Tartar Salt

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. (In foundries, a 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 the synonyms 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. Using potassium compounds can have the same effect and these 'potash' based glasses were predominantly produced in northern Europe where trees and plants rich in potassium were used in glass. 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.

Neri also used tartar to modify color in glass. The effects of tartar 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."

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.

* This post first appeared here on 5 Sept. 2014.

Vitriol of Venus

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]

To be clear, Neri is claiming a novel preparation technique for a chemical substance that was known since antiquity. I think it is quite reasonable to say that a particular personality trait led him down this path of discovery; his almost maniacal drive for purification. For a seventeenth century alchemist, it is a trait that served him well. Where other practitioners were content to use contaminated or substitute ingredients in their formulations, Neri always goes the extra mile in verifying his ingredients and using any extra filtering steps that might be warranted, no matter how time consuming. More than anything else this is what led him to such success in glass formulation, the assurance of exceptionally clear product and bright colors.

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.
* This post first appeared here on 29 Aug 2014.

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.

* This post forst appeared here on 12 September 2014.

Alberico Barbini

The island of Murano , circa 1600

attributed to Danckerts

In the early seventeenth century, Antonio Neri began preparing batches of glass for the royal family in Florence, Italy. This was a specialist vocation undertaken by alchemists, which by schooling, Neri was. His job as “conciatore” involved procuring the ingredients, preparing, mixing and melting them and working with the glass artisans, adjusting the consistency and colors for the work being done. It was a position that carried great prestige, and Neri’s book on glassmaking [1] would cement his name in history. 

Shortly before Neri was born, in 1576, the grand duke of Tuscany, Cosimo I de’ Medici, brokered a special deal with the doge of Venice to have master glass artisans come to Florence and teach their secrets. These men were from the island of Murano; the most famous center of glassmaking anywhere. There is only scant evidence that Neri himself traveled to Venice and perhaps only once, but there is no doubt that he benefited greatly from the knowledge of Muranese workers in Florence, Pisa and Antwerp during his lifetime. 

Over the intervening centuries, the title of the glass batcher changed, but the tradition and prestige of glass formulation continued well into the middle of the twentieth century. In fact, even today, among the small glass manufacturers that compose the studio glass movement, the glass batcher is considered to be something of a modern alchemist; keeper of the arcane knowledge of  the chemicals and amounts necessary to produce special colors and adjust properties of the glass.

Now, fast forward four centuries from Neri's Italy; in the early 1920s, a Milanese lawyer named Paolo Venini partnered with a Venetian-born antique dealer friend, Giacomo Cappellin, to start a new glass factory on Murano. [2] Even as recently as this, the glass batcher still held a respected position both within the factory and the community. Through several incarnations over the next half century Venini grew a world-wide reputation for innovative designs, of which color played an important part. They are specifically associated with the fazzoletto (handkerchief) style vase and the incalmo technique of fusing two or more colors of glass seamlessly in a single furnace-blown piece. 

In 1925, Cappellin split from Venini and took many of the craftsmen with him, in 1933 the new business was acquired by Pauly & C. Again, chemical knowledge and the artistry of reproducing ancient colors made a worldwide reputation. [3] As ownerships changed hands like cards in a game of poker, artisans shuffled between factories. It is easy to lose track of the individual glassworker. Even for a period so recent, many records exist only in the heads of the family members still living on the island. 

In 1956 the Stazione Sperimentale del Vetro (Experimental Station for Glass) was started on Murano with the mandate to preserve and promote the technical aspects of Italy’s glassmaking heritage. [4] The new institution was regarded by some traditionalists with great suspicion, but as we will see, others embraced the resource.

I recently sat down with renowned glass artist Emilio Santini, who today carries on a six-centuries-old family tradition in glasswork. [5] Emilio had recently called home, to Murano, which led to his father’s recollection of an uncle, who worked making color for Venini and Pauly. Here Emilio recounts the conversation:

Alberico Barbini was the uncle of my father, Mario Santini and the man in charge of making the glass batch “partie” (Venetian) “partite” (Italian). He was the brother of my grandmother, Delfina Barbini. He was not the only one [in my family] who worked for Venini in the early days but the most respected. At Venini he worked formulating glass after another great batch maker, [Albino] Carrara. 

In the early to mid [twentieth] century the batch maker still held an important position in the factory, not like now, you know, and he kept his formulations quite secret, although this relative of mine, Alberico, was smart enough to use the most modern technology available at that time. 

He was different from other batch makers in that when the Stazione Sperimentale del Vetro opened, he made extensive use of it in reproducing colors. At that time, and even now to an extent, the institution was not seen as good for traditional Murano glassmaking. 

He later moved on to Pauly where he was in charge of reproducing the glass colors that were in use in the seventeenth, eighteenth and nineteenth centuries. First, he assisted in remaking broken or missing pieces in private collections, then later in making reproduction antique stemware at Pauly that was impossible to distinguish from the originals. 

You must realize that all this does not come from documents but from the memory, still very sharp and lucid, of my father.

Addendum: On 7 August 2016, at the age of 96, Mario Santini died, surrounded by his family at his home on Murano.


[1] L’Arte Vetraria, (Neri 1612).
[2] Paolo Venini http://en.wikipedia.org/wiki/Paolo_Venini also see https://www.facebook.com/pages/Venini/198475426829887
[3] Pauly & C. Compagnia Venezia Murano http://en.wikipedia.org/wiki/Pauly_%26_C._%E2%80%93_Compagnia_Venezia_Murano
[4] Stazione Sperimentale del Vetro  http://www.spevetro.it/indexENG.htm
[5] Emilio Santini http://www.cmog.org/bio/emilio-santini
* This post first appeared here on 25 Feb 2015.

Filippo Sassetti

Goa, India 1509

Later distinguished as a renowned glassmaker and alchemist, Antonio Neri was born into a patrician household. In the Florentine baptism records, his entry was made on a Thursday, the first of March, 1576. He was born the previous evening, to Dianora Parenti and Neri Neri. His godmother is listed in the document as Ginevra Sassetti. Not a great amount is known about her; she was from a prominent family, at the time in her late fifties. However, there are indications that other members of her family interacted with the Neri's. Her nephew Filippo mentions Antonio's father favorably several times in letters, providing a fascinating glimpse into the way disease was diagnosed and treated.

When Antonio was born, his father Neri Neri was in his early thirties, and already a highly regarded physician. Baccio Valori was director of the famed Laurentian Library in Florence and steward of the Medici's simples (medicinal herbs) garden. He was friend to Neri Neri and godfather to Antonio's oldest sister Lessandra. Between 1583 and 1588, Valori received letters from a mutual friend, Filippo Sassetti, who was living in Goa and Cochin – trading settlements in India. Filippo was a native Florentine; he attended university in Pisa with Valori and they became lifelong friends. After Sassetti's father was forced to sell the family home to pay off a debt. Filippo moved to Lisbon and became a spice trader. Not suited for a desk job, he soon set sail seeking adventure in the orient. 

In a 1586 letter to his old friend Valori, Sassetti discusses an Indian remedy against the plague, with a substance called bezoar. The bezoar stone is a mass that develops and becomes trapped in the digestive systems of certain animals. It often resembles a smooth rock. Some thought ground bezoar to be a universal antidote to any poison. Sassetti was puzzled about how the grindings of bezoar could work to cure the plague. Its Aristotelian elemental properties would not be a match for correcting the imbalance of humors in the body. "This is a principle," he explains, taught to him by Neri Neri. "I have thought about it and I can not understand how it works, because the plague is of the same corruption and this is a lack of heat inherent in the humidity. And the stones, if I recall correctly, they have a cold and dry complexion, hence may not precede the restoration of heat. Messer Neri one time did me the favor of telling me." 

In another letter to Baccio Valori, Sassetti notes that he has collected rare varieties of cinnamon in his travels along the Malibar coast in India. His intention was to rediscover the species thought to be a powerful cure of disease by the ancients. He planned to send a parcel of seeds of these and other medicinal plants. "If it pleases God, in the coming year, I will send this to you, so that you may see it all, together with our Messer Neri Neri, who graces my memories." Later he writes that he is sending Baccio the discourse on cinnamon, which he has compiled, along with some plants. These, it later turned out, were water damaged in the journey. He had hoped for some help from Neri Neri on the question of whether the cinnamon he collected from the island of Zeilan [Ceylon], is the same thing as the curative cinnamon of Mantua described by the ancients. Valori was an authority on these matters in his own right. As librarian for the Medici's imposing collection of books and manuscripts, he had vast academic access. As keeper of the simples garden, he had first hand experience in horticulture and its derivative medicinal cures. 

The principles of "humorism" were passed down from celebrated physicians of the ancient world, like Galen, Hippocrates and Dioscorides. It was thought that the cure of disease was dependent on the restoration of balance between four substances in the body: blood, phlegm, black bile and yellow bile. In turn, each of these was associated with one of the Aristotelian elements: air, water, earth and fire respectively. Each was further associated with specific symptoms and characteristic traits of the patient, even their psychological outlook and physical complexion. This system formed the foundation of Western medicine and was taught and practiced well into the nineteenth century. Although, within Antonio Neri's lifetime newer experimentally based methods did start to take hold. A decade after his father's death, in a 1609 letter, Antonio boasts about his success in curing disease in Antwerp using the methods of the medical upstart Paracelsus. It is unlikely that his father would have approved.

*This post first appeared here 13 August 2014.

Alchemy School

Frontispiece woodcut from

 De Chemia Senioris, by Zadith ben Hamuel, 1566

A common notion holds that alchemists were eccentrics, lone practitioners working in dingy basements, cut off from the rest of the world. This was a myth already well established in glassmaker Antonio Neri's time, but far from the whole truth. In the early seventeenth century, alchemy was practiced in medicine and pharmacy, in precious metals refining and even in the preparation of artists' supplies. The glassmaker was in good company. Where Antonio Neri received his training is unknown, but there are intriguing clues. 

We turn first to Antonio's own father, Neri Neri, the royal physician to the Medici family. According to historian Giulio Negri, he received his medical degree at the prestigious Studio Fiorentino, the forerunner of today's University of Florence. At the time, it had already been in operation for two centuries, having been granted a charter in 1348 by Holy Roman Emperor Charles IV. The charter was a response to a personal appeal by Archbishop Piero Corsini. Antonio Neri's own distant relative, Ser Giovanni Neri, later became Corsini's secretary, so a family legacy of attendance is not out of the question. That our priest might attend his father's alma mater is pure speculation, but it seems foolish to doubt that he started his alchemy education at his father's knee, in his own home.

The manuscript entitled Treasure of the World that Antonio devoted to "all of alchemy" was completed in 1600, but started two years earlier. On a page near the beginning, dated 1598, the twenty-two year-old clearly identifies himself as a "priest." Church rules forbade anyone from becoming a novice before the age of sixteen, which for Neri would have been in the spring of 1592. Full ordination as a Catholic priest typically took six years, meaning in 1598 Neri only recently underwent the 'laying on of hands' ceremony by the archbishop, confirming his title. The inescapable conclusion is that Neri learned his craft while in seminary and the Church sponsored his education. 

The identity of Neri’s order is a mystery, but the few scattered pieces of the puzzle that we do have allow for some interesting speculation. The list of candidates having some connection to the priest and the means to support, if not supply an education is not long. The five names that stand out are the Dominicans, the Carmelites, the Augustinians, the Knights of Malta and the Benedictines. The Dominicans were noted for their scholarship and ran two apothecaries in Florence. The Carmelites are named in the deposition notes taken by Agnolo della Casa, which identify Neri’s confessor as such. The Augustinians counted a Francesco Neri as abbot of their San Clemente monastery who worked for Don Antonio de’ Medici at the Casino in 1619. Antonio’s aunt, Faustina, apparently entered an Augustinian convent after the death of her husband.  Also, though Neri’s confessor was a Carmelite, he also served as the parish priest of an abbey run by the Canons Regular of the Lateran—an independent Augustinian congregation. The Knights of Malta ran two churches in Florence and Neri can be connected to both.  The knights followed the rule of Augustine and enjoyed a close relationship with the Augustinians. The order traces its roots to the crusades  and has various associations with alchemy such as George Ripley. Their main presence was on Malta, though in 1565 they suffered a devastating defeat there to the Ottomans. Neri was not a knight, but he could have occupied a place in their clergy. In Florence, any resources for schooling in alchemy by the knights would have been overseen by its most prominent local official; that official was Neri’s benefactor Don Antonio de’ Medici, Grand Prior of Pisa. The Benedictines were also associated with Neri’s family and had the means to provide him with an education in alchemy. He was born in the parish district of Benedictine church, San Pier Maggiore. His father was buried in the Cistercian (reformed Benedictine) church of Cestello. His sister  committed to a Benedictine order (the Camaldolese). After his ordination, in 1601, Priest Antonio Neri lived across the street from the Vallombrosan (Benedictine) mother church, Santa Trinita.

In any case, as royal physician Neri's father was an esteemed member of the court and Antonio would have enjoyed rare access to its inner sanctum. The grand duke's own laboratory at the Galleria dei Lavori certainly would have been a familiar haunt for our alchemist-priest.

This post first appeared here in a shorter form on 2 October, 2013.

Sal Ammoniac

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.

Sal Ammoniac,
natural formation

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 each of 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.
* This post first appeared here on 22 August 2014.