Thévenot Continues East

Stained glass windows of the Nasir al-Mulk 'Pink Mosque', Shiraz, Iran

Photo by Domiri Mohammad Reza Ganji.
(Click to enlarge)

Previously, we followed the progress of seventeenth century tourist Jean de Thévenot, noting his comments about glass as he traveled. He sailed from Rome to Malta to Constantinople to Egypt. He then continued overland through Syria and sailed down the Euphrates River toward the Persian Gulf.  At Basra he turned around and headed north, picking up the Tigris River to Baghdad where he continued eastward to Persia. In Isfahan he described numerous species of plants, animals and insects. Further south he took note of a city where glassmaking captured his attention:

The people of Schiras [Shiraz, Iran] are very witty and the city hath given birth to most of the best poets of Persia. There is much glass made there, and several glass-shops are in town, though they work not constantly in their glass-houses, but let the fire go out after they have employed a certain quantity of materials. They make their glass of a white stone, almost as hard as marble, which they get in a hill four days journey from Schiraz and it is very clear: especially they make great bottles as clear and delicate as in any other place in the world; but it is wonderfully strange how they can blow the great bottles they call ‘Caraba,’ which are as thick as one finger and hold nearly thirty quarts of wine; these bottles are covered with the straw of canes. [1]

Preceding Thévenot in Shiraz by a number of years (1627) was the British traveler, Sir Thomas Herbert, who stated that there was “…no part of the Orient showing better or richer wine.” [2] The mutually beneficial association between the production of wine and glass is one that appears in numerous locations throughout history. That both crafts should occur here, at the center of activity for this region’s premier vineyards should be no surprise. 

The region’s ‘Shirazi’ wines have been connected by various legends to the French Rhone variety now known as ‘Shiraz,’ but the vineyards in Iran are now defunct, and no definite conclusions have been reached, except that if a kinship exists, it is a very ancient one. In other quarters, Marco Polo mentioned Persian wines [3] and Omar Khayyam praised them throughout his Rubaiyat. [4]

At the same time that Thévenot passed through the region, so did fellow Parisian Jean Chardin (Sir John Chardin) who spent about eighteen months visiting (1666-7). It is unknown if the two travelers met. In his own published diary Chardin stated  “The art of glass-making; there are glass houses all over Persia, but most of the glass is full of flaws […] The glass of Chiras [Shiraz] is the finest in the country” and he went on to say that “Moreover, the art of glass-making was brought into Persia within these four score [80] years. A beggarly and covetous Italian taught it at Chiras for the sum of fifty crowns.” [5]

This last passage is often quoted in reference books without comment, to the point that it has become quite famous. At the risk of stating the obvious, the notion that one man, a foreigner, down on his luck, could single handedly bootstrap an entire industry that would fully mature throughout Persia in eighty years is absurd on its face. Beyond that, it is something of an insult to a culture that current scholarship credits with key developments in the invention of glass more than five thousand years ago. [6] Chardin’s condescendence toward Persian artisans and craft in general is well demonstrated throughout his book. His claim is plain enough, however if we want to be charitable, we could speculate that he misunderstood his source, who actually told him that the Italian was responsible for showing European style glassmaking to a well established technical community in Shiraz. Historian Stefano Carboni identifies a fifteenth century downturn and says “in Iran the industry was revived with the help of European, mostly Venetian, craftsmen in Isfahan and Shiraz from the seventeenth century.” [7]

[1] Thévenot v.2, p. 125, 126
[2] Thomas Herbert  “A Relation of Some Yeares Travaile, Begunne Anno 1626.” (London: Stansby and Bloome, 1634), p. 133.
 By Thomas Herbert   also see http://www.saddleflasks.com  “An extensive reference site devoted to Late Persian glass.”
[3] By Marco Polo, “The travels of Marco Polo, the Venetian,” trans. by William Marsden (London: J.M. Dent, 1926), p. 41 (bk.1 ch. 15).
[4] Omar Khayyam, “Rubaiyat of Omar Khayyam” trans. by Edward Fitzgerald (Boston: Branden Books, 1989), for example, stanzas VI, XI, XII, XLI, LVI.
[5] John Chardin “Sir John Chardin's Travels in Persia” (New York: Cosimo, 2010) p.275  (abridged English translation of 1724 original).
[6] For instance, see  https://en.wikipedia.org/wiki/History_of_glass http://www.iranicaonline.org/articles/glass ,  https://en.wikipedia.org/wiki/Sasanian_glass .
[7]  Stefano Carboni, “Glassware” in Medieval Islamic Civilization: An Encyclopedia edited by Josef W. Meri (New York, Routledge, 2005) v. 1, p. 298.

Travels to the East

Jean de Thévenot, from

"Relation d'un voyage fait au Levant" (1664)

In 1652, at the age of eighteen, a wealthy Frenchman named Jean de Thévenot finished his studies at the University of Paris. He celebrated his achievement with a grand tour that would take him, not just through Europe, but unexpectedly half-way around the world, where among other things he would find glass being made. 

In Rome, he befriended fellow Parisian, Barthélemy d'Herbelot, where they conspired to travel together to the Levant. 

Circumstances detained d'Herbelot and after waiting five months in Malta, Thévenot gave-up on his companion and set out on his own to Constantinople. Four years later, in 1659. He returned home only to prepare for an even more epic adventure, one that would last until his 1667 death in Azerbaijan from an accidental pistol shot. 

Thévenot kept a travel diary, he picked up languages easily and endeavored to blend-in to local culture as much as possible. Throughout his travels he made keen observations of people, customs and of the natural world around him. He published a volume of his adventures to great acclaim, two more would follow after his death. In 1687 his work was translated into English, when it found a whole new audience. 

Of special interest to us are his numerous observations about the glass trade. This was a subject to which he had no special interest or connection, but his natural curiosity and communication skills open a window into an otherwise poorly documented piece of the glass history puzzle.

On Malta, even before embarking for the Far East, he notes that “sore eyes” are a problem because of the bright sun on the white (limestone) earth of the island “which makes many commanders and knights wear green spectacles”; certainly an early incarnation of sunglasses. [1] In Constantinople (today Istanbul) he visited the great mosque Hagia Sophia and remarked “it is full of lamps and curiosities in glass balls, of which one for instance, contains  a little galley, well rigged, another a model of the mosque in wood and the rest a great many pretty knacks of that nature.” [2] Having booked passage out of Alexandria, Egypt on an English gun boat, he explains that the sailors kept track of their speed with a “little slat and very thin piece of wood tied to a line and when they throw it into the sea, they turn a half-minute sand glass […] every seven fathoms of the line making a mile in an hour.” [3] This is the origin of the nautical unit of speed known as the 'knot', the method of paying out line spaced with knots tied in the line at intervals of  8 fathoms - 47 feet 3 inches (14.4 m). This method of reckoning progress with a line was used well into the nineteenth century, the units are still used today, both for boats and aircraft.  A vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour. [4]

In Damascus, Syria, he visited the great mosque there (Umayyda). Some natives kindly offered to take him in, disguised with a turban on his head, but he declines, fearing that if discovered, he will be forced to choose between his life and his Christian faith. Nevertheless he walks around the tremendous structure and observes that “The pavement is all of lovely stones that shine like lookinglass” and he continues “I went up to the terrace-walks, to the windows of that mosque, which are made like the windows of our churches and have panes of glass set in plaster, which are wrought into figures.” [5]

West of Aleppo, Syria, on the banks of the Euphrates River, Thévenot explains that, “barks loaded with glass (of which I will presently speak,) go to Bassora [Basra].” A ‘bark’ or ‘barque’ was a small three masted sailing ship. “While I was at Aleppo, the Sheik Bandar hired a bark to carry five or six hundred cases of glass, which he sent to the Indies.” And “I wondered to see that they who baled up these chests for the Sheik Bandar, tumbled them so rudely that they broke all the glass; but they told me, 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 lookinglasses to see themselves in. That glass is all over laid with quicksilver on one side and is a very salable commodity in the Indies and profitable to the merchants.” [6]

One implication from this passage is that the named Sheik Bandar ran a glassmaking operation in Aleppo. It is interesting to note that Florentine glassmaker Antonio Neri had an uncle, his father’s brother Francesco, who was a merchant living in the Tuscan enclave inside Aleppo about sixty years earlier.

In the next installment we will continue to follow the thread of glassmaking references in the chronicles of Thévenot’s travels which take him to Persia, where he finds a glassmaking center.

[1] Jean de Thévenot, “The Travels of Monsieur Thevenot Into The Levant” (London: H. Clark, 1687) v.1, p. 6.
[2] Ibid, p. 22.
[3] Ibid, p. 268.
[4] See Wikipedia http://en.wikipedia.org/wiki/Knot_(unit).
[5] Ibid, v.2, p 17.
[6] Ibid, p.40.

Neri in Pisa

Majolica vase by Niccolò Sisti,

decorated in the grotesque style.

Antonio Neri's career in glassmaking took him from the city of his birth, Florence, to Pisa, Antwerp and possibly other places yet to be confirmed, such as Rome and Venice. Under the reign of Grand Duke Ferdinando de' Medici, a glass furnace at Pisa became an important source of diplomatic gifts in both glass and ceramics. Antonio Neri worked at this facility in the first years of the seventeenth century. Later, the same foundry would receive an order for exceptionally clear glass to be used by Galileo in his telescopes. It is unknown how that particular project worked out, but the furnace master, Niccolò Sisti, made a name for himself supplying glassware to the Vatican, the king of Spain and many nobles throughout Italy and Europe. Undoubtedly, Neri's glass career was strongly influenced by his tenure in Pisa with Sisti. 

In the early seventeenth century, there were several glass furnaces in Pisa. One was run at the pleasure of Grand Duke Ferdinando by Niccolò Sisti. Raised in Norcia in Perugia, he likely learned his trade at an early age;  Sisti's father, Sisto de' Bonsisti, was said to be an expert in making paste gems. This would account for the son's apparent skill in the medium of glass in addition to his ceramics prowess for which he was previously employed at the Casino di San Marco in Florence. For Neri, working at Sisti's glass house in Pisa played an important role in his glassmaking education. Sisti would serve three Medici grand dukes, Francesco I, Ferdinando I and Cosimo II. When work came to a stop at the Casino di San Marco, after Francesco’s death, Sisti may have opened his own factory in Florence for a short time, but then moved to a new facility in Pisa.

 In 1592, Grand Duke Ferdinando set up a glass shop in the central part of Pisa, along the north bank of the Arno River. This furnace was staffed by Muranese workers and was located in the city center, along the river. Archaeologists have unearthed its remains in the courtyard of what is now 43-44 Lungarno. The operation was capitalized with a loan of five hundred scudi made by Ferdinando I to Sisti, with a special mandate: he was to introduce new forms of pottery to the region. In addition to glass, the furnace at Pisa would produce soft-paste porcelain and majolica ceramics. These were both forms that Sisti had helped to develop when he worked in Florence at the Casino; he was involved in Francesco’s quest to duplicate Chinese porcelain.

In 1602, Neri was to be found working alongside Sisti at the Pisan furnace. According to his own account, this is where he worked on special colors, and collected river stones for glass frit. Here he made kermes based paints, enamels and used ferns as an alternative plant salt for glass. In all likelihood, he would have had access to the nearby botanical gardens and the small adjacent laboratory located just a few blocks from the glass furnace. 

Early in 1604, the priest would make his trip north to Antwerp to visit his friend Emmanuel Ximenes. During Neri's seven year absence, Sisti's projects included cristallo table service for the Vatican, and special glass for the lenses of Galileo's telescopes. Upon Neri's return from Flanders, we again find him working in Pisa, this time on alchemy. In a copy of his last known manuscript, a heading reads, "Techniques copied from an old book here in Pisa."  The university at Pisa was an intellectual center and a repository of technical knowledge. There, Neri had access to a wide range of materials in the libraries. The furnaces and laboratories provided him with hands-on experience, but there can be little doubt that he was a voracious reader as well. On the same page of this manuscript appears the date 26 January 1614. This is the last known specific information on the priest's whereabouts, since he would be dead within the year, at the age of thirty-eight.

*This post first appeared here in a shorter form on 18 October 2013.

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.

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.

Reflections on the Mirror

Jan van Eyck

The Arnolfini Portrait (1434)

L’Arte Vetraria, Antonio Neri's 1612 book, would eventually become the glassmakers' bible throughout Europe. By 1900 it had been translated into five different languages besides the original Italian; English, Latin, German, French, and Spanish (and in this century Japanese). Because of its seminal importance in the spread of glass technology, often overlooked are a few recipes at the back of the book, which have only a tenuous connection to the main subject.

Among these is a metallurgical formula for making convex mirrors. Neri gives instructions for producing what we would now call a "white bronze" that may be cast into a rounded form and polished to take on a highly reflective surface finish. This "spherical" form of mirror was popular throughout the Renaissance. It reflected a wide-angle view of the space in which it was hung, but at the cost of distorting the image. Nevertheless, upon looking into such a mirror, objects are still quite recognizable. 

Here is Neri's prescription:

A Mixture to Make [Mirror] Spheres:
Have 3 lbs of well-purified tin, and 1 lb of copper also purified. Melt these two metals, first the copper, then the tin. When they fuse thoroughly, throw onto them 6 oz of just singed red wine tartar, and 1½ oz of saltpeter, then ¼ oz of alum, and 2 oz of arsenic. Leave these all to vaporize, and then cast [the metal] into the form of a sphere. You will have good material, which when you burnish and polish, will look most fine. This mixture is called acciaio and is used to make spherical mirrors.

Of note is the fact that the word Neri uses for this alloy, acciaio, translates to "steel." Over the intervening four centuries, the meaning of this term has been refined so that today it denotes not simply a hard white metal, but a specific range of alloys containing iron and carbon, which Neri's alloy does not. 

This recipe and a few others in the book show the breadth of Neri's experience in arts other than glassmaking. It is a conclusion greatly amplified by a perusal of his other manuscripts on alchemy and medicine. There is good evidence that our priest was a voracious reader, however he was also quite cautious about repeating techniques only after he had verified them personally. Besides, artisans never wrote down much of this knowledge – only passed in confidence between trusted parties – since, in a very concrete way, superior knowledge represented a competitive advantage over ones rivals. Even if Neri was in the business of divulging secrets, it is safe to assume that many of the artisans and craftsmen he interacted with were decidedly not. Apparently, Neri was not familiar with the process of mirroring glass directly with mercury/tin amalgam; a process for which Venetian glassmakers had already become famous for perfecting. It is an interesting omission from his book, since he almost certainly would have seen examples in Florence and in Antwerp.

Two centuries before Neri, the beginning of the fifteenth century saw the invention of moveable type printing in Germany, but also the mastery of perspective illustration in Italy. The contribution of printing to early modern science is well documented, less obvious is the role playerd by artists and perspective illustration. Moveable type made possible the mass production of books; what did get committed to paper now stood a much better chance of survival and transmission. Perspective illustration played a more nuanced role, one that ultimately brings the convex mirror back into the discussion.

Jan van Eyck
The Arnolfini Portrait (detail).

In Venice and especially in Florence (Neri's hometown), perspective drawing became the rage among artists, largely due to the Italian translation of a book entitled Deli Aspecti, or "Alhazen's Book of Optics." Suddenly, paintings were made to look three-dimensional, with a realistic sense of depth to them. The new techniques were largely kept in Italy, but interest spread across Europe. Patrons placed great value on work depicting scenes in correct perspective, and in excruciatingly accurate detail. 

In Flanders, in 1434, Jan van Eyck produced "The Arnolfini Portrait," (above). Behind the main subjects, hanging on the wall is a convex mirror. The reflection in the mirror shows the backs of the two subjects, but also two other figures further back, one of which is thought to be the artist himself, and beyond him a strong light source. The image in the mirror is distorted exactly as one would experience in real life. 

There is growing speculation that among the secrets of "realist" (or naturalist) painters was a growing arsenal of optical tools and lenses used to map out and understand the attributes of perspective. The mirror, in the Arnolfini Portrait was a sort of boast of the artist's proficiency in recreating reality on the canvas.

The point is that here is a case where art led science into new realms. Painters started to take great pains in reproducing reality "as it is" on canvas. Soon minor experimenters like Neri and major luminaries like Galileo were taking great pains to do the same. They strove to observe nature "as it is," not as was prescribed in ancient texts, or dictated by authority. Once that process started, awareness of the world grew and there was no turning back.

Finally, it is amusing to note that in his many manuscript illustrations, Antonio Neri himself never quite mastered perspective drawing, although he did try.

* This post first appeared here 17 January 2014.

Casino di San Marco

The Casino di San Marco, Florence
Location of Antonio Neri's first glassmaking job

In 1612, Antonio Neri wrote the first book entirely devoted to making glass from raw materials. It was called L’Arte Vetraria, or in English, 'The Art of Glassmaking'. When Neri put pen to paper for his book, he had already been making glass for over a decade. He had the opportunity to learn his craft from some of the experts in the field. At the beginning, his first known experience in glassmaking was at the laboratory palace of Don Antonio de’ Medici, a prince from the ruling family of Tuscany. 

The Palace was called the Casino di San Marco. “Casino”, we might innocently guess indicated some kind of gambling hall, which it was not.  Instead, "Casino" was Italian parlance for a palace that was informally organized like a small country house with the living quarters on the ground floor. It was built by Don Antonio’s father, the former Grand Duke, as a place where Nature’s secrets would be discovered and new inventions would be made. Neri worked at the Casino for a couple of years before moving to Pisa and then to Antwerp, all the while making glass. He returned to Florence to publish his book, in which he thanked Don Antonio for his long patronage. 

Don Antonio's Casino was as much a grand concept as it was a physical space. Completed to his father’s specifications in 1574, it evolved into a prince's palace par excellence. Within its walls, grand dinners were held, productions were staged and poetry was read. In 1605 Michelangelo Buonarroti the younger staged a play there titled "The Christmas of Hercules." In its chambers, music was performed, philosophy debated and diplomacy conducted. In its laboratories, alchemy was nurtured, and glass was formulated. It was a sort of grand royal conservatory, melding together art, letters, drama, music and science. From its courtyard, hunters set forth into the Tuscan hills in search of unicorns, and within its workshops, artisans explored the territory of new materials and natural secrets.

The Royal Foundry, as it was also called, became a place of pride for Grand Duke Ferdinando. It was a place that visiting dignitaries specifically asked to see and tour. Behind the doors of the Casino di San Marco, Antonio Neri and his associates worked their magic. This is probably where he first learned the secrets of Venetian style glass composition and undoubtedly much more. He assisted the prince in his research, formulated herbal remedies and helped in the production of luxury gifts for visiting dignitaries.

This was the way that I made chalcedony in the year 1601, in Florence at the Casino, in the glass furnace there. At that time, the task of scheduling furnace-work fell to the outstanding Mr. Niccolò Landi, my close friend and a man of rare talent in enamel work at the oil lamp. I made many pots of chalcedony in the furnace there. I never deviated from the method stated above, I always prepared the materials well and it always came out beautifully in all my proofs.[1] 

[1] L'Arte Vetraria, Antonio Neri 1612, p. 41.

* This post first appeared here in a shorter form on 12 August 2012.