Dear Readers,

As you may have seen elsewhere, in mid February my wife and I suffered the loss of our home in a fire, in the hills of central Massachusetts. The good news is that we got out safely and had no animals in our care at the time. The fire crews were able to contain the fire from spreading, in what turned into a 3-alarm, 5-hour-long ordeal in subzero temperatures; they did amazing work, and no one was injured. The bad news is that all of my physical historical materials and research of 30 years have gone up in smoke. As a result I have decided to suspend this blog for the time being. It will remain online as a resource for those interested in the history of glass and glassmaking in the seventeenth century and beyond. I do intend to resume writing when I can, but for now my time and energy are required in getting us back on our feet.

Friends are providing temporary shelter for us nearby and our intention is to rebuild as soon as possible. To those who have reached out with a steady hand, to those who have opened their wallets, and offered advice in our time of need, we thank you from the bottom of our hearts. In what are already difficult times for all of us, you have made a huge difference in our lives.

Paul Engle
6 March, 2021

Friday, June 30, 2017

Turquoise Glass

Turquoise glass stamp
of calif Mustadi  c.1170.
It is estimated that turquoise is among the earliest gems ever mined. With colors that vary from pastel green to a bright sky blue, it has adorned Egyptian sarcophaguses of 5000 years ago, 3000-year-old Chinese art, Aztec death masks and the domes of Persian palaces. 

When traders brought it to Europe from the Mideast, it became known as "turks" or "turquoise" after the old French for "Turkish." While it has never been mined in Turkey, the most highly valued Persian stones were imported there and used extensively for trade. Polished pieces were famously mounted on Turkish equestrian saddles, in the belief that the material conferred sure-footedness and protection from injury during a fall.

As one of the first gems to be collected and traded, turquoise was also one of the first to be imitated. Egyptian faience blue is an early forerunner of glass. It is more porous than glass, but it contains all the same ingredients and could be cast into forms that look just like solid turquoise. In the seventeenth century, the genuine mineral and its imitation continued to hold importance. In Antonio Neri's book L'Arte Vetraria, the subject is mentioned several times; he offers one recipe to restore faded stones by soaking them in almond oil. For turquoise colored enamels he presents two different shades. On the subject of glass, he notes that "Sky Blue, or more properly turquoise, is a principal color in the art of glassmaking" and "I have made this color often, because it is very necessary in beadmaking and is the most esteemed and prized color in the art."

To make his imitation turquoise glass, Neri starts with a batch of high quality transparent aquamarine blue, to which he adds a specially prepared variety of common salt. "Add it little by little, until the aquamarine color loses its transparency and diaphany becoming opaque."

Take the sea salt known as black salt or rather coarse salt, since the ordinary white salt that they make in Volterra would not be good. Put this salt in a frit kiln or oven to calcine, in order to release all moisture and turn white. Next, grind it well into a fine white powder. This salt now calcined should be stored for the use of making sky blue or rather turquoise color as described below.

Sea salt is mostly composed of sodium chloride, which is like table salt that we use for food. However, it can include significant additional minerals, as implied by Neri’s description of it as "black salt." Additional elements can include sulfur, potassium, manganese and more. Regrettably, he leaves us with no further clues to its identity, nor does he explain why the recipe would not work as well with the salt available from Volterra. He goes on to advise that the mix should be used quickly, because if left to sit in the furnace, the glass would start to revert to an ugly transparent color. The remedy for this is to add more salt. He finishes with some practical advice for glassmakers about adding salt to molten glass:

The furnace conciatore should take careful note here, when you add this salt, if it is not well calcined it always bursts. Therefore, you should be cautious and shield your eyes and vision, because there is a danger you could be hurt. Add the doses of salt little by little putting in a bit at a time pausing from one time to the next until you see the desired color. With this, I do not rely on either dose or weight, but only on my eyes. When I see that the glass reaches the desired level of color, I stop adding salt. This all comes with experience. 

* This post first appeared her in a slightly shorter form on 9 April, 2014.

Wednesday, June 28, 2017

Glass Headhunters

Berkshire Glass Works cane from 1878 –
Charles Flint collectionThese were novelty items 
made by glassworkers after hours.
(hollow, filled with the fine quality sand of the area)
Since early days, the technical aspects of making and manipulating hot glass have remained a closed and secretive business. Down through the ages, those with inside knowledge of this art have been highly valued and highly sought after. Even with the circulation of technical manuscripts and the ultimate publication of the technology in Antonio Neri’s 1612 book L’Arte Vetraria. The beating heart of the craft remained at the furnace among those with hands-on experience. [1] These artisans could and often did make the difference between success and failure in a business that was notorious for sending substantial fortunes up in smoke.  


In some places, strict laws forbade glass workers from leaving their employ and forbade outsiders from attempts to lure them away. Recruiting seasoned talent could be a delicate if not clandestine undertaking. This was as true in the ancient world as it was through the Renaissance and it also played a significant role in the 18th and 19th century for the nascent American glass industry.

Many have heard of the legendary prohibition forbidding Renaissance Venetian glass workers from travel abroad. The fear was that they might divulge secrets of their craft to outsiders, thereby compromising the virtual monopoly on high quality luxury glassware made on the fabled island of Murano. Many also have heard that the penalty for violating these rules was death at the public gallows located between the columns at Saint Mark's square.  While there were laws on the books that listed possible penalties as severe as death, the records show that no glass worker was ever executed for leaving and many did leave. In fact, glass workers were sometimes part of state brokered deals to exchange technology.

These Venetian laws have also led many to the incorrect conclusion that the glassmakers were held captive and treated like prisoners. Nothing could be farther from the truth; glass workers were treated like rock-stars of their time. The daughters of glassmakers were allowed to marry into the nobility, a privilege granted to no other guild. [2]

Early American efforts to recruit experienced glass workers provide some amusing stories. In 1894, William G. Harding, a principal in the Berkshire Glass Works in Massachusetts wrote a detailed history of glassmaking in the region.  Harding’s research was meticulous, drawn from factory records, official legal filings and personal correspondence. Two stories in particular relate the great lengths pursued in recruiting experienced European glass workers to New England.


The first concerns Robert Hew[e]s, who despite repeated failures in starting a glassworks in the late 1700s, finally partnered in Boston with one Charles F. Kupfer newly arrived from the Duchy of Brunswick in Germany. Together they formed Boston Crown Works on Essex street.  Kupfer immediately returned to Germany to recruit workers, as harding records,
“Mr. Kupfer upon his arrival at his old home, found it no easy matter to get his blowers. The works belonged to the Duke of Brunswick, and it was a penal offense either for the men to leave, or for him to entice them away. He was obliged to conceal his designs and operate in the dark, but succeeded in escaping in the night with a set of workmen and sailed from a German port before being overtaken. After a long voyage they landed in Boston and met with a Royal reception. So much interest in the new enterprise had been awakened in the citizens of Boston, that they turned out en masse…” [3]


The other story of clandestine recruiting related by Harding concerns a venture started in Sand Lake, about 10 miles east of Albany, New York around 1806.
“They had to import their skilled workmen. Mr. William Richmond, a Scotchman, was the Superintendent of their works. He went abroad to procure workmen. Disguised as a mendicant [monk/priest], with a patch upon one eye and playing upon a bag-pipe, he wandered through the glass district of Dumbarton in Scotland and engaged his blowers to cross the Sea. With great difficulty they secreted their tools on Ship-board, for it was a penal offense for glass-workers to leave Scotland as well as Germany.” [4]


[1] Antonio Neri, L’Arte vetraria, distinta in libri sette, del R.[everendo] P.[rete/ padre] Antonio Neri fiorentino. Ne quali si scoprono, effetti maravigliosi, & insegnano segreti bellissimi, del vetro nel fuoco & altre cose curiose. All’Illvst.mo et eccell.mo Sig., Il Sig, Don Antonio Medici (Florence: Giunti 1612).
[2] A daugher of a glassmaker could marry into the nobility, which was a great honour for a family, but strategically, the son of a glassmaker had no such privilege, meaning that there were no inheritance rights for the family.
[3] Collections of the Berkshire Historical and Scientific Society, (Pittsfield: Sun Printing, 1894),  p. 37-39
Note that Robert Hews is also known as 'Hewes' in other sources.
[4] op cit. p. 39-40.

Monday, June 26, 2017

San Giusto alle Mura

Window of  Santa Maria del Fiore cathedral,
Florence, Italy.
In Florence, at the very end of the street on which Antonio Neri spent his youth, Borgo Pinti, was the residence and estate of the Archbishop. Beyond were the city walls and the enormous wooden doors of the Porta Pinti gate (115 foot, or 35 meters tall). Just on the other side of the gate, which in Neri’s time was normally closed and guarded, once stood the San Giusto alle Mura monastery, built in the thirteenth century. Despite the similar name, there is no connection between the Ingesuati monks of San Giusto and the modern order known as the Jesuits, which was not formed until 1534 and recognized by the Church in 1540.

The monks at San Giusto were famous for the stained glass windows they made; hence one of numerous theories that the street name 'Pinti' may be a contraction of 'dipinti 'or 'dipintori' (paintings or painters). Using their own glass furnaces, the Ingesuati monks provided windows for the Neri family's church Cestello and for Santa Maria del Fiore among other churches. They also ran an art school and were famous for making the color pigments used by painters, producing a coveted ultramarine blue. Their customers included the likes of Leonardo, Michelangelo, Botticelli, Del Sarto, Ghirlandaio and Filippo Lippi. 

Apparently, the Ingesuati's artistic devotion was not matched by their religious observance. In his Lives of the Artists, Giorgio Vasari recalls the less than complimentary sentiments of the monk's own in-house chaplain, a certain Servite monk named Fra Martino. He notes that the monks do not read Mass, and that they, "do nothing but say paternosters ['our Father...'], make glass windows, distill herbs for sweet waters, dig their gardens, and perform other works of similar kind, but do not study or cultivate letters."

Antonio Neri has a slightly more positive opinion about the value of stained glass windows. In the introduction to L'Arte Vetraria, he waxes poetic: 
Glass is also a great ornament to God's churches since, among other things, many beautiful windows are made, adorned with graceful paintings, in which the metallic colors are so intense and vivid that they seem like so many oriental gems. 
The windows that inspired these lines may well have been made by monks of San Giusto. As a child, Antonio Neri had seen the striking windows in Cestello and in the city cathedral. It would be nice to be able to connect him to the Ingesuati, but in 1529, long before his birth, their entire complex just outside the Pinti Gate was dismantled in defensive preparation for the siege of Florence. The Florentine military cleared away the structures near the outside of the city walls. The monks of San Giusto alle Mura moved to the much smaller Calza Convent on the oltrarno, on the opposite side of town near the Porta Romana gate. They did not rebuild the glassworks at the new location and it is doubtful that any of the glass workers would have still been alive by the time Antonio Neri came of age.

This post first appeared here in a slightly shorter form as "Glass Monks" on 30 September 2013.

Friday, June 23, 2017

Montpellier

Montpellier, France, in the seventeenth century.
(Attribution unknown)
Montpellier is an old city in southern France. It stands about halfway between Marseille and the Spanish border along the Mediterranean Sea (strategically located slightly inland to avoid pirates). First documented in the tenth century, it is one of very few French cities that developed without the influence of ancient Roman occupation; it is a pure product of the local region. It became a center of intellectual learning and attracted students from throughout Europe. Around it sprung a number of supporting arts not the least of which was glassmaking. Once famous for its fine glassware, today this centuries long heritage is all but forgotten, yet when we dig into the literature, we find a surprise connection to one of the oldest legends in the history of glass.

Since before the Renaissance, Montpellier was an established center for medical and legal education, a strong tradition that continues at the university there; today, it houses the oldest running medical school in the world. This prestigious institution "was founded perhaps by people trained in the Spanish medical schools; it is certain that, as early as 1137, there were excellent physicians at Montpellier University." [1] In 1529, Nostradamus entered to study for a doctorate in medicine, but shortly thereafter, he was expelled when it was discovered that he previously worked as an apothecary; a 'manual' skill that was banned by the school's rules of conduct.

Paradoxically, these impugned 'manual' arts account for some the region's more intriguing activity. Along with medicine, the area became known for the production of paint pigments, for glassmaking and finally for alchemy. All of these turn out to be closely related to each other, but perhaps not obviously so. Throughout the Renaissance, apothecaries were responsible for a wide range of distillations and extracts used by physicians to treat disease. They were also the de facto suppliers of pigments and other fine art supplies and even sourced some of the materials for glassmaking. Glassmakers often relied on painters to embellish their products, painters used ground glass in their pigments and apothecaries needed glassmakers to produce the flasks, beakers and other alchemical equipment required for their profession.

An anonymous Montpellier manuscript of the fourteenth century, called the Liber diversarum arcium [Book of Various Arts], offers us one of the most complete guides to the production of pigments to have survived from that period. [2] Another, later writing of the sixteenth century offers an extensive collection of glassmaking recipies brought to Montpellier from Venice. This one is titled Recette per fare vetri colorati et smalti d’ogni sorte havute in Murano 1536 [Recipes to make colored glasses and enamels of every kind as in Murano, 1536]. [3]

Local history points to the town of Claret just north of Montpellier as the seat of regional glassmaking. Beginning in 1290, the oak forests on the Causse de l'Orthus attracted glassmakers and their families. "So maybe the oaks got used for fuel. (A 'causse' is a geological term for a limestone plateau.) [also a material of glassmaking] At any rate, the glassmakers were ennobled by the King and formed a guild of premium glassmakers whose wares were sold all over Europe from the market at Sommières." [4]

In the early seventeenth century, Pierre-Jean Fabre (1588-1658) studied medicine at Montpellier where he discovered the works of Paracelsus, to which he became a devotee. [5] After securing a medical degree, he returned to the nearby town of his birth, Castelnaudary, to work as a doctor. Eventually, he was awarded the status of "Royal Physician" by Louis XIII, probably for his work on treating victims of the plague with chemical preparations. [6]

Fabre's first book, of a total canon numbering sixteen volumes, was on the subject of alchemy and medicine titled "Palladium spagyricum" 1624. [7] The book, written in Latin, contains advice on the transmutation of metals, turning water into "good wine" and elixirs to cure all disease. It contains one recipe that is of particular interest on the subject of glassmaking; a malleable form of glass, known in legend since the Roman Empire as Vitrum Flexile.

See my previous post to take a closer look at Fabre's specific recipe for a glass that is malleable at room temperature and trace a bit of the legend's history.

[1] Wikipedia, “University of Montpellier” https://en.wikipedia.org/wiki/University_of_Montpellier.
[2] Mark Clarke: Mediaeval Painters' Materials and Techniques: The Montpellier Liber diversarum arcium (London: Archetype Publications, 2011).
[3] Montpellier 1536, MS. H. 486: Recette per fare vetri colorati et smalti d’ogni sorte havute in Murano 1536, Bibliothèque de l'Ecole de Médecine de Montpellier, see also Zecchin 1987, v.1 p 247-276. Although the manuscript is dated 1536 it is probably copied from much earlier Venetian sources.
 [4] Ed Ward, Blog: City on a Hill, 1 Nov. 2010 post “Where the Glass-Blowers Were.” http://wardinfrance.blogspot.com/2010/11/where-glass-blowers-were.html . Also see Halle du Verre regional glass museum website http://www.cc-grandpicsaintloup.fr/-Halle-du-verre-.html .
[5] Paracelsus (1493-1541) was a Swiss born physician and alchemist who looked to nature rather than ancient texts for remedies to disease. He was widely condemned durring his lifetime but became very popular after his manuscripts were printed in the late sixteenth century.
[6] The definitive reference on Fabre is Bernard Joly: La rationalité de l'alchimie au XVIIe siècle (France: Vrin, 1992), pp. 35-50. A good English treatment can be found in Allen George Debus: The French Paracelsians: The Chemical Challenge to Medical and Scientific Tradition in Early Modern France (Cambridge: Cambridge University Press, 2002) pp, 75, 76.
[7] Pierre-Jean Fabre: Palladium spagyricum Petri Ioannis Fabri doctoris medici Monspeliensis ... (Toulouse: Bosc, 1624), p. 276. Later translated into several English editions, notably by William Salmon: Polygraphice: Or the Arts of Drawing, Engraving, Etching, Limming, Painting … (London: T. Passenger & T. Sawbridge, 1685), pp. 598, 599.




Wednesday, June 21, 2017

Vitrum Flexile

Roman Emperor Tiberius - Glass paste cameo
 c 20ACE by "Herophilos, Son of Dioskurides"
In the first century CE, references appear in the literature for a malleable form of glass --that is to say flexible-- the method for which is reported as lost. This 'vitrum flexile' was a material that supposedly could be worked with a hammer like metal; not brittle but plastic, yet retaining the other favorable properties of glass. In the ancient world, historians Strabo (c. 63 BCE–24 CE), Pliny (c. 23–79 CE), Petronius (c. 27–66 CE) and others recount the story of a hapless artisan who brought his great discovery to Roman emperor Tiberius. Fearing the devaluation of his wealth, the emperor had the glassmaker executed on the spot and his workshop destroyed. The implication being that the inestimable value of a malleable glass would crash the markets for gold and silver. [1]

Since then, the legend has resurfaced in various forms, notably at periods in history of technological upheaval; times when innovative knowledge threatened to 'disrupt' the established order. One incarnation has the sophy of Persia gifting a set of malleable drinking glasses to the king of Spain, Philip III, around 1610. Just then, new trade deals with the Middle East rattled the European economy and Venetian glass craftsmen fanned out through Europe, disrupting local glass furnaces and guilds with their superior techniques. [2] Another version tells of a French sculptor bringing his malleable glass-work to Cardinal Richelieu (1585-1642), of Dumas' Three Musketeers fame. According to the story, that particular artisan’s reward was life in prison. The tale takes place in a tumultuous political period in French history and appears in print at the dawn of the so-called industrial revolution. [3]

Chronologically, this last story aligns nicely with the publication, in southern France, of a Latin book of alchemical recipes by royal physician Pierre-Jean Fabre (1588-1658). Contained in his volume is a prescription for a malleable form of glass, presumably the fabled vitrum flexile. Fabre's book was titled Palladium Spagyricum, 1624. [4] Spagyricum is a reference to spagyrics, the specific brand of chemistry practiced by sixteenth century alchemist-physician Paracelsus. Palladium translates to 'protector' or 'savior'. As an aside, it is interesting to note that Fabre developed an elaborate philosophy which integrated chemistry as a 'sacrament' to Catholic theology, but that is a story for another day.

In 1685, Fabre's recipes were nicely translated into English and tucked into the end of a book otherwise devoted to the art of drawing, by William Salmon [5]. Here is the full recipe "To Make Malleable Glass" as rendered in Salmon's book:

I.        Take oyl of Luna, twenty drachms: oyl of Mercury, or its water seven times rectified, one pound: mix them together and distill them.
II.      Repeat this distillation till the oleum Lunae rises with the water of Mercury in distillation. 
III.     Distill this water again until it is fixed, and converted into a fixed oyl, and this repeat four times. 
IV.     In the fourth time the oyl of Luna is fixed with the oyl of Mercury, so that they render glass malleable; for so great is the viscosity in your oyls, that it removes the brittleness of the glass, and so leaves it of a malleable temper. 
V.      The reason is, because that the radical moisture of the glass is multiplied by the radical moisture of the metals. Which is plentiful and turgent or swelling in the oyls of Luna and Mercury. 
VI.     And if [in] this oyl made volatile, diamonds should be dissolved, and then digested into a fixt oyl, it would transmute all glass into diamonds, only by projecting this oyl onto melted glass. 
VII.   There are also other precious stones comprehended within this oyl, when it is made volatile, and digested, and fixed again by digestion continually for the space of a year. 
VIII.  Also this oyl can turn glass into precious stones of any kind whatsoever, if therein (being made volatile) precious stones of the same kind have been dissolved, and digested with it into a fixed oyl. 
IX.     For as metals are included in their fixed oyls: so are precious stones in theirs, as Raymundus Lullius doth witness in many places; the which thing we shall teach you in the following chapter. 
 Elsewhere in the book, it is explained that 'oyl of Luna' is silver dissolved in acid, and 'oyl of Mercury' is a sublimation of mercury and saltpeter. [6] From a purely technical standpoint, the formula is credible in that both mercury and silver were successfully used as additives to glass and they do integrate into the matrix. Notably, Antonio Neri used both of them in his chalcedony glass. In Neri's case he was using these metals to produce color, although he does not attribute a specific tint to these ingredients. Under some circumstances, silver is known to produce an attractive blue. It should also be noted that Renaissance glassmakers used similar silver-mercury formulas to produce a reflective layer on finished glass mirrors, in a process that resembled gilding. They formed what was known as "mercury glass." It is not beyond the pale to speculate that experiments would be conducted to add such concoctions directly to the glass melt. In the end, though, there is no indication that these additives would produce a malleable glass.

As far as I am aware, this is the first example of a specific recipe for malleable glass uncovered in the literature. If nothing else, it is an important marker for further research into the history of glassmaking.


[1] Strabo: Geography, v. 8; Pliny: Naturalis Historia XXXVI.lxvi.195; Petronius: Satyricon 50.7; Also recounted by Casius Dio (c.150–235 CE): Historia Romana 57.21.7; Isidore of Seville (c. 560–636 CE): Etymologiae XVI.16.6, ‘De vitro’; Suetonius; Ibn Abd Alhokin; John of Sailsbury.
[2] Knolles, Grimstone, Johnson: Richard Knolles' The General Historie of the Turkes (London: Adam Islip, 1621).
[3] Neri 1697 (Introduction). A French translation of Florentine glassmaker Antonio Neri’s 1612 book L’Arte Vetraria [The art of making glass] by Jean Haudicquer de Blancourt. Also see my earlier post here http://www.conciatore.org/2014/07/flexible-glass-reprise.html .
[4] Pierre-Jean Fabre: Palladium spagyricum Petri Ioannis Fabri doctoris medici Monspeliensis ... (Toulouse: Bosc, 1624), p. 276. Later translated into several English editions, see note [5].
[5] William Salmon: Polygraphice: Or the Arts of Drawing, Engraving, Etching, Limming, Painting … (London: T. Passenger & T. Sawbridge, 1685), pp. 598, 599.
[6] To more adventurous readers: DO NOT TRY THIS AT HOME, or anywhere else, ever. Vaporized mercury is a powerful neurotoxin. Small amounts can cause permanent brain damage and multiple organ failure. Furthermore, this recipe uses powerful acids and nitrates, which are extremely dangerous even in a controlled laboratory setting. Even if you have little regard for your own health and safety, consider those around you; this includes loved ones, family, children, pets, neighbors and the emergency workers who will inevitably be left to clean up your mess.

Monday, June 19, 2017

The Material of All Enamels

Léonard Limosin, Allegory of Catherine de' Medici as Juno,
French, 1573, Polychrome enamel  on copper and silver.
In L'Arte Vetraria, Antonio Neri's recipe book on glassmaking, he devotes the sixth chapter to making enamel. For Neri, this was a tinted form of opaque glass favored by jewelers and goldsmiths. The material was ground into a fine powder, added to a binder and painted onto glass or metals, usually copper, gold or silver. Once dry, the item was fired over a flame or in a kiln so the enamel would fuse to form a durable glossy coating. Talented workers could use various colors to paint entire scenes.
“We see ornate enameled metals in many colors and they make a pleasant and noble sight; they entice others to look and take notice.”
Neri begins by showing how to produce what he calls “the material to make all enamels.” This is a neutral-white base to which he then adds various metal oxide pigments to produce color.

He starts by mixing together thirty pounds of pure lead and thirty-three pounds of pure tin, both in a finely divided state. He heats them in a low temperature kiln that has a wide, accessible hearth. He roasts or "calcines" the metals, raking the powders around with special iron tools for many hours. This has the effect of oxidizing the metals without melting them.

He sifts the mixture and boils it in a kettle of pure clean water. The kettle is removed from the heat and the contents are allowed to settle for a while. The water is then carefully poured off, carrying with it only the finest particles still in suspension. This liquid is saved, while the sediment at the bottom of the kettle is sent back for reprocessing in the kiln. He repeats the "decanting" procedure many times, and then carefully evaporates the accumulated liquid over a low fire. What remains is an extremely fine powdered tin and lead oxide mixture.

Neri tells us that fifty pounds of this oxide is to be mixed with an equal weight of powdered cristallo frit. Cristallo was the coveted glass perfected by the Venetians on the island of Murano. "Frit" is the granulated glass before it is put into the furnace and melted. The recipe for cristallo had remained a state secret for over a century. It was the clearest, finest glass that money could buy and items made from it commanded top dollar among the richest families in Europe. Even after production methods became known to outsiders, Venice still controlled many of the raw materials through exclusive trade agreements around the Mediterranean. Neri was first to actually publish the recipes for making cristallo, in this very same book. It was made with pure white quartz pebbles from Pavia, mixed with purified salts derived from the Levantine kali plant, and decolorized with manganese from Piedmont.

In order to complete the enamel base material, Neri adds eight ounces of white tartar salt (made from the dregs of wine), sifts the mix and carefully heats it in terracotta pots for ten hours. The result is ground again and stored in a in a dry place, in a sealed container for future use.

The rest of the chapter is devoted to coloring this enamel base material; he always starts with a batch of either four or six pounds. He uses a large furnace pot to melt the enamel because even though the amount is relatively small, some of the pigments cause the batch to froth and swell violently. After adding the pigments, he lets the glass cook for a while, adjusts the color as necessary and then "washes" it several times. In this process, he throws ladlefuls of molten glass from the furnace-pot into large vats of cold clean water. The effect is to remove excess plant salts from the glass, which would ultimately foul the enamel. Finally, he forms the glass into individual dollops of about five ounces each; a size to which the goldsmiths were accustomed.

For green enamel, Neri uses copper and iron oxides in various proportions, for blues he uses "zaffer," which is a cobalt oxide. He mixes green and blue pigments to obtain turquoise colors. Manganese produced a red wine color, for yellow, he adds the unrefined dregs of red wine (potassium) with a pinch of manganese. Violet is a mix of manganese and copper oxides.

Finally, a word to the wise: Do not attempt to duplicate these recipes; fine lead powder is dangerous enough, molten lead enamel will evolve fumes that cause heavy metal poisoning. Remember that Antonio Neri was dead by age thirty-eight.

* This post first appeared here 11 July 2014.

Friday, June 16, 2017

True Colors

The European Roller [Pica Marina]
Antonio Neri's book, L'Arte Vetraria, is devoted to making glass from raw ingredients found in nature. Many of his finished creations were intended to also resemble the natural world. A number of colors are meant to mimic the appearance of gems and minerals, others are named after plants and animals. Some are easily recognized today, even if they are not as familiar as they were in the seventeenth century. One of his recipes will make "a wonderful pimpernel green," while others evoke peach and orange blossoms. An entire section of the book is focused on paints that are named after the flowers from which the colors are extracted. Many of these plants have remained common: poppies, irises, violets, lilies, carnations and red roses. Others are less so: the mallow, pomegranate, broom and borage flowers.

In addition to flora, the fauna make a few notable appearances in Neri's book. In chapter 16, in the preparation of iron oxide pigments, he advises that after fifteen days in the furnace, the product will be finished when it takes on the purple color of the peacock. In chapter 73 he gives a method for "tinting rock crystal the color of a viper" and chapter 121 is the method for a glass which is "red like blood."

Named in several chapters is a shade of 'celestial blue,' which Neri likens to the color of the "gazzera marina." Common bird names pose a special challenge for translation in that they, like the birds themselves, never seem to settle in space or time for very long. Vernacular names of a species can change from one century to the next, one region to another, even between adjacent valleys and several species can share the same name. It is with this admonition that we attempt to flush out the elusive gazzera marina.

Consulting a modern Italian dictionary draws the eye to the similar sounding 'gazza marina' (alca torda), known in English as the razorbill. This sea bird inhabits coastal cliffs, but alas, as a close relative of the penguin, it dons only black and white formal attire. Digging deeper we find poet Gabriele d'Annunzio, "At Dawn" carefully tracking the gazzera marina across a salty marsh, in his Halcyon. This time the poet himself throws us off the trail with his description, since no bird sports five digits but the chicken. Turning to etymology, we find another potential match in the magpie (pica pica); it is a credible but unconvincing fit with its blue and white plumage.
Aldrovandi's pica marina
Combing the references of Neri's own sixteenth century, we find the best candidate is the roller (pica marina). This bird was described by naturalist Ulisse Aldrovandi, a friend of Don Antonio de' Medici's father and guest at the Casino di San Marco, where Neri later worked. Other contemporary authors list the gazzera marina as a synonym to Aldrovandi's pica marina. Neri's Latin translator Frisius (1668) and his German translator Geissler (1678) agreed, both sighting the "Pica Marina" in their works.

This post first appeared here on 13 Sept 2013.

Wednesday, June 14, 2017

The Cardinal's Ceiling

From "Tesoro del Mondo" (Treasure of the World)
Antonio Neri 1598-1600
In the years 1598-1600, newly ordained Florentine priest and alchemist Antonio Neri was hard at work on a manuscript which he titled Tesoro del Mondo (Treasure of the World). [1]  One illustration near the front shows an allegorical map in which six roads all lead to the Vatican at its center. A Latin inscription translates as, "The different ways to Rome" followed by "Qui pot[est] capere capiator 'He that can take, let him take it.' Taken in context, this Biblical reference ( Matthew 19:12) apparently refers to the various alchemical 'paths' leading to the philosopher's stone, but the choice of imagery suggests that Neri spent time in the city of seven hills. [2] It is a tantalizing clue to his travels, although there is no direct confirmation. 

If Rome did figure in the young Neri's itinerary, a visit to Cardinal Francisco Maria Del Monte would have been de rigueur. The Medici family ruled Neri's home region of Tuscany and Cardinal Del Monte was the Medici's informal ambassador in Rome. He was a dedicated patron of the arts, an amateur alchemist, a collector of glass and a trusted successor to Grand Duke Ferdinando in the College of Cardinals. More significantly, he was a close friend and advisor to Neri's sponsor Don Antonio de' Medici ever since that prince was a child.  Del Monte's biographer Zygmunt Waźbiński offers, "It is very likely that Cardinal Del Monte, with his interest in glass, had known then (in 1598) the [future] author [Neri] of L'Arte Vetraria." [3]
Michelangelo Caravaggio, c. 1597
Casino Ludovisi.

As the sixteenth century ended and a new one dawned, Del Monte sheltered the rough-and-tumble painter Michelangelo Caravaggio, whom he set up with an in-house studio and an allowance. However, in 1606, the master of Realism fled Rome after reportedly murdering a tavern waiter over a tennis wager, but not before executing his only known fresco on the vaulted ceiling of Del Monte's own alchemy laboratory. Looking out over Rome, on the panoramic Pincio, in the Villa that later became the Casino Ludovisi and is now known as the Casino dell'Aurora, Caravaggio put his brush to work. According to early biographer of artists, Gian Pietro Bellori, he executed the oil painting on the vaulted ceiling of the small alchemical laboratory (now a corridor) sometime between 1597 and 1600. [4] Depicted in the mural are the three brothers Jupiter, Neptune and Pluto: the masters of the universe. The image is a double allegory of the three basic chemical substances of Paracelsus (salt, sulfur and mercury) and the four Aristotelian elements (air, earth, water and fire). Jupiter with the eagle stands for sulfur and air, Neptune with the seahorse stands for mercury and water and Pluto with the three-headed dog Cerberus stands for salt and earth. Jupiter is reaching out to move the central celestial sphere in which the sun (fire) revolves around the earth. [5] 

The villa was a relatively secluded retreat where the Cardinal could entertain guests discretely, including his friend Galileo–Del Monte and his older brother Guidobaldo helped land Galileo the chair of mathematics at the university in Pisa. It would be interesting to hear the astronomer’s comments on Caravaggio's tribute to heliocentrism.


[1] Neri 1598-1600, f.xxviii-v.  (see bibliography).
[2] For more on the alchemical interpretation of this illustration see Grazzini 2012.
[3] Neri 1612.
[4] Bellori 1672, pp. 197-216.
[5] Wallach 1975, pp. 101-112.

* this post first appeared in a slightly different form on 4 July 2014.

Monday, June 12, 2017

Neri & the Portland Vase

The Portland Vase
(British Museum)
287 years ago this month, (12 July 1730) marks the birth of Charles Darwin's grandfather, English potter Josiah Wedgewood. He founded the company that still bears his name, a name that has become synonymous with the iconic blue with white bas-relief cameo-themed jasperware pottery.  

What is less well known is that the style was developed over several years by Wedgewood in an attempt to copy a particular ancient glass object, now called the Portland Vase. This piece was and still is regarded by many as the pinnacle of ancient glass art. The vase was made around the time of the birth of Christ and shortly after the invention of glassblowing. The prevailing theory states a dark, cobalt blue vase was blown and then coated in a second thin layer of white glass. The piece was then carefully sculpted, probably by a gem carver, by grinding the white over-coat glass into various mythological scenes. The figures stand on dark blue ground that was revealed by completely grinding away areas of white, leaving only the under-layer. 
Wedgwood's Sydney Cove Medallion

Alternate thinking has the piece cast or blown into a mold which contains powdered white glass in the appropriate areas. [1] 
Both theories have their points, and the wide differences only serve to emphasize how little we actually know about ancient methods and technology. Having said that, the alternate theory, it seems to me, has an up-hill battle to gain acceptance over the prevailing one.

What is especially revered by aficionados, and gave Wedgewood the most trouble in replicating, is the delicate carving of the white glass. The figures depicted around the vase in various scenes are not monochromatic, but expertly shadowed just like a fine painting. This, it is commonly thought, was achieved by grinding the white glass so thin that the dark blue under-layer starts to show through, making gradations of lighter and darker features. A face or a hand was shaded by making the white glass slightly thinner on shadowed areas. Wedgewood's solution was to subtlety tint the white clay he used, which was then applied to a blue clay vessel and fired in a kiln. One of his early successes, owned by Darwin, can be viewed at the Victoria and Albert Museum in London.

Today the original Portland Vase can be viewed at the British Museum where it has taken a place of pride almost since the museum’s inception. A series of unfortunate accidents and one act of intentional destruction have broken the vase several times, but it has been painstakingly pieced back together and restored so that cracks are minimized. One of these events occurred during the Roman Empire, when the bottom of the vase was replace by a circular medallion of the same style cameo glass. In modern times, the vase was the subject of a nineteenth century contest, with a prize of 1000 pounds, to make an accurate reproduction in glass. The winners of that contest were glass blower Philip Pargeter and engraver John Northwood. Their piece is on display in the Corning Museum of Glass in New York.

The vase was uncovered in the late sixteenth century during an excavation, when the hunt for ancient tombs around Rome was in full swing. It was presumably used as a funerary urn in what, at the time was thought be the tomb of Emperor Alexander Severus. It's first owner after discovery was none other than Cardinal Francesco Maria del Monte, patron of the arts, alchemist, glass collector and Medici family confidant, of whom I have written here before. The cardinal was a lifelong advisor to Don Antonio de' Medici, who was in turn, the patron of glassmaker Antonio Neri. There is every chance that Neri and Del Monte knew each other, although no such record has yet been found. Del Monte is known to have visited the Casino di San Marco in Florence at the time that Neri was making glass there and Neri is conjectured to have visited Rome a couple of years earlier. 

If Neri the priest was ever granted audience with the cardinal in Rome at his main residence, the Palazzo Madama (now occupied by the Italian Senate), it is easy to imagine a tour of the cardinal’s extensive glass collection, which he displayed in a special room dedicated to the purpose. Such a tour would not be complete without an examination of what would become the most famous piece of glass in history, the Portland Vase, by the man who would become the most famous glassmaker in history, Antonio Neri. "Go ahead, take it – hold it up to the light."

[1] For more on this see http://rosemarie-lierke.de/English/Cameo_glass/cameo_glass.html

Friday, June 9, 2017

Galleria dei Lavori

Giovanni Stradano  (Jan van der Straet) 
Alchemy Studio, 1571
(Inside the Uffizi Galleria dei Lavori)

In 1560, Cosimo I, Duke of Tuscany, commissioned Georgio Vassari to begin construction on the Uffizi Palace in Florence. Two wings of the structure frame a long, narrow courtyard leading out to banks of the Arno River. Today it houses one of Europe's premier art museums, but its original design was as the central administration of the Medici government. The lower floor held offices of the regional magistrates, and the upper floor of the west wing (above the mint) held a variety of workshops highlighting Tuscan industry. Grand Duke Cosimo de' Medici built a glass furnace there, which he staffed with Muranese masters of the art. He won their expertise through long, hard negotiations with the doge of Venice. 

A 1571 painting by Giovanni Stradano is entitled the Alchemy Studio. It shows Cosmo's son, Francesco I, in the Uffizi surrounded by laboratory equipment and workers. Under the watchful eyes of a senior alchemist, he stirs a chemical preparation over a stove with intense concentration. The prolific glassware in this scene drives home the close relationship between glassmaking and scientific investigation.

By 1588 Francesco's brother, Ferdinando I de' Medici, formally declared this space the Galleria dei Lavori or 'gallery of the works'. There is no direct evidence that Antonio Neri gained his education in alchemy at this facility, but it makes a very attractive candidate. Of note to this story is that a demonstration was performed for Ferdinando de' Medici in Rome that purported to turn half of an iron nail into gold; the work of German alchemist Leonhard Thurneysser. In the 1590s, when Neri was being schooled, several accounts describe that the nail (chiodo) remained on display for some time in the Galleria. Neri mentions the nail in his Discorso and Thurneysser is discussed in a 1601 letter to the priest from his friend Emanuel Ximenes.

After Neri's death in 1614, his Medici sponsor, don Antonio commenced a search for the glassmaker's secret of transmutation, which Neri had promised. In testimony given by a royal goldsmith, who had, in July of 1596, witnessed a demonstration in which "gold" was made by Neri, he pressed the glassmaker, who told him that the transmutation was a technique learned from a German, done with ordinary vitriol.  

It is interesting to note that when iron is soaked in a solution of "blue vitriol" now known as copper sulfate, an ion exchange reaction takes place, where the liquid deposits copper and takes up iron from the nail. It would be well into the 18th century before this chemistry was adequately understood. What the royal goldsmith would have seen is  a dull iron nail turn the color of yellow metal before their eyes. Perhaps the goldsmith was not given the opportunity to further test the sample. 

This post first appeared on 16 August 2013.

Wednesday, June 7, 2017

Weights and Measures

Ford Madox Brown,  The Manchester Murals: 
"The Proclamation Regarding Weights and Measures, 1556."
In his book L'Arte Vetraria, Antonio Neri's glass recipes depended on precise amounts specified in units as small as the 'grano,' [grain] named after the weight (mass) of a single grain of wheat or barley. In interpreting his formulas, the glassmaker must understand the quantities he used. For us, there are unfamiliar units like the 'fiasco' and the 'dita.' The dita or digit was simply the width of a finger. A fiasco or flask was the volume of a glass wine bottle, about two-and-a-quarter liters in Florence or two-thirds of a US gallon - about half of British imperial gallon. (As an aside, there are many fanciful stories of how the word 'fiasco' came to be synonymous with failure or disaster, perhaps the most believable is that the losers of competitions or bets were expected to buy the next round of drinks.)

In addition to unfamiliar units, there is the problem of standardization; a pound in Florence weighed different from a pound in other areas as close as Massa or Piedmont. Each Italian city maintained its own set of master weights and volumes to which merchants were expected to adhere. In reality, the differences were minor and may have been more attributable to politics than accuracy. Since antiquity, commodity merchants realized that if their own set of weights used in sales were ever so slightly below the norm, over time a savings would be realized, not large but significant. Towns could apply this principle as well; it paid to set standards slightly above or below neighboring towns from which one was buying or selling various goods. In truth, the differences were not great simply because successful commerce demanded that buyers and sellers could agree and strike a deal.

Even in different countries throughout Europe and the Mediterranean, we find close agreement in the various units of measure. Neri's first translator, Christopher Merrett, made an interesting substitution in his 1662 English version of L'Arte Vetraria. In chapter 132, Merrett writes "six pints of water" for Neri's "libre sei di acqua," changing pounds into pints. At first, it seems odd to be converting weight into volume, but this was perfectly valid. At that time in England, the pint was defined as exactly a pound (of wine or beer). Sailors were often each allotted a pint a day; the pint was also one-eighth of a cubic foot. (A cubic foot was equivalent to a gallon.) This system was very convenient for shipping companies who needed to calculate cargo volume and ballast in their trade ships as well as avoid mutiny caused by running out of beer at sea. Later, in 1824 King George IV increased the gallon from eight to ten pounds of water, invalidating Merrett's substitution.

Other conversions were more problematic. As absolute measurements varied from place to place, the size of a batch would be larger or smaller; not a big worry. However, ratios were of critical importance to a recipe. Just as in baking a cake, an entire batch of glass could be ruined by changing the ratio of materials. This sort of difficulty was especially prevalent with the size of an ounce; the troy and apothecaries system were based on a twelve-ounce pound while the avoirdupois system used a sixteen-ounce pound. When Merrett wrote his translation, England had officially been under the avoirdupois system since Henry VIII (although, In 1588, Elizabeth I complicated matters further by raising the weight of a pound by about twenty-one percent.) Meanwhile, Florence and much of Europe continued to use the troy system.

English glassmakers who wished to use Neri's book as a working document would need to know which system to use. Merrett's direct translation added a hurdle that would confuse the unaware. In order to approximate Neri's intended composition under the prevailing avoirdupois system, Merrett's "ingenious" (as he called them) British readers would need to decrease by 1/5 quantities specified in pounds, and increase ounces by 1/15.

This post first appeared on 18 September 2013.

Monday, June 5, 2017

Thévenot in India

Antique gold Arsi finger ring,
 Rajasthan India.
This is the third and final installment of a series that has followed seventeenth century French tourist Jean de Thévenot from Europe to the Levant and then into Syria. Now he travels to India. We have specifically looked into his diary with an eye toward passages that mention glass or glassmaking. While our intrepid traveler had no special connection to this art, he did possess a keen, inquisitive mind; collectively, his observations about glass give us a glimpse into the state of affairs in the Middle and Far East in the mid 1600s. 


We left off with Thévenot as he headed up the Tigris River toward Baghdad, in the autumn of 1663. While he was anxious to see Mughal India, actually getting there presented some difficulty due to hostilities between the Dutch, British and Portuguese, which extended to their trade operations around the world. After a first attempt was aborted, he made a strategic retreat to Isfahan and bided some time with shorter excursions from there. Finally, in the autumn of 1665 he booked passage on the originally English ship “Hopewell” recently purchased by an Armenian trader and captained by an Italian. [1] The ship departed from Basra and made port at Surat, India in January of 1666.

The city of Agra is in the Northwestern part of India, a thousand kilometers from Surat and the coast; it is known most famously as the home the Taj Mahal. When Thévenot passed through, he noted of the women “They wear a great many [rings], and as they love to see themselves, they have always one with a looking-glass set in it, instead of a stone, which is an inch in diameter.” [2]

These rings, set with a mirror, are known as “arsi” and can still be found in some areas around the country. Indeed, Sharma and Seth note in their 1997 book on contemporary regional costumes and ornaments that mirror rings were popular in the northern most reaches of India. In the western Himalayas at Chamba and as throughout India, they are still worn today. “Arsi or arsu means a mirror. An ornament with this name is a ring fitted with a round mirror or a looking-glass. It is usually worn on the thumb of the right hand. With the help of arsi, the hill woman can look at herself in the mirror and feel assured of her beauty in such places like fairs and festivals. Thus she can stealthily have a glance in the mirror whenever she desires, even in the company of males without feeling awkward.” [3]

Another reference states that in the seventeenth century arsi rings were worn by both men as well as women, but I have been unable to confirm this. In any event, they appear to have been wildly popular. On an earlier expedition through Aleppo, Syria, Thévenot observed “five or six hundred cases of [mirrored] glass” being shipped down the Euphrates River. When he expressed surprise at the rough handling, he was told “that it mattered not, though it were all broken into pieces, because the Indian men and women buy it only to have little pieces set in rings, which serve them for looking-glasses to see themselves in.” [4]

Thévenot’s first landing was in Surat on the west coast of India, about 300km north of Mumbai. In 1688, Captain Alexander Hamilton landed at the same port and recorded, “The [Muslim] women wear gold rings on their fingers, and sometimes one on their thumbs, with a small looking-glass set in it.” [5] Other travelers also noticed the rings:  In the 1660’s Frenchman Souchu de Rennefort observed similarly, “They wear also many [rings] on their fingers, and among the rest, one with a small looking-glass in it, which serves them to contemplate themselves.” [6]

The earliest account I have been able to find recounts not a glass mirror but one of metal. On 25 September 1637, ambassadors from the Danish duke of Holstein were visiting the King of Persia and were entertained by six dancing women from India. The women were accompanied by their husbands who played musical instruments. “Some of them had bracelets of pearl, others of silver, but they had all rings on their fingers, and among the rest, they had upon the thumb, upon which in the place where the stone should be, there was a piece of steel, about the bigness of a crown-piece of silver, and so well polished that it served them for a looking-glass.” [7]

As these accounts suggest, vanity may well have been the motivation for the popularity of the arsi rings, but it is worth noting that mirrors did play a role in some religious practices. Wikipedia states, “The Nizhal Thangals and Pathis have, in their sanctuary, a mirror to reflect the images [of] worshippers. […] The mirror's placement symbolizes that God is inside oneself and it is of no use to seek God elsewhere.” [8] In some Muslim weddings of Southern India, a traditional ritual is called ‘Arsi-Mushaf’ or “the mirror ring and the Quran,” in which the newly betrothed observe each other through a mirror.

Thévenot stayed in India for over a year and crossed the country to its East Coast. Finally, he returned to Surat, sailed to Persia and traveled north back to Shiraz. He spent the summer of 1667 at Isfahan, after suffering an accidental gunshot wound. In the autumn, he started north for Tabriz, but died on the way at Meyaneh on 28 November 1667.


[1] Armenians in Asian Trade in the Early Modern Era, ed. Sushil; Kevonian Chaudhury (Keram). (France: Les Editions de la MSH, 2008) p. 106.
[2]Jean de Thévenot: The Travels Of Monsieur De Thévenot Into The Levant: In Three ..., Volume 3
 (London: Archibald Lovell Faithorne, 1687)v. 3,  p. 38.
[3] Kamal Prashad Sharma, Surinder Mohan Seth: Costumes and Ornaments of Chamba (New Delhi: Indus Publishing,1997), p.113
[4] Jean de Thévenot: “The Travels of Monsieur Thévenot Into The Levant” (London: H. Clark, 1687), v.2, p.40.
[5] Alexander Hamilton, A New Account of the East Indies: Giving an Exact and Copious ..., Volume 1(London: C. Hitch; and A. Millar, 1744) v. 1, p. 165
[6] Gabriel Dellon, Jodocus Crull, Souchu de Rennefort: A voyage to the East-Indies: giving an account of the isles of Madagascar (London: D. Browne, 1698) p. 25
[7] Adam Olearius, John Davies, Johann Albrecht von Mandelslo: The Voyages & Travels of the Ambassadors from the Duke of Holstein, to the ... (London: Thomas Dring, and John Starkey, 1662), p.277


[8] Wikipedia: https://en.wikipedia.org/wiki/Ayyavazhi_rituals