Scraping the Barrel

4th century BCE philosopher Diogenes

(supposedly lived in a wine barrel)

by Gaetano Gandolfi (1792)

To seventeenth century glassmaker Antonio Neri, "tartar" was a well-known byproduct of the winemaking process. If we chill wine or grape juice to below 50 degrees (10 deg. C.) crystals of tartar start to form and once they do, then tend not to dissolve back, even at room temperatures. Today, these crystals are commonly found in a powdered form, in kitchen cupboards as "cream of tartar." Bakers and cooks use it to stabilize whipped egg whites, and it has a number of other applications. 

Neri used it in his glass to add sparkle, a trick known to Venetian glassmakers as early as the 1400s. It was obtained from the dregs at the bottom of wine barrels. To understand how this works, it is useful to know that Florentines, Venetians and most southern Europeans made glass from crushed up quartz pebbles or sand mixed with a specific flux known as "glass salt." This salt was rich in sodium carbonates, which greatly reduced the melting point of the quartz. It allowed artisans to work the material at the temperatures easily achieved in their furnaces. Tartar turns out to be very similar, except that it is rich in potassium rather than sodium. 

Potassium atoms are bigger and heavier than sodium atoms and when light passes through a piece of potassium-fluxed glass, it bends and refracts more. This effect is not as pronounced as when adding the even heavier lead to form fine crystal, but it still adds noticeable sparkle to finished pieces. Using all tartar as a flux has the undesirable effect of reducing the workability of the hot glass. Outside the furnace, it becomes stiff quicker and artists have less time to create fancy shapes and forms. The solution to this dilemma is to use a mix of sodium and potassium fluxes together, which is exactly what Neri did. 

In his 1612 book L'Arte Vetraria, he shows how to prepare tartar and then adds it to a number of his glass recipes saying, "The tartar is the secret way to produce more salt and to make cristallo which is whiter and of rare beauty." Here is Neri’s prescription:

To make Purified Tartar Salt you should obtain tartar, which is also called gruma, from barrels of red wine in which it forms large lumps, however do not use powder. Roast it in earthenware pots amongst hot coals until it becomes calcined black and all its sliminess is roasted away. It then will begin to whiten, but do not let it become white, because if you do the salt will be no good.  

Calcine tartar this way: put it in large earthenware pans full of hot common water, or better yet in glazed earthenware pans then made to boil on a slow fire. You should do it in such a way that in two hours the level of the water will slowly decrease to one-quarter, at this point lift it from the fire and leave it to cool and to clarify. Now decant off the liquid, which will be strong lye and refill the pans containing the remains of the tartar with new common water. In the way stated above, boil as before and repeat the procedure until saltiness no longer charges the water. 

At this point, the [decanted] water is impregnated with all the salt. Filter the lye clear and put it in glass chamber pots to evaporate in the ash of the stove over a slow fire. In the bottom, white salt will remain. Dissolve this salt in new hot common water and leave it in the pans, letting it settle for two days. Then filter it and return it to chamber pots to evaporate over a slow fire. In the bottom, a much whiter salt will be left than the previous time. Now dissolve this salt in fresh hot common water and leave it to settle for two days. Evaporate, filter and repeat everything as before. Overall, repeat this procedure four times to dissolve, filter and evaporate the salt of tartar. This will make the salt whiter than snow and purified from the vast majority of its sediment.

When mixed with sifted polverino, or rocchetta, with its doses of tarso [quartz] or sand, this salt will make a frit that in crucibles will produce the most beautiful crystallino and common glass, which one cannot make without the accompaniment of tartar salt. Without it [tartar], good fine crystallino can be made, nevertheless with it, it will be the absolute most beautiful.

*This post first appeared here on 16 May 2014.

Pebbles from Pavia

A Bridge on the River Ticino, near Polleggio,

William Pars (1742‑1782).

In the sixteenth and seventeenth century, a type of glass known as 'cristallo' was the absolute pinnacle of the art. Its recipe was invented in Venice and guarded there as a state secret. Its name derived from the mineral it was designed to mimic: rock crystal. As clear as water, rock crystal was valued since ancient times for carving into cups, vessels and other objects of art. Today we know it as a form of quartz, but in Roman times it was thought to be a type of frozen or coagulated water.

In the early 1600s, when Antonio Neri started making glass in Florence, the grand duke's craftsmen were routinely carving this hard and brittle rock crystal into complex thin shapes, a process that took great skill and effort. Due to the expense involved in producing a piece, this art was the exclusive province of extremely wealthy individuals. Thus, objects made from rock crystal were considered markers of status. The recipe for cristallo was a very great secret indeed, but its real value lay in the specific materials used. Even if the recipe found its way out of Murano, which it inevitably did, the Venetian's tight trade network ensured a monopoly on many of the ingredients. It is said that even the furnace crucibles for cristallo were made from a specific clay gathered in Constantinople.

Cristallo was not only exceptionally clear, but for the artist it had working properties like no other glass. Thin, complex shapes were possible in cristallo that could never be duplicated in common glass. The secret for making cristallo came to Florence in the late 1560's, only a few years before the birth of Antonio Neri, who would learn the techniques and go on to publish the recipe for the first time anywhere.

 After protracted overtures, which involved diplomats, spies and the archbishop of Florence, Grand Duke Cosimo I managed to negotiate with the Venetian Doge and Senate for a Muranese master and two assistants to come to Florence and teach the way to make cristallo. It is likely that the raw materials were all purchased through the Venetians, at least initially. By the time Neri wrote his book, L'Arte Vetraria, in 1612, the Florentines were already finding alternate sources. In Venice, the ingredients of cristallo were prescribed and controlled by strict laws. The Florentines did not have this constraint and were free to experiment.

In the second recipe of Neri's book, he spills the beans on where the Venetians procured the single most important ingredient for cristallo, the pure quartz stones which account for the material's clarity. Notice in the following excerpt that Neri mistakenly thinks that the white river stones are a form of marble and also notice the alchemical language he uses to describe the process in which the stone is "transmuted" into glass.

When you want to a make cristallo that is beautiful and fully perfect, see that you have the very whitest tarso. At Murano they use pebbles from Ticino [Pavia], a stone abundant in the Ticino River. Tarso, then is a species of very white hard marble [quartz]. 

In Tuscany, it is found at the foot of Mount Veruca in Pisa, at Seravezza, at Massa near Carrara, and in the Arno River both above and below Florence. In other places as well, common stone is often recognized, which is seen to have the same qualities as tarso; it is very white and does not have dark veins, or the yellowish appearance of rust, but is spotless and pure. Take note that any stones that will spark with a piece of steel or strike plate, are apt to vitrify and will make glass and cristallo. All those stones that do not make sparks with a piece of steel or striker as above will never vitrify. This serves as advice for being able to distinguish stones that have the ability to transmute their form, from those that cannot be transmuted. 

Start with this same tarso, as fair and as white as possible. Grind it finely into powder in stone mortars. Do not use bronze or any other metal for this purpose or the stone will take in the color of the metal, which then would tinge the glass or cristallo, and make it imperfect. The pestle must be iron by necessity but at least the other materials will not have the possibility of causing any effect. Pulverize the tarso well and sift with a fine sieve. It is important that the tarso is ground as finely as flour, so that it will all pass through a fine sieve.

* This post first appeared here on 30 May 2014. 

The Glass of 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.

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 would have been regarded credible by 17th century and earlier practitioners 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 specific tints to the 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 the 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 have been conducted by alchemists 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. Last, we should note that prolonged exposure to mercury vapor causes irreversable neurological and organ damage. It undoubetly contributed to the demise of alchemists, gilders, milliners and many others who worked with it throughout history. 

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.

Glass: A poem by Henry Schoolcraft

Note: This is an abbreviated version of my piece appearing in the Autumn/Winter 2016 issue of the NAGC Bulletin. Many thanks for their permission to share it here. A copy of the complete article is available through inter-library loan from the numerous public and art museum libraries which subscribe to this journal, (including the Rakow Library at The Corning Museum of Glass). The Bulletin can also be obtained directly from its publisher, the National American Glass Club.

Glass: A poem by Henry Schoolcraft

In the final years of the 1700s, a third generation family that was living in New York’s Hudson River Valley welcomed a new son, Henry Rowe Schoolcraft (1793-1864). They welcomed him into a newly formed country, brimming with promise and expectation, the United States of America. His father was the superintendant of a new window glass factory near Albany. The family boasted a long line of military men, but perhaps more importantly, a long line of adaptable, self-motivated, life-long learners and young Henry was no exception.  

With the help of his father and like-minded family friends, Henry parlayed a rural education into private instruction in Latin, a premier collection of scientific books, and a museum quality mineral collection.  In 1809, at the age of 16, he started a hand-written literary magazine called “The Cricket” in which he published short pieces of prose and poetry among a circle of friends. His time at Union College was cut short by the opportunity to manage a glass factory further west on the shores of Seneca Lake, near Geneva, New York.

Along with his father, Henry went on to become one of the most sought after glass factory guru’s in New England. In 1814, he was running the Vermont Glassworks on the shore of Lake Dunmore. He had set up an experimental furnace with Prof. Frederick Hall from the college in nearby Middlebury.  Henry used the facility to research glass composition for a hefty book he was writing on the subject. Managing by day, experimenting by night, he still found time for his literary pursuits. It was here, in the autumn of 1814, that he composed a remarkable poem titled “Glass” in which he compares commonplace personalities of the early 19th century to the vitreous material of which he was so familiar.

Until now the poem has never been published beyond the first few stanzas.  “Glass” runs for 268 lines of rhyming couplets in a lose meter. The handwritten manuscript is archived at the Library of Congress. It begins with an assessment of mankind: [1]

1 Mankind resemble glass; they are, like it, For use or fashion, show or service fit; Some bright and fair, some dull and more obscure, These prized as good, those, estimed poor; 5 To grace a kitchen, or a parlour made, As use is most consulted, or parade; But all as various; and eke they are, As frail, as brittle, and as keen a ware. Their bases differ, as our chemists say, 10 This made of sand, that fashioned out of clay Yet shall we, in both compositions find, Similitude in beauty, use and kind. To man, tis true some small objections lie In point of texture and transparency, 15 But though we grant him, in material blind, Yet lacks he not, transparency of mind And we no surer faults in each detect By rays of light, than rays of intellect. So nice the processes, the art requires, 20 So pure th’ ingredients, so intense the fires, Where tumours grow, where phthysic’s fitful breath, Forbodes the public faith, a sudden death. Felons, freckles, frightful fire warts, Are all disclosed as clear as limpid quartz. 25 His voice and pen are graced with equal skill, To lash, report, or advocate a bill. Speak without nostrums, clear his throat when lost, But ever loudest, when they shuffle most. Alike to him, the subject, time or stage, 30 Fierce to discuss, and ready to engage If finance—there Blaberius is at home If raising troops, he votes with general glum. In peace he’s noisy, but if wars involve’ He blasts the foe by one august “Resolve.” 35 Prate, prate, prate, prate! the error of the land, His voice, by every vulgar breeze is fanned Nor learn from Witherspoon his course to run, The simple cause, “to stop when he has done.” (Read full poem)

NOTES
(Line numbers are referenced in parenthesis)
The exact manuscript title as written by Schoolcraft is: GLASS, | A Satire Poem. | Lake Dumnore, 1814.
(4) Estimed: Vernacular loanword from the French, estime; valued.
(7) Eke: also.
(10) “Feet of clay” is an expression referring to a weakness or character flaw. The phrase derives from the interpretation of the dream of Nebuchadnezzar, King of Babylon, by the prophet Daniel as recounted in the “Book of Daniel.” (Daniel 2:31–33, 2:41–43).
(21) Phthisic: a wasting illness of the lungs, such as asthma or tuberculosis; phthisis. Any wasting disease. A person suffering from phthisis.
(23) Felon: a carbuncle or other localized infection of the skin. Fire warts: “The hand that reached farthest down on the shovel is burned forever with calloused fire warts.” William E. Bain, Frisco Folks: Stories and Pictures of the Great Steam Days of the Frisco Road (St. Louis-San Francisco Railway Company) (Denver: Sage Books, 1961), p. 96.
(25) In the ms, “Graced” is struck out and replaced by a word that is smeared and illegible to me.
(27) Nostrum: a medicine, especially one that is not considered effective, prepared by an unqualified person.
(31) Blaberius: possible Latinization for ‘one who blabbers’. Also blaberus: a genus of giant Central American cockroach.
(35) Prate: to talk foolishly or tediously about something.
(37) Witherspoon: John Knox Witherspoon (1723–1794).

Footnotes:

[1] Paul Engle, “Glass, A Poem by Henry Schoolcraft” in Glass Club Bulletin, of The National American Glass Club, No. 230, Autumn/Winter 2016, pp. 5-14.

Cross Pollination

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


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

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

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

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

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

For lead crystal artisans, he has this advice:

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

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

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

*This post first appeared here on 19 March 2014.

Zaffer

Antique Apothecary jars,

cobalt blue glass.

As best as I can remember, the first time that I really noticed glass was at four or five years old, at my grandmother's house in Queens, New York. The sunlight filtering through a low window caught my eye with a brilliant blue glint through a small cobalt glass bottle.  My grandmother held it up to the light for me and I was enchanted; transported into a realm of exquisite pure color.

Little did I know that the spell cast on me at such a young age had been cast on Egyptian pharaohs of the eighteenth dynasty and on Persian princesses, two thousands years ago, by their cobalt glass jewelry. In all three cases, the deep rich blue of cobalt oxide glass was responsible. Today, the source of ancient Middle Eastern cobalt is unknown, possibly West Africa, but more recently, in the Renaissance; it was mined in Hungary, in Bohemia and in German Saxony, where it was called "zaffer," after its sapphire color.

Legend tells that sixteenth century silver miners in Germany amassed a hoard of smaltite thinking it was silver ore. When they tried to smelt it, the arsenic which cobalt ores always have, evolved highly toxic fumes that made them sick. Discouraged and maligned, they said the product of their labors was cursed by goblins; they named it "kobald" (cobalt) after the evil spirits. The theme of 'evil spirits' (toxic fumes) was common in mining circles. A mythology persisted from ancient times up until the eighteenth century that divided the spirits into two groups; mischievous, and malevolent. The mischievous spirits played tricks on the miner's perception and equipment, the malevolent spirits could stop a man dead in his tracks, literally. 

Regardless of the difficulties both terestrial and otherwise, a strong market developed for the newly found "kobald" among artists for paint, potters for glazes, and glassmakers. The Saxon miners gained a reputation for producing the finest zaffer.

In his glassmaking book L'Arte Vetraria, Antonio Neri describes his method for purifying and preparing zaffer for use in glass. It is a recipe that would stand the test of time, still quoted by authors into the nineteenth and twentieth century.

To Prepare Zaffer, Which Serves for Many Colors in the Art of Glassmaking

You should get zaffer in large pieces and put it in earthenware oven-pans holding it in the furnace chamber for half a day. Then put it into iron ladles to inflame it in the furnace. Heat it well, then take and sprinkle it with strong vinegar. When cold, grind it finely over a porphyry stone into glazed earthen pots with hot water. Then wash more water over it always leaving the zaffer to settle in the bottom.

Now gently decant, to carry away the sediment and impurities of the zaffer. The good part and pigment of the zaffer will remain in the bottom. The pigment remains are now prepared and purified to be far better than it was at first, which will make clear and limpid pigment. This zaffer should be dried and kept in sealed vessels for use, which will be much improved over the original.

Until the mid 1700s zaffer had been associated with silver and copper mines, and was commonly thought to be a derivative of copper. It was Swedish chemist Georg Brandt who finally isolated the new metal, and gave it the name which honors the miners and the subterranean spirits which still can cast a spell on us through its deep pure blue color in glass.

* This post first appeared here in a slightly different form on 4 April 2014.