Society of Lynxes] a group of naturalists who formed an early version of what would later be called "scientific societies." The book was tailor made for such groups who were interested in performing their own experiments, however, sales did not exactly catch fire among the public. 

A few decades later, another scientific society was formed in London, with a charter signed by no less than King Charles II. The Royal Society really gave Neri's book a major boost when in 1662; founding member Robert Boyle commissioned Christopher Merrett to translate the work into English. [3] A year earlier, a second edition had been printed in Florence and a year later, another Italian edition appeared in Venice. [4]

From there, the book took off, sprouting multiple new translations in the Netherlands, Germany, France and Spain. There are many interesting stories of how the book spread across Europe; one of the most fascinating deals not with the book itself but with a publisher. Without any doubt, Sir Thomas Phillipps was the most colorful of any of Neri's printers. In 1826, Phillipps' press issued a reprint of Merrett's original English translation, which was by then over a century and a half old. [5]

L'Arte Vetraria, or "The Art of Glass" as it was dubbed in English, had passed its prime as the bible of glassmakers. As one would expect, methods and technology had matured considerably over the intervening two centuries. Nevertheless, Phillipps is a character for the ages. By his sixth birthday, he already owned over a hundred books; his grand ambition was to own one copy of every book ever printed. He was born in Manchester, the product of a clandestine relationship between a textile baron and a woman to whom his father was not married. Nevertheless, he appears to have been well cared for and inherited what Wikipedia says was a "substantial estate." [6] A fortune that he promptly started to whittle away, spending lavishly on books and manuscripts. He attended University College Oxford and within a few years, he was made a fellow of the above-mentioned Royal Society. 

Depending on where you stand, Phillipps was a classic example of British eccentricity, a brilliant and dedicated preservationist or a completely obsessed crazy-man. By the end of his life, he amassed an estimated sixty thousand manuscripts and forty thousand books. At the time it was the largest such private collection in the world. He housed his treasure in a castle that he had built for the purpose, Broadway Tower, in Worcestershire (see photo above). It is said that he would walk into bookstores and buy the entire stock; his agents around Europe provided a steady stream of new material. Apparently, he himself possessed a sense of humor about his odd obsession, coining the term "vello-maniac" (referring to the vellum bindings common to many books of that period).

The story does have a darker side, albeit with a silver lining. In 1842, Phillipps started collaborating in research with James Halliwell, then an undergraduate at Cambridge studying Shakespeare. Halliwell became romantically involved with Phillipps eldest daughter Harriett, but Phillipps refused consent for them to marry (which they did anyway). Meanwhile, Phillipps had run through the family fortune and started to borrow heavily. He developed paranoia against Halliwell ever gaining control of the collection. He entered negotiations to donate the books and manuscripts to the British Library, but his conditions were unpalatable and a deal was never reached. He wanted to stipulate that the order of books should never be reshuffled and that no Roman Catholic, especially his son-in-law, ever be permitted to touch or view the collection. He became so fearful  about Halliwell that he hired 250 men to move the collection, which took two years, at which point the abandoned castle started to fall into ruins. 

In the end, Phillipps died at the age of 79 in 1872. After a court decision, Harriett did inherit her father's collection and Halliwell did gain control. The silver lining is that he and his wife carefully dispersed the collection to some of the most prestigious libraries in Europe, a project that took multiple generations to finish. In fact, the final parcel of books from the Phillipps collection sold at auction in 2006, at Christie's.

[1] Neri 1612.
[2] Cesi 1614a, 1614b.
[3] Neri 1662.
[4] Neri 1661, Neri 1663.
[5] Neri 1826.
[6] "Thomas Phillipps" Wikipedia, http://en.wikipedia.org/wiki/Thomas_Phillipps .

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.