The Blue Tower

"The Blue Tower" Jozef Linnig 1868.

There are three known facilities where priest Antonio Neri worked as an alchemist formulating glass in the early seventeenth century; in Florence, Pisa and Antwerp. If he did work elsewhere, it must have been for a relatively short period since his time at these three locations accounts well for his entire career. Of the three, he is known best for his work at the Casino di San Marco, on the north side of Florence. It is also the facility about which the most is known, since its owner was Medici prince, Don Antonio. However, a good argument can be made that the facility in Antwerp, about which much less is known, was the one most influential to his career as a glassmaker.

Neri traveled to Antwerp in early 1604 to visit his friend Emmanuel Ximenes (Pronounced Se-men-ez), where he stayed for seven years. Ximenes was an international trader (known then as a 'banker') from one of the wealthiest families in Flanders. At the time, Antwerp stood at the center of the bloody Dutch war for independence from Habsburg Spain. The population of the city was a shadow of its former self, after being sacked and burned by Spanish troops a couple of decades earlier in what has become known as "the Spanish Fury." A Dutch blockade of Antwerp's seaports had strangled commerce, but for the ultra-wealthy, life went on.  

"Antwerpen, het Arsenaal" Jan Wildens, 17th Cent.

 In his book on glassmaking, L'Arte Vetraria, [1] Neri names "the most courteous gentleman Filippo Gridolfi" as the owner of the glass factory in Antwerp. Indeed, records show that Gridolfi was the latest in a long line of owners who had been granted exclusive rights to make the exalted Venetian style glass known as cristallo. Under the management of Gridolfi and his wife Sara Vincx, the luxury glass business thrived. In the 1590s, shortly after their marriage, they employed seventeen Venetian workers. 

The most fashionable street in Antwerp was the Meir. This was the address of  Ximene's palace, as well as of his brother in law, Baron Simon Rodrigues d'Evora, who happened to be the most prestigious diamond dealer and jeweler in the region; he was known locally as "the little king." Gridolfi and Vincx had one, and later a second retail space for their glassware here. The factory and furnaces were located a few blocks away, near the fortress wall that ringed the city. Records indicate it was in a district called  the Hopland, near -- or possibly also in -- a huge structure called the "Blauwe Toren" [Blue Tower] which had at various times functioned as an armory. In this period, a below street level canal led from the basement of the tower directly to the Meir, in later years it was filled in. Just on the other side of the city wall was a mote with access to the network of waterways which connected towns and villages throughout the region; this too was eventually turned into usable real estate when the wall was demolished in the nineteenth century. This situation of the glass production makes perfect sense. They needed to bring in heavy materials, ship delicate product and occupy a space which was not in danger of burning down the city should disaster strike. 

Blue Tower, 1860. Edmond Fierlants.

Today the foundations of the Blue Tower are preserved just below street level in a busy traffic square. Over the centuries, surrounding structures came and went. A small number of contemporary depictions do exist. Two illustrations that give a flavor of the neighborhood are shown here. One sketch by Jan Wildens  is not in the best of condition, but shows the tower and a few nearby structures from canal level in the seventeenth century. This might well have been typical of the view from a barge making deliveries. The factory would need a steady supply of pure quartz river stones used to make the exceptionally clear cristallo glass. A second view by Jozef Linnig, shows the neighborhood more clearly albeit in 1868. By then a furniture maker was located to the left of the tower, and another structure stood where the canal once was. Also of interest is an early photograph of the tower before it was demolished.

What we know of Neri's experiences in glassmaking come mostly from his book. His activities in Florence included making aquamarine colored glass for beadmaking and chalcedony glass with its multicolored swirls. In Pisa, he made emerald green, pimpernel green and celestial blue glass, he experimented with enamels, constructed a frit kiln and made glass using fern plants. From his early glassmaking activity in Florence, Neri seems to build momentum in Pisa. In these two locations he spends at most four years, in Antwerp he spend seven years, and there is no indication that he is slowing down, in fact quite the opposite. There he made artificial gems, a "beautiful aquamarine so nice and marvelous, that you will be astonished." He tinted rock crystal "the colors of balas, ruby, topaz, opal and girasol." He "built a furnace that held twenty glass-pots of various colors" He made ultramarine, the deep blue pigment valued by painters more highly than gold. Finally in 1609, in Antwerp, at Gridolfi's shop he made "the most beautiful chalcedony that I have ever made in my life" and presented two vessels of this glass to the prince of Orange.

[1] Neri 1612.

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.

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.

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"

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.

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.

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.

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