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. 

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. 

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

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.

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?"

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.

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.