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, February 28, 2014

Happy Birthday

Child in swaddling , Andrea della Robbia
Ospedale degli Innocenti
Photo: Kaushal Groningen, Netherlands 2007
Depending on how you count, today, tomorrow or ten days from now is the 438th anniversary of the birth of priest, alchemist and glassmaker Antonio Neri. It is also probably the 400th anniversary of his last birthday before death, but let us not dwell on the negative. 

The big day might be today or tomorrow —not because of any problems with record keeping, but because Neri was a leap year baby, born on 29 February 1576. As my friend Steve will tell you, (by the way, happy birthday Steve) in such situations, one must make do in off years by celebrating on 1 March. It is also perfectly legitimate to peg the glassmaker's birthday at ten days from now, because in 1582 ten days were deleted from the calendar, in order to make up for an eleven minute per year discrepancy between the leap year system and the actual solar year. A significant accumulation of time had built up since the Roman Empire. Easter, which is the first Sunday after the first full moon after the equinox,  was slipping back earlier and earlier in the calendar year. This caused Pope Gregory VIII to act on the recommendations of his best mathematicians and fix the calendar date of the equinox to around 20 March. It is true that history can be very complicated sometimes, but we can keep it simple by celebrating Neri's birthday as he did, on the last day of February or the first day of March, as the case may be.

When I first wrote about Neri's birth in this blog, back on 9 August (Bisextile) of last year, I noted, "Antonio was born to a Florence still very much in the grip of February." I have not read a specific account of the weather for that winter in Florence, but the line was inspired by a vision of frigid conditions. However, as regular reader of this blog Maria recently observed, for the thermal towns in the hills above Florence, late February can be a time of "green grass and bloomed mimosa, under an unbelievable blue sky. Spring arriv[ing] with all its strength and vitality… winter only a [distant] memory." Another factor pulling in Neri’s favor for a warm weather birthday is that, due to the Julian calendar discrepancy mentioned above, the Spring equinox happened much earlier, around 10 March. 

Most Catholic births occurring within Florence were registered as soon as the child was baptized, which took place in the ancient octagonal basilica standing directly in front of Florence's main Cathedral, Santa Maria del Fiore, or as it is more affectionately known "the Duomo." 

The baptistery record for Antonio Neri reads:
Thursday, 1 March 1575:  Antonio Lodovico was born to Mr. Neri Jacopo and Dianora di Francesco Parenti, residents of San Pier Maggiore parish. The time of birth was 29 February, at 3 hours 25 minutes past sunset. The godparents are Francesco di Girolamo Lenzoni and Ginevra di Federigo Sassetti.
The year is recorded as 1575 because in those days, Florentines celebrated the New Year on 25 March, as a result, January, February and most of March we considered to be part of the previous year. Today, we say he was born in 1576, joining a growing family already composed of younger siblings Lessandra, Jacopo and Francesco.

Celebrating the event were his father, thirty-six year old Neri Neri, and twenty-one year old mother Dianora. Neri Neri was already a famous physician and later the royal archiater to Grand Duke Ferdinando. Dianora was the daughter of Francesco Parenti, Michelangelo's lawyer. Tradition dictated that births were celebrated with a house party open to friends and neighbors. Thirty-four year old Francesco Lenzoni, Antonio's godfather would certainly have done his best to attend. His family included Florentine senators and Francesco himself would later become Tuscan ambassador to Spain. Godmother Ginevra Sassetti, in her late fifties, was also from a prominent family. Her nephew Filippo would send plant specimens back from India to be inspected by Neri Neri and their mutual friend Baccio Valori who would become director of the Laurentian Library in Florence. 

Antonio Neri, would go on to learn the finer points of alchemy and glassmaking, developing new formulas and techniques that would be applied throughout Europe. He published the world's first book entirely devoted to formulating glass. It seems especially appropriate that we take a minute to pause and raise a toast (in glass, of course) to his accomplishment and to the end of February, looking forward to warmer days ahead.

Wednesday, February 26, 2014

Dyed In the Grain

Dyeing wool cloth, from "Des Proprietez des Choses"
Bartholomaeus Anglicus, 1482
British Library Royal MS 15.E.iii, folio 269
In his book on glassmaking, L'Arte Vetraria, Antonio Neri presents a number of recipes for paint pigments used to decorate finished glassware. One recipe (#119) is for crimson red, from kermes [kur-meez], prepared by a method of his own invention, which he developed while working in Pisa in 1602–1603.

Since antiquity, throughout Europe and the Near East, kermes was a highly valued red colorant because it formed a pigment that resisted sunlight, humidity and temperature. Kermes red can be found in prehistoric cave paintings, Egyptian scrolls and the robes of cardinals and kings. Words in many languages used to describe bright red, "crimson" and "carmine" among them, are derived from the name "kermes." The pigment is produced from the bodies and eggs of a small type of insect that feeds on the sap of evergreen oak trees throughout the Mediterranean region. In the spring, the female kermes insects and their eggs were harvested. The small eggs surrounding the edges of the insect body resemble kernels of grain, hence the expression "dyed in the grain." For medicinal purposes, kermes pastes were used to disinfect wounds and served as an effective contraceptive. 

To extract the color, Neri starts with a flask of "the very best grappa," which is a potent kind of liquor made by distilling the skins, seeds, stems and pulp of grapes, leftover from wine making. To this, he adds a pound of alum and one ounce of the dried kermes insects, ground finely and sifted. He agitates the mixture, at which point the grappa will "color beautifully" and then lets it sit. After four days, he adds four ounces of alum dissolved in water and pours the mixture into a stocking that has been sewn into the shape of a cone. The stocking hold most of the color, while letting the grappa pass through. 

Alum is another material used since antiquity. It was widely available in Neri's time as a mined mineral, which could actually be several different chemical species with similar properties. Today, chemists know it as a "flocculant"; it neutralizes the electrical charge of finely suspended particles in a liquid, allowing them to stick together and fall to the bottom. This is the secret to Neri's method, although he was not thinking in modern chemical terms, he did know that the alum precipitated the pigment from the liquid allowing it to be collected and dried.

Finally, he scoops the pigment onto pieces of linen stretched over newly fired terracotta tiles and lets it dry. He advises:
Do not spread it too thickly, because then it will not dry quickly. When there is too much moisture it will mildew, and make an ugly color. When a tile has absorbed a lot of moisture, take another new tile. In this manner, it will dry more quickly. When it is dry, remove the coating from the linens. This will be a good lake for painters, as I have made many times in Pisa. Take note that if the color is too strong you should use more roche alum and if it is too weak use less alum so that the color is according to your taste, and desire.
Through the fifteenth century, kermes was among the most sought after pigments, but by Antonio Neri's lifetime, its use was declining in favor of a new insect-based red called cochineal that Portuguese traders brought back from Mexico. Cochineal bugs inhabit the prickly pear cactus. They give a more intense color and eventually replaced kermes throughout Europe.

Monday, February 24, 2014

Pictures of Neri

MS Ferguson 67, f. xxvii-v
U. of Glasgow .
There are two known likenesses of Glassmaker Antonio Neri. The first is a portrait in ink and watercolor, drawn in 1598 by the twenty-two year old Neri's own hand. It resides in the University of Glasgow special collections department, in what is his earliest known manuscript, an alchemical treatise entitled Treasure of the World. Given his birth in 1576, this writing must have been started a very short time after Neri's ordination as a Roman Catholic priest. This manuscript contains a number of illustrations showing both men and women performing chemical work with various apparatus and furnaces, but only this one drawing depicts the author himself. He appears leaning over a glass flask in which he is collecting saliva (for a recipe to make "sale detto sputo dell uomo" or "salt called 'spit of man'"). In part, the text reads "Of me, priest Antonio Neri Florentine 1598."

The second image of Antonio Neri takes the form of a large round plaster medallion, in bas-relief. It was probably prepared for an 1841 meeting of the "Scienziati Italiani" The Italian Congress of Science. Invitations were sent around the world and in August, guests and participants converged on Florence. After opening ceremonies in the Hall of the Five Hundred of the Palazzo Vecchio, sessions took place in the Museum of Natural History, situated next to the Pitti Palace. The museum, still open today, was the first cabinet of curiosities open to the public and dedicated to education.
MS Ferguson 67, f. xxvii-v
(detail, rotation)

Today, the museum is famous for its collection of extremely realistic, life sized, wax models of human anatomy, used in the nineteenth century by medical students in understanding the placement and structure of the body's internal organs. The Specola, which means "observatory," was so named because of the astronomical telescope that it housed. Instituted by Grand Duke

Peter Leopold in 1771, the museum was intended to store and display the collected scientific instruments, books and artifacts of the Medici dynasty. It was also to be a working research laboratory, in which the grand duke himself maintained a space. It was opened to the public in 1775 and sixty-five years later the facility underwent an overhaul, in preparation for the congress of scientists. The construction included a new hall, the Galileo Trubuna, dedicated to the remembrance of great Italian scientists, with astronomer Galileo Galilei taking the place of greatest honor. The space included a number of large marble medallions showing busts of prominent scientists in bas-relief, carved by a variety of well known sculptors of the time. The artists were Cambi, Nencini, Pozzi, Gostoli, Santerelli, Demi, Fantacchiotti, Romanelli, Pampaloni, Magi and Lusini. In addition to the marble medallions, there are a number of others scattered through the museum, executed in identical style, but in gesso. One from this second grouping shows the portrait of Antonio Neri. The artist is not known, although it is reasonable to conclude that the gesso pieces were executed by some of the same artists that carved the marble likenesses for the Tribuna.
Neri Medallion, Specola, Florence
Another possibility, just as likely is that the gesso medallions were prepared later, perhaps for museum director Hugo Schiff who, in the early 1880s founded the  Chemical Institute of the University of Florence, which included a large lecture hall "adorned with medallions and busts of the most famous chemists."

The Neri medallion presents something of a mystery in that it was executed over two centuries after his death, but the model for this likeness is unidentified. His image, in some form or other, must have been available from which the sculptor could work. To date, no such likeness other than the above has been found; the possibility of another image holds out hope for as yet undiscovered source material from the glassmaker's lifetime.

Friday, February 21, 2014

A Question of Religion

Ordination of St. Augustine,
Ambrogio da Fossano (Il Bergognone).
In 1612 Florence, Italy, Antonio Neri wrote L'Arte Vetraria, the first book entirely devoted to formulating and producing glass. Since glassmaking involved an intimate knowledge of chemistry, it is not so surprising to learn that he was an alchemist. However, many are surprised to learn that Neri was a priest in the Catholic Church. In fact, based on the timing of his first manuscript on alchemy, he is almost certain to have learned his craft while in training for the priesthood. 

As historian Luigi Zecchin pointed out, the Florentine Archdiocese records for this period were destroyed in a fire. Unfortunately, no other mention has been found that would confirm the particular sect to which Neri belonged, but there are intriguing clues. First, there are a few common sense deductions: We have the fact that he spent a great deal of his time in laboratories and glass foundries, which makes him an unlikely candidate to have led a parish. He is described in several sources as poor, but we know he came from a wealthy family; his father was the personal physician to the grand duke of Tuscany. This suggests that his sect required a mendicant oath of poverty. These are interesting clues, but they do little to narrow the field; there were at least a dozen sects in Florence that met this description, among them Carmelites, Benedictines, Dominicans, Augustinians and the Knights of Malta.

After Neri’s death, his sponsor Prince Don Antonio de' Medici had a number of associates questioned in an attempt to recover the priest’s secret recipe for the philosopher's stone. From the testimony, we know that Neri's confessor was Benedetto Vanda, of the Carmelite run Santa Maria Maggiore church. The story is that Vanda's relatives were suspected of pressuring Neri for the precious secret on his deathbed.

Another tantalizing passage is written by scholar Girolamo da Sommaia, a historian and prior of the convent church of the Knights of Saint-Etienne. Da Sommaia criticizes Neri for his claims of transmutation, but at the same time drops a very interesting clue about the priest’s affiliation.  "Antonio [Neri] who had died in Florence five or six years earlier and was from San Jacopo in Campo Corbolino [church], said that he had the 'stone,' which he found in a pen-written book of secrets." San Jacopo is a church that the Knights Templar occupied since 1256 and when that order died out, the Knights of Malta took it over. They were a military order for whom Don Antonio de’ Medici held the title of Grand Prior of Pisa. 

Another possibility for Neri was the Dominicans. While it is true that they ran the feared Inquisition, they also ran two apothecaries in Florence that catered to the royal family. One was directly across the street from the Casino di San Marco, where Neri made glass at the beginning of his career. Any training for apothecaries would also have broad applicability to the field of alchemy. 

Closer to home, the Neri family's neighborhood church was at the Cistercian monastery Cestello (a Benedictine offshoot), and their parish church was the nearby Benedictine cathedral of San Pier Maggiore. The Cistercians did provide a young Galileo with his early mathematical training and notable among the Benedictines in Florence was Abbot General Orazio Morandi, who harbored a strong interest in alchemy. But any implication here to Neri’s home order is tenuous at best. 

Evidence suggests that one of Antonio's sisters became an Augustinian nun and a brother may have become an Augustinian Abbot, suggestive yes, but nothing that could be called conclusive. 

Was the famous glassmaker Antonio Neri Carmelite, Benedictine, Dominican, Augustinian, a Knight of Malta? Until more convincing evidence comes to light, for now we must say that we simply do not know.

Wednesday, February 19, 2014

Spanish Ferretto

Covered crucible similar to
Neri's Stratification of copper.
lchemistische Gefäße, (1681)
u.a. Destillierhelm, Retorte (detail)
In his 1612 book on glassmaking, L'Arte Vetraria, Antonio Neri describes how to prepare a variety of metal pigments for glass. Among them is "Spanish ferretto," a copper based pigment. Neri describes the process in plain language, but definitely through the eyes of an alchemist. He writes:
To make ferretto requires nothing more than a simple calcination of copper, where the metal is opened so it can impart its pigment to the glass. When this calcination is done well there is no doubt to anyone that a very interesting diversity of colors appear in the glass. This calcination may be done many ways, but I will put down two that are not only easy, but have been used by me many times for a variety of beautiful effects in the glass. The first method follows here. 
For Neri, "calcination" is the process of breaking a metal down into a powdered form using heat. Notice that he says the copper must be "opened" so that it can color the glass. The thinking here is that the colors are normally hidden inside the metal and that by roasting it in the furnace, the metal is "opened" and those hidden colors become exposed and available to tint the glass. Elsewhere, Neri implies that all the colors of the rainbow are hidden in the glass itself, and that metal pigments cause certain of them to be revealed. 
You should get thin shims of copper the size of a florin [coin] and have one or more goldsmith's crucibles ready. In the bottom of them, you should make a layer of pulverized sulfur, then a layer of the shims, and over them another layer of pulverized sulfur, and one of copper shims, and so on. With this method, fill the crucible in what is otherwise called a stratification. Cover the crucibles, coat them well with refractory clay, dry and place in an open oven to vent amongst burning coals and put a strong fire to them for two hours. Allow them to cool and you will find calcined copper, which will come apart with the fingers, as if it were dry earth. It will rise in color to a blackish-reddishness; this copper should be ground fine, passed through a sieve and kept well secure for use in coloring glass.
To Neri's mind, the result is copper that has been transformed into an "opened" state, ready to impart its color to the glass. To a modern chemist the result could be analyzed and would most likely show a mixture of copper sulfides, copper oxides and perhaps some unreacted sulfur and copper. Through a simple process he has produced a cocktail of different materials. In a very hot furnace, sulfur would tend to be driven off as  toxic, smelly, sulfur dioxide gas, leaving behind copper oxides. The two prevalent copper oxides are red and black in color, as suggested by Neri's statement: "It will rise in color to a blackish-reddishness." How they would tint glass would depend on further preparation of the glass and on what temperatures were achieved in the furnace. 
This second way to make ferretto is much more laborious than the first; nonetheless, it will produce extraordinary effects in the glass. Instead of stratifying the copper in the crucible with sulfur, stratify it with vitriol. Now calcine it, leaving it in the furnace chamber,  near the eye for three days. Remove it, stratify it again with new vitriol and leave it to reverberate as above. Repeat this calcination with the vitriol six times at which point you will have a most noble ferretto whose colors will produce extraordinary effects.
"Vitriol" is a caustic sulfur compound that comes in two varieties: blue and green. When added to water, they can be described essentially as copper or iron dissolved in a sulfuric acid solution (copper for blue, iron for green). Neri does not specify which to use, green vitriol would add iron to the recipe while blue vitriol would simply increase the amount of copper. He then says to leave the preparation "near the eye for three days." The "eye" was a central hole in the furnace floor exposing the flames of the combustion chamber below; it was the hottest part of the furnace, the pots of hot glass were usually arranged around it in a circle. "Reverberation" was a term for indirect heating; in other words not directly exposed to the flames.

Copper oxide in glass can produce a sky blue, a green or a vibrant red. Pure copper can make a dark ruby red color. Iron oxide creates a blue-green and, Neri claims, also a blood red. Sulfur in combination with iron makes a yellowish to amber color. Many of these colors depend not only on the glass formulation, but on the artisan who makes the finished piece. How the glass is "struck," that is: heated, cooled and reheated, can affect the color dramatically. Even today, the only sure way to see what colors are possible with this recipe is to reproduce it and experiment. Through a simple recipe for copper pigment we see just how complex glassmaking could be. Neri’s explanation of metals being "opened" to expose hidden colors is elegant. It was based on observation and it guided him and artisans to make glass creations in a wonderful range of colors. The fact that Neri’s understanding of four-hundred years ago was less accurate than our understanding today is hardly surprising. We should not be surprised at the same outcome four-hundred years from now.

Monday, February 17, 2014

Glass or Rock?

Rock crystal ewer, Egypt (1000-1050)
V&A Museum, #7904-1862
Today, a sharp distinction is made between glass and rock, but in the early seventeenth century, differences in the two materials were not so well defined. One was the product of nature and the other of art, but after that the lines begin to blur. Philosophers debated weather glass should be classified as artificial stone, and why not? It is a material that was actually made from crushed up rocks (quartz and calcined limestone) with the addition of plant salts. In a very accurate sense, it is a form of artificial rock. 

In his 1612 book L'Arte Vetraria, Florentine glassmaker Antonio Neri repeatedly illustrates the thinking that glass was an artificial form of rock. The very first part of the book concerns itself with cristallo glass, which was considered to be an imitation of natural rock crystal. He devotes a whole section to the imitation of the colorful stones variously known as chalcedony, jasper and oriental agate. About these he writes: 
It is often said, and it may well seem to be true, that art cannot match nature. However, experience in many things shows, and this is particularly true of colors in glass, that art not only challenges and matches nature, but by far exceeds and surpasses it. Why, if you did not see it for yourself, you would find it hard to believe the beauty and great variety of interplay seen in these particular chalcedonies.
Another entire section of the book is devoted to artificial gemstones: rubies, sapphires, emeralds, topaz, chrysolite; he even uses crushed natural gems to color his glass. He describes a "sky blue even more beautiful, from the garnets of Bohemia." 

An earlier 1540 book that Neri read closely was by Italian metallurgist Vannoccio Biringuccio, called De La Pirotechnia. This was the first book entirely devoted to mining and metal foundry practices. Biringuccio was from Siena, but was considered something of a folk hero in Neri’s nearby Florence because he oversaw the casting of iron cannons for the city's defense in the great siege of 1529–30. His book contains a short six-page chapter devoted to glass where he writes:
[I]t [glass] is one of the effects and real fruits of the art of fire, because every product found in the interior of the earth is either stone, metal or one of the semi-minerals. Glass is seen to resemble all of them, although in all respects it depends on art.
This is an observation that Neri echoes almost verbatim in the introduction of his own book, and in this light, it is not so difficult to see what connects glassmaking to alchemy. Neri was in the business of learning nature's secrets, and then using them to create new materials that were even better than the originals. These are aims quite familiar to any modern materials engineer. Neri and his contemporaries were successful up to a point. They were able to create artificial gems and other items that were impressive in color and clarity, yet they lacked some key properties of their natural counterparts, most notably hardness. 

Based on Neri's earliest known writing Treasure of the World, started in 1598, he was already familiar with mining practices before his glassmaking activities started and over a decade before he would write the book. He devotes this early manuscript to "all of alchemy, its furnaces, instruments and the mining of metals." Around 1600 he started work at Prince Don Antonio de' Medici's Casino di San Marco laboratory. Here, he may have had the opportunity to interact with characters such as Filippo Talducci (1543- c.1615), celebrated Florentine chemist and mining engineer, several of whose relatives worked at the Casino. In his 1613 manuscript Discorso, Neri strongly hints that he has personally been to more than one mine in connection with his alchemical activities. "I would not say this, had I myself not had the good fortune of being in such a mine from which, with much artifice, was extracted a small quantity of real gold liquor, which was the true golden seed. […] To this day I have never found another mine like it, and therefore suitable for this purpose." 

Today, we hardly associate glass with the raw materials from which it is composed, just as we hardly ever think of metals in their unrefined state. Antonio Neri was more closely connected to the earth, by virtue of his profession, but also because daily life in the early seventeenth century was filled with such activity; refining raw materials into useful forms had a direct and immediate impact on quality of life. Although glass is now manufactured in highly automated facilities, far away from our daily lives, it is still essentially the same product that Neri made. The next time you come in contact with a piece of glass, to pour a drink or look through a window or read the text on a screen as you are probably doing right now, stop for a minute and think of it as Neri did four centuries ago, as artificial rock.

Friday, February 14, 2014

Telling Time

The face of the clock at S.M Fiore in Florence,
Painted by Paolo Uccello (1443).
In his 1612 book on glassmaking, many of Antonio Neri's recipes depend on timing. In two recipes, he uses recitation as his method. "Mix this tartar with the sifted kermes, and when the water in the kettle boils, put in all the kermes, and let it dye the water, reciting the Miserere Psalm once." (ch. 117.) The 50th (51st) psalm begins "Miserere mei, Deus..." (Have mercy upon me, oh God...). Assuming he was using the Vulgate version adopted by Clement VIII in 1592, recital takes about 2 minutes 15 seconds without rushing. "Mix the powders, and always give them to the glass in six portions, stirring the glass well. Set the interval from one portion to the next by reciting the [Apostles'] Creed." (ch. 65.) There are shorter versions, but assuming he used the creed of Pius IV, adopted at the council of Trent in 1564; recitation takes a little under 3 minutes.

There are dozens of other instances where Neri calls for periods in time ranging from hours to days to months. In several cases he specifies the duration of a half-hour, implying the use of a clock or timer of some kind. So, it is worth taking a closer look at exactly how timekeeping worked in his era. In the early seventeenth century, water clocks and hourglasses were long common, and small spring driven mechanical clocks were becoming fashionable, although very few have survived until today. Judging by the unusual precision of birth times in the baptism entries for Antonio and his siblings, it seems likely that the family owned an accurate clock. For example, his own birth is recorded as 29 February, at 3 hours 25 minutes past sunset. This level of accuracy in the matter of birth was sometimes employed in anticipation of better astrological charts.

It was common for a European town to have a public clock in their city hall or principal church; Neri’s home town of Florence, Italy, had both. In 1353, Nicolò di Bernardo built the city's first public clock for the Palazzo Vecchio. (It was replaced by a German clock in 1667, which is still there today). In 1443, Angelo Niccolai degli Orologi, (a grandson of the above Nicolò) built a second municipal clock, this one for Santa Maria del Fiore, installed inside the cathedral above the main doors. Compared to modern clocks, this one has some unusual features: The single hand runs counterclockwise, mimicking the motion of the shadow on a sundial. The twenty four hour mark makes its appearance at the bottom of the dial. (The actual clock mechanism was replaced in 1761 by Giuseppe Bargiacchi, but keeps time identically).

These clocks were built after the invention of the escapement (the part that goes tick-tick, tick-tock), but before pendulums had been incorporated. Galileo realized the advantages of pendulums in timekeeping during our glassmaker Neri’s lifetime, although they were not acted upon for another half-century. The accuracy of any clock depended on the ability of its mechanism to keep a steady pace, and in the early seventeenth century, a fifteen minute error was not uncommon. The clocks at the Palazzo Vecchio and Santa Maria del Fiore were checked regularly and adjusted based on the readings of a nearby sundial, so the time also shifted with the seasons. 

In Florence, and many other Italian cities, the custom was to start counting hours at sunset. Each day was divided into twenty-four equal hours. The start of the Church’s liturgical day was actually signaled a half hour after sunset with the ringing of the bells for the Ave Maria prayer during evening Vespers service. One o’clock was one hour past sunset, etc. This first hour was called "l’or di notte," [the night hour] and contrary to what one might think, it did not signal the beginning of a new calendar day. Each new day began with the ringing of the Campanile bells at sunrise. This Italian system of timekeeping (hora itálica) had been practiced for over a millennium, it was established by Julius Caesar for the Roman Empire. Not until 1750 did Italians adopted the current (French) system of two twelve hour shifts beginning at midnight.

Wednesday, February 12, 2014


Dragon-stem goblet, Venice, Italy,
(or in the Venetian style), 17th cent.
Corning Museum of Glass 51.3.118.
Venetian cristallo is quite literally the glass that made Murano famous. Ultimately, royal courts and wealthy families throughout Europe coveted glassware of this type. It had the clarity of its namesake mineral, rock crystal, and its working properties were such that one could make extremely thin, yet complex pieces. At a time when glass made from dirty sand and fireplace ash was churned out cheaply and quickly around Europe, cristallo was the absolute pinnacle of the glassmaker's art.

Murano glassmaker Angelo Barovier gets credit for the development of cristallo around the year 1450. However, it is a mistake to think that suddenly, he exclaimed "eureka" and burst out of his workshop with an entirely new invention. The predecessor of cristallo was what Antonio Neri called cristallino, which already incorporated some of the advantages. Barovier may well be responsible for bringing together the ultimate refinements that elevated cristallino to a new level of perfection, but these techniques individually were all available and utilized by glassmakers at least fifty years earlier. 

Barovier had attended lectures by noted alchemist Paola de Pergola, at the School of Rialto. This indicates that he was thinking along the lines of a chemist in putting together a repeatable regimen for an exceptionally clear, bright, workable product. The real genius in cristallo was in controlling the purity and quality of all the materials through Venice's extensive trade network in the Mediterranean. Even if the recipe leaked out, exclusive trade agreements blocked access to the raw materials. Local ordinances tightly controlled source materials used in the furnaces to ensure consistency, from the quartz river pebbles crushed for frit, to the plants used to make the flux, to the manganese which eliminated any slight tinting. Requirements even stipulated the making of the furnace crucibles from a specific variety of clay from Constantinople.

Barovier's innovation would become a tradition that would be carried on by countless glassmakers and ultimately by our Florentine priest, Antonio Neri, more than a century and a half later. Neri describes the Venetian methods, but then goes on to innovate with variations of his own. Numerous family manuscripts in Venice documented the method to make cristallo; what Neri did was to publish these relatively secret techniques and make them available to anyone who could read his book, and many did. 

For silica, the main ingredient in glass, Neri says the craftsmen on Murano specifically used quartz river pebbles (tarso) from the Ticino River in Pavia. He describes special procedures to pulverize the stones without contamination, into a powder "ground as finely as flour." Next, he makes the flux (glass salt), which allows the quartz to melt at lower temperatures. He says to use the ash of the kali plant from Syria (polverino and rocchetta). This plant ash is very rich in sodium carbonates; he extracts and purifies it in a process called lixiviation. Neri purchased the starting material in a charred state, which reduces it weight and volume for shipping. From 300 pounds of ash, he usually produced 80-90 pounds of salt. The ash was boiled in cauldrons full of water, strained, filtered, evaporated and dried leaving the all important glass salt. Into each cauldron, he mixes ten pounds of tartar—the dried dregs scraped from the inside of red wine barrels—a material high in potassium carbonates. Today, we know the soda component is responsible for the favorable property of long working times for artisans before the hot glass stiffens, the potassium adds sparkle. The final ingredient was two pounds of lime (calcium oxide) per one hundred pounds of salt, which is added to the dry salt because it is not water soluble. This stabilized the glass against future degradation by moisture over time. 

200 pounds of powdered quartz mixed thoroughly with 130 pounds of the salt forms the basis of the frit. He raked the powder around in a hot kiln for about five hours, until "nut sized" pieces began to form. Now this cristallo frit,—which Neri calls bollito—was carefully packed to remain dry and allowed to age for three or four months, when it was ready to melt in the furnace. If the glass should have a slight green tint from iron tools, it was corrected with manganese (oxide), specifically mined in the Piedmont region. The cristallo was boiled for up to six days and repeatedly washed by ladeling the hot glass into cold water and then remelting.

The result was a glass that was a pleasure for gaffers to work and make finished pieces over which royalty clamored. Cristallo was uniform in consistency, it could be blown into molds or worked freehand into complex shapes, like the iconic "dragon goblet" form, which became a hallmark of the Venetian masters.

Monday, February 10, 2014

Gold Ruby Redux

A gold florin.
Legend claims gold ruby glass
 was discovered when a nobel threw
a gold coin into a glass maker's crucible.
Antonio Neri is best remembered for writing L'Arte Vetraria. It was the first printed book entirely devoted to the formulation of glass, which he published in Florence, Italy, in 1612. If we were to single out just one of his more than a hundred recipes, covering glass, lead crystal, paste gems and enamels, it would have to be his prescription for "Transparent Red" ruby glass made with gold. This recipe still captivates glass artists today, as it has since Neri wrote the book. In fact, gold ruby glass is closely tied to the lore of alchemy and has intrigued experimenters as well as artists and collectors since the Roman Empire, possibly before.

Alchemists had long thought gold to be the perfect metal and that all other "lesser" metals (read: lead, tin, copper, iron, mercury and silver) could be coaxed to fully "mature" into gold. Experimenters thought that if they could capture the "essence" of the king of metals, it could be used to "seed" the other metals, and transmute them into pure gold. This is where ruby glass comes into the discussion. In general, glass is colored by the addition of finely powdered metals. Depending on the metal and how it is treated, a whole rainbow of colors can be produced in glass. Alchemists were convinced that the color was an indication that this "essence" of the metal had been released into the glass. 

For artists and collectors, gold ruby is simply a very attractive color; the difficulty of producing it and working with it only adds to its cachet. Transparent red in glass can be produced other ways, notably with copper, but copper red has a slightly more orange color. Gold ruby, on the other hand, has a characteristic red color that can have slight hints of purple. It can be made light and ethereal or dark and heavily saturated, but viewed next to its competitors, it has a very distinctive hue that experts pride themselves on recognizing.

Neri’s recipe involves moistening gold powder with "aqua regia," which we know as a mixture of nitric and hydrochloric acids. He then spreads this wet mixture on an earthenware pan and heats it in the furnace "until it becomes a red powder, which will take place after many days." Here is that color change that alchemists looked for as an indication of transformation; we know today that Neri was producing gold chloride. This is one of the very few chemical compounds that gold forms and in fact, this is one of the main things that makes gold so special: it does not rust, nor corrode or tarnish, which are, in the end, all chemical reactions between the metal and its environment.

Neri directs his readers to sprinkle, little by little, the gold chloride into the glass melt. He says to "Use fine cristallo, thrown in water many times." Cristallo is the exceptionally clear glass invented by Venetian craftsmen, and "washing" was a technique to remove excess water soluble flux and other contaminants. He finishes his instructions abruptly by saying this method "will make the transparent ruby red glass; but you must experiment in order to find it." In other recipes, Neri goes to great lengths to explain his methods in detail, here he seems content to barely scratch the surface. Much speculation has taken place over the reason for this surprisingly short recipe. Was he ordered, perhaps by his Medici overlords, to keep details to a minimum? Some have wondered if Neri even knew how to produce gold ruby; the short recipe may have been a cover for his lack of knowledge.

Doubts about Neri's gold ruby glass recipe grew after his death, when it was discovered by other experimenters that the addition of small amounts of tin into the mix produced the ruby color quickly and reliably. This compound of tin and gold chloride was called "Cassius purple" after one of its inventors and its color. In some circles it was thought that the tin was an essential ingredient, a lost secret that had been rediscovered. The argument was that gold chloride alone could not produce the color, it must be combined with tin in the form of Cassius purple. However, this is not the case. 

In an 1846 edition of the Journal of the Franklin Institute (ser. 3, v. 11), professor of chemistry and natural philosophy, E. L. Schubarth, cites numerous investigators who demolish this theory. He wrote:
It must not be imagined from this, as some persons have lately stated, that it is necessary to use gold [combined with tin] in the state of Cassius purple.
Neri, at the end of the sixteenth and commencement of the seventeenth century, stated, that in order to stain glass a ruby color, it was only necessary to employ calcined chloride of gold. At a later period, Libar wrote to the same effect, and Merret certified that he had proved the efficacy of the process. In 1834 Golfier Besseyre stated, in the Journal of Pharmacy, that Douault Wieland colored his paste with perchloride of gold only. Lastly, in 1836, Fuss writes, that in Bohemia all the ruby-colored glass was prepared with chloride of gold only, and that glass might be stained red as well with metallic gold, as with oxide of gold or Cassius purple.
It is therefore a fact known for some time, that glass may be stained red, without either Cassius purple or oxide of tin, with [only] metallic gold or preparations of gold. In the glass-works of Bohemia and Silesia perchloride of gold only is used, without the addition of oxide of tin, in order to produce their fine rose or carmine-colored glass.
Of the men cited, Douault-Wieland was a Parisian jeweler who was famous for his artificial gems and crystal glassware. He was praised for his skills by Napoleon. Paul Golfier-Besseyre was a well respected French chemist. Besides many other endeavors, he worked for the glass industry and performed numerous experiments on the formulation of glass. He produced a gold ruby using the same ingredients as Neri. He determined good color could be achieved by letting a new batch of the glass age for a protracted period of time at temperatures below the melting point of gold. Periodically, he removed the glass from the furnace and poured it into water to wash it. The result was a yellowish glass when molten, but when a gaffer finished a piece it was gently reheated and the ruby color developed. 

Friday, February 7, 2014

The Golden Nail

Portrait of Leonhard Thurneysser
Frans Floris de Vriendt (1519/20 - 1570)
Of all the stories of transmutation by alchemists, one of the most interesting is the story of the "golden nail" in which Ferdinando de' Medici witnessed, with his own eyes, a demonstration that purported to turn half of a common iron nail into pure gold. The nail in question became a treasured possession of Ferdinando and was displayed for many years at the Galleria dei Lavori, in the Uffizi palace, in Florence. 

It is all but certain that glassmaker and alchemist Antonio Neri saw the nail, probably many times in his career. In his 1613 manuscript Discorso he says:
Some argue that the possibilities of this art are demonstrated clearly through the experience of the 'nail' [chiodo], which is seen in the Galleria [dei Lavori] of the grand duke of Tuscany, of which one part is solid iron and the other which was immersed in some sort of liquor is recognized to be pure gold.
It is interesting that Neri does not commit here, to the conviction that this "is" transmutation, only that "some argue the possibilities." The story was recounted by numerous chroniclers and became a favorite subject of speculation. Was this a case of a cleaver deception? A century later, it was still being talked about: here is Otto Tachenius, in his Hippocrates Chymicus (1677) quoting then Cardinal, later Grand Duke Ferdinando I de' Medici. 
Mr. Leonhard Thurneysser in my sight and presence, turned an iron nail heated in the fire, and immersed in an oil, into gold; done at Rome the 20th day of November after dinner.
So it would seem that at least the Grand Duke was convinced.

Thurneysser was the son of a goldsmith from Basel, and a devotee to the methods of Paracelsus. He became intrigued with alchemy and made a fortune touring the courts of Europe, putting on demonstrations. When Antonio Neri was about fourteen years old, cir.1590, Thurneysser passed through Florence.* In later testimony by Neri associate Guido Melani, a metals refiner, the priest had confided in him that he himself had learned a gold transmutation recipe from a German, who used the techniques of Paraselsus. It is conceivable that this was Thurneysser. 

Skeptics proposed a very plausible explanation: that a special nail was prepared in advance, half gold soldered to half iron. The entire nail was then recoated with a thin layer of iron, perhaps deposited chemically. In the demonstration, the special nail would find its way into Thurneysser's hand, and with great flourish be heated and then dipped into the secret oil, which was aqua fortis, what we know today as nitric acid. The iron coating on the nail would fizzle and sputter in the acid and dissolve away to reveal the pure gold interior.

Those calling themselves "alchemist" ran the gamut from small time confidence men right through to early modern scientists and everything in between. To complicate things further, when they were found in the same room together, the scientist might not be so motivated to unmask the huckster. Thurneysser's demonstration clearly fired Grand Duke Ferdinando's imagination, and may well have influenced him to make a place at court for Antonio Neri.

* UPDATE: 24 Feb 2014, recent scholarship has cast serious doubt that Thurneysser was ever in Florence. This makes a meeting with Neri unlikely. I hope to make this the subject of a future blog post – stay tuned.

Wednesday, February 5, 2014

The Duke’s Oil

Trajan's Column, Rome
Giovanni Battista Piranesi (1758)
In the seventeenth century, alchemy was a dangerous business. Yes, there were risks of sanctions by the authorities, which could be very harsh, but great dangers also lurked in the chemicals themselves. Some like lead and mercury accumulated in the tissues slowly, over a period of years, others could kill a man within a few minutes. Cardinal Francesco Maria del Monte had personal knowledge of just how deadly the products of alchemy could be.

In Rome, Del Monte was the unofficial ambassador to Florence and the Medici family. He regularly greeted dignitaries from around Europe and dazzled them in his sumptuous palace. He was an avid glass collector, a patron of the arts and more quietly a dedicated student of alchemy. He was a lifelong friend to Don Antonio de' Medici and visited the prince's laboratory in Florence several times. This is where Antonio Neri was making glass early in his career. Later, Neri worked at a secondary Medici glass furnace in Pisa, where the cardinal had fancy glass table service made for the Vatican.

About a two mile walk from Saint Peter's Basilica, over the Tiber River, directly toward the Colosseum, is Trajan's Column. It commemorates Emperor Trajan's victory in the Dacian Wars at the beginning of the second century. It displays a scroll in base relief that winds all the way from the pedestal to the capital. The monument is large enough to contain an internal staircase leading to an observation platform at the top. In 1587, it was crowned by a bronze statue of Saint Peter that still stands today; the initial model was sculpted by artist Tommaso della Porta, who was under the patronage of Cardinal Del Monte. 

Giovanni Baglione picks up the story in his book Lives of Painters, Sculptors and Architects:
That man [della Porta], I think, suffered mentally and it showed at the end of his days. When he felt some kind of tingling in his abdomen, he went to the Cardinal del Monte his friend and master and asked for some of the "grand duke’s oil" that he hoped would relieve the tingling. The Cardinal indulged him; gave it to him and said that he should apply it only to the wrists and only a little, because the oil was potent and it could make him feel sick. He took it and went back to his house and after dinner he sent for the barber, to administer the medication, and while the messenger went on, Tommaso impatient and simpleminded, applied the oil himself and instead of touching the wrists, as the Cardinal had instructed, he lathered the arms, chest, body and entire abdomen, so that the powerful oil went to the heart and in fact killed him. The barber arrived to medicate him, found him dead and all attempts at revival were in vain. Tommaso della Porta, was buried at Santa Maria del Popolo.
The "grand duke's oil," was widely known, and widely cited in references throughout Europe well into the 19th century. Its other name was oil of tobacco – essentially a distillation of almost pure nicotine. In very small doses, it acts as a stimulant of the central nervous system, in slightly higher doses it is a narcotic, even greater, but still relatively small amounts act as a quick and lethal poison absorbed directly through the skin. Ingesting a single pill capsule of typical size full of pure liquid nicotine is more than enough to kill an adult in short order.

This story has one final twist. Antiques dealer Domenico Lupo was one of the men present at the reading of Della Porta's will on 7 March 1607. Twenty-five years later, an inventory of Lupo's assets listed a "small figure half old and half new that is said to be of Prior Ant. Neri," either the glassmaker or possibly his great uncle.  

Monday, February 3, 2014

Saint Philip Neri

Saint Philip Neri
In the final quarter of the seventeenth century, a certain holy man in Rome practiced charity in its humblest form. A native of Florence, a man named Filippo Neri (1515-1595) made visits every day to plague victims in the hospitals. He prayed for patients in their last hours and brought food for those abandoned by their families. He walked among the poor and destitute, eating just from the alms he received. He lived what he preached and set an example of Christianity stripped of pride and envy. In unconventional style, he led walking tours of the churches in Rome. Although the practice of venerating the living as saints received strong discouragement by the Church, Filippo Neri nevertheless realized effective sainthood during his lifetime. His followers credited him with numerous miracles. 

Conventional history places the exact location of Filippo Neri's birth in Florence on the south side of the Arno. However, local folklore suggests an alternate location: in one of two rooms of the same Borgo Pinti house later owned and occupied by Antonio Neri's family. The common family name of Neri naturally leads to the question of whether or not the saint and the glassmaker were of common ancestry. Antonio's father, Neri Neri, maintained that his own father, Jacopo, was a cousin to the holy man. 

A full-length image of Filippo Neri himself appears in a corner of the Neri chapel, On Borgo Pinti in Florence. Giovanni Cinelli, writing in 1677, tells us of Neri di Jacopo (Neri Neri):
It was his intention to dedicate [the chapel] to his relative Filippo Neri; it is possible that Jacopo di Neri, father of M[esser] Neri Neri was the cousin of Filippo Neri then still living, today Saint Philip. But [the dedication] was not to be, because in pressing to oversee its completion and delays in the canonization of the Saint, the dedication was changed to Nereo and Achilles, which was finished by Alessandro per the will.
Because the canonization was delayed, it would have been inappropriate to dedicate the chapel to Filippo, so two of his favorite saints were substituted.

The assertion that Neri the medical doctor and Neri the holy man were true blood relations has yet to be verified. However, there are positive signs: the saint's well-established genealogy meshes with records of Antonio Neri's family housed at the state archives in Florence. In fact, both sets of records—of the alchemist and of the saint—share a single file in the archives. These documents indicate a common ancestry at the level of third cousins. The elder Jacopo Neri and Filippo Neri (later Saint Philip) appear to have shared a great-great-grandfather. It is a remote connection, but one that was a source of  pride for Antonio’s father. 

There is also a notable similarity of family crests; the shield of Saint Philip Neri's family feature three stars on a blue field, that of Antonio Neri's family features  a  banner with three stars against a blue rampant lion. The Saint's genealogy is well established, but the matter is complicated in that Antonio's branch of the family left Florence around the turn of the sixteenth century. Here we lose track of them for one generation. Regardless of the difficulties, there is mounting evidence that Antonio's fourth-great-grandfather, Michele di Neri, was the brother of Saint Philip's second-great grandfather Ser Giovanni di Neri. A further association with Filippo Neri lies with Antonio Neri's maternal grandfather, Francesco Parenti, who served as attorney for the saint’s sister Caterina in the execution of the holy man's will.

Filippo Neri was unusual for his time. He was a champion of the common man, and he was humble to a fault; not a leader by force, by wealth, nor by charisma, but by gravitas. Antonio Neri's father seems to have been a man from the same mold, as exemplified by the absence of self-import declarations or artifice. He admired Filippo Neri, and we can guess that he shared the holy man's philosophy. Filippo never wanted  and protested strenuously against any aggrandizement. We see this trait follow through with Antonio. In his manuscripts and in the book on glassmaking, there is no evidence of boasting, or name-dropping, nor claim of superiority. What we see is a humble quest to understand nature, and to be of service to mankind.