The Saint's Glassmaker Cousin

Saint Philip Neri,  holding lilies, the symbol of Florence

attr. unknown,prob. after Giovanni 
Francesco Barbieri (Il Guernico)

In the final quarter of the seventeenth century, a certain holy man in Rome practiced charity in its humblest form. A native of Florence, a man named Filippo Neri (1515-1595) made visits every day to plague victims in the hospitals. He prayed for patients in their last hours and brought food for those abandoned by their families. He walked among the poor and destitute, eating just from the alms he received. He lived what he preached and set an example of Christianity stripped of pride and envy. In unconventional style, he led walking tours of the churches in Rome. Although the practice of venerating the living as saints received strong discouragement by the Church, Filippo Neri nevertheless realized effective sainthood during his lifetime. His followers credited him with numerous miracles.

Conventional history places the exact location of Filippo Neri's birth in Florence on the south side of the Arno. However, local folklore suggests an alternate location: in one of two rooms of the same Borgo Pinti house later owned and occupied by Antonio Neri's family. The common family name of Neri naturally leads to the question of whether or not the saint and the glassmaker were of common ancestry. In fact, they may well have been related. Antonio's father, Neri Neri, maintained that his own father, Jacopo, was a cousin to the holy man.

A full-length image of Filippo Neri himself appears in a corner of the Neri chapel, On Borgo Pinti, steps from the family homestead. Giovanni Cinelli, writing in 1677, tells us of Neri di Jacopo (Neri Neri):

It was his intention to dedicate [the chapel] to his relative Filippo Neri; it is possible that Jacopo di Neri, father of M[esser] Neri Neri was the cousin of Filippo Neri then still living, today Saint Philip. But [the dedication] was not to be, because in pressing to oversee its completion and delays in the canonization of the Saint, the dedication was changed to Nereo and Achilles, which was finished by Alessandro per the will.

Because the canonization was delayed, it would have been inappropriate to dedicate the chapel to Filippo, so two of his favorite saints were substituted.

The assertion that Neri the medical doctor and Neri the holy man were true blood relations has yet to be verified. However, there are positive signs: the saint's well-established genealogy meshes well with records of Antonio Neri's family housed at the state archives in Florence. In fact, both sets of records—of the alchemist and of the saint—share a single file in the archives. These documents indicate a common ancestry at the level of third cousins. The elder Jacopo Neri and Filippo Neri (later Saint Philip) appear to have shared a great-great-grandfather. It is a remote connection, but one that was a source of  pride for Antonio’s father.

There is also a notable similarity of family crests; the shield of Saint Philip Neri features three stars on a blue field, that of Antonio Neri's family features  a  banner with three stars against a blue rampant lion. The Saint's genealogy is well established, but the matter is complicated in that Antonio's branch of the family left Florence around the start of the sixteenth century. Here we lose track of them for one generation. Regardless of the difficulties, there is mounting evidence that Antonio's fourth-great-grandfather, Michele di Neri, was the brother of Saint Philip's second-great grandfather Ser Giovanni di Neri. A further association with Filippo Neri lies with Antonio Neri's maternal grandfather, Francesco Parenti, who served as attorney for the saint’s sister Caterina in the execution of the holy man's will.

Filippo Neri was unusual for his time. He was a champion of the common man, and he was humble to a fault; not a leader by force, by wealth, nor by charisma, but by gravitas. Antonio Neri's father seems to have been a man from the same mold, as exemplified by the absence of self-important declarations or artifice. He admired Filippo Neri, and we can guess that he shared the holy man's philosophy. Filippo never wanted  and protested strenuously against any aggrandizement. We see this trait follow through with Antonio. In his manuscripts and in the book on glassmaking, there is no evidence of boasting, or name-dropping, nor claim of superiority. What we see is a humble quest to understand nature, and to be of service to mankind.

* This post first appeared here on 3 February 2014.

What Goes Around Comes Around

The German city of Ulm in the 16th century

Georg Braun, Franz Hogenberg 1570-78

(Click image to enlarge.)

In the spring and summer of 1525, peasants and farmers throughout German speaking Europe staged a popular revolt now called the Deutscher Bauernkrieg. [1] At the heart of the matter was an oppressive system of taxation run by the Roman Catholic Church, in which little or none of the revenue was used to improve life locally. Often, action was lead by Protestant clergy, but to little effect against the mercenary armies hired by the aristocracy. In the end, up to 100,000 of the poorly armed and organized peasants were slaughtered.

Along the banks of the Danube River in southern Germany lies the ancient city of Ulm. Besides being the birthplace of Albert Einstein, Ulm was, in the sixteenth century, near the center of the Peasant’s Revolt, which brings us to a curious story which traces the migration of a technical recipe from Ulm over the alps to Venice, then to Sienna and finally Florence. The recipe is for the metal alloy to make mirrors, and it is told from one friend to another while chatting amiably in Venice.

Among other things, he said that he had made one [concave mirror] almost half a braccio across [about 13 inches], which extended the clear rays of its brightness more than a quarter of a German league when he caught the sun with it. One day, when for amusement he was standing in a window to watch a review of armed men in the city of Ulm, he bore with the sphere of his mirror for a quarter of an hour on the back of the shoulder armor of one of those soldiers. This not only caused so much heat that it became almost unbearable to the soldier, but it inflamed so that it kindled his jacket  underneath and burned it for him, cooking his flesh to his very great torment. Since he did not understand who caused this, he said that God had miraculously sent that fire on him for his great sins. [2]

The story was told to Vannoccio Biringuccio, who recalls it in 1540 in his Pirotechnia, the first printed book devoted to metallurgy. Specifically, the recipe is a variant of what today we would call white bronze, which as Biringuccio states is similar to the metal used to cast bells. He recites ancient formulations that used three parts copper and one part tin. To this was added 1/18th part of antimony and optionally 1/24th part of fine silver to give it a neutral color. Indeed, other ancient formulations for what was known as speculum metal specify a 3:1 ratio of copper to tin. He continues,

But nowadays most of the masters who make them take three parts of tin and one of copper, and melt these together. When they are melted, for every pound of this material, they throw in one ounce of tartar and half an ounce of powdered arsenic, and let them fume and melt and incorporate well. 

Biringuccio’s version reverses the copper and tin ratio from the classical composition. Compare it with Antonio Neri’s prescription which appears half a century later, it is almost identical:

Have 3 lbs of well-purified tin, and 1 lb of copper also purified. Melt these two metals, first the copper, then the tin. When they fuse thoroughly, throw onto them 6 oz of just singed red wine tartar, and 1½ oz of saltpeter, then ¼ oz of alum, and 2 oz of arsenic. Leave these all to vaporize, and then cast [the metal] into the form of a sphere. You will have good material, which when you burnish and polish, will look most fine. This mixture is called acciaio and is used to make spherical mirrors.

To be clear, the tartar, saltpeter and alum act as a surface flux - they form a layer that floats on the liquid metal, preventing oxides from forming, which can foul the melt.  their addition does not change the base alloy composition.

The similarity of the two recipes alone is not enough to draw any conclusions. Biringuccio himself reports that the contemporary artisans favored the tin rich formulation. However, there are other details to consider. The Sienese born Biringuccio was something of a hero in Florence where Antonio Neri was raised. The famous metallurgist helped cast cannons, mortars and guns for the Florentines to defend themselves in the late 1520s, when the city was under siege, just a few years after Biringuccio’s conversation in Venice with his German Friend from Ulm.

Neri was definitely familiar with Biringuccio’s book Pirotechnia. In fact, the introduction to Neri’s own book L’Arte Vetraria is patterned after the metallurgist’s survey of glassmaking.  In his chapter 14, book 2 Biringuccio wrote:

… it [glass] is one of the effects and real fruits of the art of fire, because every product found in the interior of the earth is either stone, metal, or one of the semi-minerals.  Glass is seen to resemble all of them, although in all respects it depends on art. [3]

And here is the opening to Neri’s introduction a half century later in 1612,

Without a doubt, glass is a true fruit of the art of fire, as it can so closely resemble all kinds of rocks and minerals, yet it is a compound, and made by art. [4]

Both passages go on to cover much of the same ground, albeit with a change in focus reflective of new thinking about chemistry and nature. In one sense, Neri is paying homage to his distinguished predecessor, and there can be little doubt that he read Biringuccio’s book and its technical recipes closely. 

Lastly, the story of the burning mirror itself mimics a widely known story about the Greek polymath Archimedes. About 200 BCE during the siege of Syracuse, he is said to have set invading Roman ships on fire with a concave mirror, which focused the radiation of the sun.

In fact a depiction of this scene was painted in Florence on the walls of the Uffizi Palace in 1600, when Neri was at the height of his employment for the ruling Medici family. This particular rendering would have been all but impossible for him to miss. 

Uffizi Gallery, Florence, Italy, Wall painting
showing the Greek mathematician Archimedes' mirror 
being used to burn Roman military ships. 
Painted in 1600 by Giulio Parigi.

In the years leading to the publication of Neri’s book, he left his home in Florence and traveled to visit a friend in Antwerp. If he had read the book on metallurgy early, perhaps as part of his education, then he was already familiar with the mirror alloy recipe. If he followed the route suggested by his friend, he would have taken the recipe back to Venice, and then over the Alps and likely through Ulm on his way north to the Low Countries, where he would spend the next seven years before returning to Italy. [5]

[1] For more on the German peasant wars of 1524-25 see https://en.wikipedia.org/wiki/German_Peasants%27_War
[2] Vannoccio Biringuccio, Pirotechnia. Ed., Tr. Cyril Stanley Smith, Martha Teach Gnudi (New York: Basic Books, 1959), pp. 385-390. (Original Italian published in 1540.)
[4] Ibid,  p.126 (in original, ff.41r-44v).
[3] Antonio Neri, L’Arte Vetraria (Florence: Giunti, 1612). p. iv.

[5] Special thanks to Jamie Hall (@PrimitiveMethod) for inspiring this post.

The Reluctant Glassmaker

The Sun, Robert Fludd

from Utriusque Cosmi (1617),v. 2, p. 19.
(alchemical symbol for gold)

Today, Antonio Neri is best known for his 1612 book, L'Arte Vetraria, in which he exposes the secrets of the art of making glass. In publishing his volume, he helped to fuel new discoveries in chemistry and medicine simply by making glass apparatus more available to experimenters. A 1662 translation of his book into English was one of the first acts undertaken by the newly formed Royal Society in London, at the behest of Robert Boyle. Neri himself lived for only two years after his book went to press, in his native Florence, and never saw the seeds of his labor come to fruition. If he had lived, he might well be surprised that his legacy is in glassmaking, and not in the subjects that he himself held most dear.

In his death at the age of thirty-eight, Neri missed a rapid advancement in our basic understanding of nature. In the space of only a few decades the face of science and medicine would start to change irrevocably. Soon, experimenters were finding new chemical elements and began to map out the periodic table, often with apparatus made of glass. For centuries, the ancient Aristotelian concept of air, earth, water and fire as the basic building blocks of the universe had endured. By the end of the seventeenth century, the inadequacies of the old model were becoming clear. 

But Neri was not privy to any of this. In his time, any cracks in the Aristotelian model were minor. Like his sponsor, Medici prince Don Antonio, Neri was an adherent of new doctrines of the physician Paracelsus, who rebelled against the old system, but was still very much a product of it. First and foremost, Neri thought of himself as an alchemist. While history has not generally been kind to his ilk, a true understanding of early modern science rests on the methods and reasoning developed by alchemists like Neri. 

Although alchemy covered a wide range of activities, it will forever be associated most closely with the mistaken notion that base metals such as lead or iron could be transmuted into gold. Once science had established this idea as specious, the race was on to separate "new science" from the old. It became fashionable to cast alchemists into the mold of charlatans, tricksters and self-deceived fools. While many such characters did exist, Neri was not one of them; his work was based on careful reasoning and experimentation. The final irony is that through the kind of advancements that he himself helped to pioneer, the majority of his life's work has fallen by the wayside. What has endured the test of modern science is his treatise on glassmaking.

As early as the age of twenty, Neri was demonstrating transmutation to expert gold refiners. As late as the year before his death he was writing authoritatively and coherently on the subject. To understand how this is possible – to be rational and methodical, and at the same time completely wrong – is to get a sense of the true difficulties involved in science. Based on what he was taught, what he read, and his own experimentation, Neri thought metals and other materials "matured" over time. He thought that more "imperfect" metals like lead and iron were part of a continuum that ended with the "perfect" metal gold. Furthermore, he thought that primordial "seeds of gold" left over from the creation of the earth could be mined and isolated. Like wheat and other plants, given the correct nurturing, and conditions, this seed material could be encouraged to mature into vast quantities of gold. Writing in his 1613 manuscript Discorso, he says,

The response is that the chemical art lets the gold proceed from that present and immediate cause, because this is the seed of gold, which acts naturally when art cooperates. The chemist does nothing but extract the seed from gold and apply it to suitable bodies, with which it is united to render the fruit multiplied in the same way that the farmer does. He does not produce the fruit, but provides and prepares the earth and the seed, uniting them in such a way so that they bear fruit.*

Neri thought that ultimately, for gold transmutation to be successful one needed the blessing of the Creator. He documented his process in a heavily coded (and incomprehensible) recipe he called "Donum Dei" (the most precious gift of God). This name traces to alchemical writings from as early as the fifteenth century. He maintained that those who might harm society with this knowledge or wished to profit personally or swindle others would be denied the blessing and therefore be unsuccessful. 

The remarkable thing here is that Neri's understanding of chemistry was supported at every turn by experimentation. His recorded methods, for transforming lesser metals into one-another, were repeatable and stood the test of scrutiny by contemporary experts. In the light of modern chemistry, these transformations depended on subtle physical processes and chemical reactions that would not be understood for another century or more. By performing these experiments under controlled conditions, he was taking the first steps in what would become modern science. Eventually, it would be understood that while chemical compounds can be created and destroyed by various manipulations, individual elements cannot. Today we know that iron, lead and gold were formed in the cores of ancient stars, not too different from our sun. Lighter elements are successively transformed into heavier ones under a star's "nurturing" conditions. While he lived in a period in which he had no chance of getting the particular details correct, in a poetic sense Neri was not far from the truth.

* See Maria Grazia Grazzini, “Discorso sopra la Chimica: The Paracelsian Philosophy of Antonio Neri” Nuncius 27 (2012) 311–367.

Reflections on the Mirror

Jan van Eyck

The Arnolfini Portrait (1434)

L’Arte Vetraria, Antonio Neri's 1612 book, would eventually become the glassmakers' bible throughout Europe. By 1900 it had been translated into five different languages besides the original Italian; English, Latin, German, French, and Spanish (and in this century Japanese). Because of its seminal importance in the spread of glass technology, often overlooked are a few recipes at the back of the book, which have only a tenuous connection to the main subject.

Among these is a metallurgical formula for making convex mirrors. Neri gives instructions for producing what we would now call a "white bronze" that may be cast into a rounded form and polished to take on a highly reflective surface finish. This "spherical" form of mirror was popular throughout the Renaissance. It reflected a wide-angle view of the space in which it was hung, but at the cost of distorting the image. Nevertheless, upon looking into such a mirror, objects are still quite recognizable. 

Here is Neri's prescription:

A Mixture to Make [Mirror] Spheres:
Have 3 lbs of well-purified tin, and 1 lb of copper also purified. Melt these two metals, first the copper, then the tin. When they fuse thoroughly, throw onto them 6 oz of just singed red wine tartar, and 1½ oz of saltpeter, then ¼ oz of alum, and 2 oz of arsenic. Leave these all to vaporize, and then cast [the metal] into the form of a sphere. You will have good material, which when you burnish and polish, will look most fine. This mixture is called acciaio and is used to make spherical mirrors.

Of note is the fact that the word Neri uses for this alloy, acciaio, translates to "steel." Over the intervening four centuries, the meaning of this term has been refined so that today it denotes not simply a hard white metal, but a specific range of alloys containing iron and carbon. 

This recipe and a few others in the book show the breadth of Neri's experience in arts other than glassmaking. It is a conclusion greatly amplified by a perusal of his other manuscripts on alchemy and medicine. There is good evidence that our priest was a voracious reader, however he was also quite cautious about repeating techniques only after he had verified them personally. Besides, artisans never wrote down much of this knowledge – only passed in confidence between trusted parties – since, in a very concrete way, superior knowledge represented a competitive advantage over ones rivals. Even if Neri was in the business of divulging secrets, it is safe to assume that many of the artisans and craftsmen he interacted with were decidedly not. Apparently, Neri was not familiar with the process of mirroring glass directly with mercury/tin amalgam; a process for which Venetian glassmakers had already become famous for perfecting. It is an interesting omission from his book, since he almost certainly would have seen examples in Florence and in Antwerp.

Two centuries before Neri, the beginning of the fifteenth century saw the invention of moveable type printing in Germany, but also the mastery of perspective illustration in Italy. The contribution of printing to early modern science is well documented, less obvious is the role playerd by artists and perspective illustration. Moveable type made possible the mass production of books; what did get committed to paper now stood a much better chance of survival and transmission. Perspective illustration played a more nuanced role, one that ultimately brings the convex mirror back into the discussion.

In Venice and especially in Florence (Neri's hometown), perspective drawing became the rage among artists, largely due to the Italian translation of a book entitled Deli Aspecti, or "Alhazen's Book of Optics." Suddenly, paintings were made to look three-dimensional, with a realistic sense of depth to them. The new techniques were largely kept in Italy, but interest spread across Europe. Patrons placed great value on work depicting scenes in correct perspective, and in excruciatingly accurate detail. 

Jan van Eyck
The Arnolfini Portrait (detail).

In Flanders, in 1434, Jan van Eyck produced "The Arnolfini Portrait," (above). Behind the main subjects, hanging on the wall is a convex mirror. The reflection in the mirror shows the backs of the two subjects, but also two other figures further back, one of which is thought to be the artist himself, and beyond him a strong light source. The image in the mirror is distorted exactly as one would experience in real life. 

There is growing speculation that among the secrets of "realist" (or naturalist) painters was a growing arsenal of optical tools and lenses used to map out and understand the attributes of perspective. The mirror, in the Arnolfini Portrait was a sort of boast of the artist's proficiency in recreating reality on the canvas.

The point is that here is a case where art led science into new realms. Painters started to take great pains in reproducing reality "as it is" on canvas. Soon minor experimenters like Neri and major luminaries like Galileo were taking great pains to do the same. They strove to observe nature "as it is," not as was prescribed in ancient texts, or dictated by authority. Once that process started, awareness of the world grew and there was no turning back.

Finally, it is amusing to note that in his many manuscript illustrations, Antonio Neri himself never quite mastered perspective drawing, although he did try.

* This post first appeared here 17 January 2014.

The Kabbalah

Kabbalistic Sephiroth Tree,

from Portae Lucis, Paulus Ricius (Trans.)

Augsburg, 1516.

Kabbalah is a form of mysticism practiced within the Jewish tradition. In the early seventeenth century, there was a great deal of interest in Kabbalistic teachings among Catholic alchemists and natural philosophers. It was recognized that Christian alchemy had its roots in Hermetic and earlier Arabic societies, (the word "alchemy" itself is of Arabic origin.) It was thought that the Jewish Kabbalah was yet another branch of the same traditions of relaying secret knowledge by word of mouth. 

In early modern Florence, Italy, there were some interesting connections between the Kabbalah and glassmaker, alchemist and Catholic Priest Antonio Neri. Here is Neri’s own description, of Kabbalah in his 1613 manuscript Discorso: 

Some call it Kabbalah: in ancient times fathers communicated it to their children only by voice, preserving [this knowledge] for posterity, not for history, but as simple tradition. Others finally gave it the name of 'wisdom' [sapienza] because they rightly believed it was impossible, without this art, to know perfectly the nature and the qualities of natural bodies. In order to achieve the end they wanted, which was the perfection of the bodies, they separated the pure from the impure through various chemical operations, which can all be reduced to six principal phases.*

He goes on to describe basic chemical operations that were thought to be fundamental to purifying materials, and ultimately to the production of the Philosopher's Stone. These techniques are the same as practiced in Christian alchemy, and Neri uses them in his glassmaking recipes. Clearly, he had more than a passing knowledge of the subject, and it is interesting to speculate on how he might have come to learn about Jewish alchemical traditions. 

Early seventeenth century Florence contained a city within a city: the Jewish Ghetto. A walled perimeter encircled what is now the Piazza della Republica. This was the mandated home for all of Florence's Jewish population. Each night, entrance gates were closed and locked from the outside. Within the Ghetto, residents were allowed to live and warship freely, even maintaining a Synagogue. In the daytime, the gates were opened, and residents were allowed to go about their business and leave the city with special passes. Among the Ghetto's most prominent residents was the family of alchemist Benedetto Blanis (c.1580-1647.) Blanis served as librarian to Medici prince Don Giovanni. Giovanni maintained an alchemical laboratory in his residence, which was run by Blanis, located only a short distance from where Antonio Neri was living when he first worked at the Casino di San Marco.  

Don Giovanni maintained a close relationship with Neri’s benefactor Don Antonio de' Medici. So close, in fact that when two of  Blanis' relatives were implicated in a gambling scheme, Don Antonio hid them at his residence and then spirited them away, out of Florence, in his own coach until matters cooled off. Furthermore, Blanis came from a family of doctors who must have been known to Neri's father, royal physician to Grand Duke Ferdinando. Antonio Neri was probably a couple of years older than Blanis, if they did not meet through mutual connections with the Medici family, then perhaps they met on the street. The walk for Neri, between his living quarters near Santa Trinita, and the Casino laboratories would have passed around or through the Ghetto, and the walk for Blanis to Don Giovanni's palazzo on Via Parione took him past Neri's front door. The paths of the two men may have crossed, but there is not direct evidence.

Of course, in the absence of hard facts, there are many other possibilities of how Antonio Neri might have become acquainted with Kabbalistic tradition. By taking a look at Blanis and his connections to the Medici family, we can at least see an area of cooperation between Jewish and Christian alchemists in what we might otherwise assume to be an inviolable separation.** 

* “Discorso sopra la Chimica: The Paracelsian Philosophy of Antonio Neri”, M.G. Grazzini / Nuncius 27 (2012), p. 337.
For more on Blanis, see Edward L. Goldberg, The Secret World of Benedetto Blanis. (2011).

** This post first appeared here on 6 January 2014.

Ultramarine Blue

Scrovegni  Chapel, Padua

Frescos and ultramarine ceiling, Giotto 1306.

In his fifteenth century handbook for painters, Cennino Cennini said, "Ultramarine blue is a color illustrious, beautiful and most perfect, beyond all other colors; one could not say anything about it, or do anything with it, that its quality would not still surpass." The ancient Egyptians used ultramarine to decorate the sarcophaguses of their pharos. Later, Marco Polo reported that it was made at a lapis lazuli mine in Afghanistan. Its name alludes to these far-flung origins: ultra-marine = "beyond the sea." Venetians were probably the first in Italy to learn the extraction technique and import the raw lapis. Producing the rich blue pigment from the rock was no simple task; success required an elaborate set of steps. Because of the difficulty, for a time, an ounce of ultramarine was valued more highly than an ounce of pure gold. In the legal contracts drawn up for commissioned paintings, patrons often stipulated exact amounts of the precious material for the artist to use. Beyond its beauty, its presence in a painting signaled the wealth of its owner.

In the last part of his book, L'Arte Vetraria, Antonio Neri presents his recipes for a variety of paints, including one for ultramarine. In glassmaking, drinking goblets adorned with delicate paint-work raised their value and elevated them into the realm of art. Unlike enamels, which fired into the glass, most paint, including ultramarine could not survive the furnace, requiring application only after a piece was finished. The number of different paint and lake recipes in the book indicates Neri's familiarity with the craft. This, combined with his willingness to use other painter’s materials like "smalt" in his glass formulations, hints at a still unknown chapter in the alchemist's life. Perhaps, for a period in Antwerp, he worked directly with fine artists. Here is Neri’s ultramarine:

Take fragments of lapis lazuli, which you can find plentifully in Venice and at low prices. Get fragments that are nicely tinted a pretty celestial color and remove any poorly tinted fragments. Cull the nicely colored fragments into a pot and put it amongst hot coals to calcine. When they are inflamed throw them in fresh water and repeat this twice. Then grind them on a porphyry stone most impalpably to become like sifted grain flour. 
Take equal amounts, three ounces each, of pine pitch, black tar, mastic, new wax and turpentine, add one ounce each, of linseed oil and frankincense. I put these things in a clay bowl to warm on the fire until I see them dissolve and with a stirring rod, I mix and incorporate them thoroughly. This done, I throw them into fresh water, so they will combine into one mass for my needs.  

For every pound of finely powdered lapis lazuli, ground as described above, take ten ounces of the above gum cake. In a bowl over a slow fire, melt the gum, and when it is well-liquified throw into it, little by little, the finely powdered lapis lazuli. Incorporate it thoroughly into the paste with a stirring rod.

Cast the hot incorporated material into a vessel of fresh water and, with hands bathed in linseed oil, form a round cake, proportionately round and tall. You should make one or more other of these cakes from the quantity of the material. Then soak these cakes for fifteen days in a large vessel full of fresh water, changing the water every two days. In a kettle, you should boil clear common water and put the cakes in a well-cleaned, glazed earthen basin. Pour warm water over them and then leave them until the water has cooled. 

Empty out the water and pour new warm water over them. When it has cooled, pour again, replenishing the warmth. Repeat this many times over, so that the cakes unbind from the heat of the water. Now add new warm water and you will see that the water will take on a celestial color. Decant the water into a clean glazed pan, pour new [warm] water over the cake and let it color [the water].
When it is colored, decant it and pass it through a sieve into a glazed basin. Pour warm water over the cake, repeatedly until it is no longer colored. Make sure that the water is not too hot, but only lukewarm because too much heat will cause the blue to darken, hence this warning, which is very important. 

Pass all this colored water through a sieve into the basin. It still has the unctuosity of the gum, so leave it to stand and rest for twenty-four hours; all the color will go to the bottom. Then gently decant off the water with its unctuosity, pour clear water over it and pass it through a fine sieve into a clean basin. 

Pass the fresh water through the sieve with the color stirred-up so that this color still passes through and therefore a great part of the filth and unctuosity will remain in the sieve. Wash the sieve well and with new water again pass the color through. Repeat these steps three times, which ordinarily leaves all the filth on the blue resting in the sieve. Always wash the sieve each time, cleaning it of all contamination. Put the blue in a clean pan. Gently decant off the water and then leave it to dry. You will have a most beautiful ultramarine, as I have made many times in Antwerp. 

The amount per pound of lapis lazuli will vary. It depends on whether the lapis has more or less charge of color and on the beauty of its color. Grind it exceedingly fine on the porphyry stone, as described above and you will succeed beautifully.  

For a quite beautiful and sightly biadetto blue that mimics ultramarine blue, take ordinary blue enamel and grind it exceedingly fine over the porphyry stone, as above. Incorporate it into the gum cake with the dose described above and hold it in digestion in fresh water for fifteen days as with the lapis lazuli. Follow the directions for the lapis lazuli, in all and for all, until the end. These blues are not only useful to painters, but they also serve in order to tint glasses par excellence.

"Conciatore" Book Excerpt

CONCIATORE, The Life and Times of 17th

Century Glassmaker Antonio Neri, By Paul Engle

From the Introduction:

"Under the cover of Antonio Neri's glassmaking book, L'Arte Vetraria, lays an alchemist's treasure. Centuries-old pages invite us to share in his secrets and plumb the glassmaker's art. Unfamiliar methods and ingredients discussed in his book at first may puzzle the modern reader, but soon the pieces fall into place. A careful ear will hear echoes of ancient technique, whispers that speak to the very essence of craftsmanship. A clear eye will see the hands of a master artisan manipulating raw ingredients into new materials. To read his most famous treatise is to join Antonio Neri's odyssey with nature and walk his path of discovery. Through his work, he offers a clear window into not only the world of Renaissance glassmaking but also into the upper echelons of society and into the deepest mysteries of alchemy. We can even catch a glimpse into the birth of modern science. 

A look into his personal life reveals a man who was born into the comfortable home of a royal physician. His family's circle included famous lawyers, wealthy merchants, archbishops, Vatican officials and perhaps a future saint. In his alchemical pursuits, Neri did not lead a solitary life; he sought out collaborations with others. He made friends among his technical coworkers, but also with princes and powerful international bankers. He cultivated recipes of herbal remedies and worked to cure disease among the infirmed. He came to serve a royal prince in a premier laboratory of its time, yet he worried about the social implications of his specialized knowledge.
In the pages of his book, Neri, an ordained Catholic priest, invites us into the secretive world of Renaissance glass formulation. He shows us cristallo, the coveted Venetian glass famously crafted by artisans in the style called façon de Venise. [1] This fabled creation, invented and perfected on the island of Murano, was the toast of European royalty for its finery, a tool of experimenters for its utility and the marvel of commoners for practical items like spectacles. For the first time in print anywhere, Neri revealed to the world the materials and recipes for cristallo and many other rare glasses. He detailed the secrets of color in glass from the delicate blush of peach blossom lattimo to the intense saturation of cobalt blue.

Like a fine artist, Neri conducted his craft with a deep regard for process. He tried variations and permutations of recipes that would result in the final product he was after. He took risks with expensive ingredients and he applied his experience to new areas. He helped to shine a spotlight on Tuscan glass and bring it to the attention of greater Europe. He devoted his mind to the creation of dazzling colors and his hands to the perfection of refined ingredients. 

Just as a great painter relies on the quality of pigments at hand, so must a master glass artisan depend upon the materials of the melt. For the glassblowers and furnace workers who shaped hot glass, a superior batch was crucial to superior results. A great piece of glasswork owes its form to the talent of the artist, but its substance is the province of the craftsmen who make the glass. This pairing put artistry at both sides of the furnace and made virtuoso glass world-renowned. In the early 1600s, Antonio Neri specialized in the glassmaking end of that partnership in Florence at the celebrated Medici court. This alchemist priest supplied a prince's royal artisans with the finest glass that money could buy. The quality of his work showed through the consistency and texture of his melts and through the clarity and brilliance of his colors. 

As his work spoke to the state of Florentine glass technology, it spoke as well to the state of artisanal craft (fig.1). [2] In Neri's hands, a technical recipe is akin to a composition of poetry. Each ingredient is cleaned, weighed and combined. Conditions are set, containers sealed, the fire lit and a secret of nature is revealed. Neri found his métier not in the creation of finished pieces, nor in the construction of furnaces or the forging of tools. Rather, his passion lay in the concoction of formulas, the roasting and purification of chemicals. He challenged Nature at her own game of creation. The recipes he perfected offer a chance to explore the work of a master Renaissance artisan at a time when art and science were indistinguishable. They illustrate craft practiced with all five senses.

[1] For examples, see Page, Doménech 2004.
[2] Ilardi 1993.