Dear Readers,

As you may have seen elsewhere, in mid February my wife and I suffered the loss of our home in a fire, in the hills of central Massachusetts. The good news is that we got out safely and had no animals in our care at the time. The fire crews were able to contain the fire from spreading, in what turned into a 3-alarm, 5-hour-long ordeal in subzero temperatures; they did amazing work, and no one was injured. The bad news is that all of my physical historical materials and research of 30 years have gone up in smoke. As a result I have decided to suspend this blog for the time being. It will remain online as a resource for those interested in the history of glass and glassmaking in the seventeenth century and beyond. I do intend to resume writing when I can, but for now my time and energy are required in getting us back on our feet.

Friends are providing temporary shelter for us nearby and our intention is to rebuild as soon as possible. To those who have reached out with a steady hand, to those who have opened their wallets, and offered advice in our time of need, we thank you from the bottom of our hearts. In what are already difficult times for all of us, you have made a huge difference in our lives.

Paul Engle
6 March, 2021

Friday, May 30, 2014

Pebbles from Pavia

A Bridge on the River Ticino, near Polleggio,
William Pars (1742‑1782).
In the sixteenth and seventeenth century, a type of glass known as 'cristallo' was the absolute pinnacle of the art. Its recipe was invented in Venice and guarded there as a state secret. Its name derived from the mineral it was designed to mimic: rock crystal. As clear as water, rock crystal was valued since ancient times for carving into cups, vessels and other objects of art. Today we know it as a form of quartz, but in Roman times it was thought to be a type of frozen or coagulated water.

In the early 1600s, when Antonio Neri started making glass in Florence, the grand duke's craftsmen were routinely carving this hard and brittle rock crystal into complex thin shapes, a process that took great skill and effort. Due to the expense involved in producing a piece, this art was the exclusive province of extremely wealthy individuals. Thus, objects made from rock crystal were considered markers of status. The recipe for cristallo was a very great secret indeed, but its real value lay in the specific materials used. Even if the recipe found its way out of Murano, which it inevitably did, the Venetian's tight trade network ensured a monopoly on many of the ingredients. It is said that even the furnace crucibles for cristallo were made from a specific clay gathered in Constantinople.

Cristallo was not only exceptionally clear, but for the artist it had working properties like no other glass. Thin, complex shapes were possible in cristallo that could never be duplicated in common glass. The secret for making cristallo came to Florence in the late 1560's, only a few years before the birth of Antonio Neri, who would learn the techniques and go on to publish the recipe for the first time anywhere.

 After protracted overtures, which involved diplomats, spies and the archbishop of Florence, Grand Duke Cosimo I managed to negotiate with the Venetian Doge and Senate for a Muranese master and two assistants to come to Florence and teach the way to make cristallo. It is likely that the raw materials were all purchased through the Venetians, at least initially. By the time Neri wrote his book, L'Arte Vetraria, in 1612, the Florentines were already finding alternate sources. In Venice, the ingredients of cristallo were prescribed and controlled by strict laws. The Florentines did not have this constraint and were free to experiment.

In the second recipe of Neri's book, he spills the beans on where the Venetians procured the single most important ingredient for cristallo, the pure quartz stones which account for the material's clarity. Notice in the following excerpt that Neri mistakenly thinks that the white river stones are a form of marble and also notice the alchemical language he uses to describe the process in which the stone is "transmuted" into glass.
When you want to a make cristallo that is beautiful and fully perfect, see that you have the very whitest tarso. At Murano they use pebbles from Tesino [Pavia], a stone abundant in the Ticino River. Tarso, then is a species of very white hard marble [quartz]. 
In Tuscany, it is found at the foot of Mount Veruca in Pisa, at Seravezza, at Massa near Carrara, and in the Arno River both above and below Florence. In other places as well, common stone is often recognized, which is seen to have the same qualities as tarso; it is very white and does not have dark veins, or the yellowish appearance of rust, but is spotless and pure. Take note that any stones that will spark with a piece of steel or strike plate, are apt to vitrify and will make glass and cristallo. All those stones that do not make sparks with a piece of steel or striker as above will never vitrify. This serves as advice for being able to distinguish stones that have the ability to transmute their form, from those that cannot be transmuted. 
Start with this same tarso, as fair and as white as possible. Grind it finely into powder in stone mortars. Do not use bronze or any other metal for this purpose or the stone will take in the color of the metal, which then would tinge the glass or cristallo, and make it imperfect. The pestle must be iron by necessity but at least the other materials will not have the possibility of causing any effect. Pulverize the tarso well and sift with a fine sieve. It is important that the tarso is ground as finely as flour, so that it will all pass through a fine sieve. 

Wednesday, May 28, 2014

Let’s Dance

"Preparatio Animalium" from
Treasure of the World by Antonio Neri (1598-1600)
In the sixteenth and seventeenth centuries, the Italian Renaissance began to bear fruit of a curious nature. Principles of the natural world, which had been assumed without question for hundreds or even thousands of years, began to fall under scrutiny. Groups of experimenters sprang up in the form of "academies" that were dedicated to no other proposition than the careful observation and understanding of the physical world. 

Perhaps the most famous example of this new empiricism is the legendary (and probably apocryphal) dropping of two masses by Galileo from the leaning tower of Pisa. While the demonstration may have never actually taken place, the principle that Galileo had discovered was very real; that all things being equal besides weight, a bean and a lead sinker dropped together will fall at exactly the same rate, and land simultaneously. Counter to intuition, yet undeniably the way of the world. Galileo may have picked up his experimentalist streak from his own father, Vincenzo, a musician who through trial and error investigation determined that the prescription laid down by Pythagoras for musical chords and tuning left something to be desired in the real world. 

In the so-called era of enlightenment that followed in Europe, experimentalism was tagged as a philosophical position; that 'truth' is only discovered through verified demonstration. The Royal Society, London's premier association of scientific learning, adopted the motto "nullius in verba" which roughly translates to 'take nobody's word for it' or more bluntly 'seeing is believing.' But long before experimentalism became a philosophy, experiment or "experience" as it was often called was a practical tool for getting results. 

In his book on glassmaking, L'Arte Vetraria, Antonio Neri assures us that his recipes are the result of actual practice, "not as I was told, or persuaded by any person whatsoever, but as I actually did, and experienced many times with my own hands." Like exceptional poetry, Neri's recipes are rooted in ground truth and aim to reveal his subject, as he tells us, "with the greatest clarity I am capable of." In combining ingredients, setting the stage and letting Nature take her course, raw materials almost miraculously transform into glass. Just as poetry reveals, "more than ordinary speech can communicate" (T. S. Elliot) so too Neri's technical recipes reveal his deep grasp of what lens-grinder and philosopher Baruch Spinoza called nature's immutable order.  

I would like to advance the case that before experiment became the gospel of scientific inquiry, it was a practical method that was and still is engaging on a very human level. Because most of us do not have experience in making glass, I will switch to a more familiar venue, the kitchen. Seriously. An undeniable part of the joy of cooking is that when we gain experience in a particular recipe, we come to learn the effect of various ingredients and interactions. A little more salt or a lower temperature will have one set of consequences, more of these and a different result. There are no guarantees, but slowly, over the course of many trials, we start to see the effect of our interactions. By engaging with Nature, we are joining a sort of dance, letting her lead, learning her steps. Whether it is perfecting a dish in the kitchen or making glass in a furnace or doing atomic physics, there is a powerful appeal to learning Nature's dance, one that gets to the very heart of what it means to be human. 

Monday, May 26, 2014

A Matter of Plagiarism Reprise

Francesco Lana Terzi (1631-1687)
Two years ago, my friend and colleague Maria Grazzini was researching a paper about seventeenth century alchemist Antonio Neri. In the course of her work she made a surprising discovery. An entire manuscript of Neri’s had been appropriated by the well known Jesuit polymath Francesco Lana Terzi. Terzi had added a few sentences and presented, under his own name, an otherwise word-for-word transcription as a chapter in his Prodromo. Over fifty years past Neri’s death, Terzi had somehow managed to obtain a copy of the obscure manuscript and thought well of its contents; well enough to wish he had written it himself. Maria went on to publish an analysis of that work, Neri's Discorso, which includes a full English translation (which you can find here in Nuncius). It is a fascinating look at the chemical arts in a period when experimental science was just starting to gain traction. Simultaneously, the centuries-old Aristotelian concepts of air, water, earth and fire were beginning to fade from the stage of human enquiry. Last year, Maria kindly consented to compose a post for this blog on the subject; here is what she wrote on 29 November 2013:

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 Prodromo in 1670. The entire chapter 20 is an exact reproduction of Neri's Discorso. 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. L'Arte Vetraria was widely read and its reprints and translations appeared over the centuries. 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

Friday, May 23, 2014

Tinsel Glass

From Diderot's Encyclopedia, machinery to hammer brass into thin sheets.
To this day in the field of glassmaking, color is still a subject about which manufacturers hold their cards very close to the breast. It is very unusual to coax anyone in this trade to speak freely about exactly what materials are used to produce a specific color and for good reason – competitive advantage. In this respect, attitudes have not changed very much from the early seventeenth century when Antonio Neri blew the doors open with his book of glass recipes. L'Arte Vetraria, discussed, for the first time in print, a whole rainbow of different shades in terms of specific materials and amounts. 

Since then, a number of his formulations have become obsolete or fallen into disuse. This has happened for no other reason than the raw ingredients he used are not easily obtainable or reproducible today. Since the state of industrial chemistry is far ahead of where it was in his time, the basic metal oxides are now simply ordered from a catalog and mixed to produce the maker's specific color palate their customers expect. The result is that many of the shades of color Neri produced have not graced the end of a gaffer's blowpipe for centuries; they certainly could be duplicated today, but there is simply no call to do so.

One of the interesting raw ingredients that he used four hundred years ago is tinsel. Yes, this is the ancient relative of what we still use for holiday decoration. Neri advises, "Take orpiment, also known as tinsel and to save money purchase some that has already been used for decorative wreaths and garland." Tremolante is the specific word he uses; it has the same root as the English "tremulous" and "tremble." In modern Italian, it means to flicker or shimmer. The groundbreaking early dictionary first published by the Florentine Accademia della Crusca in the seventeenth century gives Neri credit for the first use of the term in this context, but if it was a common product, the word must certainly have been in use earlier. To confuse matters, Neri describes tinsel as a kind of "orpiment." (orpello) This term was also used to refer to arsenic sulfide, a highly toxic mineral used as a golden paint pigment, but in this recipe he uses the word only to refer to the golden color of tinsel.  

Neri's tinsel was made of brass, which is an alloy of copper and zinc. While zinc had been isolated as a pure metal, notably by Paracelsus, Neri knew it only by its oxide which he called zelamina. He cut the tinsel into tiny pieces with a scissors and then 'calcined' it, heating it in a covered crucible among live coals for four days. He was careful not to let it reach a temperature that will melt the metal. He removes it from the fire, grinds it into a black powder, then reheats it for another four days. By the end of Neri’s process both the metals would be oxidized. This product, he tells us, makes a blue color in glass reminiscent of the feathers of the "gazzera marina" bird, "holding the middle between aquamarine and the color of the sky when it is very clear and serene" There are several possibilities for the identity of the gazzera marina, the most likely seems to be the European Roller (Coracias garrulus). It is a species that is known for its striking appearance in flight; its brilliant blue breast contrasts against black flight feathers. 

In a second brass recipe (# 21), the snippings are mixed with powdered sulfur and heated in the live coals of the furnace firebox for a day. He then grinds it as before and reheats it for a protracted period of ten days in the hottest part of the furnace "near the eye." Neri advises that the product can be used for transparent red, yellow and in chalcedony glass. He uses calcined tinsel in two of his chalcedony recipes but we never see a further mention in the book for transparent red or yellow glass. In the first part of this recipe, the sulfur likely reacts with the zinc-copper alloy in the tinsel to form sulfides of the metals. In the second part, the sulfides are decomposed by the high heat to form oxides and most or all of the sulfur is driven off as noxious sulfur dioxide gas. This method could well produce better oxidation of the metals and therefore a better quality colorant. If the sulfides do not completely decompose, some interesting possibilities arise in the melt. Copper sulfides have the potential to be reduced to pure metal in a reheating maneuver done by the glass artist called 'striking.' This might produce the wonderful transparent red known as copper ruby glass. Zinc sulfides in glass, produces a white or opaline glass. The only way to know for sure what the old recipes would do is to make a batch and put it in the hands of an artist.

Wednesday, May 21, 2014

A Deeper Accomplishment

From Antonio Neri, "Treasure of the World"
MS Ferguson 67, f. 22r.
For the past four centuries, Antonio Neri has been best known as the author of L'Arte Vetraria, the first printed book solely devoted to the art of glass formulation. It is a work committed to the subject of refining raw materials and combining them into a range of glasses, over a rainbow of colors. 'First into print' is a notable distinction, but one that Neri surpasses with ease by a deeper accomplishment. His book provides a rare glimpse of skilled practical knowledge. This was an era when prized techniques were frequently lost to subsequent generations; lost because artisans so often spared the pen. Their precious knowledge went purposely unrecorded, passing in strict confidence from master to apprentice working side by side. Neri preserved the old techniques like no other document has.

That 'first into print' is what we remember him for highlights an age-old problem that dogs historians. It is a simplification that puts a convenient handle on Neri, but at the same time, it de-emphasizes the fact that he was not working alone. It plays into a narrative that history, in general, happens in a parade of discrete jumps due to the brilliant discoveries of individuals working in isolation. This is confirmed by the mythology surrounding Neri – that he was a mysterious lone alchemist, wandering around Europe, evading those who would steal the secret of the philosopher’s stone. A similar narrative is applied to one historical figure after another, a form that is so appealing that it fills many history books of our schoolchildren and dictates the story lines of popular television productions (of a certain ilk) about the history of science and technology.

This is not to deny the limelight to anyone. Neri is a comparatively minor contributor and in my humble opinion definitely deserves recognition and even celebration. The danger is that by reducing history to a list of lone individuals making breakthrough discoveries, we distort the truth of how things are done and more to the point; we miss out on the far richer adventure of what really happens.

Never mind that Neri's book chronicles the work of hundreds or thousands of glassmakers that came before him or that he probably would have been far more grateful to be remembered for his work in alchemy and medicine. What sticks is 'first into print.' The reality is that he had the substantial resources of the Renaissance Medici court at his disposal. There is strong evidence based on his own manuscripts and drawings that he worked among a group of at least a dozen colleagues of both sexes, exchanging ideas, experimenting and urging each other on; a mode that no scientist would deny is far closer to the way discovery and innovation really happen. 

This cultural defect in our perception of history is by no means a recent development. Even in Neri's own time, the early seventeenth century, the 'lone man' paradigm was well established. He and his contemporaries thought along similar lines about alchemists Arnold Villanova, Ramon Llull and Paracelsus. Physicians like his father idolized Galen and Dioscorides.

For the first time in history, we each have a tremendous chunk of the past at our fingertips in the form of the internet. It is a golden opportunity, not to be fed history, but to discover it for yourself and perhaps for the rest of us. There is no shortage of connections yet to be made and libraries around the world are availing their treasures freely to anyone with an interest. For a great adventure and an exercise in critical thinking, pick a discovery attributed to your favorite figure in history and ask the question "on whose shoulders was she standing?"

Monday, May 19, 2014

From Beads to Belief Reprise

A modern lampworked bead being made
In his book L'Arte Vetraria, Antonio Neri makes sixteen distinct references to the production of glass for beads. In chapter 22 he gives a recipe for 200 to 300 pounds of aquamarine colored glass for beadmaking cane. 'Cane' is the term for glass drawn out into thin rods and cooled, to be used later, over an oil lamp. The canes are heated in the flame and wound around a metal wire, forming individual "spiei" beads which can then be decorated with others of different colors. Neri says:
I demonstrated this method of making aquamarine in Florence in the year 1602, at the Casino, and I made many batches of it for beadmaking cane, which always resulted in a most beautiful color.
After cooling, the beads were removed from the wire and often strung as rosaries. Using these beads in the recital of prayer dates back at least to the thirteenth century. In 1569, only a few years before Neri's birth, Pope Pius V officially established devotion to the rosary. As a priest, the production of glass for beads may have formed a part of Neri's ecclesiastical duties.

It is worth spending a moment considering the end use of these beads. These carefully formed bits of glass were spread around the world. They could end up as trade currency in any number of locations from the Americas to Africa to Asia to the far east. As mentioned above, they also could find use locally as sets of  rosary beads, known as  "paternostri" or "our fathers." In both cases they were invested with a value that transcended the raw materials. In the former case it was purely monetary; a unique unit of trade that was distinctive, artful and difficult to reproduce. In the latter case, they served as sequential placeholders in prayer, as objects made by man in the fashion of natural stones or gems, which were physically held and invested with hopes and dreams.  

In chapter 47, Neri describes a garnet colored glass which is appropriate for small "ferraccia," or pan-fired beads. For these, small lengths of cane were nipped off and pierced with a sharp metal point. A large number of these were then placed in an iron pan, in the furnace, and agitated in order to round them. Neri would supervise the production of beadmaking cane not only in Florence, but also in Pisa, and possibly in Antwerp.

The praying of the rosary is sometimes started with a recital of the Apostles' Creed, and Neri makes use of that in the recipe for an emerald-green lead-glass in chapter 65:
…Mix the powders, and always give them to the glass in six portions, stirring the glass well. Set the interval from one portion to the next by reciting the creed.
Assuming he used the creed of Pius IV, adopted at the council of Trent in 1564, recitation takes a little under three minutes. Later in the book, in chapter 117, he uses Psalm 51(Have mercy upon me, oh God...) to time the extraction of kermes dye. At first blush, it might seem that religion would be at odds with alchemy and glassmaking. In reality, practical elements of Neri's religious life integrate seamlessly with his work at the furnace and in the laboratory.

Friday, May 16, 2014

Scraping the Barrel

4th century BCE philosopher Diogenes
(supposedly lived in a wine barrel)
by Gaetano Gandolfi (1792)
To seventeenth century glassmaker Antonio Neri, "tartar" was a well-known byproduct of the winemaking process. If we chill wine or grape juice to below 50 degrees (10 deg. C.) crystals of tartar start to form and once they do, then tend not to dissolve back, even at room temperatures. Today, these crystals are commonly found in a powdered form, in kitchen cupboards as "cream of tartar." Bakers and cooks use it to stabilize whipped egg whites, and it has a number of other applications. 

Neri used it in his glass to add sparkle, a trick known to Venetian glassmakers as early as the 1400s. It was obtained from the dregs at the bottom of wine barrels. To understand how this works, it is useful to know that Florentines, Venetians and most southern Europeans made glass from crushed up quartz pebbles or sand mixed with a specific flux known as "glass salt." This salt was rich in sodium carbonates, which greatly reduced the melting point of the quartz. It allowed artisans to work the material at the temperatures easily achieved in their furnaces. Tartar turns out to be very similar, except that it is rich in potassium rather than sodium. 

Potassium atoms are bigger and heavier than sodium atoms and when light passes through a piece of potassium-fluxed glass, it bends and refracts more. This effect is not as pronounced as when adding the even heavier lead to form fine crystal, but it still adds noticeable sparkle to finished pieces. Using all tartar as a flux has the undesirable effect of reducing the workability of the hot glass. Outside the furnace, it becomes stiff quicker and artists have less time to create fancy shapes and forms. The solution to this dilemma is to use a mix of sodium and potassium fluxes together, which is exactly what Neri did. 

In his 1612 book L'Arte Vetraria, he shows how to prepare tartar and then adds it to a number of his glass recipes saying, "The tartar is the secret way to produce more salt and to make cristallo which is whiter and of rare beauty." Here is Neri’s prescription:


To make Purified Tartar Salt you should obtain tartar, which is also called gruma, from barrels of red wine in which it forms large lumps, however do not use powder. Roast it in earthenware pots amongst hot coals until it becomes calcined black and all its sliminess is roasted away. It then will begin to whiten, but do not let it become white, because if you do the salt will be no good.  
Calcine tartar this way: put it in large earthenware pans full of hot common water, or better yet in glazed earthenware pans then made to boil on a slow fire. You should do it in such a way that in two hours the level of the water will slowly decrease to one-quarter, at this point lift it from the fire and leave it to cool and to clarify. Now decant off the liquid, which will be strong lye and refill the pans containing the remains of the tartar with new common water. In the way stated above, boil as before and repeat the procedure until saltiness no longer charges the water. 
At this point, the [decanted] water is impregnated with all the salt. Filter the lye clear and put it in glass chamber pots to evaporate in the ash of the stove over a slow fire. In the bottom, white salt will remain. Dissolve this salt in new hot common water and leave it in the pans, letting it settle for two days. Then filter it and return it to chamber pots to evaporate over a slow fire. In the bottom, a much whiter salt will be left than the previous time. Now dissolve this salt in fresh hot common water and leave it to settle for two days. Evaporate, filter and repeat everything as before. Overall, repeat this procedure four times to dissolve, filter and evaporate the salt of tartar. This will make the salt whiter than snow and purified from the vast majority of its sediment.
When mixed with sifted polverino, or rocchetta, with its doses of tarso [quartz] or sand, this salt will make a frit that in crucibles will produce the most beautiful crystallino and common glass, which one cannot make without the accompaniment of tartar salt. Without it [tartar], good fine crystallino can be made, nevertheless with it, it will be the absolute most beautiful.

Wednesday, May 14, 2014

The Importance of Being Diligent

Fennec fox pup, 2008
Everland Zoo, South Korea. 
In his 1612 landmark book about making glass from raw materials, there is a specific term that Antonio Neri uses repeatedly: "diligence." I count forty-two distinct instances spread throughout the book. Even so, in all of these occurrences, not once does our priest-alchemist uses this term in a casual manner; each appearance is in a critical step, in which he urges his readers to pay extremely close attention to what they are doing. 
If you want to have fine crystal, then in this you must exercise great diligence; when the frit is made with this careful attention, it will be white and pure like snow from heaven.
And
Then you must stir the glass with a paddle, but when the tinsel is calcined well and as directed, it swells so much that it could make all the glass go out of a large crucible. So use diligence in this.
And
All lead precipitating out of the glass must be removed with diligence, throwing it away, so that it does not make the bottom of the crucible break out, as can happen.
One might well ask, why so much attention to diligence? To be sure, there are many important aspects to the successful outcome of a batch of glass. Yet Neri singles out the seemingly simple act of paying attention. One reason is to avoid disasters. The last two quotes above imply that he has seen his share of these.

There is no question that glassmaking is a technically demanding process, where many things can go wrong. But there is more to it than that; Neri’s admonitions may have more to do with developing the proper attitude in a glassmaker. At first, it might seem that a recipe is a recipe is a recipe and as long as one follows it, mental state has no bearing on the situation. Yet as surprising as some may find it, this is definitely not the case. Materials and conditions vary in ways that cannot always be measured. What a recipe specifies is strictly limited by our perceptions and to quote the bard, "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."

Unlike some more intellectual pursuits, glassmaking falls into a category of activity in which there is no room for self-indulgence. It does not work to throw the ingredients into a furnace and walk away, assuming that they will react the way we anticipate. They will react, rather, according to the physical laws of nature. Diligence could make the difference between a minor correction and a disaster. For the headstrong, this can be a rude awakening. A would-be glassmaker is forced into a confrontation with stark, unforgiving reality. What one wants or expects has no bearing on the situation, only what one does, and when.

Neri makes clear that this philosophy of diligence is not only required by the novice, but also by the seasoned professional conciatore.
This entire exercise depends on the practice of being a worthy and diligent glass conciatore, because neither sure weight nor measure can be given.
And
The diligent furnace conciatore will meticulously remove any lead that has returned to its metallic state from inside the pot.
And
When working this glass, use the same diligence that the skilled masters use and in so doing you will make material that is perfectly true to the jasper, agate and chalcedony of the orient.
In the early seventeenth century, to be a glassmaker meant becoming a careful observer, ever mindful that Nature does not care a whit what you think. 

Monday, May 12, 2014

Don Antonio de’ Medici

Don Antonio de' Medici
Frontispiece from Pierfilippo Covoni 1892
In 1612, Priest Antonio Neri published his book of glassmaking recipes. L’Arte Vetraria went on to become a primary reference for glass artisans throughout Europe. He dedicated his book to Prince Don Antonio de' Medici the son of Grand Duke Francesco I:
In all consideration, it is my proud duty to dedicate this book to none other than you, most Illustrious Excellency; for you have always been my outstanding patron. You are a gifted leader in this and in all other noble and worthy developments made continually in all the arts.
As an eleven year-old, Don Antonio was slated to succeed his father as the next Grand Duke of Tuscany, but that situation changed quickly. In the autumn of 1587 the young prince lost both of his parents in the space of a few days. They both fell extremely ill and died within a short time of each other. Rumors flew that they had been poisoned, but forensic investigators have found pernicious malaria pathogens in Francesco’s remains, a disease with symptoms consistent with the reports of physicians on the scene. Historians trace their infection to an outing in the damp forest a few days earlier, where they had probably been bitten by mosquitoes carrying the disease. 

The boy’s uncle, Cardinal Ferdinando took charge, consolidated power and excluded Don Antonio from the royal succession, although he was given a prominent place at court as a diplomat. As part of a deal that he would never marry, he was allowed to keep the title of Prince of Capestrano, to which was added Grand Prior of Pisa, in the Knights of Malta. The deal also gave him possession of the laboratory facility that his father had built and several other properties. That laboratory, the Casino di San Marco would become the prince’s residence and the place where Antonio Neri would learn about glass formulation.

Poor health attended Don Antonio from his first months through the end of his life. Doctors and medical examinations were to become a regular part of his routine; they may well have inspired his later pursuit of medicinal cures, as well as his foray into alchemy, which also involved Antonio Neri. At some point, probably as a teenager, Don Antonio contracted syphilis, a condition that may well have been treated by Antonio Neri’s father who was physician to the royal family.

The prince had played a major part in Neri's life, elevating him into the upper stratum of Florentine craftsmen and to the forefront of alchemical research in Europe. However, in another manuscript, Discorso, we see a different side of Neri. On the subject of turning base metals into gold, the priest was less forthcoming:
I would add that God's providence over human affairs must not easily allow many to acquire this art, particularly not the great princes. It should not be made clear and common to the vulgar, because in this way, gold and silver and consequently coins lose their value, so that the good order of human trade will be disrupted and we should go back to the ancient barter of things that are necessary to a civil life, creating great disruption and confusion.
Although never allowed to marry, over his lifetime Don Antonio managed to have a number of children; his last three sons were ultimately legitimized by the pope as Medici heirs. In the end, it was the slow, progressive ravages of syphilis that brought him down. He died in 1621, at the age of forty-five, unable to leave his bed. He was given a proper funeral, and interred at the Medici chapel of princes in Florence.

Friday, May 9, 2014

Washing Molten Glass

Washing, sorting and carrying cullet
Denis Diderot 1772
One of the continuing frustrations with the study of glassmaker Antonio Neri, is that there is no known example of his glass to be found anywhere. It is very possible that pieces do survive, but so far, none has been tied to him or his recipes. At first it might seem to be a straightforward task of analyzing the composition of likely candidates and comparing the results to his formulas. Unfortunately, this plan does not hold water. Even if a recipe for glass was followed exactly, the result will have a different composition from the starting materials. One reason is that before the hot glass was crafted by artisans, a new batch was typically "washed" by flinging ladlefuls of molten glass into great vats of cold, clean water. In his 1612 book L'Arte Vetraria Neri wrote:
After a while, when the glass is well fused, take it out of the crucibles and throw it into large earthenware pans or clean sturdy wooden tubs filled with fresh water. This step of throwing the glass into water has the effect of causing the water to remove a kind of salt called Alkali salt [glass gall], which ruins the cristallo and makes it dark and cloudy. So while it is still being worked let the glass spit out this salt, a substance quite foul, then return it to clean crucibles. Carry out this flinging into water repeatedly as necessary. In order to separate the cristallo from all its [alkali] salt, this should be repeated to the satisfaction of the furnace conciatore [glassmaker].
This step, he assures us, is absolutely necessary for the finest glass, but also helps improve the most common glass:
If you throw it into water at least one time, what you will have will be beautiful and clear. The same is true for common glass, which once brought to perfection you should return to the crucibles for use. It will be bright, fine and quite satisfactory to work in those jobs that require it. […] when a more than ordinary fine glass is desired it is necessary. Beyond becoming very white[clear], it calcines and clarifies nicely with few impurities.
This technique becomes even more critical for Neri's lead crystal, in fact, any glassmaker who ignored this step for a leaded glass did so at risk of a major disaster.
In a few hours everything will have clarified, now purify it by throwing it in water. Inspect the glass carefully before returning it to the crucible. All lead precipitating out of the glass must be removed with diligence, throwing it away, so that it does not make the bottom of the crucible break out, as can happen. Return the glass that was thrown in water to the crucible and leave it to clarify for a day.
In addition to washing the glass, sometimes the top layer of a melt was skimmed off and discarded because it contained contaminants that floated to the surface. To complicate matters further, molten glass can stratify in the crucible, meaning the composition might vary from top to bottom and from the center of the pot to the edges. 

Scientists and historians have collaborated to see what can be learned from period samples of glass. When attention is focused on the composition of a single type of glass, like Venetian style cristallo for example, one might expect a wide variation. The opposite turns out to be true. Even with all of these factors conspiring to change the glass composition, remarkably the analysis shows it is quite difficult to tell apart glass that was known to be made in Florence from that of Antwerp or Venice. Recent efforts have centered on identifying miniscule amounts of trace materials in the old glass that were unique to the raw ingredients of a specific region. Meanwhile, Antonio Neri's glass continues to elude us, even though it might be sitting on the shelves of museums around the world, right in front of our eyes.

Wednesday, May 7, 2014

The Neri Chapel

The Vision of St Bernard, by Pietro Perugino (1448–1523)
The c. 1598 altarpiece that was commissioned 
for Cestello by Antonio Neri’s father
On a narrow unassuming street called Borgo Pinti on the northeast side of Florence, there are two structures in particular which are of great interest in the study of seventeenth century glassmaker Antonio Neri. The first is the family’s residence at number 27, now a hotel, but largely intact and the second is the church located a few steps further north, now known as Santa Maria Maddalena dei Pazzi. 

In the sixteenth and early seventeenth century, the church was part of a Cistercian monastery known locally as “Cestello” It was attended by Antonio’s royal physician father Neri Neri, his grandfather, Jacopo and it is safe to assume, the rest of the family. This is where the medical doctor would later be buried. In 1598, he was laid to rest in the chapel that Poccetti and Passignano reworked to his specifications; both were well-respected fine artists of the time. One author would later refer to the space as “the famous Neri chapel.” The royal physician asked, in his will, that his remains never be moved outside of his beloved homeland. He provided money for what amounts to a complete restoration of the entire property. The work in the chapel and the main church was a top to bottom renovation and must have taken several years to complete; today it is considered Poccetti’s crowning achievement. In earlier times, the monks of Cestello had played a trusted role in pre-Medicean Florence, collecting and counting the beans used in votes of the Signoria (town council), and holding the keys to the Palazzo Vecchio.

The chapel and the church still stand, but the occupants changed in 1628-29. Pope Urban VIII was seeking better accommodations for two of his nieces who were Carmelite nuns on the other side of the Arno River at San Frediano Monastery. He asked that the Cistercian brothers, against their protestations, exchange properties with the nuns, who brought with them the remains of Sister Maria Maddalena de’ Pazzi, the influential mystic who died in 1607. The church was renamed in her honor after canonization in 1669. 

The Cistercian’s archives record that:
In 1598 Doctor Neri remodeled in more honorable form the chapel which was originally built by Tommaso del Giglio, in the year 1505, which had since become occupied by the cobblers guild, who had begun to meet there and which he feared they wanted to usurp. Maestro Neri approached the Grand Duke [Ferdinando I] in order to have authority to free it from the hands of the cobblers and enlarge and redo it from the foundation and have it all painted in frescos by the hand of Bernardino Poccetti and dedicated to the honor of Saints Nereus and Achilleus.
Far more than the mere renovation of the chapel, the royal physician played a central role in the rehabilitation of an ancient and venerated church, a church that today continues as a testament to Poccetti’s great talent. Tommaso del Giglio, the former owner of Neri’s chapel and successful apothecary supplied Cestello as well as many Florentine hospitals with medicines and other staples. That the cobblers had occupied the chapel might seem strange. What possible claim could the band of shoe-makers have to this space? The simple answer is that Del Giglio was himself a member of their guild, perhaps the cobbler’s most famous member. About 1462 he moved his family to Florence from Montevarchi, where he was trained as an apothecary. For whatever reason he could not gain membership to the guild in Florence, so instead he joined the subordinate cobblers’ guild but retained his practice as an apothecary. He was still subject to the  rules, regulations and periodic inspections of the authorities. Eventually he attained the honor of apothecary to the ruling Medici family. A century after his death, it seems the chapel and the church itself was falling into disrepair; the cobblers, with the family’s blessing met there on a regular basis.

The Cestello monastery, of which the church was a part, served as an early home to the famed Accademia del Disegno (Florentine Academy of Design). The city’s greatest artists, sculptors and architects were all members, Giambologna not least among them. The rooms of the monastery were used to store artistic works and teach classes. For the members it served as a place to meet and plan projects for the city and royal family. A young Galileo Galilei would study mathematics here under Ostilio Ricci. 

It is unknown if the Neri chapel serves as the last resting place for the children of royal physician Neri Neri, among them his most famous son, glassmaker Antonio Neri, who died in 1614 at the age of thirty-eight.

Monday, May 5, 2014

Eyes of a Lynx Reprise

The seal of the Accademia dei Lincei.
In the spring of 1612, Florentine priest Antonio Neri published his book on glassmaking. L'Arte Vetraria was the first printed book devoted to the formulation of glass from raw materials, but unfortunately for him it did not exactly take the world by storm, at least not at first. Sales were such that a number of copies still exist from the initial printing; they remain in pristine condition, never bound. Initially, the book received scant attention, but it was noticed. In fact, within a couple of years word had reached Rome, where Prince Federico Cesi, the founder of a scientific society asked a Pisan member of his group to obtain a copy. That other member would go on to become one of the most famous scientists in history. Meanwhile, L'Arte Vetraria gained prestige and readers, slowly but steadily.  By the end of the century, Neri’s book would be translated into English, Latin, German, French and then back into English from the French. It became the bible of glassmakers throughout Europe. Here is what I wrote about it last year on 1 August:

In 1614, the year of Antonio Neri's death, naturalist Prince Federico Cesi wrote to his good friend Galileo. He complained of the difficulties in getting material from the Roman libraries, urging the astronomer to send him a copy of Antonio Neri's book.
The poor management of these libraries in Rome makes me feel continually thirsty for good books that come to light, which I can use for my study of compositions. They are scarcely giving me the titles, and after a long wait, only a tenth of what I asked. […] now I hear that printed in Florence is L'Arte Vetraria by Priest Antonio Neri, and I think there is some good in it. Please, your lordship, send me a copy, and believe me that I will gladly give them trouble.
 Shortly after, having received the book the prince wrote,
I thank your lordship for the book on glass, which I find very rich in experiments and beautiful artistry.
In 1603, Cesi founded the Accademia dei Lincei (Society of the Lynxes), an early scientific society whose members (with eyes as sharp as a lynx's) eventually included both Galileo Galilei and Giambattista della Porta. Within a few months of Neri's death, his book was already on its way to making history.

Friday, May 2, 2014

Book of Secrets

Title page, L'Arte Vetraria,
by Antonio Neri (1576-1614)
Today, we recognize L'Arte Vetraria as the first printed book devoted to the art of glass formulation. It is a work committed to the subject of refining raw materials and combining them into a variety of glasses, over a rainbow of colors. 'First in print' is a notable distinction, but one that Neri surpassed with ease through a deeper accomplishment. His book provides a rare glimpse of skilled practical knowledge. This was an era when prized techniques were often lost to subsequent generations because artisans so often spared the pen. Their precious knowledge was kept far away from paper, passing in strict confidence from master to apprentice working side by side. Trade secrets were guarded possessions. Recipes committed to writing were an invitation for prying eyes—in the case of virtuoso glass, an invitation to be compromised by individual competitors and by rival states. This is what makes Neri’s book of glassmaking recipes extraordinary. In an age of secrecy, L'Arte Vetraria was a deliberate exposition, a lucid guide to the art by a seasoned professional. He intended it for the enlightenment of those with no other qualification than a "kind and curious spirit." He assures us that "given a bit of experience and practice, as long as you do not foul-up on purpose, it will be impossible to fail." 

Books of secrets have been a part of our culture since history began. More than the mysticism they imply, they chronicle the development of various technologies and show us in a literal sense how we got to where we are today. They play a unique role in preserving types of knowledge taught by doing. For one practiced in a particular art, a book of secrets was a roadmap, sequencing new steps on a landscape that was already familiar. Neri's L'Arte Vetraria is a prime example of this genre; it documents the chemistry of glassmaking in the late Renaissance and it highlights the link between alchemy and the arts. But Neri takes on an increased challenge by inviting the novice to partake in his craft. He created a document that spoke to the uninitiated of his own time and still speaks to us today. Neri and the other masters of his day may be long gone, yet his painstaking, jargon-free instructions tell us with exact language what those master glassmakers were doing. 
Be warned in particular to give careful consideration to the colors for which exact and determined amounts cannot be given. Indeed, with experience and due practice learn and with the eye and judgment know when a glass is colored sufficiently and appropriately for the work at hand. 
These books have unique characteristics that distinguish them from other forms of writing. The author must have one foot in the learned world of letters and the other foot in the intuitive world of craft. Working at the Casino di San Marco and elsewhere, Neri and his fellow artisans think in images, smells and textures. They have a first-hand detailed experience that does not lend itself to written words with ease. The essence of an artisan's work defies accurate capture between pages, yet Neri verbalizes these procedures in a clear narrative. When he cannot give exact amounts, he explains with care the decision making process that must take place.

"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." From the contents of his glass recipes, we can see his bottom-up thinking. He starts with details gained from hands-on experience and forms his conclusions based on that knowledge. In sharp contrast to other authors of the period, Neri presents no grand theories of nature. Nor does he struggle to fit glass into a larger abstraction. Many contemporaries debated at length over the true essence of glass—whether it was more like metal or mineral and therefore possessed one set of essences over another. Perhaps more significant, Neri does not impose extranatural explanations on the results of his chemistry; instead he follows nature. The top-down approach is not his way, he interacts with his materials, he observes how they behave and he encourages the desired result by optimizing favorable conditions. 

On a practical level, alchemists interacted with nature to transform materials in ways other arts could not. Sculptors could use physical tools to transform a block of marble into a statue, but the substance of the marble was unchanged. Ironsmiths could forge a suit of armor and weavers could transform fibers into cloth. However, it was alchemists who made the fabric dyes permanent. It was alchemists who could dissolve a block of marble with reagents before one's eyes. To common men and women, the alchemist's world of transmutation must have seemed magical. Books like Neri’s gave a glimpse into the real-world mechanics of these mysterious arts.