Chalcedony Glass Reprise

17th century ribbed bottle,
Brescia, Italy.

This item was first posted last year on 27 September, just as the foliage in New England was beginning to turn, trees suddenly becoming a riot of bright color. Now, on the cusp of April, in anticipation of spring flowers, it seems appropriate to reprise a celebration of Antonio Neri’s most colorful creation; chalcedony glass. Through his clever technique, Neri was able to throw every color he knew into one glass pot and come up with, not mud, but the opposite—a swirly rainbow glass that defies verbal description. Somehow, he achieves a balance that blends a full range of colors in a way that seems natural and harmonious. While many glass creations survive from the seventeenth century, none is directly attributable to Neri’s glass formulation. But, in my opinion, this piece from Brescia comes close to our alchemist’s own description. Here is the original post:

One of the more exotic varieties of glass described in Antonio Neri’s book, L'Arte Vetraria, is Chalcedony. It is also one of the most labor intensive, exacting recipes and consequently a 'high stakes' risk for losing the entire batch after considerable work. Nevertheless, Neri assures us that the end result is worth the trouble; he describes it as:

Adorned with so many graceful and beautiful areas of undulations and enhanced with the play of diverse, lively, flaming colors.”

Chalcedony is a natural mineral, known and admired since antiquity. It occurs in a variety of translucent colors and is most valued when swirls of many different colors are present together in the same piece. In the Roman Empire, it was prized for seals and signet rings; its fine-grained structure allowed intricate carving without fractures. Like many other rare natural materials, it was sometimes supposed to have mystical healing properties. Chemically, chalcedony is identical with quartz or silica, the main ingredient of glass. However, unlike the fabricated substance, the mineral is formed of networks of microscopic interlocking crystals that are responsible for its favorable properties. Small amounts of impurities between the crystal grains cause the swirls of color.

Neri presents three variations of chalcedony glass that span his career as a glassmaker. The first he describes as "the way that I made chalcedony in the year 1601, in Florence at the Casino, in the glass furnace there." The last was made "in the Flemish city of Antwerp, in January of the year 1611" where he presented "His Excellency, the Prince of Orange with two vessels of chalcedony [glass] which delighted him greatly."

His friend Emmanuel Ximenes was anxious to learn the secrets of this glass as early as July of 1603, when he wrote: 

The details of the last chalcedony [glass], which you promised to send to me, did not come in the letter: but I had to recant by the time I got to the end […] I see and understand, that Your Lordship is not at leisure, but in fact busy at work in the service of Christianity... 

Neri advises that in order to bring out the swirls of color, the glassblower must 'strike' (cool and reheat the piece) several time.

Unfortunately, it is not advisable to attempt replication of Neri's chalcedony glass today, as it contained a cocktail of toxic ingredients. While these are relatively harmless once locked inside the glass, in preparation and especially in the hot molten glass melt, vapors of mercury and arsenic can be deadly. At the very least, exposure can be expected to cause permanent neurological and liver damage. (The term "mad as a hatter" comes from the unfortunate side effects of inhaled mercury vapors in the formation of felt hats.) In addition, Neri's extensive uses of strong acid reactions in these preparations make sudden eruptions and severe chemical burns a very real danger.

Pure Technique

Antonio Neri, MS Ferguson 67, f. 40r
Filtering apparatus (1598-1600)

It is plain from the contents of Antonio Neri's book about glassmaking, that he was very careful about the purity of his ingredients. In fact, is not too strong to say he was obsessive—and for an alchemist, this turns out to be a very useful trait. It means that he was paying close attention to the materials he used. That alone, went a long way to ensuring consistent results in his preparations. Exactly how filtering, purification and the physical processing of materials were done in the early seventeenth century provides some fascinating insight into the technology of the time. It also demonstrates that his results were as least as good as what can be accomplished today with modern equipment, albeit at a considerably slower pace. Many of these techniques were based on the clever use of water.

Enamels are a type of glass, which is used in very thin layers over metal or sometimes on glass items as a decoration. They are "painted" on an article and then fired over a flame or in a kiln where they fuse and become permanent. When applied by a skilled artist, enamels can be made to form images like a fine painting, but very durable. In the recipes for his enamels, Neri requires that tin and lead oxides be blended together, but he wants them to take the form of extremely fine powder, much finer than what could be produced by a sieve. The way he achieves this is to put the powders in water. They are not soluble, but what happens is the larger particles settle to the bottom while the finest ones remain suspended in the water, giving it a milky appearance. After a prescribed interval, he carefully pours off (decants) the liquid into another vessel, leaving the heavier sediment behind. He then evaporates the liquid over a low fire, effectively having separated out the very finest components of the powder. 

He used a variation of this method to purify materials that are soluble, like the glass salt that he made from plants. Lightly charred plants, ferns for example, were boiled in water. In this case, any contaminants that did not dissolve settled out and the remaining liquid was evaporated, leaving purified product. In other recipes, he dissolves metals in acid to achieve the same effect; many impurities did not dissolve and were left behind. It is a very basic method, yet extremely effective. 

It was also a part of his chemical philosophy. In the introduction to the glass book, Neri makes reference to work he did in the 'spagyric' arts. In his unpublished writings, he elaborates on this further. Paracelsus coined the word ‘spagyric’ in his book Liber Paragranum, where he argues medicine should be based solely on the physical laws of nature. The word derives from two Greek terms: 'spao' meaning to separate, and 'ageiro' meaning to combine. The underlying philosophy recurs throughout the history of alchemy. To enhance the special properties of a material, break it down, to its separate constituents, then purify each and recombine them for a more potent product. Herein lay the bones of Neri's empirical methodology. It has a frame built on the processes of reduction, purification and recombination. Fleshed out with skilful hands, these methods show up consistently throughout his glass recipes. He successfully utilizes the technique with both plant and mineral ingredients, in the preparation of basic materials and pigments, and throughout his medicinal work.

The Béguines of Mechelen

A Béguine of Antwerp,
from Pierre Hélyot,
L'Histoire des ordres monastiques… 1719 (v.8)

Five years into his stay in Antwerp, on 21 February 1608, Antonio Neri posted a letter to a friend in Florence. The letter was addressed to the house of Zanobi Bartolini—likely the son of Neri’s late former landlord Alamano, also the nephew of Emmanuel Ximenes, Neri’s host in Antwerp. The letter provides strong evidence that however much time Neri devoted to making glass, he also devoted considerable attention to his interest in medicine. 

In this letter, the priest describes his success with medicinal cures. He also references experiments he carried out in Brussels and at the Hospital of Malines, in Mechelen. In particular, he praised Paracelsus’ recipe for ‘theriac of mummy,’ and its superiority to Galen’s ‘theriac magna’. Theriac was an ancient medicinal remedy, often taking the form of a thick honey based syrup. It often contained numerous herbal ingredients. It was thought to be a cure for any poison and used as a way to stave off the plague. Mummy or mumia was a compound composed of just what one might think: the ground up flesh of ancient Egyptian bodies. 

The Hospital of Malines was an ancient one, started in the thirteenth century by a society of lay Catholic women called Béguines. In their 1907 book A History of Nursing, Dock and Nutting note:

Through the whole time of the active career of the Béguines, nursing remained an important branch of their work. One of their most beautiful settlements was at Malines, where there were over 1500 Sisters, not including their dependents. This would appear to have been a nursing center of importance, for Helyot says that the nursing in many hospitals was provided for by orders arising from the Béguines of Malines. […] The building were surrounded with extensive gardens and trees, and had an ample water supply. ‘The sick were nursed there’ he [Helyot] wrote ‘with all the skill, refinement and sweetness that might be expected from the appearance of the place. *

The Béguines were not nuns. They did live in communal housing, and did devote themselves to a pious lifestyle, but without formal cloister, without renouncing their possessions, and taking only a temporary vow of chastity, able to leave at any time, for instance to get married. They formed corporations throughout the Low Lands and into France and Germany that were self sustaining and largely independent of local control. These were huge organizations of women, working for themselves, under their own roofs and by their own rules. They produced crafts and textiles, they schooled nurses and they ran hospitals. Because they existed on the fringes of Church control, they were downplayed or even resented within the hierarchy. One result is that their achievements have largely been forgotten by history. When Mathias Hovius, the Archbishop of Mechelen, toured the facilities in 1601 he took the petty action of requiring Béguines who chose to keep lap-dogs to pay a fine to the Church. In 1630, Bishop Malderus of Antwerp defended the women in an extraordinary letter. He wrote,

The Order of the Béguines is truly not a religious order, but a pious society, and compared with the former complete consecration is as a preparatory school in which the piously inclined women of Belgium live after a pattern highly characteristic of the temper and mind and the character of the people. For this people is jealous of its liberty and will be led rather than driven. Although it is beyond a doubt more meritorious to devote one’s self to the service of heaven by vows of perpetual chastity, obedience, and poverty, and though there are many pious women in Belgium who are so disposed, yet most of them shrink from this irrevocable vow. They prefer to remain inviolably chaste rather than to promise to be so; they are willing to obey, but without formally binding themselves to obedience; to rather use their poverty in reasonable outlays for the poor than to give it at once up for good to all; rather voluntarily renounce daily the world than immure themselves once and forever.*

At the beginning of the seventeenth century, the hospital was used to treat wounded Spanish and Italian soldiers fighting in the war against the Dutch. By 1607, just before Antonio Neri wrote his letter, the staff at the hospital numbered fifty, “including seven doctors, eight surgeons, and three surgeon’s mates.”**

As the son of a grand duke’s personal physician and grandson of a surgeon, there can be little doubt that Neri had ample familiarity with medical procedure. It seems likely, given the circumstances, that in Mechelen he was lending his expertise to ease the ravages of war, helping to heal wounded soldiers.

* Lavinia L. Dock, Mary Adelaide Nutting, A History of Nursing (Putnam, 1907) v. 1, pp. 268, 269.

** Geoffrey Parker, The Army of Flanders and the Spanish Road, 1567-1659 (Cambridge Univ. Press, 2004), p.141.

Sara Vincx

Still life with façon de Venise wineglass,
Alexander Adriaenssen (1587-1661)
Antwerp. 

In honor of Women’s History Month, I am reprising this post, first published on 4 October 2013. In the 1590s, after the death of her husband, Sara Vincx ran a successful glassmaking business in the city of Antwerp. She is the first documented female owner of a glass furnace anywhere. 

The Dutch Eighty Years' War for independence from Spain was heating up in Flanders; towns were being pillaged and burned to the ground throughout the Low Countries. Even so, Vincx ably managed a crew of Venetian expatriates and successfully defended her glass patents in court. Later, she remarried to Filippo Gridolfi. The two went on to open a sales shop on the Meir and welcomed glassmaker Antonio Neri to work at their facility. Neri was living in the city on an extended seven year long visit to his friend and fellow alchemical experimenter Emmanuel Ximenes. Here is the original post:

The seven years that Antonio Neri spent in Antwerp were arguably the most formative for his knowledge of glassmaking. While his first exposure to the art was in Italy, a large portion of the skills and recipes exhibited in his book trace to his activities in the Low Countries. Neri writes "This will make a beautiful aquamarine so nice and marvelous, that you will be astonished, as I have done many times in Flanders in the city of Antwerp to the marvel of all those that saw it." On tinting rock crystal: "In Antwerp, I made quite a bit of this, some ranged in tint from an opal color that looked very beautiful, to a girasol, similarly nice." On equipment: "In Antwerp, I built a furnace that held twenty glass-pots of various colors and when fired for twenty-four hours everything fused and purified." He also speaks of chalcedony glass, paste gems  and ultramarine paint all crafted in Antwerp. 

During Neri's visit, the premier glass factory in Antwerp was operated by Filippo Gridolfi and Neri was on good terms with him. Gridolfi and his wife possessed an exclusive license to produce cristallo glass in the Venetian style (façon de Venice). The license, or patent as it was called, passed down from previous owners, was quite a valuable part of the operation. Employed in his shop was a steady stream of craftsmen from Murano. They produced the finest glassware for the elite class of Antwerp and surrounding areas. Because these craftsmen were bringing the secret techniques with them, they worked outside of the guild system, through special arrangements with the local authorities.    

Before Gridolfi, the furnace was run, and run with success, by his then soon-to-be wife, Sara Vincx (or Vincks). She was the widow of the former owner, Ambrogio de Mongarda. Gridolfi had previously worked in the shop under Mongarda, who had been in the business for twenty years. Vincx was pressed into service by unhappy circumstances. In 1594, Ambrogio returned alone to Venice to recuperate from gout, but by the following year he was dead, leaving Sara to both run the glass shop and care for at least eight young children. Sara Vincx carries a distinction as the first documented female owner of a glass furnace anywhere. She took an active role in the business as attested by lawsuits she filed, and won, against rival shops that violated her patent. She also expanded the furnace and hired two new artisans to increase production.

Despite the war and the blockade of the Scheldt River in Antwerp, the glass furnace there thrived and reached its zenith under Vincx and Gridolfi. Soon after their marriage, seventeen employees were counted working at the shop. They established their own retail presence on the Meir, selling high-end cristallo to the elite within steps of the Ximenes palace and the d'Evora jewelers. Their glass operation enjoyed top-rung status, and no doubt, Antonio Neri's involvement must have bolstered the reputation of the firm even further.

Red Like Blood

Dionysos in a ship, sailing among dolphins,
(iron oxide red and black glazes)
bowl discovered at Vulci, Viterbo.
Artist: Exekias (c. 530 BCE)

The use of iron oxide, or "rust" as it is commonly known, as a pigment is ancient. In fact, it is one of the oldest colorants in human history. It is found in the earliest cave paintings and in shells and cups as a residue of body paint, used by peoples who lived tens of thousands of years ago. It is found as solid minerals and also as iron rich clay, occurring in many variations, taking the colors of red, yellow, orange, green, grey and black. In the Iron Age, workers learned to produce some of these oxides directly, as byproducts of the forging process. Of course, until relatively recently it was not known that these were "oxides," only that they were colorant materials associated with iron.

The three most common forms all occur as dark grey or black mineral, but each possesses distinctive properties. "Wüstite" (FeO) is often found in meteorites, "hematite" (Fe2O3) forms a red powder when scraped, appearing to bleed, hence the name and finally, "magnetite" (Fe3O4), which is magnetic. These oxides can occur chemically bound with water, as mixtures and in different crystal structures, forming a family of compounds. The iconic red and black pottery of the Greeks was colored with iron oxide; the red (or orange) was hematite and the black was magnetite. Chinese "celadon" glaze is a green-blue that resembles jade; it is derived from an iron oxide (FeO), which does occur in nature as wüstite, but in this case forms chemically in the potters kiln.

Iron, as a pigment in glass, can be responsible for several different colors, notably green and according to Antonio Neri also red. Today red from iron is common in pottery glazes, but not in glass. In his 1612 book, L’Arte Vetraria, Neri does not offer a specific recipe for iron red, but in chapter seventeen he teases us with this passage:

This second way to make crocus martis although very easy should not be disparaged, but rather highly regarded, since crocus produced this way causes the glass to appear a rather bright blood red.

Crocus martis was the alchemical name for the red oxide of iron (Fe2O3). Neri’s iron red may depend on making a suspension of the finely ground powder in the glass. It is questionable how stable it would be in the furnace; eventually the powder would dissolve in the glass turning it transparent green. But as mentioned above, this oxide is successfully used in red pottery glazes. For glassmakers in the seventeenth century, not iron but copper was the most common pigment for producing red, yet here he presents us with an intriguing alternative. However basic crocus martis might be, Neri holds it in great esteem, using his alchemical reasoning to explain that it has the power to expose colors which are usually hidden in the glass. He continues:

The way to make it is like this: Obtain some iron filings, although steel is better if you are able to get it. Mix it well in a terracotta oven-pan with strong vinegar, which is sprinkled only until it is moist throughout. Now spread it out in the pans, and put it in the sun to bake. When the sun is clouded, leave it in the open air to dry. Now turn it into powder. If it leaves any hard lumps, sprinkle and moisten them with new vinegar, leave it to dry again and then pulverize, as above. This work should be repeated eight times, then grind and sift it through a fine sieve, which will make a very fine powder the color of brick dust. Store this in well sealed vessels for use in the coloring of glass.

From this prescription, we can guess that he was producing a mixture of hematite and iron acetate. The fact that iron does not appear as a red pigment in other glassmaking references makes his statement something of a mystery, perhaps to be solved by engaging our glassmaker's own favorite activity: experimentation. 

Cross Pollination

The art of stonework,
from MS Ferguson 67, f. 7r, (1598-1600)
Antonio Neri.

Throughout the Renaissance, Florence Italy was famous for its artistic output. Names like Donatello, Michelangelo and Giambologna graced the tongues of patrons across Europe. But the secret to the city’s fantastic creativity did not rest solely on individual superstars. The ruling Medici family had found a way to harness the talents of their subjects and use the fruits of their artistic labor as a powerful political tool. 

Starting in the late sixteenth century, at Christmas time, boatloads of fine glass, ceramics, jewelry, stonework, and art sailed from Tuscan ports as gifts to the royal families of Europe, who accepted the offerings gratefully. The Vatican, the Holy Roman Empire, Spain and France all had ambitions, at one time or another, to make Florence their own. These gifts, time and again, helped to smooth ruffled diplomatic feathers, reassure old allies and play the mighty kingdoms against each other, keeping Florence relatively unmolested. What the Florentines lacked in military might, they made up for in sheer artistic creativity.

At home, this strategy depended on the constant attraction of new talent and deep support of all the arts. At the Uffizi palace, Grand Duke Ferdinando set up  a kind of innovation center, called the Galleria dei Lavori (Gallery of the Works), where new techniques were pioneered. His father, Grand Duke Cosimo had already built a glass furnace there, staffed by Venetian masters imported from Murano. In adjacent areas, stone cutters worked minerals collected from around the world into fabulous inlaid table tops and floors in an art called pietre dure. Goldsmiths worked with gem cutters to create exquisite jewelry. Designers and illustrators brought the natural world into new creations that integrated these arts together for the first time. 

This was the world in which a young Antonio Neri grew up; the son of a famous physician, he matured into an alchemist with a profound respect for the healing arts, but also into a glassmaker—a conciatore—to the Medici prince Don Antonio. A key to Florence's creative output was the Medici innovation of housing artists of different disciplines under one roof. A cross pollination of ideas took place that spurred new ideas in individual arts, but also gave birth to the creation of objects which combined the talents of several different arts. Fine wooden furniture graced with inlaid stone, glass used to imitate exotic minerals and rock crystal, fanciful goblets and pitchers that integrated metalwork, glass, shell and other exotic materials.

This culture of cross pollination can be seen throughout Antonio Neri's work, in the variety of different glass recipes and also in his knowledge of the ways his glass was to be used. In his 1612 book, L'Arte Vetraria, he says:

Because in order to make vessels and drinking glasses where the glass is thin, you must really load it with a lot of color, but for making large cane for beads not so great a charge of color is necessary. For making thin cane for small beads, you must charge it well with color. In working the glass, you must apportion it with more or less color according to the purpose it must serve.

For lead crystal artisans, he has this advice:

To work lead glass into various drinking glasses or other vessels, or even to draw cane for beadmaking, it is necessary to raise the punty [out of the melt], and to make a gather of glass by turning. Take it out, let it cool somewhat and then work it on a well-cleaned marble [marver]. The marble should be somewhat cool, and well bathed with water before use.

This practice will ensure that the paste of the lead glass does not pull up any of the marble. The glass will always gall marble not bathed in water. Some chips will incorporate into the work, giving it an ugly look. Therefore, frequently flush the marble with fresh water for as long as you are working the glass. Otherwise, all its grace and beauty will be lost.

Unlike his famous brethren Donatello, Michelangelo and his neighbor Giambologna, Antonio Neri was not a superstar and as an alchemist he did not work alone; he was part of a team. He ably represents the small army of workers who supported the Medici creative machine that spread fine craftwork throughout Europe. 

Women in Early Modern Alchemy

Antonio Neri, 1598-1600,
MS Ferguson 67, f. 25r.

In honor of Women's History Month, is a post that was first published here on 30 October 2013. There is little doubt that women have participated in the practice of alchemy since its beginnings. Maria Prophetissima, also known as Mary the Jewess, is perhaps the best known female alchemist. None of her writings are known to have survived, but she is thought to have lived around the third century. Legend tells that the "bain-marie" (double boiler) is named after her.  

In the seventeenth century, One of Antonio Neri’s manuscripts depicts three women running chemical equipment. It is likely that these were nuns, trained in the same Church sponsored educational system that produced Neri. Convents were often expected to be self sufficient, and many ran their own pharmacies. Antonio Neri had sisters as well as brothers, and at least one sister entered a convent located on the north side of Florence, near the laboratory where he practiced alchemy and made glass. The fact that specific names have not been associated with Neri’s  three female co-workers should not deter us from celebrating their contribution to the birth of early modern science.

Within a year of his ordination in the Catholic Church, Antonio Neri began an ambitious treatise, illustrated in his own hand, devoted to "all of alchemy." Six of the illustrations in this manuscript, completed in 1600, show women tending equipment. What is remarkable is that, in the historical record, female participation in alchemy is otherwise extremely rare. 

Two pictures show female alchemists at work. In both cases, the 

Antonio Neri, 1598-1600, 
MS Ferguson 67, f. 35r.

technician stands behind a dedicated piece of apparatus, facing forward, giving the impression of propriety in an arranged portrait. The first drawing depicts a furnace and vessels used to make liquid mercury from its ore. The other shows a different type of furnace with a 'tower,' used as an efficient way to cook ceruse (white lead oxide). These images are part of a larger set of two dozen similar drawings that each illustrate the equipment used to prepare a specific product, many include a furnace and glassware. Nine of these show a single individual, (or in one case two men) tending the equipment. 

Three other illustrations in the manuscript are notable for their

Antonio Neri, 1598-1600, 
MS Ferguson 67, f. 37r.

engagement of women. These pictures show details of kitchen and nursing work; what might be termed more traditional female roles in the sixteenth century. Two of these illustrations are devoted to the respective arts of preparing plants and animals. They show women working alongside men performing various tasks. A third illustration shows medicinal fogging tents tended by a woman. Inside one tent, a male patient sits on a bench, exposed and breathing fumes pumped in by a large vessel perched over a fire.

These images also present clues to the circumstances of Antonio Neri's work environment. We may well be looking at operations inside the Casino di San Marco soon after prince Don Antonio de' Medici's occupation of the facility. The presence of women among Neri’s colleagues indicates a social setting with a camaraderie not displayed in other alchemical works of the period.