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, January 29, 2016

Iron Into Copper

The recovery of copper from vitriolated waters,
from De Re Metallica, 1556, by Agricola (Georg Bauer).
In Discorso, one of the last manuscripts written by Antonio Neri before his death, he reveals several transmutation recipes. One describes turning iron into copper; it is instructive because it uses common materials that we can identify and because the chemistry is now well understood.

Take some iron sheets and lay them in vitriol water, being immersed in that, they will rust. Scrape off this rust, which will be a red powder, melt it in a crucible, and you will have perfect copper. The same effect can be had from various waters that are naturally vitriolated, because they flow through mines of vitriol, such as those of a source some distance from Leiden, and another below the fortress of Smolnik, [now in Slovakia].

Vitriol is an acidic sulfate dissolved in water, it could be made in the laboratory, but it also occurred naturally around mining operations where sulfurous minerals were present. Alchemists knew this solution as "oil of vitriol" and "spirit of vitriol." The mine that Neri references in Smolnik became famous for transmutation. As late as the eighteenth century, scientists and experimenters from around Europe made the pilgrimage to see the effect for themselves and tried to figure out what was happening. It may be a surprise to some readers, but following the above instructions will, in fact, produce copper just as Neri claimed. There is no deception or sleight of hand involved; the explanation is straightforward, but first, Neri treats us to a rare glimpse of his own reasoning on the subject:

Some estimate and not without reason, that this experiment, being used to prove the transmutation of metals, is not suitable for this purpose. They say that the vitriolated waters become such because they are already heavy with the corrosive spirits of sulfur, having passed through the copper or iron mine, these waters corrode copper in the same way aqua fortis corrodes silver. So that really the substance of the copper remains in the water, which attacks the surface of the iron, which always remains iron. However, if that were true then the iron would not get consumed, or if it were consumed it would mix with the substance of the corroded copper in the water, and if it were fused, it would remain a mixture of iron and copper. And yet in this experiment, all the iron is consumed; it is reduced by the vitriolated water into powder, […] which in the fusion is still pure copper, so there should remain no doubt that this is a true transmutation.[1]

Given the state of chemistry at the time, Neri's reasoning is clear and rational. The iron disappears and a copper coating materializes in its place. What better evidence of transmutation could one ask for?

The key to what was actually happening is in the criticism leveled by skeptics. It turns out that they were on the right track, but neither they nor Neri had the full picture. Today, we understand it as a simple ion exchange reaction; blue vitriol water is a transparent saturated solution of copper sulfate (CuSO4), in the presence of solid iron, the liquid dissolves the iron; copper from the vitriol is deposited in its place. The two metals, copper and iron, change places: the iron dissolves, forming green vitriol (FeSO4) and copper is expelled from the solution. The result is a reduction in the amount of the iron, which is replaced by a proportional deposit of pure copper.

On a physical level, this chemical reaction is no different today than it was in the seventeenth century. What has changed is our interpretation of the experiment. What Neri viewed as a transformation of iron into copper, we now see as an exchange. There is, however, a deeper lesson in all this. As an alchemist, Antonio Neri was not being delusional or dishonest; he was careful, observant and applied his knowledge as best he could. This is no different from the way science works today. Both then and now, to be successful in unraveling nature’s secrets, one must become accustomed to a very uncomfortable situation: In the past, careful reasoning by brilliant thinkers has led to utterly wrong conclusions. The fact that much of our world is a mystery is unsettling; that the very process we use to understand it can be so flawed is harder to accept. Even more difficult is that the faculty we all rely on for survival—our own wits—can lead us so far astray.[2]

[1] For more, see Discorso sopra la Chimica: The Paracelsian Philosophy of Antonio Neri”, M.G. Grazzini / Nuncius 27 (2012).
[2] This post first appeared here on 31 January 2014.

Wednesday, January 27, 2016

The Golden Sun

The Sun, Robert Fludd
from Utriusque Cosmi (1617),v. 2, p. 19.
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.

Monday, January 25, 2016

What Goes Around Comes Around

The German city of Ulm in the 16th century
Georg Braun, Franz Hogenberg 1570-78
(Click either image to enlarge.)
In the spring and summer of 1525, peasants and farmers throughout German speaking Europe staged a popular revolt now called the Deutscher Bauernkrieg. [1] At the heart of the matter was an oppressive system of taxation run by the Roman Catholic Church, in which little or none of the revenue was used to improve life locally. Often, action was lead by Protestant clergy, but to little effect against the mercenary armies hired by the aristocracy. In the end, up to 100,000 of the poorly armed and organized peasants were slaughtered.

Along the banks of the Danube River in southern Germany lies the ancient city of Ulm. Besides being the birthplace of Albert Einstein, Ulm was, in the sixteenth century, near the center of the Peasant’s Revolt, which brings us to a curious story which traces the migration of a technical recipe from Ulm over the alps to Venice, then to Sienna and finally Florence. The recipe is for the metal alloy to make mirrors, and it is told from one friend to another while chatting amiably in Venice.
Among other things, he said that he had made one [concave mirror] almost half a braccio across [about 13 inches], which extended the clear rays of its brightness more than a quarter of a German league when he caught the sun with it. One day, when for amusement he was standing in a window to watch a review of armed men in the city of Ulm, he bore with the sphere of his mirror for a quarter of an hour on the back of the shoulder armor of one of those soldiers. This not only caused so much heat that it became almost unbearable to the soldier, but it inflamed so that it kindled his jacket  underneath and burned it for him, cooking his flesh to his very great torment. Since he did not understand who caused this, he said that God had miraculously sent that fire on him for his great sins. [2]
The story was told to Vannoccio Biringuccio, who recalls it in 1540 in his Pirotechnia, the first printed book devoted to metallurgy. Specifically, the recipe is a variant of what today we would call white bronze, which as Biringuccio states is similar to the metal used to cast bells. He recites ancient formulations that used three parts copper and one part tin. To this was added 1/18th part of antimony and optionally 1/24th part of fine silver to give it a neutral color. Indeed, other ancient formulations for what was known as speculum metal specify a 3:1 ratio of copper to tin. He continues,
But nowadays most of the masters who make them take three parts of tin and one of copper, and melt these together. When they are melted, for every pound of this material, they throw in one ounce of tartar and half an ounce of powdered arsenic, and let them fume and melt and incorporate well. 
Biringuccio’s version reverses the copper and tin ratio from the classical composition. Compare it with Antonio Neri’s prescription which appears half a century later, it is almost identical:
Have 3 lbs of well-purified tin, and 1 lb of copper also purified. Melt these two metals, first the copper, then the tin. When they fuse thoroughly, throw onto them 6 oz of just singed red wine tartar, and 1½ oz of saltpeter, then ¼ oz of alum, and 2 oz of arsenic. Leave these all to vaporize, and then cast [the metal] into the form of a sphere. You will have good material, which when you burnish and polish, will look most fine. This mixture is called acciaio and is used to make spherical mirrors.
To be clear, the tartar, saltpeter and alum act as a surface flux - they form a layer that floats on the liquid metal, preventing oxides from forming, which can foul the melt.  their addition does not change the base alloy composition.

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

Neri was definitely familiar with Biringuccio’s book Pirotechnia. In fact, the introduction to Neri’s own book L’Arte Vetraria is patterned after the metallurgist’s survey of glassmaking.  In his chapter 14, book 2 Biringuccio wrote:
… it [glass] is one of the effects and real fruits of the art of fire, because every product found in the interior of the earth is either stone, metal, or one of the semi-minerals.  Glass is seen to resemble all of them, although in all respects it depends on art. [3]
And here is the opening to Neri’s introduction a half century later in 1612,
Without a doubt, glass is a true fruit of the art of fire, as it can so closely resemble all kinds of rocks and minerals, yet it is a compound, and made by art. [4]
Both passages go on to cover much of the same ground, albeit with a change in focus reflective of new thinking about chemistry and nature. In one sense, Neri is paying homage to his distinguished predecessor, and there can be little doubt that he read Biringuccio’s book and its technical recipes closely. 

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

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

Friday, January 22, 2016

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.

Wednesday, January 20, 2016

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.

Monday, January 18, 2016

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 six different languages; 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. 

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.

Friday, January 15, 2016

Neri's Aleppo Connection

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. 

Wednesday, January 13, 2016

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

Monday, January 11, 2016

Alchemical Glassware of 1600

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, January 8, 2016

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, January 6, 2016

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.

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, January 4, 2016

Thomas Hobbes on Glass

Thomas Hobbes
by John Michael Wright , (National Portrait Gallery).
Last week we started a tour through Europe that followed the introduction of an item called a "glass drop,"  "Prince Rupert's drop" or "Dutch tear." Today we will explore the attempt of an enlightenment philosopher to explain the phenomenon. First, here is a brief refresher.

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. 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.

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. [1] 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.


[1] Thomas Hobbes, Problematica Physica, 1662 (translated in English in 1682 as Seven Philosophical Problems) pp. 36-39, 146-148.
* This post first appeared here on 7 January 2015.

Friday, January 1, 2016

Hooke's Tears

Glass drops or tears coated in glue,
after detonation, (cross section is left)
from Robert Hooke's
Micrographia 1664, between p. 10, 11.
In 1661, an Italian reprint of Antonio Neri’s book of glassmaking recipes appeared. One year later, an English translation was published in London by physician Christopher Merrett. As an appendix, Merrett included an account of “glass drops” or tears as demonstrated to the Royal Society. These were molten gathers of glass that were allowed to drip into a bucket of cold water and cool. They formed a round, bulbous front end and a tail that trailed off to a thin filament. What made them so fascinating was that the bulbous end can easily endure strong blows with a hammer, but when the thin filament tail is snapped off, the whole piece explodes into a hail of tiny fragments “and in the dark, sparks [flash] at every break of their surface.” [1]

These glass drops became a novelty at royal courts throughout Europe, given a glass furnace they were easy to make, easy to demonstrate, and never failed to amaze observers who had not seen them before. They sparked animated discussion in the many scientific societies that had sprung up; what forces of nature were involved that a piece of glass could resist a hammer yet explode into dust at the loss of its slender tail? 

In the late seventeenth century a Roman publisher by the name of Tinassi [2] regularly issued compilation of noteworthy letters. In his journal’s edition for the year 1672, he published two letters by Geminiano Montanari, a mathematics professor at the university in Bologna, both on the subject of glass drops. In the introduction, he suggests that these curiosities were
Believed to be introduced in Sweden, Holland, then in England, France and Italy; In Paris in the year 1656, many experiments were made at the Academia which met at the home of Mr. Montmor. [3] Many have written of this, among others Monconys [4] in his "Journey to England,” [5] Thomas Hobbes in his Problematica Physica, [6][…] and Christopher Merrett, which in the Latin translation of L’Arte Vetraria of Antonio Neri, [7] is inserted the experiences of the Royal [Society] of England, [and] Mr. Robert Hooke [8] in his Micrographia. [9]
At a time when the concepts of atoms and molecules were still being debated, the glass drops became a nucleus around which a new science developed of mechanical tension and compression. A simple drip of glass caused sharp minds to puzzle and to take a closer look. 

In  Micrographia, Robert Hooke wrote about how he “ground away neer two thirds of the ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off of the very tip of its slender end.”

Hooke continues to describe coating drops in fish glue (isinglass) which was tough enough to hold the piece together when the tail was snapped. “The drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacious and all over flaw’d, all those flaws lying in the manner of rings, from bottom or blunt end, to the very top or small point.” (See illustration above.)

He discovers that heating the glass drop and then allowing it to cool slowly neutralizes the explosive effect. Finally, he puts it all together: rapid cooling of the surface causes the interior to be compressed like a spring. Snipping the tail, where the skin is thinnest releases all the pent-up energy at once and the piece explodes.


[1] Tinassi 1672, p. 95.
[2] Niccolò Angelo Tinassi, active 1654-1690.
[3] Henri-Louis Habert de Montmor (c. 1600–1679), founded the Montmor Academy, which met at his house in Paris from 1657 until its dissolution in 1664.
[4] Balthasar de Monconys (1611–1665). 
[5] Monconys 1677,  for glass drops see pp. 32, 42 (fig. 4). https://books.google.com/books?id=L0b687oZRVQC
[6] 1662. Problematica Physica (translated in English in 1682 as Seven Philosophical Problems)
[7] This reference is not to Merrett’s 1662 translation of Neri (1612), but to the 1668 or 1669 edition by Frisius in Amsterdam which includes Merret’s annotations.
[8] Robert Hooke (1635–1703). 
[9] Hooke 1664, pp. 33–44.
*This post first appeared here 2 January 2015