Neri's Cabinet #3

Crystals of Copper Sulfate Pentahydrate
(Vitriol of Venus)

Vitriol of Venus was one of the most cherished items in Antonio Neri’s chemical library. In his book, L'Arte Vetraria, he describes its effect in glass this way:

To your great contentment, you will be astonished at what you see. I do not know of anybody else who has tried it this way and I Priest Antonio Neri trying it found it most marvelous, as said above, and it is of my own invention. [1]

He is so proud of his creation that he spreads the description of his method over four full chapters of the book, going into a level of meticulous detail that is extreme, even for Neri. Rest assured, dear readers, that I have taken the liberty of distilling said description down to a more manageable form for your reading pleasure. Nevertheless, our priest-alchemist clearly puts great stock in this preparation, going so far as to drop hints that this material has uses that go far beyond glassmaking: "Many things could be said here, which are omitted as not being pertinent to the art of glassmaking, which perhaps upon another occasion you will be able to judge." [2]

Before starting, he gives some general advice:

You should make the sulfurs, vitriols, ammoniac salts, and similar materials slowly, over a low fire, so they are well prepared and well opened, because a violent fire will cause great damage to them.[3]

To begin, Neri cuts thin copper sheet into small pieces half the size of a small coin. filling a crucible, he layers the copper pieces with common sulfur (known as brimstone).  He cements the vessel shut with a lid and then buries it in the hot coals of a drafted furnace for two hours.

The dark purple contents are then ground and sifted through a fine screen, mixed with six ounces of pulverized sulfur per pound and then heated in a round terracotta pan, which is sitting in the hot coals. When the sulfur starts to burn, he stirs the mixture, rolling it into balls with an iron hook so it does not stick to the pan, continuing until it stops smoking. He removes the mixture from the heat, grinds it finely, adds more sulfur and repeats the entire process three times.

Neri grinds the resulting reddish tawny colored material into powder, putting a pound of it into a large glass vessel containing six pounds of clean water and gently evaporate away a third of the water. The liquid is carefully poured off and saved. The residual solids are dried and recycled in the process. Now more solids are allowed to settle out of the "beautiful blue" liquid over a two-day period and then the liquid is filtered through a felt cone.

He heats the liquid again, this time evaporating two thirds and then puts the remaining third into glazed terracotta pans, and leaves them in a cold damp place overnight. "You will find the vitriol of copper has formed into crystalline points that mimic true oriental emeralds." The crystals are removed, dried and the liquid is further evaporated in order to obtain more crystals. To the chemist, this material is copper sulfate pentahydrate [4]; today it is sold inexpensively as a fungicide for swimming pools. One reason it was so valuable to alchemists is that when gently heated or added to water this chemical forms a sulfuric acid solution. 

This is the true flaming azure blue [tincture], with which marvelous things are made. It is most potent, and as sharp as anything known in nature today, as can easily be perceived from its odor.

However important this was in other areas of alchemy, those applications do not have any particular relevance to the blue-green tint it imparts to glass, which he does make use of throughout the book. The full recipe was so long that he continued it several times and finished as the final chapter of L'Arte Vetraria. Here are the closing words to the book:

Although I have placed here the way to make this powder with much clarity, do not presuppose that I have described a way to make something ordinary, but rather a true treasure of nature, and this for the delight of kind and curious spirits.[5]

[1] Neri 1612, ch. 31.
[2] Ibid, ch. 133.
[3] Ibid, ch. 37.
[4] CuSO4•5H2O

[5] Ibid, ch 133.

Alchemy in the Kitchen

Tesoro del Mondo, "Ars Preparatio Animalium"
Antonio Neri 1598-1600, f. 10r (MS Ferguson 67).

Between 1598 and 1600, Antonio Neri wrote a manuscript filled with alchemical recipes. He entitled it Tesoro del Mondo or "Treasure of the World" and stated that it was a book in draft form, intended for publication. It never did see the ink of a printer's press, but Neri's original did survive intact and today occupies a place of pride in the Ferguson Collection of the University of Glasgow Library. [1]

Tesoro is an ambitious work, devoted to "all of alchemy," containing numerous hand-drawn ink and watercolor illustrations; some of the pictures are allegorical, many others document practitioners working with equipment. Only passing reference is made in this manuscript to glass—its most notable appearance is as experimental vessels. 1598 was two or three years before Antonio's glassmaking career is thought to have started. His life was busy on other fronts. He had just been ordained as a Catholic Priest, undergoing the laying on of hands ceremony, probably by his neighbor on Borgo Pinti, the Florentine archbishop Alessandro Ottaviano de' Medici. 1598 was also a year of tragedy for the Neri family; by the summer, his father Neri Neri, personal physician to the grand duke, was dead of an unknown illness. The now orphaned children would soon suffer further tragedy in the unexpected death of a brother; sixteen year-old Emilio would leave them on Christmas day of the following year, in Castello outside Florence. 

The losses must have been devastating. In 1598, five of the nine children were still under the age of twenty. Without a mother or father, great responsibility must have fallen on the shoulders of the matriarch of the house, the children's elderly paternal grandmother Maddalena. [2] Even though the Neri's were a wealthy and quite well respected family, these events undoubtedly threw their lives into turmoil. It is in these circumstances that Antonio started his manuscript. The tragic events allude to the reasoning behind a cryptic Latin quote scribbled at the top of a page above the first recipe: "fuimus troes." It means, "We are Trojans no more" From Virgil's Aeneid, referring to the fall of Troy. [3] 

Early in the manuscript there is a series of four illustrations, each showing a different activity, In order, they are titled The Art of Preparation of Stones, Metals, Plants and Animals. [4] Each is filled with multiple workers engaged in various activities pertinent to the specific art. Each highlights interactions between the Aristotelian elements: air, water, earth and fire. There is no specific indication of where any of the four scenes take place, although some educated guesses can be taken. For instance, the stone workers, or lapidaries, almost certainly are an early incarnation of the famed 'Opificio delle pietre dure' working in the Uffizi's Galleria dei Lavori. But we will leave that discussion for another time. 

Of the four illustrations, "Preparing Animals" focuses on activity within a kitchen. (See above, click to enlarge). The scene is intriguing in that it appears to take place in a domestic setting. Birds hanging from the rafters represent air, fish on a grilling rack represent water, a whole carcass on the spit represents earth and fire appears as itself in several locations. I would like to suggest that this setting is none other than the Neri family kitchen and that the practitioners of the art are three of Antonio's siblings. In the middle right, a young boy is engaged in turning the spit (in green). The best candidate would be then eleven year-old Allesandro, the eventual heir to the family, whose own son named Neri would carry on the family practice as a physician. Of the two young women pictured, the three family choices are fourteen year-old Lucretia, Sixteen year-old Maria and twenty-six year-old Lessandra.

Since I am already out on a limb, I will also suggest that the methodology of alchemy lives-on today in kitchens around the world. The process of combining raw ingredients and cooking them together, of experimentation and of iteratively refining a recipe to perfection, this is not so different from what Antonio Neri and his siblings were doing four hundred years ago.


[1] Neri 1598-1600.
[2] Maddalena di Bartolomeo di Niccolò Bartoloz[z]i, married Jacopo Neri, and they gave birth to Antonio’s father Neri Neri. (ASF 599).
[3] Fuimus Troes, fuit Ilium, et ingens Gloria Teucrorum. [We Trojans are at an end, Illium has ended and the vast glory of the Trojans], The Aeneid: Book 2, Line 325.  See also the post in this blog (Conciatore.org) dated 13 June 2014.
[4] Neri 1598-1600, ff. 7r, 8r, 9r, 10r.

Manganese from Piedmont Reprise

The green tint from iron contamination
is neutralized by magenta from manganese.

For Antonio Neri, contaminants, especially metallic contaminants were the bane of producing crystal clear glass. Great care needed to be taken to ensure the purity of each ingredient at each step of the glass making process. The greatest threat of all was iron. Even small amounts will tint glass green and for Renaissance era glassmakers, nemesis iron was everywhere. It is common in quartz, the main ingredient of glass, showing up as yellow "rust stains" both in sand and stones. It turned up in the plant salts as a trace-element and finally it was in the tools. Iron was in the mortars and pestles, in the pots and kettles, in the frit rakes, in the ladles, the stirring rods and in the blowpipes. A mistake at any step could easily tint the batch, even at the final stages. Neri admonishes glass workers:

Make sure never to return the neck, where the rod attaches to the glass, into the crucible of cristallo, because there are always remains of the iron that will cause it to become dark ... 

The antidote to iron is manganese or more specifically manganese oxide, a mineral mined throughout Italy. However, Neri cautions: 

… you must always use manganese of Piedmont the way it is made for Murano, because the manganese of Tuscany and Liguria has more rust, which always make the melt dark. 

This color correction technique was known as early as the late 14th century and by Neri’s time it was a widely practiced technique in the glassmaker’s toolbox. Manganese oxide was known as a pigment in antiquity; the Magnesia region in Thessaly, central Greece was an ancient source for the black mineral. Around the year 1450, a clear crystal-like glass suitable for working into thin elaborate forms was developed in Venice. The glass was called cristallo and Murano glassmaker Angelo Barovier is often given credit. He may well be responsible for bringing together several existing techniques—manganese color correction among them — but these techniques individually were all available and utilized by glassmakers at least fifty years earlier. Barovier’s innovation would become a tradition that would become synonymous with the finest glass made anywhere, carried on by countless glassmakers and ultimately by our Florentine priest more than a century and a half later.

Removing the green tint of iron contamination with manganese is a clever trick. The manganese imparts a magenta tint to glass. As the complementary color to green, it effectively "cancels out" the green tint. The trade-off is that the glass is slightly darkened, even if neutral in color. In terms of what light does, when it passes through glass tinted by iron, green light is unaffected, while red and violet light is dampened. In effect, the green is enhanced. Now, adding manganese to the glass dampens only green light and brings the spectrum back into balance. The overall effect is that all the colors of light are slightly dampened, but by the same amount. In Neri's case, minor contamination from iron would produce only a small green tinge and the problem was corrected with a small dose of manganese. The resulting grey would hardly be noticed, especially in the thin, delicate pieces so popular at the time. To the eye of all but the most experienced expert, this decolorized glass had perfect crystal clarity.

This post first appeared here in a slightly shorter form on 14 October 2013.

Neri’s Cabinet #2

Alchemical symbols used to denote sal ammoniac.

Today we will examine "sal ammoniac," a common alchemical ingredient used by Antonio Neri in many of his preparations. In its pure form, it is a colorless crystalline material and is known to chemists as ammonium chloride. It does occur as a (rare) natural mineral, but it was also manufactured as early as the thirteenth century, as noted by alchemist Albertus Magnus in his De alchymia.[1] Neither he nor Neri provides a recipe for sal ammoniac, but other sources indicate that it was made by allowing urine to putrefy with common salt. French investigators documented another method used in Egypt in the eighteenth century. This scheme involved burning the dung of animals who fed on spring grasses and then sublimating the ammoniac out of the resulting soot. Sublimation occurs when a heated material goes directly from a solid to a gaseous state without ever becoming liquid. Sal ammoniac has this property; when heated it turns to a gas and upon cooling, turns back to a solid.

The usefulness of sal ammoniac in alchemy stems from the fact that when dissolved in water, which it does easily, it immediately dissociates into equal parts of ammonia and hydrochloric acid, which in turn will dissolve some metals, including tin, zinc, iron and (reluctantly) lead. Its most famous use was as an additive to the stronger acid aqua fortis (nitric acid). Together the two formed aqua regis which was strong enough to dissolve gold. At the time that Neri was working, the only known way to dissolve the most 'noble' of metals (gold) was with the 'king' of acids (aqua regis). Neri puts this knowledge to use in his recipe for ruby-red colored glass made with pure gold. His description is light on details, but he does clearly direct the reader to dissolve the precious metal in aqua regis, then gently evaporate away the acid to obtain the red pigment.

Elsewhere in Neri's glassmaking book, L'Arte Vetraria,[2] he uses sal ammoniac in the production of "alemagna blue" paint and in the tinting of natural rock crystal. 

Another of Neri's creations requiring sal ammoniac was Chalcedony glass. It had swirls of every color the glassmaker could produce. He achieved this feat by making extensive use of aqua regis to dissolve a long list of metals. He then gently evaporated off the acid, leaving ultrafine powdered metals, which he added as pigments to the glass melt. 

With this powder, I made a chalcedony in a glass furnace in Antwerp that was then run by a most courteous gentleman; Mr. Filippo Gridolfi. This chalcedony gave rise to work so nice and graceful, that it emulated true oriental agate, and in beauty and delightful colors by far exceeded it.

Today, chemical factories produce vast quantities of the materials used by Neri in his glassmaking exploits and in far higher purities. Having unlimited quantities of every conceivable chemical compound at our fingertips makes it difficult to appreciate the physical labor involved by seventeenth century alchemists, both in the preparation of the glass and in the production of the individual ingredients. The chalcedony glass recipe cited above must have taken workers many, many hours to produce and must have cost a small fortune. 

[1] Magnus 1958.
[2] Neri 1612.
[3] Glauber and others used the term 'sal ammoniac' to describe a related chemical (NH4)2SO4. When mixed with aqua fortis this forms a nitric-sulfuric acid solution, which does not form aqua regis, and does not dissolve gold.

The Dregs

"the struggle of fixed and volatile"
allegorical illustration from
Splendor solis [detail] 16th C.

"Dregs" were otherwise known to Antonio Neri as, terra, gruma, immondita, terrestreità and my favorite:  sporchezza. It was the "filth" and sediment left in the bottom of vessels after useful material was extracted from a preparation. These often foul-smelling substances were sometimes discarded:

Then filter out the dregs of the vitriol impregnated water; that which is yellowish you should throw away. –L’Arte Vetraria, chap. 38.

Other times, dregs were further refined A notable example was the potassium rich muck left at the bottom of aged wine barrels. This was Neri's secret ingredient in producing a fine, sparkling cristallo glass. To understand the distinction between the useful and the useless forms of dregs, we must dig deeper into Neri's philosophy.

It might be surprising to some that these lowliest of materials could play an important role in the theory of transmutation—the alchemists' ultimate quest—, which was to turn base metals into gold and silver. The idea was that a natural evolutionary process occurred in which  primordial material from the creation of the universe would, over time, mature through the lesser metals into pure gold. It was thought that this maturation was prompted by "seeds" of gold contained in the material. In Neri's view, this could be interrupted by various natural circumstances and could be restarted or sped-up through alchemical manipulation.

If one was to "purify" lesser metals into gold, it was advisable to know what needed to be removed. In his manuscript Discorso, Neri carefully explains five categories of impurity, which he then breaks down further into two sub-groups:

It should be noted in general, that in dealing with the [Aristotelian] elements in accordance with chemical philosophy, we can say that all mixed bodies in this art are discovered to contain five kinds of impure substances, which are completely dead and without any virtue or properties effective to [alchemical] operations. Two are from impure substances and three from pure substances, where all the strength, effectiveness and virtue are located specific to each mixture. Of the two [derived from the impure] one is called 'phlegm', which is to say a watery substance with no odor or taste and the other is called 'dead body' [corpo morto] or 'damned earth' [terra dannata], an earthy substance that is equally tasteless and without virtue.[1]

Indeed, in Neri's chemical philosophy, the above two useless forms of impurity (phlegm and corpo morto) are complemented by three useful forms (salt, oil or true sulfur and spirit or mercury), which are present in so-called pure materials. Researcher Maria Grazzini notes in her annotations to the manuscript that: "The chemical philosophy to which Neri refers is Paracelsian, which in addition to the four Aristotelian elements introduces the principal triad (tria prima) of salt, sulfur, and mercury. References to sulfur and mercury were already present in Arabic alchemy." [2] 

Of the other three [derived from the pure] one is called 'salt' and it is the so-called most fixed substance because it is resistant to the violence of fire; it does not flee or vanish into the air. The second is called 'oil' or 'true sulfur' because of the similarity to it, fatty and viscous. The third is called 'spirit' because it is more spiritual and volatile than all the others and even the slightest heat will cause it to dissipate into the air if it has not been bound to the salt, which is the component fixed by the oil. By its tenacious, slimy nature, [oil] acts to bind the volatile to the fixed. These three types are those of the pure substances, which are called by many other names; 'body', 'soul' [anima], 'spirit'; 'bitter', 'sweet', 'acid'; 'salt', 'sulfur', 'mercury' etc.

In them alone are placed all of the virtue and effectiveness of the minerals, the vegetables and the animals, even if the quantity of pure substance is very small in comparison with the impure in any kind of mixed body. These [three] are found in each mixed quantity of pure substance, in comparison with the ineffectual found in the impure. [3] 

In his view, it is these last three forms of impurity that hold the key to transmutation, which tends to puts dregs in a whole new light.


[1] Grazzini 2012, p. 339.
[2] Ibid, note 45, p. 339.
[3] Ibid, p. 340.

Don Giovanni

Don Giovanni di Cosimo I de' Medici

In July of 1621, a man lay dying in his bed, in his palazzo on Murano, the glassmaker's island in Venice. This fifty-four year old had recently become a father and his wife Livia was expecting a second child, but the tumor in his throat meant he would not see his two year-old son Gianfrancesco Maria grow up, nor would he live to hold his yet unborn daughter in his arms. His death would also trigger a series of unanticipated ugly events. Don Giovanni de' Medici was the son of Grand Duke Cosimo I and Eleonora degli Albizzi. He had been general of the Venetian army and before that lead Tuscan troops in Flanders, France, Hungary and served as ambassador in Madrid. But he was far more than a soldier; he was an architect who helped design the Chapel of Princes in Florence, he was a strong patron of the arts and he was a devoted alchemist. He plays a somewhat tangential role in the life of glassmaker Antonio Neri, yet their paths cross repeatedly through common associates, interests and locations.

Don Giovanni's palazzo on Murano was the grandest on the island; previously owned by the father of Grand Duchess of Tuscany Bianca Cappello. She spent time at the palazzo as a child and was the mother of Antonio Neri's sponsor, Don Antonio de' Medici. King Henry III of France stayed there on his tour of glass factories on the island. Later, the palace would be the residence of the bishop of Torcello and ultimately, in 1861, became what it is today: the famous Museum of Glass (Museo del Vetro).  If, in the winter of 1603-4, Neri followed the route through Venice to Antwerp suggested by his friend Emmanuel Ximenes, then a visit to this palazzo would have certainly been in order, although not yet occupied by Don Giovanni.

Early in his career, in the 1590s, Don Giovanni commanded troops against the Ottomans in Hungary and his young nephew Don Antonio was directly under his command. The two men would both set up alchemy laboratories in their respective Florentine residences; Don Antonio in the Casino di San Marco on the north side of town and Don Giovanni at his Casino del Parione (today the Palazzo Corsini al Parione) along the Arno River behind the Santa Trinita Church. Don Giovanni's was only steps away from the palazzo Bartolini, Antonio Neri's residence after his ordination, located in front of the church. Santa Trinita was a Benedictine church and the office of Vallombrosan Abbot-General Orazio Morandi. It is unknown if Neri had any association with the church, but Morandi also held a strong fascination with alchemy and wrote that times spent in Don Giovanni's laboratory were among his "most cherished memories." Much later, in 1630, Morandi gave testimony at court concerning a Simon Carlo Rondinelli, saying: 

I have known Signor Rondinelli for twenty years, from the time I was in Florence. I met him often there in the house of Alessandro de’ Neri. The said Rondinelli is very well versed in astrology.*

The timing places Morandi in the Neri family house when Antonio's younger brother, Alessandro (who had inherited the house), was twenty-one years old. It was shortly before Antonio's return from Antwerp.

While Neri was in Antwerp visiting his friend Emmanuel Ximenes, Don Antonio was leading Tuscan troops nearby, in Flanders, on the side of the Spanish against the Dutch independence movement. Nevertheless, he found time to submit his design for the Chapel of Princes in Florence, and to quarry marble for the project and have it shipped back to Tuscany. It is unknown if Neri and Don Giovanni ever shared a meal in Antwerp, but the decorated soldier/polymath did commission a series of paintings there, for the grand duke, to be hung in the new Medici villa 'La Ferdinanda' at Artemino in Prato. The interior decoration of the public spaces in this villa were being executed by artists Passignano and Poccetti, fresh from finishing their recent collaborative masterpieces; the Neri Chapel and Cestello church on Borgo Pinti, financed by Neri's late father.

* Translation by Brendan Dooley “Morandi's last prophecy and the end of Renaissance politics” (Princeton: Princeton Univ. Press, 2002), p. 22.

This post first appeared here in a slightly different form on September 25, 2013.

Neri’s Cabinet, Part 1

The many alchemical symbols used to denote crocus martis.

In addition to the usual eclectic mix of Antonio Neri related material that I bring to this space, I have decided to start a regular series of posts dedicated specifically to his chemical repertoire. 

A first encounter with the technical aspects of sixteenth and seventeenth century alchemy can be confusing, frustrating and more than a little disorienting. There is no shortage of records, letters, manuscripts and recipe books; the challenge lays in making sense of them in a way that relates to our current view of the world. It is understandable that alchemical materials and compounds had unfamiliar names; but the real difficulties arise with the realization that any given name might describe several different chemicals, and in fact, there may be several different interchangeable synonyms/symbols for any given name. As it happens, there were good reasons for this state of affairs and taking the time to understand them really opens up a window onto a strange and wonderful landscape of history. 

Antonio Neri considered himself an alchemist first and glassmaker second. Because of this "crossover," his work can help us to navigate details in both fields that might otherwise go without explanation. His writing broadly divides into two categories: one intended for generally curious readers and another intended only for those familiar with the arcane coded language of alchemy. We have examples of both styles by Neri and all within the period of about fifteen years. By comparing one group against the other, we can start to decode some of his more arcane passages and at the same time gain considerable confidence in his technical abilities. In the introduction to his famous book on glassmaking, L'Arte Vetraria, he wrote, "I have described every last detail clearly and distinctly in this work, I am sure that if you do not purposely foul up, it will be impossible to fail, after having acquired experience and practice.” Yet, in 1870, in the journal Nature, George Rodwell commented on another of his works, pronouncing him a “sensible chemist” on one hand, but on the other, noting that Neri had used “no less than thirty-five different names, and twenty-two symbols" to denote a single material, the metal mercury. 

We will start with his glass book, where his materials and methods are detailed with special consideration for those not familiar with the art. Then perhaps we can build on that and make sense of his more esoteric material.

In L'Arte Vetraria, Neri gives four different methods to make crocus martis. He explains: 

Crocus martis is nothing other that a refinement and calcination of iron. A means by which its pigment, which in glass is a deep rutty red, is opened and imparted to the glass. It not only manifests itself but makes all the other metallic colors as well, which ordinarily hide and are dead in the glass, dance in resplendent apparition. Since this is the way to make the hidden metallic colors appear, I have put down four ways to make it.

In the first method, Neri mixes iron filings with sulfur and then heats the mixture in the furnace for a long period. We can guess that the result is a mix of iron oxide and iron sulfide. These are the constituents of a popular red pigment of the same name (crocus martis) used in pottery glazes. In the second method, he takes the iron and sulfur mixture and sprinkles it with vinegar and leaves it in the sun for many days. The third method uses aqua fortis (nitric acid) for better effect. In the fourth and final method, Neri uses aqua regis, an even stronger acid. 

In all four cases the predominant result will be iron oxide and sulfide, but alas, chemistry is not that simple; there will be minor concentrations of other compounds depending on the acid used. We must consider that vinegar and the other acids in the seventeenth century were significantly different from those products today. They were made by different methods and contained a variety of impurities that would never be found in the current products. As Neri notes, each method produces different effects in the glass and therefore we must conclude that each, to some extent, differs in chemistry as well. In a number of green glass recipes he uses crocus made with vinegar, yet in chapter 71 he uses it to diminish the green in yellow lead crystal. In 124 he uses crocus made with aqua fortis for red glass. The lesson here is that the name of a material tells us only the basics, how it was made is at least as important if not more so.