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, December 29, 2017

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.

Wednesday, December 27, 2017

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.

Monday, December 25, 2017

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.

Friday, December 22, 2017

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.

Wednesday, December 20, 2017

"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.

Monday, December 18, 2017

Like Snow From Heaven

28th December 2005 in Florence
Photo by Marco De La Pierre
In its simplest incarnation, glass is nothing more than crushed quartz or sand mixed with 'glass salt'. This salt is the alkali carbonates of sodium or potassium. Essentially, the ash of certain plants that reduces to oxide in the furnace and dramatically lowers the melting point of the sand.

In Pliny's ancient account of the discovery of glass, the process takes place in a single step. The ingredients came together accidentally in a fire and "glass trickled out." The problem is that pure quartz does not react with the salt until it gets very hot and even then, it does so reluctantly. In a wood-fired furnace, quartz stones, even small pebbles or sand would melt with excruciating slowness. As Neri advises, "... this would only succeed after a protracted period of time and a great amount of trouble." 

'Fritting' is an intermediate step that speeds the process considerably. Glassmakers reduce the quartz to a fine powder and then mix it with the alkali salt. In the heat of a kiln, the entire content of each stone is thus exposed to the salt right from the beginning. This roasting process starts a chemical reaction between the ingredients. In the late Renaissance, the combination was then cooled and 'aged' for several months before use. When made from pure quartz river stones and the best Levantine ash, the result was what Neri calls 'bollito,' "white and pure like snow from heaven."

A third ingredient of glass, critical to its long-term stability is lime, or calcium oxide. Without the lime, glass is susceptible to attack by water. The water actually dissolves the glass, or less dramatically makes it subject to 'glass disease' or 'crizzling', a condition where the glass slowly decomposes due to humidity in the air. Waterglass is a product made without the lime. On Murano and elsewhere, it was dissolved in water and painted onto the shells of eggs to seal and preserve them. In Neri's era, lime was produced by roasting seashells. It was a key ingredient of cement, and as such was readily available. It had been a major commodity throughout the Mediterranean since the Roman Empire. Neri advises to add lime to all his glass recipes, but it is not so clear that he himself understood why it was so important.


*This post first appeared here on 11 October 2013.

Friday, December 15, 2017

Enamel

Enameled Pendant, Pope Gregory IX
Attr. Italian, mid 17th  c
In the sixth part of his book, L'Arte Vetraria, Antonio Neri presents his recipes for enamels. These are a form of glass meant to be applied in thin layers like paint, and fired quickly. In the early seventeenth century, enamels were used to decorate both glass and gold. Neri does not present any methods specifically addressing technique or application, but he does leave a number of recipes. He also praises the talent of a good friend, who worked on glass in 1601, at the Casino di San Marco in Florence.  "At that time, the task of scheduling furnace work fell to the outstanding Mr. Nicolò Landi, my close friend and a man of rare talent in enamel work at the oil lamp."

The recipes Neri presents in his book are geared towards metalwork, as he says, "In which I show the way to make all of the goldsmiths' enamels to fire over gold in various colors. Included are the rules, the colorant materials and the methods to make the fires for such enamels with exquisite diligence. I present the demonstrations as clearly as possible for this subject." He continues,
Now, this is not only a difficult art but also necessary. We see ornate enameled metals in many colors, and they make a pleasant and noble sight; they entice others to look and take notice. In addition, enameling is one of the main segments of the glass field, and quite necessary. It seems to me to cause universal gratitude and pleasure, so I will endeavor to describe many ways to make all sorts of enamels, which are special materials in the art of glassmaking. They form one of its noble domains, not common, but a particular niche, and because this work is not lacking in substance, and is pleasant, useful, and necessary, I have made this present sixth book, for the satisfaction and benefit of everyone.
Neri's interest in enamels seems to start with  Nicolò Landi. Within a couple of years, in 1603, the glassmaker’s friend Emmanuel Ximenes wrote from Antwerp to Neri in Pisa about the suitability of an enamel he had received from the priest, purposefully overloaded with color. "As far as the red glass, […] I am doing a test in enameling gold, because having such a thin layer of enamel, if it is not very full of pigment it would remain a pale color. […] If it will not grieve Your lordship, I would love to find out the composition."

The implication is that Ximenes was working with his brother in law Baron Simon Rodriguez d'Evora, a famous jeweler and diamond dealer. Soon, Neri would join them in Antwerp, however, the evidence points to a working relationship with goldsmiths before his visit.  "In Pisa, I made them [enamels] without [measuring] weights, but by rough estimate." In fact, Neri mentions goldsmiths in virtually every enamel recipe in the book, and unlike other chapters, he makes no mention of Antwerp, but only of Pisa.

As in all his endeavors, Neri pays close attention to ground truth; he is not as interested in presenting a tidy cut-and-dried recipe as he is in describing what is actually happening with the materials.
You should add the material in four doses, stirring [the melt] thoroughly each time, and leaving the glass to incorporate the powder. The way to check that the color pleases you is by proofing it, and watching to see if it is sufficiently loaded. Stop adding powder and proceed to make a goldsmith's proof [on metal]; always examine the colors to get to know them by eye, as I have always done, because in this matter, I cannot give specific doses. Sometimes the powder will tint more, other times less, therefore you must practice with your eyes to understand the colors.
* This post first appeared here 23 December 2013

Wednesday, December 13, 2017

Early Modern Aleppo

Aleppo, 1764
Antonio Neri is famous for  his 1612 book on making glass, [1] but in the late sixteenth century his father was also famous; Neri Neri, as he was called, was a graduate of  the esteemed 'Studio Fiorentino', head of the Florentine physicians and apothecaries guild, and royal physician to the grand duke of Tuscany, Ferdinando I de’ Medici.  

In those days, one of the best connections a physician could have was a reliable associate who could procure the exotic herbs and remedies prepared in the Orient. To have such a contact in one's family was even better, but perhaps best of all was an older brother who was a merchant living in the fabled city of Aleppo, located in Syria at the very end of the Silk Road. The brother of Neri Neri was named Francesco or "Franco" [2] for short and Aleppo was no ordinary city; it was a sort of international crossroads for traders connecting north and south, east and west. It was where silk and cotton were traded for wool and metals, where gold and silver changed hands for rubies and lapis, and where exotic spices and medicinal preparations could be found and exported to places like Venice and  Florence. [3] In 1583, Englishman John Eldred passed through Aleppo and recorded this:
[W]e passed forward with camels three dayes more untill we came to Aleppo, where we arrived the 21 of May. This is the greatest place of traffique for a dry towne that is in all those parts: for hither resort Jews, Tartarians, Persians, Armenians, Egyptians, Indians, and many sorts of Christians, and enjoy freedome of their  consciences, and bring thither many kinds of rich merchandises. In the middest of this towne also standeth a goodly castle raised on high, with a garrison of foure or five hundred Janisaries [Sultan’s guard]. Within foure miles round about are goodly gardens and vineyards and trees, which beare goodly fruit neere unto the river side, which is but small; the walls are about three English miles in compasse, but the suburbs are almost as much more. The towne is greatly peopled. [4]
Aleppo has been in continuous occupation since prehistoric times; at least as far back as 5000 BCE, according to archaeologists. Stones were laid there before there was paper or written language or glass for that matter. There is a legend that the Arabic name for Aleppo, 'Halab' once meant "gave out milk" and was a reference to when Abraham gave milk from his white cows to travelers as they passed through the area. 

1563, when Franco Neri was still a young man of twenty-six, living in Aleppo, both he and his father were referenced in a couple of documents.  They are still held in the grand ducal archives in Florence, written in the reign of Cosimo I de' Medici. [5] This indicates, at the very least that the Neri family was in service to the leaders of Florence three full decades before Antonio Neri would make glass for Prince Don Antonio de' Medici.

In the sixteenth century the Christians in Aleppo lived in a tightly knit neighborhood that developed as a result of an Ottoman invasion around 1400. There were four churches standing side by side in the Jdeydeh quarter, only the old Maronite Church of Saint Elias was associated with the  Roman Catholic Church. If Franco Neri was in town when the above John Eldred passed through with his two companions, it is not impossible that they could have attended mass in the same church one Sunday in late May of 1583. 

Two decades later, the Emir (prince) of Aleppo, Fakhr-al-Din II forged an alliance with Tuscany, which apparently involved both economic and military provisions. He was attempting to break free of the Ottoman Empire and is considered by some to be the father of the Lebanese independence movement. He would go on to spend a number of years visiting Italy and Florence in particular, where he formed a friendship with then Grand Duke Cosimo II. 

Today, the beautiful, ancient city of Aleppo stands mostly deserted and partly demolished by war. Some news stories sight the determination and character of the current independence movement by quoting a poet, al-Mutanabbi, who lived in the mid tenth century. He spent the better part of a decade at the royal court of Aleppo, where it is said he did his best work. His most quoted lines are from a piece sometimes called "the poem that killed the poet." A legend tells that one night he was cornered by his enemies. Ready to flee, he was reminded of his own words by a servant, which caused him to stay and fight. The poem closes this way:


The desert knows me well, the night and the mounted men. 
The battle and the sword, the paper and the pen. [6]


[1] Neri, L’Arte Vetraria. (Firenze: Giunti, 1614).

[2] Registri Battesimali Firenze, reg. 10, f. 71v.  3 Feb., 1537, born to Jacopo Neri, barber [and surgeon] from dicomano, in the parish of San Ambrogio, Florence. (A couple of blocks from the Borgo Pinti childhood home of Antonio Neri.)

[3] Gian Pietro Vieusseux, Archivio storico italiano,  vol. 141, Issues 517-518 (Firenze, Leo S. Olschki, 1983), p. 370. “His correspondence also makes several references to the activity carried out by the Venetian court who had often had occasion to attend to solicit the interests of friends or acquaintances as Francesco Neri of Aleppo, the Capponi and Rinuccini [families].” 

[4] Richard Hakluyt, A selection of curious, rare and early voyages ..., (London: R. H. Evans, 1810)v. 2,  p. 403. “The voyage of M. John Eldred to Tripolis in Syria by sea, and from thence by land and river to Babylon and Balsara. 1583”

[5] Carteggio universale di Cosimo I de Medici /XI Archivio di Stato di Firenze Inventario XI (1560 – 1564) Mediceo del Principato Filze 489-499°, pp. 162, 206; /XII (1562-1565) Filze 500-514 p. 60.

[6] al-Mutanabbi (915-965 AD). He is thought to have spent nine years in Aleppo where he composed some of his best work, http://en.wikipedia.org/wiki/Al-Mutanabbi  See also http://aminotes.tumblr.com/post/33116016101/aleppo-a-city-in-flames 

Translated into German by Friedrich Dieterici, ed, tr. Mutanabbii carmina cum Commentario Wfthidii, (Berlin, 1858-1861), pp. 481-4. vv. 1-22, then into English by Nicholson, who wrote of Mutanabbi, “Although the verbal legerdemain which is so conspicuous in his poetry cannot be reproduced in another language, the lines translated below may be taken as a favorable and sufficiently characteristic specimen of his style.” Reynold A. Nicholson, A Literary History of the Arabs (Unwin, 1907).p. 307. Subsequently Nicholson published the present version in Reynold A. Nicholson, Translations of Eastern Poetry and Prose (Cambridge: Cambridge U. Press, 1922), p. 80. 

Monday, December 11, 2017

Alchemical Glassware

Antonio Neri (1598-1600),
"Libro intitulato Il tesoro del mondo" f. 38
In the introduction of L'Arte Vetraria, his 1612 book on glassmaking, Antonio Neri discusses the technical and scientific uses of glass. He rattles off an impressive list of items, many of which are still in everyday use in chemistry and medicine:
Beyond the ease and low cost with which it is made, and the fact that it can be made anywhere, glass is more delicate, clean, and attractive  than any material currently known to the world. It is very useful to the arts of distillation and spagyrics, not to mention indispensable to the preparation of medicines for man that would be nearly impossible to make without glass. Furthermore, many kinds of vessels and instruments are produced with it;   cucurbits,  alembics,  receivers,  pelicans,  lenses, retorts, antenitors,  condenser coils, vials, tiles, pouring-vessels (nasse),  ampules, philosophic eggs  and balls. Countless other types of glass vessels are invented every day to compose and produce elixirs, secret potions, quintessences, salts, sulfurs, vitriols, mercuries, tinctures, elemental separations, all metallic things, and many others that are discovered daily. Also, glass containers are made for aqua fortis and aqua regia, which are so essential for refiners (partitori) and masters of the prince’s mints to purify gold and silver and to bring them to perfection. So many benefits for the service of humanity come from glass, which seem nearly impossible to make without it.
The glass book, as it was published by Neri, did not contain any illustrations. If we hunt around in the alchemical literature and in museums, we can find examples of the apparatus and vessels on his list, but still, we might feel disappointed at not seeing the specific pieces with which our glassmaker was referencing. As it happens, we actually can see a number of these pieces, exactly as Neri experienced them. Over a decade before writing  the glass book, when he had just completed Catholic seminary and become an ordained priest, Antonio Neri wrote a manuscript devoted to "all of alchemy" in which he shows us many of the same glass vessels. Here he lists and shows us (in the illustration, from left to right, top to bottom) a double vase, a urinal (yes, that kind of urinal), a pair of Florence flasks (the Italians now call this a pallone di Kjeldahl), a philosophic egg, another flask which Neri calls a "bozza longa," an alembic (or still-head), a retort, a bottle,  mouth-to-mouth urinals, a receiver (for a still or retort), a saucer, and assorted cups and ampules. Since many of these terms changed from place to place and over time, we can use this chart to get a much better idea of exactly what Neri was doing in his recipes. The use of urinals in his chemistry kit shows simple practicality; these were standard items made by glass factories. If a low-cost, readily available item could be used in the laboratory, so much the better.

Many of the items Neri lists were used in distillation, which was a basic technique of alchemists. A still could be set up in any number of variations, depending on the intended product, which could range from alcoholic spirits to powerful acids and other reagents. The "athanor" was a stove specially engineered to gently heat a large flask, called the "cucurbit," which contained whatever was to be distilled. The apparatus would include an "alembic"; a cap that fits on top of the cucurbit with a snout-like tube running downward from its top. The idea was that volatile ingredients would evaporate inside the cucurbit, rise up, condense in the alembic and run down its snout, to be collected in a "receiver" vessel. Sometimes, for convenience, all three pieces (cucurbit, alembic and receiver) are together referred to as the alembic. The process could be sped up significantly by adding a condenser coil, what Neri calls a "serpentine." As steam built up in the cucurbit, it was routed through its snout to a coiled tube that might be submerged in cold water. This way, the steam would condense more rapidly, sending more liquid to the receiver. Neri uses this method to produce acids in order to dissolve metal pigments for his glass, but the same basic technique is still applied today in producing industrial chemicals, medicines, perfumes and alcoholic drinks such as moonshine, brandy, vodka, rum and whisky. However, in the distillation of alcohol, metal (usually copper) containers are preferred. Neri was often producing chemicals that would react with metal, glass provided a very good solution to this problem but as he discusses at length, great pains must be taken to ensure that the glass vessels do not crack or break when heated or cooled too suddenly.

* This post first appeared here on 27 December 2015.

Friday, December 8, 2017

Torricelli and Glass

Evangelista Torricelli
by Lorenzo Lippi, circa 1647
Evangelista Torricelli (1608–1647) is remembered as the inventor of the mercury barometer. Lesser known are a number of significant contributions he made to mathematics, astronomy and physics. There is no direct connection to the Florentine alchemist and glassmaker Antonio Neri—Torricelli was only a boy of six when Neri died—yet there are unmistakable echoes left by Neri that are amplified when we examine Torricelli’s time in Florence.   

In 1632, Torricelli wrote a letter to Galileo, which began a friendship that lasted until the famous astronomer died a decade later. In fact, Galileo invited Torricelli to stay at his house where they spent the last three months of Galileo’s life working together. If Torricelli had not heard of Neri before, perhaps he became acquainted through the copy of L’Arte Vetraria that Galileo had on his bookshelf. Afterward, while preparing to return to Rome, Torricelli was intercepted by the Grand Duke of Tuscany, Ferdinando II de' Medici, who asked him to succeed Galileo as the chair of mathematics at Pisa. He was given a good salary and quarters at the fabulous palace in the center of Florence, that is now called the Medici-Riccardi.  

Historian Mario Gliozzi writes: “Torricelli remained in Florence until his death; these years, the happiest of his life, were filled with the greatest scientific activity. Esteemed for his polished, brilliant, and witty conversation, he soon formed friendships with the outstanding representatives of Florentine culture.” [1]  The ancient palace itself was largely empty in this period, inhabited by a handful of relatives, officials, intellectuals and artists connected with the Grand Ducal court. [2]

Among Torricelli’s companions at the palace were the three sons of Don Antonio de’ Medici, Antonio Neri’s long time benefactor. The boys, Paolo (1616-1656), Giulio (1617-1670) and Antonfrancesco (1618-1659) moved there in 1646. None of the brothers had personally met Neri, as they were all born shortly after his death, but they must have heard plenty about him growing up. As children, they had the run of the Casino di San Marco, the palace where Neri had made glass and pursued the secrets of alchemy. After Neri’s death, their father, Don Antonio spent significant time trying to hunt down Neri’s secret recipe for transmutation. Years later, when Giulio died in 1670, among his possessions were found a box of elixirs and “a booklet, entitled: Material of all the compounds of Priest Antonio Neri; there is a red dustcover, which says ‘experiments.’” [3] The materials were handed over to Jacinto Talducci, the Grand Duke’s chief chemist, and master of the new glassworks established in the Boboli Gardens, a man whom Torricelli depended on for glass. Talducci was also a veteran of the Casino di San Marco Laboratory; according to legend, as a boy he personally witnessed Neri’s transmutation of gold. Curiously, at Giulio’s death he was listed as living on Borgo Pinti in Florence, the same street on which Antonio Neri grew up.

While in Florence, Torricelli took a great interest in optics. Again quoting Gliozzi:
[T]here is very good evidence of his technical ability in working telescope lenses, a skill almost certainly acquired during his stay in Florence. By the autumn of 1642 he was already capable of making lenses that were in no way mediocre, although they did not attain the excellence of those made by Francesco Fontana, at that time the most renowned Italian telescope maker. Torricelli had set out to emulate and surpass Fontana. By 1643 he was already able to obtain lenses equal to Fontana’s or perhaps even better, but above all he had come to understand that what is really important for the efficiency of a lens is the perfectly spherical machining of the surface, which he carried out with refined techniques. The efficiency of Torricelli’s lenses was recognized by the grand duke, who in 1644 presented Torricelli with a gold necklace bearing a medal with the motto “Virtutis praemia.” 
The fame of Torricelli’s excellent lenses quickly became widespread and he received many requests, which he fulfilled at a good profit. He attributed the efficiency of telescopes fitted with his lenses to a machining process that was kept secret at the time but was described in certain papers passed at Torricelli’s death to the grand duke, who gave them to Viviani, after which they were lost.
Gliozzi continues to describe that in 1924 one of Torricelli’s lenses was examined optically using the diffraction grating. “It was found to be of exquisite workmanship, so much so that one face was seen to have been machined better than the mirror taken as reference surface, and was constructed with the most advanced technique of the period.”

In addition to precision glass for lenses, Torricelli depended on Talducci and the grand duke’s furnace for scientific glassware; his experiments that demonstrated the measurement of air pressure required glass tubes, sealed at one end, two ‘cubits’ long (about four feet). They needed to be strong enough to be filled with mercury (which is very heavy) without breaking. It took his colleague Mersenne a couple of years (until 1646) to match the Florentines and obtain an acceptable tube from the French glassworks. 

Torricelli worked with former employees of the Casino di San Marco laboratory who knew Neri, he lived with Don Antonio’s three sons and he took a keen interest in glass; it seems impossible for him to be unaware of Neri and the echoes of his work in Florence.

[1] Mario Gliozzi "Torricelli, Evangelista" in Complete Dictionary of Scientific Biography. 2008. Encyclopedia.com.  http://www.encyclopedia.com/doc/1G2-2830904345.html

[2] 1609-1659 - The last inhabitants of Palazzo Medici http://www.palazzo-medici.it/mediateca/en/Scheda_1609-1659_-_Ultimi_abitanti_di_Palazzo_Medici_

[3] Covoni 1892, p. 193.




Wednesday, December 6, 2017

Michel Montaigne

Michel Montaigne
Anonymous (17th century).
Michel Montaigne (1533–1592) was the proprietor of a vineyard and later a mayor of Bordeaux, France. However, his claim to fame in history is as popularizer of the writing form known as the essay. In 1580, a few months after publishing his first collection, he embarked on a grand tour of Italy by way of Austria, ending in Rome. He did this despite suffering from painful kidney stones or perhaps partly because of it; in addition to the usual tourist stops, he also sought out spas and purveyors of medicinal cures to help with his condition. Montaigne kept a travel diary, which he dictated to a servant accompanying him on the journey. 

Among his stops was a visit to Florence, where he dined with Grand Duke Francisco I de’ Medici and Bianca Cappello at the palace laboratory known as the Casino di San Marco. At the time, their son Don Antonio was a four year old toddler as was, 
in another quarter of the city, future glassmaker Antonio Neri. Within a few years both Francesco and Bianca would be dead, both stricken with pernicious malaria. Don Antonio would be sidelined as the future grand duke by his uncle, Cardinal Ferdinando de’ Medici. Don Antonio would inherit the laboratory complex and devote his time to the secrets of nature, where Antonio Neri would be employed as an alchemist and glassmaker.

What makes Montaigne’s journal remarkable is his clear, direct observation; his account is an unapologetic window into the thoughts and observations of a sixteenth century traveler. Here some excerpts from his account: 



Florence, seventeen miles, a place smaller than Ferrara, situated in a valley, surrounded by richly cultivated hills. The river Arno passes through the town, and is crossed by several bridges. We saw no fosse round the walls. Today he (Montaigne) passed two stones, and a quantity of gravel, without having had any other notice of it than a slight pain in the lower part of his stomach. The same day we went to see the Grand Duke's stables, which are very large, with arched roofs; there are very few horses of any value here: at least, there were not, when we went over them. We were shown a sheep of a very strange form; together with a camel, several lions and bears, and an animal as big as a large mastiff, but of the form of a cat, all striped black and white, which they called a tiger.  
We looked over the church of St. Lawrence, where the flags are still hanging, which we lost under Marshal Strozzi, in Tuscany. In this church, there are several excellent pictures, and some statues by Michael Angelo. We went to see the cathedral, a magnificent structure, the steeple of which is faced with black and white marble; it is one of the finest and most sumptuous churches in the world. […] 
The same day we went to see the duke's palace. This prince spends a good deal of his time in making imitations of oriental precious stones and chrystal: he has a great taste for alchemy and the mechanical arts, especially architecture, of which he has a more than ordinary knowledge. Next day, M. de Montaigne ascended, the first of us, to the top of the cathedral, where there is a ball of gilt brass, which, from below, seems about the size of your head, though when you get up to it you find it capable of holding forty persons. […]  
Messrs. d'Estissac and Montaigne went to dine with the grand duke, for such is his title here. His wife occupied the post of honour; the duke sat on her right, next to him sat the duchess's sister-in-law, and next to her husband, the duchess's brother. The duchess is a handsome woman, according to the Italian notion of beauty, with a countenance at once agreeable and dignified, and a bosom of the most ample proportions. M. de Montaigne had not been with her long, before he thoroughly understood how she had managed to wheedle the duke into entire subjection to her will, and he had no doubt she would be able to retain him at her feet for a long time to come. The duke is a dark stout man, about my height, with large limbs, and a countenance full of kindliness: he always takes his cap off when he meets any one, which, to my mind, is a very agreeable feature in his character. He looks like a healthy man of forty. On the other side of the table were the cardinal, and a young man of about eighteen, the duke's two brothers. When the duke or his wife want to drink, they have presented to them a glass of wine and a decanter of water, in a sort of bason; they take the wine, and pour as much of it as they do not want into the bason, filling the glass up with water; and when they have drunk it, they replace the glass in the bason, which a page holds for them. The duke took a good deal of water; the duchess hardly any. The fault of the Germans is to make use of glasses out of all proportion too large; here they are in the extreme the other way, for the glasses are absurdly small. I do not understand why this city should be called, par excellence, the Beautiful: it is handsome, no doubt, but not more so than Bologna, and very little more so than Ferrara; while Venice, beyond all comparison, superior to it, in this respect. No doubt the view of the city and its suburbs, from the top of the cathedral, has an imposing effect, owing to the immense space which the suburbs occupy, covering, as they do, the sides and summit of all the neighbouring hills for two or three leagues round; and the houses being so close to each other that they look almost like streets. The city is paved with Hat stones, but in no sort of method or order. […] 
[T]he style of living at the boarding-houses is miserable, though they charge for gentlemen more than twelve crowns a month. There is nothing to amuse you here, or to exercise either body or mind; there is neither fencing, nor riding, nor literature. Pewter is very scarce all about here; you are seldom served in any tiling but coloured earthenware, and that generally dirty. Thursday morning, 24th November, we left this place, and proceeded through a country which did not appear to us very fertile, though it was cultivated on all sides, and thickly inhabited. The road was rough and stony, and, though we went on without stopping, it was not till very late that we got to Sienna, thirty-two miles, four posts.
 Montaigne 1842: Michel de Montaigne, The Complete Works of Michael de Montaigne: Comprising the Essays ... ed., William Hazlitt (London: Templeman, 1842). pp. 564-566.





Monday, December 4, 2017

A Philosophical Explosion

Glass drops demonstration in slow motion
Previously, we started a tour through Europe that followed the introduction of an item called a "glass drop,"  "Prince Rupert's drop" or "Dutch tear." [1] Today we will explore the attempt of an enlightenment philosopher to explain the phenomenon. First, take a look at the dramatic video (above) of an actual glass drop exploding in slow motion.

In the late seventeenth century, the demonstration of glass drops was sweeping through the parlors of Europe. Consisting of nothing more than palm sized piece of glass with a bulbous nose and a tail that tapered to a point, this little item became a topic of fascination for intellectuals and experimenters alike. [2] Formed by simply letting a gob of glass drip into a bucket of cold water, the fat end could endure strong blows with a hammer, yet snap off the slender tail and the whole piece would erupt into a hail of glass dust and fragments.
Thomas Hobbes
by John Mitchel Wright,
(National Portrait Gallery)

Robert Hooke conducted a series of experiments, and observed the results carefully under a microscope. He arrived at conclusions that were largely correct even though the very nature of matter was still under debate. The molten glass on the surface of the drop cooled rapidly, shrunk, and compressed the interior. The result was a highly stressed surface that resisted the hammer. Snapping the tail caused a shock wave of cracks to propagate through the drop, releasing the tension, shattering the entire object into fragments no larger than a grain of sand.
Fig. of glass drop,
Thomas Hobbes, Problematica Physica, 1662 

Enlightenment philosopher Thomas Hobbes was less successful in his attempt to explain the phenomenon, yet not entirely off the mark. [3] Hobbes asks us to consider all matter as possessing "circular internal motion" even when the object as a whole is at rest. He reasoned the heat generated in a glass furnace increased this internal motion both in its "compass" or extent and in speed. When the drop was quenched, the glass that hit the water first has its internal motion changed:
Because the main drop A comes first to the water, it is therefore first quenched, and consequently the motion of the parts of that drop, which by the fire were made to be moved in a larger compass, is by the water made to shrink into lesser circles towards the other end B, but with the same or not much less swiftness.
He further reasons that this action causes the glass to form a structure like threads that run the length of the drop:
Seeing also this motion in every small part of the glass, is not only circular, but proceeds also all along the glass from A to B, the whole motion compounded will be such as the motion of spinning any soft matter into thread, and will dispose the whole body of the glass in threads, which in other hard bodies are called the grain.
Finally, he concludes that all these "threads" are bundled together tightly at the tail end of the drop. When the tail is snapped, 
By the breaking of the glass at C, [the threads] be all at once set at liberty; and then all at once being suddenly unbent, like so many brittle and overbent bows, their strings breaking, be shivered in pieces.
A somewhat tortured connection could be made between Hobbes' theory of internal motion and molecular kinetics, but it is a stretch. The truth of the matter is that his explanation of the glass drop demonstration is elegant and unfortunately, it is also wrong. How did Robert Hooke arrive at a correct conclusion while Hobbes and many others failed? It is a good question because it gets to heart of how successful science is done. Part of the answer lay in Hooke's careful experimentation and detailed observations; he tests his theories wherever he can, and extends his senses with instruments like the microscope. Hobbes develops a series of analogies, but he never devises experiments to test them. To be fair, both men end with conclusions that go beyond what could be observed or measured at the time, and in that realm either one of them could have stumbled. In the end, a correct theory can only be one that does not contradict what actually happens in nature.

In science, obsessive testing and measuring is certainly necessary to arrive at correct conclusions, however it is not sufficient. In other words, there is no guaranteed path to ensure a correct explanation. For this reason alone it is essential to understand that the universe does not follow the laws of physics, it is the other way around; the universe does what it does whether we have a rule for it or not. The 'laws' are our best guess at how nature operates; calling them by that name is a bit pretentious. However, when these laws have been tested repeatedly by our brightest minds, when we observe they are consistent with nature whether peering at the infinitesimal through a microscope or across the galaxy through a telescope, that is what makes science worthy of celebration. [4]


[1] Paul Engle, Conciatore Blog, 2 January 2017; http://www.conciatore.org/2017/01/hookes-tears.html
[2] Niccolò Angelo Tinassi , ed., Il Giornale de Letterati: per tutto l'anno 1672 (Rome : Nicolò Angelo Tinassi, 1672), p. 95.
[3] Thomas Hobbes, Problematica Physica, 1662 (translated in English in 1682 as Seven Philosophical Problems) pp. 36-39, 146-148.
[4] For an interesting rhyme about glass drops recited by Benjamin Franklin see Engle, "Benjamin Franklin and his Gathering of Glassmakers" in Bulletin of the National American Glass Club, Spring/Summer 2016.
Video Credit: Glass drops demonstration in slow motion. courtesy of the American Ceramics Society http://ceramics.org/ceramic-tech-today/video-glass-science-of-prince-ruperts-drop-captured-with-high-speed-cameras
* This is an updated version of a post that first appeared on Conciatore Blog, on 7 January 2015.