Glass Blowers

Berkshire Glass Works cane from 1878 –
Charles Flint collectionThese were novelty items 
made by glassworkers after hours.

(hollow, filled with the fine quality sand of the area)

Since early days, the technical aspects of making and manipulating hot glass have remained a closed and secretive business. Down through the ages, those with inside knowledge of this art have been highly valued and highly sought after. Even with the circulation of technical manuscripts and the ultimate publication of the technology in Antonio Neri’s 1612 book L’Arte Vetraria. The beating heart of the craft remained at the furnace among those with hands-on experience. [1] These artisans could and often did make the difference between success and failure in a business that was notorious for sending substantial fortunes up in smoke.  

In some places, strict laws forbade glass workers from leaving their employ and forbade outsiders from attempts to lure them away. Recruiting seasoned talent could be a delicate if not clandestine undertaking. This was as true in the ancient world as it was through the Renaissance and it also played a significant role in the 18th and 19th century for the nascent American glass industry.

Many have heard of the legendary prohibition forbidding Renaissance Venetian glass workers from travel abroad. The fear was that they might divulge secrets of their craft to outsiders, thereby compromising the virtual monopoly on high quality luxury glassware made on the fabled island of Murano. Many also have heard that the penalty for violating these rules was death at the public gallows located between the columns at Saint Mark's square.  While there were laws on the books that listed possible penalties as severe as death, the records show that no glass worker was ever executed for leaving and many did leave. In fact, glass workers were sometimes part of state brokered deals to exchange technology.

These Venetian laws have also led many to the incorrect conclusion that the glassmakers were held captive and treated like prisoners. Nothing could be farther from the truth; glass workers were treated like rock-stars of their time. The daughters of glassmakers were allowed to marry into the nobility, a privilege granted to no other Venetian guild. [2]

Early American efforts to recruit experienced glass workers provide some amusing stories. In 1894, William G. Harding, a principal in the Berkshire Glass Works in Massachusetts wrote a detailed history of glassmaking in the region.  Harding’s research was meticulous, drawn from factory records, official legal filings and personal correspondence. Two stories in particular relate the great lengths pursued in recruiting experienced European glass workers to New England.

The first concerns Robert Hew[e]s, who despite repeated failures in starting a glassworks in the late 1700s, finally partnered in Boston with one Charles F. Kupfer newly arrived from the Duchy of Brunswick in Germany. Together they formed Boston Crown Works on Essex street.  Kupfer immediately returned to Germany to recruit workers, as harding records,

“Mr. Kupfer upon his arrival at his old home, found it no easy matter to get his blowers. The works belonged to the Duke of Brunswick, and it was a penal offense either for the men to leave, or for him to entice them away. He was obliged to conceal his designs and operate in the dark, but succeeded in escaping in the night with a set of workmen and sailed from a German port before being overtaken. After a long voyage they landed in Boston and met with a Royal reception. So much interest in the new enterprise had been awakened in the citizens of Boston, that they turned out en masse…” [3]

The other story of clandestine recruiting related by Harding concerns a venture started in Sand Lake, about 10 miles east of Albany, New York around 1806.

“They had to import their skilled workmen. Mr. William Richmond, a Scotchman, was the Superintendent of their works. He went abroad to procure workmen. Disguised as a mendicant [monk/priest], with a patch upon one eye and playing upon a bag-pipe, he wandered through the glass district of Dumbarton in Scotland and engaged his blowers to cross the Sea. With great difficulty they secreted their tools on Ship-board, for it was a penal offense for glass-workers to leave Scotland as well as Germany.” [4]

[1] Antonio Neri, L’Arte vetraria, distinta in libri sette, del R.[everendo] P.[rete/ padre] Antonio Neri fiorentino. Ne quali si scoprono, effetti maravigliosi, & insegnano segreti bellissimi, del vetro nel fuoco & altre cose curiose. All’Illvst.mo et eccell.mo Sig., Il Sig, Don Antonio Medici (Florence: Giunti 1612).

[2] A daugher of a glassmaker could marry into the nobility, which was a great honour for a family, but strategically, the son of a glassmaker had no such privilege, meaning that there were no inheritance rights for the family.

[3] Collections of the Berkshire Historical and Scientific Society, (Pittsfield: Sun Printing, 1894),  p. 37-39
Note that Robert Hews is also known as 'Hewes' in other sources.

[4] op cit. p. 39-40.

A matter of Plagiarism

Francesco Lana Terzi (1631-1687)

Conciatore is pleased to reprise the guest-post of independent researcher Maria Grazzini. Maria studied Antonio Neri under the late Professor Paolo Rossi, philosopher and historian of science at the University of Florence. In 2012, Dr. Grazzini published an annotated English translation of Neri's manuscript in the journal Nuncias. [1] In the course of her research, she discovered a plagiarized version of the manuscript, published by 
a famous Jesuit professor in Brescia. His version matches Neri's handwritten manuscript of 1614 word for word. Here is what Maria had to say on the subject:

The seventeenth century Jesuit scientist Francesco Lana Terzi (1631-1687) is famous for his design of a "flying boat"; he has been immortalized as the father of aeronautical engineering. What is not generally known is that he plagiarized the entire text of Antonio Neri's manuscript Discorso.

The original was never published by Neri, perhaps due to his premature death, but even as a manuscript, it must have circulated widely. It would be interesting to know the history of its diffusion, in order to understand how it became the subject of plagiarism. Lana Terzi, well known in the Italian Academia of the late seventeenth century, published his  in 1670. [2] The entire chapter 20 of his Prodromo is an exact reproduction of Neri's. Lana Terzi was fascinated by experimentation and manual arts. The Jesuit order refused their members permission to write about magic and alchemy; Jesuits with such esoteric interests could never write books directly devoted to these subjects, however, they could write works on the different aspects of natural philosophy. In this broader context chemical philosophy could be admitted.

Title page of Lana Terzi's Prodromo

Neri was popular in his own time for his glassmaking knowledge. His L'Arte Vetraria  was widely read and its reprints and translations appeared over the centuries. [3] Nevertheless, Neri enjoyed a considerable reputation among his contemporaries also for his 'chemical philosophy'. Discorso is a complete treatise on the subjects of chemistry and philosophy, to all appearance not different from many others written during the sixteenth century. It holds a similar structure, with an introduction defining the subject and the description of procedures. The final part lists possible objections raised against the validity of chemistry and gives Neri's timely responses. In this sense Discorso belongs to the alchemical traditions and Neri shows his deep knowledge of the Paracelsian doctrine and literature. Even so, the main features of the new 'scientific' mindset are present in Neri's treatise: the study of "the great book of nature" and the value of experimental practice. The traditional reliance on the authority of ancient wisdom loses its legitimacy. "We should not so easily give credence to all the histories," Neri claims, but we should "prove the possibility of this art of transmutation with certain […] experiences". Knowledge is acquired "with the practice of many experiences." It does not come from a divine revelation or from the study of many books.
There is no contradiction between the alchemist Neri and the glass-conciatore Neri; the will of gaining a deep knowledge of nature, based on the observation and experimentation, is common to both. Neri is always 'the technician' and never 'the philosopher'. Alchemy, the "Great Art," is the result of a deep study of nature and its aim is not to give an imitation of nature, but to make it perfect.

The 'modernity' of Neri can also be understood in his way of talking about chemical philosophy. He does not pretend to teach eternal truths, but only to indicate the way to achieve greater knowledge, by "understanding the modus operandi of nature." Consequently, the writer does not use the form of a dogmatic essay, but that of a conversational chat, or 'discourse'.

It would be interesting to discover how Lana Terzi came into possession of Neri's manuscript. Perhaps he was attracted by the mixture of old and new which was also a predominant theme of his time, when different models of knowledge coexisted and intertwined. Discorso offered him the chance of introducing the topic of alchemy without being accused of magism.

-M. G. Grazzini

[1] Grazzini 2012.
[2] Lana Terzi 1670.
[3] Neri 1612, 1613.
* this post first appeared here on 20 November 2013.

Turquoise Glass

Turquoise glass stamp

of calif Mustadi  c.1170.

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 offers one recipe to restore faded stones by soaking them in almond oil. For turquoise colored enamels he presents two different shades. On the subject of glass, 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. 

* This post first appeared her in a slightly shorter form on 9 April, 2014.

A Cardinal's Ceiling

From "Tesoro del Mondo" (Treasure of the World)

Antonio Neri 1598-1600

In the years 1598-1600, newly ordained Florentine priest and alchemist Antonio Neri was hard at work on a manuscript which he titled Tesoro del Mondo (Treasure of the World). [1]  One illustration near the front shows an allegorical map in which six roads all lead to the Vatican at its center. A Latin inscription translates as, "The different ways to Rome" followed by "Qui pot[est] capere capiat" or 'He that can take, let him take it.' Taken in context, this Biblical reference ( Matthew 19:12) apparently refers to the various alchemical 'paths' leading to the philosopher's stone, but the choice of imagery suggests that Neri spent time in the city of seven hills. [2] It is a tantalizing clue to his travels, although there is no direct confirmation. 

If Rome did figure in the young Neri's itinerary, a visit to Cardinal Francisco Maria Del Monte would have been de rigueur. The Medici family ruled Neri's home region of Tuscany and Cardinal Del Monte was the Medici's informal ambassador in Rome. He was a dedicated patron of the arts, an amateur alchemist, a collector of glass and a trusted successor to Grand Duke Ferdinando in the College of Cardinals. More significantly, he was a close friend and advisor to Neri's sponsor Don Antonio de' Medici ever since that prince was a child.  Del Monte's biographer Zygmunt Waźbiński offers, "It is very likely that Cardinal Del Monte, with his interest in glass, had known then (in 1598) the [future] author [Neri] of L'Arte Vetraria." [3]

Michelangelo Caravaggio, c. 1597
Casino Ludovisi.

As the sixteenth century ended and a new one dawned, Del Monte sheltered the rough-and-tumble painter Michelangelo Caravaggio, whom he set up with an in-house studio and an allowance. However, in 1606, the master of Realism fled Rome after reportedly murdering a tavern waiter over a tennis wager, but not before executing his only known fresco on the vaulted ceiling of Del Monte's own alchemy laboratory. Looking out over Rome, on the panoramic Pincio, in the Villa that later became the Casino Ludovisi and is now known as the Casino dell'Aurora, Caravaggio put his brush to work. According to early biographer of artists, Gian Pietro Bellori, he executed the oil painting on the vaulted ceiling of the small alchemical laboratory (now a corridor) sometime between 1597 and 1600. [4] Depicted in the mural are the three brothers Jupiter, Neptune and Pluto: the masters of the universe. The image is a double allegory of the three basic chemical substances of Paracelsus (salt, sulfur and mercury) and the four Aristotelian elements (air, earth, water and fire). Jupiter with the eagle stands for sulfur and air, Neptune with the seahorse stands for mercury and water and Pluto with the three-headed dog Cerberus stands for salt and earth. Jupiter is reaching out to move the central celestial sphere in which the sun (fire) revolves around the earth. [5] 

The villa was a relatively secluded retreat where the Cardinal could entertain guests discretely, including his friend Galileo–Del Monte and his older brother Guidobaldo helped land Galileo the chair of mathematics at the university in Pisa. It would be interesting to hear the astronomer’s comments on Caravaggio's tribute to heliocentrism.


[1] Neri 1598-1600, f.xxviii-v.  (see bibliography).
[2] For more on the alchemical interpretation of this illustration see Grazzini 2012.
[3] Neri 1612.
[4] Bellori 1672, pp. 197-216.
[5] Wallach 1975, pp. 101-112.

* this post first appeared in a slightly different form on 4 July 2014.

San Giusto alle Mura

Window of  Santa Maria del Fiore cathedral,

Florence, Italy.

In Florence, at the very end of the street on which Antonio Neri spent his youth, Borgo Pinti, was the residence and estate of the Archbishop. Beyond were the city walls and the enormous wooden doors of the Porta Pinti gate (115 foot, or 35 meters tall). Just on the other side of the gate, which in Neri’s time was normally closed and guarded, once stood the San Giusto alle Mura monastery, built in the thirteenth century. Despite the similar name, there is no connection between the Ingesuati monks of San Giusto and the modern order known as the Jesuits, which was not formed until 1534 and recognized by the Church in 1540.

The monks at San Giusto were famous for the stained glass windows they made; hence one of numerous theories that the street name 'Pinti' may be a contraction of 'dipinti 'or 'dipintori' (paintings or painters). Using their own glass furnaces, the Ingesuati monks provided windows for the Neri family's church Cestello and for Santa Maria del Fiore among other churches. They also ran an art school and were famous for making the color pigments used by painters, producing a coveted ultramarine blue. Their customers included the likes of Leonardo, Michelangelo, Botticelli, Del Sarto, Ghirlandaio and Filippo Lippi. 

Apparently, the Ingesuati's artistic devotion was not matched by their religious observance. In his Lives of the Artists, Giorgio Vasari recalls the less than complimentary sentiments of the monk's own in-house chaplain, a certain Servite monk named Fra Martino. He notes that the monks do not read Mass, and that they, "do nothing but say paternosters ['our Father...'], make glass windows, distill herbs for sweet waters, dig their gardens, and perform other works of similar kind, but do not study or cultivate letters."

Antonio Neri has a slightly more positive opinion about the value of stained glass windows. In the introduction to L'Arte Vetraria, he waxes poetic: 

Glass is also a great ornament to God's churches since, among other things, many beautiful windows are made, adorned with graceful paintings, in which the metallic colors are so intense and vivid that they seem like so many oriental gems. 

The windows that inspired these lines may well have been made by monks of San Giusto. As a child, Antonio Neri had seen the striking windows in Cestello and in the city cathedral. It would be nice to be able to connect him to the Ingesuati, but in 1529, long before his birth, their entire complex just outside the Pinti Gate was dismantled in defensive preparation for the siege of Florence. The Florentine military cleared away the structures near the outside of the city walls. The monks of San Giusto alle Mura moved to the much smaller Calza Convent on the oltrarno, on the opposite side of town near the Porta Romana gate. They did not rebuild the glassworks at the new location and it is doubtful that any of the glass workers would have still been alive by the time Antonio Neri came of age.

This post first appeared here in a slightly shorter form as "Glass Monks" on 30 September 2013.

True Colors

The European Roller [Pica Marina]

Antonio Neri's book, L'Arte Vetraria, is devoted to making glass from raw ingredients found in nature. Many of his finished creations were intended to also resemble the natural world. A number of colors are meant to mimic the appearance of gems and minerals, others are named after plants and animals. Some are easily recognized today, even if they are not as familiar as they were in the seventeenth century. One of his recipes will make "a wonderful pimpernel green," while others evoke peach and orange blossoms. An entire section of the book is focused on paints that are named after the flowers from which the colors are extracted. Many of these plants have remained common: poppies, irises, violets, lilies, carnations and red roses. Others are less so: the mallow, pomegranate, broom and borage flowers.

In addition to flora, the fauna make a few notable appearances in Neri's book. In chapter 16, in the preparation of iron oxide pigments, he advises that after fifteen days in the furnace, the product will be finished when it takes on the purple color of the peacock. In chapter 73 he gives a method for "tinting rock crystal the color of a viper" and chapter 121 is the method for a glass which is "red like blood."

Named in several chapters is a shade of 'celestial blue,' which Neri likens to the color of the "gazzera marina." Common bird names pose a special challenge for translation in that they, like the birds themselves, never seem to settle in space or time for very long. Vernacular names of a species can change from one century to the next, one region to another, even between adjacent valleys and several species can share the same name. It is with this admonition that we attempt to flush out the elusive gazzera marina.

Consulting a modern Italian dictionary draws the eye to the similar sounding 'gazza marina' (alca torda), known in English as the razorbill. This sea bird inhabits coastal cliffs, but alas, as a close relative of the penguin, it dons only black and white formal attire. Digging deeper we find poet Gabriele d'Annunzio, "At Dawn" carefully tracking the gazzera marina across a salty marsh, in his Halcyon. This time the poet himself throws us off the trail with his description, since no bird sports five digits but the chicken. Turning to etymology, we find another potential match in the magpie (pica pica); it is a credible but unconvincing fit with its blue and white plumage.

Aldrovandi's pica marina

Combing the references of Neri's own sixteenth century, we find the best candidate is the roller (pica marina). This bird was described by naturalist Ulisse Aldrovandi, a friend of Don Antonio de' Medici's father and guest at the Casino di San Marco, where Neri later worked. Other contemporary authors list the gazzera marina as a synonym to Aldrovandi's pica marina. Neri's Latin translator Frisius (1668) and his German translator Geissler (1678) agreed, both sighting the "Pica Marina" in their works.

This post first appeared here on 13 Sept 2013.

Galleria dei Lavori

Giovanni Stradano  (Jan van der Straet) 

Alchemy Studio, 1571
(Inside the Uffizi Galleria dei Lavori)

In 1560, Cosimo I, Duke of Tuscany, commissioned Georgio Vassari to begin construction on the Uffizi Palace in Florence. Two wings of the structure frame a long, narrow courtyard leading out to banks of the Arno River. Today it houses one of Europe's premier art museums, but its original design was as the central administration of the Medici government. The lower floor held offices of the regional magistrates, and the upper floor of the west wing (above the mint) held a variety of workshops highlighting Tuscan industry. Grand Duke Cosimo de' Medici built a glass furnace there, which he staffed with Muranese masters of the art. He won their expertise through long, hard negotiations with the doge of Venice. 

A 1571 painting by Giovanni Stradano is entitled the Alchemy Studio. It shows Cosmo's son, Francesco I, in the Uffizi surrounded by laboratory equipment and workers. Under the watchful eyes of a senior alchemist, he stirs a chemical preparation over a stove with intense concentration. The prolific glassware in this scene drives home the close relationship between glassmaking and scientific investigation.

By 1588 Francesco's brother, Ferdinando I de' Medici, formally declared this space the Galleria dei Lavori or 'gallery of the works'. There is no direct evidence that Antonio Neri gained his education in alchemy at this facility, but it makes a very attractive candidate. Of note to this story is that a demonstration was performed for Ferdinando de' Medici in Rome that purported to turn half of an iron nail into gold; the work of German alchemist Leonhard Thurneysser. In the 1590s, when Neri was being schooled, several accounts describe that the nail (chiodo) remained on display for some time in the Galleria. Neri mentions the nail in his Discorso and Thurneysser is discussed in a 1601 letter to the priest from his friend Emanuel Ximenes.

After Neri's death in 1614, his Medici sponsor, don Antonio commenced a search for the glassmaker's secret of transmutation, which Neri had promised. In testimony given by a royal goldsmith, who had, in July of 1596, witnessed a demonstration in which "gold" was made by Neri, he pressed the glassmaker, who told him that the transmutation was a technique learned from a German, done with ordinary vitriol.  

It is interesting to note that when iron is soaked in a solution of "blue vitriol" now known as copper sulfate, an ion exchange reaction takes place, where the liquid deposits copper and takes up iron from the nail. It would be well into the 18th century before this chemistry was adequately understood. What the royal goldsmith would have seen is  a dull iron nail turn the color of yellow metal before their eyes. Perhaps the goldsmith was not given the opportunity to further test the sample. 

This post first appeared on 16 August 2013.