Monday, September 29, 2014

Lixiviation Reprise

Salsola Kali plant,
used in Mediterranean glassmaking.
A long time ago, perhaps as long ago as the Stone Age, our ancestors discovered that mixing water with the ashes from the previous night's fire makes a good washing-up liquid. Not the solids, but what dissolves in the water forms a mildly caustic lye solution. It cleans dirty hands, and oily hair. The more concentrated the lye, the more pronounced the cleansing effect. When the solids are strained out and the liquid is evaporated, left behind is a crystalline salt known as potash. This process of extracting the soluble components of charred plant material is known as lixiviation. Mix potash with tallow and you have soap, spread it on your fields and you have a good fertilizer, put it in a very hot furnace with powdered sand, and you have glass. In simple, everyday human activity we see the roots of modern chemistry. The English word ‘potash’ is derived directly from the process described above: made in a pot with plant ash. It lends its name to the chemical element potassium, a major constituent and a key ingredient for many glass recipes.

Besides potassium, plant ash can also contain significant quantities of sodium, magnesium and calcium. They occur in different amounts depending on the species and on its habitat. Plants are literally composed of the nutrients in the soil from which they grow. Mineral compounds that dissolve in water are brought in through the roots and become part of the plant. In northern European forests, salt from the ash of oak and beech trees and fern plants was used for potassium glass as far back as the middle ages. In the more arid Mediterranean regions, scrub vegetation from the coastal marshes made both sodium and potassium glass, namely with the soda and kali plants. The soda plant lends its name to sodium and the kali plant lends its name to a group of chemical elements, which we now call the alkali group. Of these two plants, salsola soda is high in sodium and very low in potassium, salsola kali is more equal between the two. The high sodium carbonate content of the soda plant and a few other species is unusual, but soda accounts for most glass made, even today. Most other plants are potassium rich. 

To make glass, the material was lixiviated: boiled, filtered, purified and dried. The raw plant material was lightly charred to reduce moisture content; this prevented rotting and reduced volume and weight significantly for shipping. Neri experimented with the ash of many other plants as well and he does not hesitate to mix salt from different sources to achieve a desired effect. He found suitable glass salts can be made from ferns, blackberries, broad bean (fava) husks, cabbage, thorn bushes, millet, rush and marsh reeds. What Neri did not know was that virtually all of these plants produced a salt that was heavily laden with potassium. Potash glass has a fundamentally different character than soda glass. He knew quite well that fern glass had a different workability and appearance from soda glass, but he was over a century too early to understand why. Highly purified, potash glass sparkles in the light more than soda glass. It is denser, giving better refraction of light, yet it is also more difficult to work since it stiffens quickly on the blowpipe.

Friday, September 26, 2014

A Network of Alchemists

"The Alchemist" 1558, Pieter Brugle the Elder.
(Click to enlarge.)
Mention the word 'Alchemist' and the images that spring to mind are likely the same ones that have been around for centuries. Perhaps you will imagine something like Pieter Brugle’s 1558 depiction; a fool, whose head is filled with fantasies of conjuring gold. He spends all his earnings on exotic chemicals while his children go shoeless, the cupboard goes bare and his family starves. No? Then perhaps a more classical rendition; a white bearded mystic stirring a cauldron in a deserted castle, summoning unearthly forces, bending the will of nature.    

Outlandish characters like these may have existed, but as a fringe element at best.  For every secluded wizard or "get rich quick" schemer there were many more alchemists who lived otherwise unremarkable lives and went to work every day. They interacted with colleagues and used their knowledge to provide valuable services like making painter's pigments or medicines or refining metals. Seventeenth century glassmaker and Catholic priest Antonio Neri fell into the latter category. Another departure from the typical caricature of alchemy is that it was very much a plural endeavor; it was practiced not primarily in isolation but by well connected networks of people, at least in late sixteenth century Florence.

Neri's father was the chief physician to the grand duke of Tuscany, and as such probably had something to do with Antonio's education and with the position that he landed in Florence at the renowned laboratory of Medici prince Don Antonio. Even before his prestigious appointment, Neri wrote an illustrated manuscript in which he shows a number of young men and some women his own age working at the business of alchemy. A few of them are identified by name and must have been Antonio’s friends: Anibal, Martin, Hiroem and Pietro. [1] 

The women alchemists depicted in the manuscript are not specifically identified, but a strong possibility is that they were nuns from one of the nearby convents. These facilities often maintained their own pharmacies and ran cottage industries that produced and sold goods to raise funds. Alchemy practiced by women is an area of study which still needs much research, but it is not too much of a stretch to think the nuns used alchemical techniques to distill their own medicinal remedies and produced their own paint pigments. The famous painter Suor Plautilla Nelli resided in the Dominican convent across the street from the laboratory. Sculptor Suor Caterina Eletta was a nun at the same convent around Neri's time and was the daughter of Stefano Rosselli, the royal apothecary, another profession steeped in alchemy. Her uncle Fra Anselmo ran the Dominican's apothecary at San Marco, literally a few steps from the laboratory's front door. Suor Caterina was surrounded by relatives deeply involved in alchemy, how could she not be familiar with the subject?

At Don Antonio's laboratory, the Casino di San Marco, or the Royal Foundry as it also became known, Neri worked closely with Agnolo della Casa, another Florentine of the same age. In fact, all three men, Neri, Della Casa and Don Antonio were all born within a year of each other around 1576. Della Casa took notes on Antonio Neri's experiments in Florence over a period that spanned more than a decade. He filled literally thousands of pages. Much of this material is devoted to transmutation and the philosophers stone, both were subjects dear to Don Antonio de' Medici, their boss. The notebooks also indicate a lively correspondence with other chemical experimenters around Italy and wider Europe. Neri carried on a correspondence with his friend Emmanuel Ximenes who lived in Antwerp, a city that would become Antonio's home for seven years. 

The network of alchemy in Florence reached outwards to other experimenters and it also reached forward in time. Knowledge was passed from one generation to the next by schooling children in the art. From another branch of Della Casa's family came two brothers, Ottavio (1596) and Jacinto (Giacinto) Talducci della Casa (1601).  As youngsters they were said to have learned alchemy at the knee of Don Antonio. A century later, historian Giovanni Targioni-Tozzetti chronicled that these boys would go on to serve Grand Duke Ferdinando II de' Medici  and continue the work by directing the Real Fonderia when it was moved after Don Antonio's death, from the Casino to the Boboli Gardens. Ottavio would become director of the Royal Foundry. [2]  

Jacinto became a parish priest a few kilometers east of Florence, but he was pressed back into service as an alchemist after his brother died. He succeeded Ottavio as director of the Royal Foundry under Francesco Redi. Little is known about Jacinto's contributions to chemistry, but it must have been a remarkable life. He saw the germ of experimentalism really take hold; it would continue to grow and become the basis of our own modern science. Jacinto died in 1700 at the age of 99, he was the last surviving member of Don Antonio's band of alchemists and quite likely the last living soul to have personally met Antonio Neri.

[1] Neri 1598-1600, ff. 22r, 23r, 24r.
[2] Targioni-Tozzetti 1780, p. 127. Don Antonio de' Medici died in 1621.

Wednesday, September 24, 2014

A Third Eye Toward History

The Law of One.”  Lex Simone  (Houston Tx). 
I spend a great deal of my time learning about history because, well, I enjoy it. I suspect I am not alone in that and really, what better reason could there be? As a reader, I enjoy immersing myself in a world different from our own, yet one that did exist and is a part of what makes us who we are now. I also enjoy writing about history. As Samuel Johnson aptly observed, "The only end of writing is to enable the readers better to enjoy life, or better to endure it." [1] Here at Conciatore, when I write, I try to give you that with the most accurate story possible. I verify the material with primary sources, which is to say documents that were written at the time. I also consult secondary sources, for the opinions of others who have seen those same documents. When there are problems, I let my readers know. 

As a reader of history, most of what I consume is from secondary sources, books, the web and sometimes television. Occasionally, I will wonder about the credibility of a source; at times you may have felt the same way. There is a lot of good material out there, but sadly, there is also a lot of garbage. If you have only a passing interest in history, it can be hard to tell the difference. As a writer of history there is a strong temptation to spend a lot of time and energy correcting and debunking false impressions about what went on in the past. Since this blog is devoted to seventeenth century glassmaker Antonio Neri, the subject of alchemy looms large and to put it politely, alchemy is an area fraught with misimpressions.

True, a good takedown of bad history is a thing of beauty, but as a writer, that is not my path. Debunking another's carelessness or stupidity can be tedious, painstaking work and you have to like it. The same wrongheaded statement that took ten seconds and no thought to put down, takes any number of reference books, hours of thought and more hours of carefully constructing a response that is at once respectful, accurate and decisive. The result, more time than not, is that the critic comes off sounding angry and the offending writer remains in their blissful little bubble of ignorance. Members of the historical "choir" applaud and innocent bystanders tend to wonder about all the bluster. In the end, one dime-store historian is refuted and three more pop up.

Rather than make some clueless sot into an example, I would much rather invite you to develop the critical faculty to detect historical nonsense for yourself and come to know it when you see it. If you care enough about history to care about when it is correct, a tool that you will find very useful is what I call a "third eye." In eastern philosophy, the third eye is an embodiment of greater awareness. The specific connotation that I am invoking here is to realize that when you read history, you look through a lens that is colored very much by the present. There is no choice in the matter, we are here, now and that colors our perception. We have a natural tendency to relate past history to our own lives and society and that is fine as long as it is done knowingly. Our concerns were not necessarily their concerns; our view of  right and wrong, of the world, of time, of the universe is likely quite different from a hundred or a thousand years ago. Using one's third eye simply means staying mindful that we ourselves are also in a period of history that has its own strange proclivities.

The more you use your third eye, the stronger it will become. One of the more common types of nonsense is generated when history is used to justify an unstated agenda. There is a very good example that relates directly to Antonio Neri's time and place, early seventeenth century Italy. Two of Neri's contemporaries who went on to become far more famous are Galileo Galilei and Giordano Bruno. Galileo's confinement and Bruno's burning at the stake are regularly bandied about as examples of the persecution of scientists by the Catholic Church and of the eventual triumph of science over religion. Did your eye blink? Both of these myths are a result of projecting current feelings about science and religion into the past. The short version: Galileo was a practicing Catholic and Bruno was executed for issues that had nothing to do whatsoever with "science."

Another common agenda is that history is a manifest destiny; that by definition, it describes one long march of progress; that we in the present are smarter, more intelligent, generally superior to our predecessors precisely because we have the benefit of all previous discoveries, innovations, etc. Did your eye blink now? This agenda has led to a particularly warped view of alchemy. 

When your eye starts to wince, there is a very simple remedy: Google the subject at hand. Wikipedia may not be infallible, but thousands of dedicated volunteers run the site and it is an excellent place to see if there is controversy involved. You may find actual events vary significantly from what you learned in school or on television. Whatever your level of interest, think critically about what you read and think about why the writer or speaker put it in those particular words. I can almost guarantee that with an attentive third eye, history will be even more rewarding. As a bonus, you will be on the way to thinking like a first class historian. I work at it all the time and I love it. In the next post, we will take a closer look at what alchemy really was for Antonio Neri in the seventeenth century.

[1] Review of Soame Jenyns' "A Free Enquiry into the Nature and Origin of Evil, 1757"

Monday, September 22, 2014

Deadly Fumes Reprise

Antonio Neri handled very dangerous materials on a daily basis. He used strong acids, which if splattered could easily burn flesh, or cause blindness. He handled poisonous compounds containing arsenic, mercury and lead. If ingested, or inhaled as fumes these materials caused progressive, irreversible damage to internal organs and especially to the nervous system. There is no question that Neri did take chances with his health, but he was not naive. He knew very well many of the potential dangers and others he could well imagine. In chapter 74 of his book L'Arte Vetraria, he describes a way to tint rock crystal with beautiful colors. He wrote: 
Take orpiment of that really tawny orange-yellow color and pulverize 2 ounces of this along with 2 ounces of powdered crystalline arsenic, 1 ounce of pulverized crude antimony, and 1 ounce of sal ammoniac. […] Perform this entire operation under a large chimney to draw the fumes out of the room. These fumes are not only harmful but also quite deadly. Return to see if the coals have died down, because for the work to come out nicely, they must be burning well and full. For the remainder, leave and let the fire run its course with no one in the room with the work, for it is dangerous; the harsh materials will smoke quite a bit. Leave it to finish all fuming by itself and then extinguish the fire and spread the coals.[1]
In the spring of 1603, Neri was working in Pisa and became seriously ill. The specific cause and symptoms of his ailment are not known. He could have been harmed by one of his own experiments, or just as easily fallen prey to an infection or one of many other maladies prevalent in the early seventeenth century. He postponed his planned visit to Antwerp in order to recuperate. Finally, on 2 May 1603, his friend Emmanuel Ximenes wrote: "Praise God that your indisposition has ended ... if the Pisan air is suited to your recovery then do not change it." [2]

In the winter of 1603-4 Neri embarked on what would become a seven-year-long visit to his friend's palace in Antwerp. There, he would learn many new techniques, and ultimately have special glass vessels made and presented to Philip William, Prince of Orange. Upon his return to Tuscany in 1611, he sat down to write the book for which he is most remembered, L'Arte Vetraria. Two years after publication, in 1614, the priest would be dead. According to the only known account, printed over two centuries later by Francesco Inghirami.
Meanwhile, Neri became gravely ill, so he called the prince to come to him, having the promised the secret [of the philosophers stone]. But the Medici, who was in the countryside, took too much time; the patient died before the prince could be with him. Don Antonio was not quieted and he questioned all of Neri’s friends to see if he could find the information, but his efforts were in vain, as they should be in so groundless a science, although Giacinto Salducci [sic.] said that he had seen great things, specifically a powder that fixed mercury into gold. [3]

[1] Neri 1612, ch. 74.
[2] Ximenes 1601–11, also see Zecchin 1987–89, v. 1, pp. 165–169.
[3] Inghirami 1841–44,v. 13, pp. 457–458 probably based on Targioni-Tozzetti  189.

This post first appeared here in a slightly shorter form on 30 October 2013.

Friday, September 19, 2014

Neri's Cabinet #6: Saltpeter

Saltpeter beds, 1683 English ed.
Beschreibung allerfurnemisten mineralischen Ertzt
by Lazarus Ercker. (
Prague, 1574).
In my last post, dogs seemed to be popping up everywhere, even though they were essentially unrelated to the subject at hand; never one to be satisfied with enough of a good thing, I think I will keep the ball rolling.

In the era of glassmaker and alchemist Antonio Neri (the early seventeenth century), it was commonly assumed there was a direct causal connection between the "macrocosm" (stars, planets etc.) and the "microcosm" (the very small), with human life on earth standing in the balance, in-between the two. This philosophy forms the basis for astrology, which in Neri's time was utilized for all sorts of decisions and the planning of events. Even so, there was much debate about what the exact connections were and how they worked. This cosmic theory of the very large being directly connected to the very small is an ancient idea that precedes even the discovery of saltpeter, today's topic of discussion. Saltpeter was the critical ingredient of gunpowder, fireworks, fertilizers, medicines and as we will see, even the preparation of materials for glassmaking. It undoubtedly held an important place in Antonio Neri's alchemical cabinet. 

From our vantage point on Earth, Sirius is the brightest star in the heavens. As such, it has a rich history in almost every ancient culture. The Egyptians used it to base their calendar; when the star made its last appearance for the year, rising just ahead of the sun, it foreshadowed the coming season of Nile flooding (and abundant crops). To the ancient Greeks, this event signaled a hot, dry summer ahead. In the constellation Canis Major, the main star is Sirius, which  is also commonly known as the "dog star," hence the expression, "dog days of summer." [1]

This week in September, Sirius makes its reappearance in the evening sky. Just after dusk, you can find it following the sun toward the horizon to the west. Since it is the brightest star in the night sky, it tends to be visible before other stars. In Renaissance Italy, this evening event heralded the end of summer’s heat and the start of cool autumn rains. Which, among other things, meant it was time to harvest the saltpeter, before it washed away. 

Chemically, saltpeter is potassium nitrate, [2] although several similar compounds have traditionally been referred to by the same name. The term derives not from the name Peter, but from the Latin word for rock "petra"; it often forms on the walls of caves as mineral deposits, hence "salt from rocks." 

In China, where saltpeter was first put to use in gunpowder, it was widely collected from caves. Eventually it was discovered to be more prevalent where bat droppings were to be found. As a result, a new  "organic" open air method of production soon gained favor.

You may have noticed this; when animal dung sits in the barnyard for a while and there has not been any rain, a powdery white deposit starts to form on what is exposed to the air. That white powder is saltpeter. In France, saltpeter production turned into a cottage industry, with large beds being maintained, covered from the rain. Beds were prepared several ways, but the most straightforward was to mix dung with potassium rich wood ash and straw and let it sit for up to a year, then flush out the saltpeter with water. The liquid was carefully collected and further purified.

As far as I know, Antonio Neri does not speculate in any of his writing about the natural process by which saltpeter forms, but one of his contemporaries does. Polish born alchemist and medical doctor Michele Sendivogius made a name for himself at the court of Holy Roman Emperor Rudolf II, in Prague. Sendivogius was convinced that saltpeter was a product of the air around us. He thought it was the congealed spirits of air and considered it "the food of life." He supported his argument with the fact that saltpeter makes a wonderful fertilizer for plants. He outlines his theories in A New Chemical Light which published in Frankfort in 1604, the same year Neri would have attended the spring fair there, if he followed the travel advice of his friend Emmanuel Ximenes. It was the year Neri embarked on what would become a seven year visit to Antwerp. [3]

While he was visiting in Antwerp, Neri makes particular use of saltpeter in his recipes for his colorful chalcedony glass "adorned with so many graceful and beautiful areas of undulations and enhanced with the play of diverse, lively, flaming colors." [4] He presented "His Excellency, the Prince of Orange, with two vessels of this chalcedony, which delighted him greatly." [5] In the recipe for this exotic glass, he makes extensive use of aqua fortis, acids for which saltpeter was an essential ingredient. These were the strongest acids known and the only way to dissolve precious metals like silver and gold. Neri uses a few gallons of these acids in the preparation of the ingredients for a single batch of his chalcedony glass. These acids were themselves thought to be composed of common water that had been infused with "powerful spirits." If Neri shared Sendivogius' reasoning, he might have thought that the process of making the acid was one of transferring the spirits of the air into water.

[1] Due to precession of the equinoxes, the date when Sirius rises and sets with the sun has shifted later by  about 25 days. In the Egyptian calendar of 3000 BCE the start of "dog days" coincided with the summer solstice.
[2] It is also called niter, with the chemical formula KNO3, composed of potassium, nitrogen and oxygen. 
[3] Again, there is no direct evidence of Neri's route, or that he was familiar with Sendivogius or the book. In Discorso (Neri 1613), he does mention alchemist Alessandro Scotus, who was released from prison by Sendivogius in 1590, after a conviction of practicing alchemy in public. See Grazzini 2012 p.346, n.55. 
[4] Neri 1612, p. 34.
[5] Ibid, p. 48.

Wednesday, September 17, 2014

The Art of Metals

Fig. 1: Antonio Neri, "Ars Preparatio Metallor[um]"
in Tesoro del Mondo, f. 8r.
Recently we examined three of a set of four illustrations drawn by priest Antonio Neri in a manuscript started in 1598.[1] They show various "arts" being practiced involving items found in nature; plants, animals, stone and today's subject: metals. 

Metals and their chemical manipulation concern Neri's work both as a glassmaker and as an alchemist. Most of the colorful pigments he uses in his glassmaking derive from metals; white from tin, green from iron, red from copper and gold, blue from cobalt, although Neri knew this last one only as a mineral called "zaffer." As an alchemist, metals were the subject of medicinal cures and of course were the focus of transmutation—the quest to turn one metal into another. In another manuscript written towards the end of his life, he indicates that he spent time in mines, where it was thought that metals "grew" underground as "veins" which nourished the earth. [2]

After an examination of Neri's "Art of Preparing Metals" we will take a look at another picture on the same subject, this time a painting titled the "Goldsmith's Workshop" by Alessandro Fei. It was executed a few years before Antonio was born, but bears some remarkable similarities in subject matter.

First, the manuscript illustration (fig. 1, click to enlarge): At center left, we see a special furnace construction which the label tells us is for "reverberation and calcination." Two crucibles sit inside, exposed to the heat. These are both procedures with which Neri was quite familiar. In the recipes of his glassmaking book, L'Arte Vetraria, [3] he speaks numerous times about what was called "calcination"—the reduction of a metal into what is usually a powdered oxide form. [4] This was a fundamental operation in producing the pigments for glass. "Reverberation" was exposing a material to secondary heat reflected from the inner walls of the furnace chamber; it was a more even heat than that produced by a direct flame.

Above the reverberation furnace is a foundry furnace, used for melting metals. Because of the high temperatures that needed to be achieved, it has a large bellows attached to force air into the fire causing a "blast" effect, which causes the fire to burn faster and hotter. Resting on the hearth is a long pair of pincers used to insert and remove crucibles of molten metal.

To the right, we see a curious arrangement of two glass retorts, each feeding into the other. They sit on purpose built stoves. The chimneys are capped by dome shaped dampers to control the draft and paddle mechanisms in front regulate heat under the glassware. A worker tends the apparatus, and the caption below reads "for extraction of the quintessence." Neri's other writing makes plain that this "quintessence" was a material that exhibits such a harmonious blending of the four essences: air, water, fire and earth that a new fifth essence (supposedly) emerged with extraordinary properties. To the right is a similar stove set-up with a single retort which is labeled "distilling." This station might have been used in preparation of the acids needed to purify metals.

At lower right, a blacksmith is hammering a piece of iron into a sword on an anvil. High-carbon "steel" was being made and used in the Medici court at the time, and that may well be what the smith is working with. Around him are several examples of his art, including two finished swords, a large copper bowl or cauldron, and a covered drinking stein made of tin.

To his left, we find a goldsmith, also hammering on an anvil, fashioning a silver platter. Displayed behind him are a variety of his handiwork, including more platters, gold necklaces and crosses and other ornamentation. A number of tools hang along the bottom of the anvil station, and behind it a small dog is curled up on the floor. 

Fig 2: Alessandro Fei (Barbieri)
"Goldsmith's Workshop" c. 1572.
About twenty-five years before Neri wrote his manuscript, Alessandro Fei painted a similar picture (fig. 2). Here we are treated to a view of a royal foundry housed in the yet to be completed Uffizi palace. [5] There is a remarkable concordance between this painting and Neri's illustration, right down to a small dog, hanging around the goldsmith's bench. 

The central figure of the painting is  Francesco de' Medici, seated in the foreground, inspecting his father's gold crown at a workbench. The dog is playfully engaging with the future Grand Duke, while on the opposite side of the bench, two other men are amiably discussing their work, perhaps silver chasing.To the left of Francesco, a younger man examines a gold ewer in the company of an older goldsmith seated across the table. The artisan is wearing spectacles and (although it is hard to see) he holds a small hammer in his hand. A worker to Francesco’s right is also intently engaged in his work. In the right mid-ground we find a small furnace with a tall chimney leading upward. On the mantle are displayed a number of gold and silver items, including platters, vessels and chains or necklaces. To the left, four men are busy seated around a large workbench. Behind that group, toward the center of the picture, are two men working at an anvil and three more at another bench on the right, accompanied by a second small dog. In an enclosed area in the background we see two large open furnace hearths, with their fireboxes glowing from underneath and men working in close proximity. In the far left background is a group entering the work area, including a figure in a yellow cape accompanied by a third dog.

The one element present in Neri's illustration that is missing in the painting is the glassware. Metalwork was a venerated and mature art long before Neri's era, which is underlined by the similarity of the two scenes, even though they are a quarter century apart, the tools, equipment and work methods are identical for all intents and purposes. There is no doubt that chemistry and distillation apparatus were used by the earlier metals artisans, the fact that Neri chose to emphasize this aspect of the work is a clear indication of his own interest and a foreshadowing of his future involvement in the production of the glass itself.

[1] Neri 1598-1600.
[2] Neri 1613, Grazzini 2012. 
[3] Neri 1612.
[4] In several of Neri's glass recipes the result of "calcination" is a sulfide.
[5] Beretta, 2014.

Monday, September 15, 2014

The Discovery of Glass Reprise

Giovan Maria Butteri,
"The Discovery of Glass"
Studiolo of Francesco I de' Medici
Any self-respecting Roman historian living in the first century could tell you the story that glass was first discovered by Phoenician sailors. They were temporarily grounded at the bay of Haifa, near the Belus River, in the shadow of Mount Carmel, forced ashore by a storm. Needing to eat, they improvised a fire on the beach in order to cook their food. Using natron, a mineral they were carrying as cargo on the ship, they built up a stove. To their amazement, in the heat of the fire, the natron mixed with the beach sand started to melt and liquid glass trickled out.

Actually, ever since Pliny the Elder, the author of most famous version of this story, skepticism abounds about how much of it was true. Nevertheless, if we gently tease apart the loose threads of this yarn we find that it is not without substance. First, there is the location; not just any port in a storm, this region was the site of a thriving glass industry as early as the sixth century BCE, due to the exceptional, pure white sand at the outlet of the Belus river. Archaeologists have excavated ancient glass furnaces at the nearby cities of Tyre and Sidon.

Next, the sodium carbonates in natron do indeed form glass when mixed with fine sand and brought to a high temperature, but this takes strong, concentrated heat, likely more than could be provided by a cook's beach fire. Natron is a hydroscopic mineral – this means it pulls moisture out of the surrounding environment. The water is locked into its solid crystal structure, where it remains until it is released either chemically or through heat. Natron can hold a remarkable amount of water, up to two-thirds of its weight. This is why it was used extensively to preserve mummies in Egypt; it dried out the bodies, quickly preserving them. While the story of the Phoenician sailors deserves a healthy dose of skepticism, it is also easy to see how the decomposition of the natron in the fire, resulting in the release of briny liquor, might be misinterpreted as glass.

In Neri's telling, natron does not make an appearance. Instead, the sailors use 'kali,' a coastal plant that is rich in alkali salts, to fuel their fire. The salts in kali are substantially similar to natron and, according to the story, triggered a similar result. Kali ash was a well-known ingredient in glass making. Neri used it in his own glass recipes, so the substitution is not surprising, but this version of the story does appear to be unique in the literature. It is interesting to note that Lodovico Domenichi, who was good friends with Neri's grandfather, tells a version of this story in his translation of Pliny's Natural History. Here the sailors use natron, but in the next paragraph, Domenichi describes how local natives used the plants to make their own glass.

The above depiction of the discovery of glass was painted by Butteri, one of a select group of painters for the Medici court in Florence. The work was commissioned to hang in the secret "studiolo" of Francesco de' Medici, a barrel vaulted room tucked under a staircase in the Palazzo Vecchio in the early 1570's. It was only accessible through secret passages, one leading from Francesco's bed chamber. Another passage lead to an unmarked door on the street and a third passage led to the secret treasury room once used by his father, Grand Duke Cosimo I. The walls and ceiling were entirely filled with paintings, the lower ones concealing cabinets full of oddities of nature, precious gems, coins, alchemical concoctions, and other treasures. Presumably, the cabinet behind Butteri's "Discovery of glass" would house some of the intricate Venetian glass vessels for which the craftsmen of Murano had become world famous. Shortly before the room was completed, a small number of these glass masters were allowed to teach their secrets in Florence by special arrangement with the Venetian government.

This post first appeared in a shorter form here on 9 October 2013.

Friday, September 12, 2014

Neri's Cabinet #5: Sulfur of Saturn

The Roman Goddess Ops, 'sweet'-heart (and wife)
of Saturn, Peter Paul Rubens c. 1630,
“Abundance (Abundantia).” [1]
Antonio Neri’s book on glassmaking, L'Arte Vetraria, devotes an entire chapter to making artificial gems. These are made with an especially dense, refractive form of lead glass—what today would be called lead crystal. He made it in small batches, in sealed ceramic vessels; each infused with various metal oxide pigments to give characteristic jewel tone colors.  His secret ingredient for making the finest artificial gems was a material known as "sulfur of Saturn." He writes:
You will have jewels of marvelous beauty in every color, which by far surpass those described above, made with ordinary minium. Because with this true sulfur of Saturn, they will surpass all others by far more than I can write here, as I have seen and made many times in Antwerp.[2]
This "ordinary minium" that he speaks of is one of several oxide forms of lead, also known as 'red lead,' it is bright red or orange in color. As a stable red pigment it was well known to ancient Byzantine and Persian illuminators. [3] It was so popular, in fact, that the word used to describe small intricate pictures 'miniature,' is derived directly from 'minium.' [4] The intricate embellishments in manuscripts ultimately took on the name of the scribes' favorite color.  In glass, minium does not impart red or any other color on its own, but does add 'sparkle' and made Neri's jewels highly refractive to light. 

In the recipe, he uses white vinegar and he reacts it with finely ground minium through a laborious process. The acetic acid in vinegar chemically combines with the minium to form lead acetate, which alchemists called "sugar of Saturn" because it had a distinctively sweet taste (more on that later). [5] Lead (Saturn) could be added to the melt in a number of different forms including acetate, carbonate and various oxides. The heat of the furnace reduces them all and the result is essentially identical glass from any of these sources. The lead acetate has one major advantage that set it apart from the others. Lead acetate is soluble in water and therefore it can easily be purified of contaminants and to a much higher degree. It can be filtered, allowed to stand and decanted after any insoluble impurities settle out.

In other references "sugar of Saturn" and "sulfur of Saturn" are considered synonyms. This is not the case with Neri, for him they are two different substances; the 'sugar' is a precursor for his final product, sulfur of Saturn:
Left in the bottom will be a salt as white as snow, and as sweet as sugar. Repeat the dissolution, and filtering, and evaporation with common water three times. This is the required sugar of Saturn. 
Keep it to calcine in sand in a glass flask or ball in a furnace over a moderated fire for many days. It will further calcine to a color that is much redder than cinnabar, and more finely impalpable than sifted grain flour. This is the required true sulfur of Saturn; purified from the sediment, foulness and blackness that were upon the lead at first. [6]
It would be a reasonable guess that by heating the acetate for "many days" he is reducing it back to minium, its more basic, bright red oxide state, but this time in a greatly purified form.

Unfortunately for his health, in this recipe for sulfur of Saturn, Antonio makes extensive use of heating and evaporation. Even more unfortunate is that in a number of steps he judges the potency of his product by taste. Lead acetate is highly toxic; because it is soluble in water, it enters the bloodstream easily. It attacks the nervous system, accumulates in the bones and can cause organ failure. It is quite likely that by breathing the fumes and tasting crystals of sugar of Saturn, Neri was contributing to his own demise at the relatively young age of thirty-eight. Lead acetate was not the only toxic substance he handled regularly, but it was certainly one of the worst for his health. 

 It does not follow that he was totally ignorant of the risks he was taking. The dangers of heavy metals were recognized from early times. Pliny speaks of the noxious fumes from lead furnaces, and Plutarch opined that lead and mercury mines were "unwholesome and pestilent places." Neri’s own father followed the work of Dioscorides, who wrote that ceruse (lead carbonate), taken internally, could be fatal and that certain sweet wines could adversely affect the abdomen and the nerves.

Ancient Romans discovered that when wine started to turn to vinegar, it could be boiled down in lead lined pots to produce a highly sweet syrup called sapa. A late Roman cookbook made extensive use of sapa, which presumably contained considerable lead acetate. [7] It has been conjectured that  lead laced sapa contributed to poisoning among the Roman aristocracy. While lead acetate is a deadly poison, it is a step too far to imply that it contributed to the fall of the Roman Empire.

[1] Alchemical tradition does provide for an association between the metal lead and the Roman god Saturn. However, there is no such association between 'sugar of Saturn' and either of his consorts Ops or Lua, although Ops, the goddess of abundance (opulence) does rather nicely represent the chemical that made Neri's most opulent artificial gems possible.
[2] Neri 1612, ch. 91.
[3] Chemically, this is Pb3O4, also known as Lead (II,IV) oxide, triplumbic tetroxide. Historically, it was called minium and red lead.
[4] The accepted etymology of ‘miniature’ is from ‘minium,’ but may have been influenced by similar Latin terms such as  minor, minimus, minutus, etc.
[5] Lead acetate comes in two forms; Pb (C2H3O2)4 and Pb (C2H3O2)2, both are toxic; the later variety is soluble in water.
[6] Neri 1612, ch. 91.
[7] “Saba” endures today as a popular grape syrup, albeit without the lead.

Wednesday, September 10, 2014

The Art of Preparing Plants

Antonio Neri, Tesoro del Mondo, f. 9r.
"Arts Preparatio frugu vel Piantar."
Recently, we examined two illustrations from a set of four drawn by glassmaker Antonio Neri. Each of these is devoted to a different "art"; preparing animals, stone/minerals, plants and metals. All four depictions appear in his earliest known writing, a manuscript devoted to alchemy, which was produced over a period of two years starting in 1598, when he was just twenty years old. He started writing shortly after his ordination as priest and the work was completed before he was employed making glass for the royal family. Absent any direct citation of glassmaking, the manuscript does show a familiarity with the kind of individual skills required for that art. Among the things Neri would need to know was the ability to make "glass salt" from certain dried plants. Presently we will look into the third of the illustrations, which he calls "The Art of Preparing Fruits or Plants." [1] All of the activities depicted here relate to food and drink, yet they could easily be applied toward other purposes.

The first written evidence of Antonio’s involvement in glassmaking was still a couple of years off, but the illustrations in this manuscript tell more of the story. While there is scant reference to glass in the text, the pictures are filled with examples of specialized vessels for chemical production and investigation. From these figures we know he was at least exposed to the glassmaking profession earlier, while still studying for the priesthood. Indeed, the first sentence of his 1612 book on glassmaking, L'Arte Vetraria, begins: "I have spent years of my youth laboring around the glassmaking craft, and experimented with many fine and marvelous effects." [2]

At center-left of the illustration at hand, we see a male farmer holding a flail, perhaps going about the business of threshing wheat, which appears in a bale behind him. Figuring prominently above the farmer (upper left) is a large mechanical apparatus that appears to be a gristmill powered by a waterwheel. A conical bag feeds grain or possibly corn from above into the central hole of a horizontal grinding stone supported by a large rectangular box. We can easily imagine that the gears shown on the front of the box control the drive or the gap between the stones. Wheat, of course, was an ancient well established staple. Corn was introduced as a direct result of Columbus' voyage to Cuba and by Neri's time, corn was being widely cultivated throughout southern Europe, northern Africa, and even as far as China.

Returning to the illustration, on the immediate left of the mill is a woman, who we can guess, is fashioning rolls or small loaves from dough made with flour from the mill. Below her, (center right) is a boy using a long paddle to put the balls of dough into a baking oven. In effect, Neri is showing us the full chain of events from harvesting to finished baked goods. 

Further down, another woman works over a large basket of herbs, which appear destined for three large glassware stills to her right. In his book, Neri presents numerous recipes for extracting paint pigments from flowers using similar methods.

At the bottom of the illustration, a third woman stands in a large wooden tub crushing grapes with her bare feet, as grape juice runs into a pan on the right. To her left are three wine barrels standing side-by-side. 

For us, the connection to alchemy might seem tenuous with the possible exception of the distilling stations. For Neri, there was a deep lesson here about the way nature works; in his later manuscript Discorso, he uses the growth of grain as a metaphor for "multiplying" the "seeds" of gold inherent in primordial material left over from the creation of the world. 
This is confirmed by the example of seeds, of which a single grain is capable of producing a hundred or a thousand, as long as you sow them in a commensurate place. Take the further example of fermentation, in which one small part is sufficient to ferment a large mass. Nor is it contradictory to say that the metals do not produce seeds, like herbs and plants, because even though nature by itself has no power to take the seed out of gold, however, aided and encouraged by art, [nature] will do that which it does not do by itself. So that art begins where nature ends, and art will perfect the seed, which in gold is merely begun. [3] 
Given knowledge of how to work in harmony with nature and bring about the right conditions, he was convinced that a small quantity of material could be converted into a large amount of precious metal. The illustration on the art of preparing plants simply showed a different manifestation of the same principle; he is showing how grain multiplies in the fertile earth, it is then transformed through the addition of water and fire into nourishment.

[1] Neri 1598–1600, f. 9r.
[2] Neri 1612, p. ii.
[3] Grazzini 2012, p. 454, (Neri, 1613).

Monday, September 8, 2014

Art and Science Reprise

Jacopo Ligozzi,1518,  fanciful glass vessels,
ink and watercolor on paper.
Antonio Neri's writing on glassmaking and alchemy was distinguished from that of many contemporary authors in that his work was all deeply rooted in hands-on experience. His contemporaries were often content to repeat century's old teachings about the four Aristotelian elements; that chemical interactions could be predicted through an analysis of the balance between hot and cold, dry and wet. But more and more, these notions were being discarded and replaced. It is common to cite the invention of instruments, and other technical developments; these factors certainly did contribute to advancement. But many different forces worked toward the emergence of early modern science, and one in particular is so obvious that it is easily overlooked: artists.

Working with hot glass was a profession in which attention to nature was essential: artists did not have the luxury of fanciful explanations of physical processes. They were obliged by their work to learn the ways glass mixed, moved and behaved in the furnace, not as they imagined it should, but as it actually did. The only way to achieve the complex forms and vessels for which master glassblowers were renowned was through long experience. Failure to understand the glass and predict its properties accurately resulted in failure of the piece.

Neri was immersed in this environment and the same principles applied to his own work in formulating the glass. Ancient theories had little value if they did not accurately predict nature. Like the glass artists, the way forward for Neri was careful attention and hands-on experience. He learned the value of starting with highly purified ingredients for his glass melts. He learned that too much glass salt resulted in a putrid 'gall' that would need to be skimmed off the molten surface. Substituting salts made from fern plants, for the Kali based ones from the Levant, produced a more lustrous glass, yet it stiffened more quickly for the glassblowers.

A glass artist's work also serves as a kind of narrative. For those familiar with the techniques, a finished piece of glass work can be 'read' like a story: The handles were put on last, before that, perhaps a thin bead of color was applied to the lip of the vessel. And the work started as a blown bubble of glass, shaped and opened with special tools. Each step is an insight into the artist's technique, but also into the way nature itself operates. Each motion was a well practiced negotiation between the artist and the properties of the material.

On one hand, an artist's job was to produce objects contemplated for their physical beauty and cultural significance. On the other hand, the act of producing these objects created an environment where accurate reasoning flourished. By collecting artists and employing them together, the Medici rulers of Tuscany were creating a cauldron effect where experiences collected, stewed and nature's secrets unraveled.

This post first appeared here on 23 October 2013.

Friday, September 5, 2014

Neri’s Cabinet #4

So-called "wine diamonds," (harmless)
Potassium bitartrate deposits which can accumulate
in bottles and barrels of wine.
Tartar salt is an example of an alchemist's chemical that is a byproduct of another process, in this case winemaking. In his book L'Arte Vetraria, [1] Antonio Neri uses it in his glassmaking for two very different effects. The first application is to improve the appearance of the glass and the other is to modify colors. In addition to uses in glass, tartar also finds its way into his recipes for red paint made from the dried kermes insect [2] and for cast bronze mirrors, as a flux. (Flux keeps the metal bright and shiny while in a molten state). [3]

Neri notes that tartar also went by the name of "gruma" to which we can add greppola and argol. He warns readers several times to "leave behind the [dried] powder of the [raw] tartar, which is no good" and that "you should have tartar, from the dregs of red wine, which is better than white wine." [4] Nevertheless, he does specifically use white wine tartar in his recipes for rosichiero, a transparent dark red enamel. [5] In his recipe for producing tartar salt [6] he directs the reader to obtain the raw material from emptied wine barrels, but elsewhere in the book he seems to prefer to use the large crystals of tartar that have “vitrified naturally in bottles of wine.” [7] Chemically, tartar is a potassium compound formed through a reaction with tartaric acid, a major constituent of grape juice. [8] 

The effect of tartar in improving the appearance of glass can be readily explained. Most of the glass that was made in Italy in the seventeenth century used sodium-based additives to lower the melting temperature of finely ground quartz powder; these formulations are known as soda-based glasses. Potassium compounds can have the same effect and 'potash' based glasses were predominantly produced in northern Europe where trees and plants rich in potassium were used. Potassium is a heavier element and it produces a denser, more refractive glass, giving it more sparkle, although not as much as lead imparts to crystal. Unfortunately, potassium also makes the glass harder to work for the artisan. Potash glass stiffens more quickly as it cools, whereas soda glass remains workable for a longer time before requiring reheating in the furnace. Many of Neri's recipes blend the two additives, which we can imagine gives some of the advantages of both.

The effects of tartar on Neri's colors in glass are exemplified in a number of passages throughout the book. He uses it as the sole pigment in his recipe for pearl colored glass, but he warns, "Once obtained, you must work the color quickly, because it will dissipate." [9] Conversely, he also uses tartar to produce a black colored enamel, combining it with manganese [oxide], which by itself imparts a magenta color. [10] 

The first step in making Neri's purified tartar salt is to obtain the raw "gruma, from barrels of red wine in which it forms large lumps." Next, he gently roasts it in terracotta pots "until it becomes calcined black and all its sliminess is roasted away. It then will begin to whiten, but do not let it become white, because if you do the salt will be no good." Now, he boils it in water for two hours, evaporating off three-quarters of the liquid. After filtering, he lets the remaining liquid "lye" cool in pans, allowing any sediment to settle to the bottom. He gently pours off  (decants)  the liquid which is further processed on the stove, this time in glass containers. The result, after full evaporation over a slow fire is a “white salt” left in the vessel. He dissolves this in hot water, filters it again and allows more sediment to settle out for a period of two days. Again, the liquid is decanted and evaporated in a glass container. The filtering and evaporation process is repeated four times, resulting in a product that is "whiter than snow."

Antonio Neri's final remarks for this chapter are as follows:
“When mixed with sifted polverino, or rocchetta, with its doses of tarso or sand, this salt will make a frit that in crucibles will produce the most beautiful cristallino and common glass, which one cannot make without the accompaniment of tartar salt. Without it, good fine cristallino can be made, nevertheless with it, it will be the absolute most beautiful.” [11]

[1] Neri 1612.
[2] Ibid, ch 116, 117.
[3] Ibid, ch 113. Note that in glassmaking, the term 'flux' has a different meaning than in metallurgy.
[4] Ibid,  ch 41. 
[5] Ibid, ch 125.
[6] Ibid, ch 11.
[7] Ibid. ch 46.
[8] Pure tartar takes the form potassium bitartrate KHC4H4O6.
[9] Neri 1612, ch 60.
[10] Ibid, ch 102.
[11] Ibid, ch 11. Polverino and rocchetta are thought to be forms of dried Salsola Kali plants. Tarso is Neri's term for white quartz river stones. Cristallino was a Venetian style glass that in quality fell between common glass and the premium cristallo, for which Murano became famous.

Wednesday, September 3, 2014


Antonio Neri, Tesoro del Mondo, 1598-1600
f. 7v, "Ars Preparatio Lapidum"
Last week we looked at an illustration in Antonio Neri's early manuscript Tesoro del Mondo or Treasure of the World.  This week we explore another illustration from the same set of four. This one is labeled "The Art of Preparing Stone," the picture shows five men working with various pieces of equipment related to the art. [1]

In the upper-left a lapidary works at a polishing wheel. It turns at low speed, driven by a belt which is powered from below, possibly by a foot pedal. The artisan holds two polishing fixtures against the surface of the disk, while four more stand at the end of the table. Under this workstation is an inscription in Italianate Latin that reads "Accontiare et lustrare pietre praciose" [preparing/dressing and polishing precious stones]. Behind the lapidary are shelves holding finished pieces. They range from small objects that appear to be rings, to cups, vessels and large bowls, presumably all made from stones, gems or minerals. 

Proceeding clockwise to the upper-right side of the image, we arrive at a worker tending a furnace with iron tools. Inside is a crucible sitting in the flames. Below is the firebox, and underneath that is the word "Calcinare" [calcination], which in Neri's parlance refers to the process of breaking down a material into a powder usually through the use of heat. Neri uses this method extensively in his glass formulations; in his book L'Arte Vetraria, [2] almost every colorant discussed is a metal which requires "calcination" before use in the glass melt. In the case of stone, Neri uses the furnace to make the main ingredient of glass. He breaks down quartz stones into powder by repeatedly heating them and then quenching in cold clean water. The rocks fracture into coarse granules which are then ground into a fine powder.

The middle-right of the illustration shows a worker checking on a distilling apparatus. This consists of a small stove and three pieces of glassware.  The "body" holding the raw material to be evaporated or sublimated is capped by a "head" that sports a long snout leading to a "receiver" vessel which collects the finished product.  Stills were useful in producing everything from alcoholic spirits like grappa to acids and reagents. Their specific use in stonework is not clear, possibly in dissolving precious metals from the constituent minerals in stone.

The lower-right portion of the image depicts two men seated at a low bench, each holding specialized tools used to shape "alabaster, marble and porphyry." Finally, in the lower-left we see a specialized mortar and pestle used to grind stone and minerals into a fine powder.

The two benches and the distilling stove all bear a distinctive diamond shaped insignia with a small circle at its center. The two men in the lower portion of the illustration appear to be working on a stone inlay version of this same pattern.  The implication is of an identifying symbol, but a specific affiliation is elusive.

 This technique of creating designs entirely in colorful gems and minerals (pietre dure) is an ancient one revived by the Medici family, specifically by its first three grand dukes.  In the 1560s Cosimo de' Medici employed two such artisans (commessi) in the courtyard of the Palazzo Vecchio. By the 1570s a larger group was working out of Francesco de' Medici's new palace, the Casino di San Marco. In 1588 Ferdinando de' Medici moved them into the Galleria dei Lavori [Gallery of Works] at the Uffizi Palace where they were named the "Opificio delle Pietre Dure." [workshop of hard-stone]  There the organization thrived and refined the art of creating inlaid stonework to the point of producing realistic life-like scenes. Their work graces the most opulent spaces in Florence, including the Chapel of Princes and the interior of Santa Maria del Fiore. The Opificio delle Pietre Dure continues to operate to this day. The organization has been charged with the maintenance and conservation of many of Italy's great works of art. They maintain a worldwide reputation for excellence. [3]

It seems well within the realm of possibility that Neri's illustration indeed depicts an early incarnation of the Opificio. The artisans working in Pietre dure were handling precious materials and as such might not be readily accessible to the general public. The fact that Antonio Neri's father was a prestigious member of the Medici royal court all but ensured his entree to the royal workshops.

[1] Neri 1598-1600, f. 7v.
[2] Neri 1612.
[3] Official website:

Monday, September 1, 2014

Top Physician Reprise

Frontispiece from Ricettario Fiorentino 1597 ed.
In 1580, when Antonio Neri was four years old, just after the birth of his brother Vincenzio, both his father and grandfather were together granted full Florentine citizenship by Grand Duke Francesco I de' Medici. In Tuscany, citizen status was an honor conferred to a small fraction of the population and often through inheritance at around the age of thirty. The fact that Neri Neri gained citizenship at the age of forty and did so together with his father, Jacopo, shows it was not legacy, but perhaps their medical prowess that lead to the award. This period also corresponds to the first appearance of the unique coat of arms that distinguish this branch of the family. The same arms adorn the central panel of the vestibule ceiling at the Neri's residence. Citizen status bestowed the advantage of direct representation in the government and the right to hold public office. It also carried responsibilities to the city, to its leaders and to the Church. One requirement of citizenship was possession of a domicile within Florence. The baptism register listed Antonio and all of his siblings as residents of San Pier Maggiore parish long before the citizenship grant. However, it is in the 1580s that we see the first reference to Neri Neri's ownership of the palazzo at what is now 27 Borgo Pinti. 

Within a few years, Antonio's father would publish his work on cures for paralysis and by the end of the decade he was appointed personal physician to the new grand duke, Ferdinando de' Medici. The 1590's saw Antonio taking vows, and beginning his career in the Church. The road to priesthood ran on a parallel track to an apprenticeship in a trade. The completion of a trial period lead to becoming a novice at the age of sixteen, then deacon and finally priest. Meanwhile, Antonio's father, along with another doctor and two apothecaries was chosen by the entire Florentine College of Physicians to revise and update the famed Ricettario Fiorentino.[1] This book was the gold standard of doctors and pharmacists throughout Europe. The Ricettario was the official reference for medicinal cures in Tuscany. The law required every apothecary to own a copy and to supply its listed formulas to customers. Many regard this volume as the first European pharmacopoeia. It was a systematic standardization of drug recipes and dosages. Throughout the Medici reign, updated editions appeared as knowledge progressed. The book is a major landmark in the history of medicine. The edition authored by Neri's father and colleagues, in 1597, proved so popular that in 1621 it was reissued without change.

There can be no doubt that Antonio's father and his work had a profound influence on the priest. In the introduction to his book on glassmaking, L'Arte Vetraria,[2] he proclaims his desire to publish his own work on chemical and medical [spagyric] arts, saying "I believe there is no greater thing in nature in the service of humanity." In his recipes he uses the terminology of physicians; adding chemicals in 'doses' and measuring 'ana' (in equal parts). In a 1608 letter to a friend, [3] Antonio describes his great success with medicinal cures of Paracelsus, "to the great wonderment of Antwerp." The priest also references experiments he carried out in Brussels and at the Hospital of Malines.

[1] Neri, Benadù, Rosselli, Galletti 1597.
[2]Neri 1612.
[3]Neri 1608.
This post was first published here in a slightly different form on 16 October 2013.