Wednesday, August 16, 2017

The Dregs of Alchemy

"The struggle of fixed and volatile" 
allegorical illustration from
Splendor solis [detail] 16th C.
To 17th century Italian glassmaker and alchemist Antonio Neri, "Dregs" were otherwise known as terra, gruma, immondita, terrestreità and the evocative sporchezza. It was the "filth" and sediment left in the bottom of vessels after useful material was extracted from a preparation. These often foul-smelling substances were sometimes discarded:
Then filter out the dregs of the vitriol impregnated water; that which is yellowish you should throw away. –L’Arte Vetraria, chap. 38.
Other times, dregs were further refined. A notable example was the potassium rich muck left at the bottom of aged wine barrels. This was Neri's secret ingredient in producing a fine, sparkling cristallo glass. To understand the distinction between the useful and the useless forms of dregs, we must dig deeper into Neri's philosophy.

It might be surprising to some that these lowliest of materials could play an important role in the theory of transmutation—the alchemists' ultimate quest—which was to turn base metals into gold and silver. The idea was that a natural evolutionary process occurred in which  primordial material from the creation of the universe would, over time, mature through the lesser metals into pure gold. It was thought that this maturation was prompted by "seeds" of gold contained in the material. In Neri's view, this could be interrupted by various natural circumstances and could be restarted or sped-up through alchemical manipulation.

If one was to "purify" lesser metals into gold, it was advisable to know what needed to be removed. In his manuscript Discorso, Neri carefully explains five categories of impurity, which he then breaks down further into two sub-groups:
It should be noted in general, that in dealing with the [Aristotelian] elements in accordance with chemical philosophy, we can say that all mixed bodies in this art are discovered to contain five kinds of impure substances, which are completely dead and without any virtue or properties effective to [alchemical] operations. Two are from impure substances and three from pure substances, where all the strength, effectiveness and virtue are located specific to each mixture. Of the two [derived from the impure] one is called 'phlegm', which is to say a watery substance with no odor or taste and the other is called 'dead body' [corpo morto] or 'damned earth' [terra dannata], an earthy substance that is equally tasteless and without virtue.[1]
Indeed, in Neri's chemical philosophy, the above two useless forms of impurity (phlegm and corpo morto) are complemented by three useful forms (salt, oil or true sulfur and spirit or mercury), which are present in so-called pure materials. Researcher Maria Grazzini notes in her annotations to the manuscript that: "The chemical philosophy to which Neri refers is Paracelsian, which in addition to the four Aristotelian elements introduces the principal triad (tria prima) of salt, sulfur, and mercury. References to sulfur and mercury were already present in Arabic alchemy." [2] 
Of the other three [derived from the pure] one is called 'salt' and it is the so-called most fixed substance because it is resistant to the violence of fire; it does not flee or vanish into the air. The second is called 'oil' or 'true sulfur' because of the similarity to it, fatty and viscous. The third is called 'spirit' because it is more spiritual and volatile than all the others and even the slightest heat will cause it to dissipate into the air if it has not been bound to the salt, which is the component fixed by the oil. By its tenacious, slimy nature, [oil] acts to bind the volatile to the fixed. These three types are those of the pure substances, which are called by many other names; 'body', 'soul' [anima], 'spirit'; 'bitter', 'sweet', 'acid'; 'salt', 'sulfur', 'mercury' etc.
In them alone are placed all of the virtue and effectiveness of the minerals, the vegetables and the animals, even if the quantity of pure substance is very small in comparison with the impure in any kind of mixed body. These [three] are found in each mixed quantity of pure substance, in comparison with the ineffectual found in the impure. [3] 
In his view, it is these last three forms of impurity that hold the key to transmutation, which tends to puts dregs in a whole new light.

[1] Grazzini 2012, p. 339.
[2] Ibid, note 45, p. 339.
[3] Ibid, p. 340.
* This post first appeared here on 20August 2014.

Monday, August 14, 2017

Glass Salt

Diderot, d'Alembert, L'Encyclopédie (1772) Raking Out Roasted Frit
Making glass from raw materials involves several steps. In his 1612 book on glassmaking, L'Arte Vetraria, Antonio Neri breaks the process down into parts so that, "given a bit of experience and practice, as long as you do not purposely foul-up, it will be impossible to fail." Pure white sand, or preferably quartz river stones which Neri calls "tarso" is broken up and pulverized into a fine powder. The initial work can be done by heating the stones in a furnace, then dropping them into a vat of clean cold water, where they will fracture due to the thermal shock. The process was often repeated multiple times. From there, the pieces are pulverized in a stone mortar and pestle. Stone, because metal tools would contaminate the quartz, and in the end tint the glass. Finally, a powder is obtained by grinding with a stone tool on a flat granite "porphyry stone." This powdered quartz is the main ingredient of glass.

The second critical ingredient is the flux, what Neri calls "glass salt" or "soda." This can be obtained from mineral sources, but European glassmakers in the seventeenth century extracted all their salt from certain plants. The powdered quartz was mixed with the salt and a third ingredient, which is critical, lime. Lime is simply calcium oxide used by builders to make cement. It is nothing more than pulverized seashells roasted to a high temperature. Neri advises using two pounds of lime for every hundred pounds of salt. He specifies that it should be added to all his frit recipes, but it is not clear that he understood its critical importance; without lime, the glass would be subject to attack by mere water, eventually decomposing. This mixture of soda, lime and silica when heated in a kiln would chemically react forming "frit." The combined materials were raked around in a kiln for a long period (many hours) and finally formed nut sized pieces. It was cooled and heaped into piles in dry cellars where it was aged for a time. This is where some real "magic" in glassmaking takes place. The glass salt or soda dramatically lowers the melting temperature of the quartz, all the way down to a point that was easily achieved in a wood fired furnace. When a batch of glass was made, the aged frit was then melted in furnace crucibles and skimmed to remove excess salt, which floated on the surface; it could foul the glass, and smelled terrible. The melted glass, now ready to work, was sometimes colored and finally made into objects by gaffers. 

Neri obtained his glass salt from products shipped by traders from the Levant (eastern Mediterranean). It was supplied as the dried, partially charred remains of special plants that grow in arid seaside conditions. Shipping them this way cut down on weight and volume, and prevented rotting. These Soda and Kali plants contain large amounts of sodium carbonates. This is a white powder, chemically identical to what we know as "washing soda." He advises, 
In buying either of these make sure it is richly salted. This may be determined by touching it with the tongue in order to taste its saltiness; but the surest way of all is to do a test in a crucible and to see if it contains much sand or stones, a thing common in this art and very well known by glass conciatori.
He crushes any large pieces of the product in a stone mortar, and sifts the result through a fine screen, ensuring that most of what remains is salt.  
As the common proverb of the art of glassmaking says: a fine sieve and dry wood bring honor to the furnace. Then with any of these sodas, 100 pounds of soda ordinarily requires 85 to 90 pounds of tarso.
Neri sets up large cauldrons of clean water over brickwork stoves, adds the plant product and boils the water. He strains the insoluble parts out and reduces the liquid by evaporation until crystals of the salt start to form on the surface. He skims these off and continues the process. Finally he carefully dries the product. Our glassmaker describes several variations of this process, including one in which he takes extreme measures to ensure the purity of the salt and clarity of the finished glass. In all, this is a task that could easily take several weeks to perform for the amount of frit to fill a single pot for the gaffer to work.

Not content with the established materials, our glassmaker experimented extensively with other plants: 
[U]se the husks and stalks of fava beans after the farmhands have thrashed and shelled them. With the rules and diligence prescribed for the Levantine polverino salt, extract the salt from this ash, which will be marvelous, and from which a frit can be made using well-sifted white tarso, as is described throughout this work. A very noble frit will result, which in the crucible will make a crystal of all beauty. The same may be made from the ashes of cabbages, or a thorn bush that bears small fruit, called the blackberry, even from millet, rush, marsh reeds, and from many other plants that will relinquish their salt. *
*These other plants produce potassium carbonate salts with similar properties to sodium carbonate.
** This post first appeared here 9 December 2013.

Friday, August 11, 2017

Art and Science

Jacopo Ligozzi,1518,  fanciful glass vessels,
ink and watercolor on paper.
Antonio Neri's writing on glassmaking and alchemy was distinguished from that of many contemporary authors in that his work was all deeply rooted in hands-on experience. He worked in the early 17th century, when art and science were different sides of the same endeavour to understand the world. His contemporaries were often content to repeat century's old teachings about the four Aristotelian elements; that chemical interactions could be explained through an analysis of the balance between hot and cold, dry and wet. But more and more, these notions were being discarded and replaced. It is common to cite the invention of instruments, and other technical developments; these factors certainly did contribute to advancement. But many different forces worked toward the emergence of early modern science, and one in particular is so obvious that it is easily overlooked: artists.

Working with hot glass was a profession in which attention to nature was essential: artists did not have the luxury of fanciful explanations of physical processes. They were obliged by their work to learn the ways glass mixed, moved and behaved in the furnace, not as they imagined it should, but as it actually did. The only way to achieve the complex forms and vessels for which master glassblowers were renowned was through long experience. Failure to understand the glass and predict its properties accurately resulted in failure of the piece.

Neri was immersed in this environment and the same principles applied to his own work in formulating the glass. Ancient theories had little value if they did not accurately predict nature. Like the glass artists, the way forward for Neri was careful attention and hands-on experience. He learned the value of starting with highly purified ingredients for his glass melts. He learned that too much glass salt resulted in a putrid 'gall' that would need to be skimmed off the molten surface. Substituting salts made from fern plants, for the Kali based ones from the Levant, produced a more lustrous glass, yet it stiffened more quickly for the glassblowers.

A glass artist's work also serves as a kind of narrative. For those familiar with the techniques, a finished piece of glass work can be 'read' like a story: The handles were put on last, before that, perhaps a thin bead of color was applied to the lip of the vessel. And the work started as a blown bubble of glass, shaped and opened with special tools. Each step is an insight into the artist's technique, but also into the way nature itself operates. Each motion was a well practiced negotiation between the artist and the properties of the material.

On one hand, an artist's job was to produce objects contemplated for their physical beauty and cultural significance. On the other hand, the act of producing these objects created an environment where accurate reasoning flourished. By collecting artists and employing them together, the Medici rulers of Tuscany were creating a cauldron effect where experiences collected, stewed and nature's secrets unraveled.

* This post first appeared here on 23 October 2013.

Wednesday, August 9, 2017

Benjamin Franklin and Glass

Note: This is a shorter version of a piece appearing in the Spring/Summer 2016 issue of the NAGC Bulletin. Many thanks for their permission to share it here. A copy of the complete article is available through interlibrary 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.

Benjamin Franklin and His Gathering of Glassmakers

Portrait of Benjamin Franklin, lampworked glass murrina, 
2016, by Stephen BoehmeRivertonUtah
Benjamin Franklin (1706-1790) became famous in his own lifetime as a printer, author, inventor, statesman, diplomat and scientific investigator. The man gracing the hundred-dollar bill has been celebrated for his work in a formidable range of fields, so perhaps we should not be surprised to learn of one that has largely escaped notice. In fact, there is an extraordinary further chapter to be told. Franklin fostered a lifelong fascination with glass and spent considerable energy in efforts to attract talent from Europe to work in America.

Glass and glassmaking garnered not only Franklin’s own enthusiasm, but also that of his family and friends. He worked closely with artisans on two continents and applied his considerable knowledge of glass to areas ranging from music to optics to electrical experimentation. On his European diplomatic missions, he tirelessly encouraged foreign glass workers to set up shop in the colonies. In the decades before America gained independence, he recognized and promoted the vital importance of glassmaking. Unbeknownst to many, Benjamin Franklin played a sustained and influential role in the formation of the American glassmaking industry. 

His connections to the field were wide ranging; his older, favorite brother, John Franklin, became co-founder of a glass factory in Braintree Massachusetts from the late 1740s to early 1750s. [1] In Philadelphia, Benjamin befriended Thomas Godfrey (1704–1749), a glazier, optician, glass and instrument maker who rented space from Franklin to work on new inventions. Lambert Emerson was another glass related acquaintance and fellow Freemason; an émigré from Dublin who advertised in Franklin’s newspaper The Pennsylvania Gazette as a “looking glass maker at the Sign of the looking Glass in Front Street, Philadelphia.” [2] Franklin’s neighbor, Caspar Wistar, was a German glassmaker from Cologne. He owned the nearby glassworks at Alloway Creek in Salem County, New Jersey, just twenty miles south of Philadelphia. Besides making windows and bottles, Wistar manufactured special “philosophical” glassware for Franklin, used in his electrical investigations. 

But Franklin had much more than a passing familiarity with glassmaking. In 1746, he advised Connecticut businessman Thomas Darling on the particulars of running a glass foundry, referring to Wistar’s New Jersey operation. In his correspondence, Franklin consistently referred to his neighbor’s ‘Wistarburgh Glass Manufactory’ as “our glasshouse,” strongly implying a business relationship with Wistar. He is credited with several of his own glass inventions. Two popular items that particularly employed glass were bifocal spectacles and his musical armonica. 

Over his lifetime, Franklin traveled to Europe four times between 1725-75. In London, Paris and on side excursions throughout Europe, he was in frequent contact with glassmakers and he spent considerable effort encouraging them to immigrate to America. 
He understood the strong potential of a glass industry as an economic driver and as a window to groundbreaking scientific discoveries. Critically, he also understood the value of inviting foreign workers to participate in the American dream. In London, he frequented the Royal Society (of scientific investigators) and was correspondent and houseguest of such luminaries as Joseph Priestly, David Hume and Erasmus Darwin. Glass was a hot topic of discussion in these circles due to the recent development of electrostatic generators and Leyden jars, which all had critical components made of glass. 

Franklin continued his efforts to woo glassmakers to America, but plainly, it was not always easy. In a correspondence of 1771, we see a rare pessimism rear its head. In Philadelphia, Joseph Leacock, a cousin of his wife, partnered with a local tanner to start a glass factory on what is now Richmond Street. They wrote to Franklin in London hoping to find workers, but his reply was not encouraging, “It is always a Difficulty here to meet with good Workmen and sober that are willing to go abroad. I heartily wish you Success in your laudable Undertaking to supply your Country with so useful a Manufacture…” [3] He had already seen a deal fall apart a couple of months earlier. Dutch glassworker Jacob Schaub borrowed money from Franklin to book passage across the Atlantic bound for the Stiegel Glassworks in Lancaster, Pennsylvania. Unfortunately, Schaub then failed to appear for work. [4]

After nearly four decades championing an American glass industry, word seems to have gotten around. Although his responses are not available, glassmakers wrote to Franklin from around Europe. In 1778, he received a letter from French master glassmaker Müller de la Piolotte, who explained his family’s long history in the art, starting with his ancestors in the Black Forest of Germany. The 43-year-old bachelor had worked in Champagny, Burgundy and in the Alsace-Lorrain regions of France. 

By 1783, the war was over; Britain conceded and signed an armistice with the United States. Franklin received official permission to entertain applications from those willing to immigrate to the former colonies to work; the floodgates opened and finally he received the interest among glassmakers that he had sought all along. Among the letters from many diverse tradesmen around Europe, in July he received one from Bremen, Germany. The family of Herman Heyman thanked Franklin for letters of introduction. They asked for the ambassador’s consideration of “a Plan which we lately received from one of our principal Glass Manufacturers in upper Germany, who intend to establish a Glass Manufactory in Nord [sic] America.” [5]

In October, he received a letter from a Paris glassmaker who worked for the famed Brossard family of Normandy. This man, Sutter, had heard rumors that Franklin was looking for master glassmakers to work in Philadelphia. He offered his services and suggested that he could convince several other glass workers to accompany him. [6]

In January of 1784, Franklin again heard from the Heyman family, in Germany, who wrote,
… to inform you that three other Gentlemen with me Considered most Earnestly … to Erect a Glass-Manufactory in some part of the United states, and we Chused Maryland to be the properest Country for it. … One of my three Friends Mr. John Fried Amelong who had the Mánage of a Glass Manufactory here in Germany will go himself in the spring by the first Vessell [sic] over to Baltimore and take the Direction of the intended Establishing Glas[s] Manufactory, he Carries besides him 80 more Families all Experiented to our Purpose in the Vessell for Baltimore [sic]. [7]

In February of 1784, Caquery de Mezancy wrote to Franklin, on behalf of five other French glassworkers. He had come from a well-known glassmaking family and a month earlier, he discussed with Franklin his desire to establish a glassworks in America. Franklin assured him that once there, they would have no trouble finding a partner who would furnish all necessary funds; he also indicated that they would receive free passage on an American ship. [8]

In 1785, Franklin himself boarded one of those ships and returned to America for good. Even into his eighties, as a senior statesman-scientist he was engaged and still thinking about glass. In 1787 his good friend, astronomer and mathematician David Rittenhouse wrote him this note, perhaps about a sample of copper ruby or gold ruby glass, in which the color develops upon reheating, a so-called 'striking glass':
I broke a little bit off the colourless end of the Glass Tube and placed it in the focus of the Burning Glass leaving it there several minutes, but no change was produced in its Colour. After examining it I exposed it again to the collected rays of the Sun without observing the least change in its colour, but touching it with the end of a small splinter of Cedar wood the wood took fire and the Glass immediately became a fire red. [9]
Franklin and Rittenhouse enjoyed a regular Wednesday appointment, when they met with others and talked about their interests. Thomas Jefferson once commented that he would happily trade a week in Paris for a single evening shooting the breeze with Franklin and Rittenhouse at one of their gatherings. [10]

Franklin’s America was driven by the promise of fresh talent flooding in from abroad. In the realm of glassmaking, he spent a lifetime courting workers from foreign lands to settle here and become his trusted friends and neighbors. Perhaps we should end with a light-hearted but poignant piece of advice written in his Poor Richard’s Almanac, in August of 1736 when he was just thirty-years-old, “Don't throw stones at your neighbors, if your own windows are glass.” [11]

 [1] The glass factory in Braintree Massachusetts was founded by Joseph Crell, John Franklin and Peter Etter in the late 1740s. In 1752, others assumed management. See Carla J.Mulford, Benjamin Franklin and the Ends of Empire, Oxford: Oxford Univ. Press, 2015, p. 156. Thanks to Gail Bardhan of the Rakow Research Library of the Corning Museum of Glass for her assistance on this point and many others throughout the article.
[2] The Knight of Glin, James Peill, John Rogers, Paul Mellon Centre for Studies in British Art., et al (2007), Irish Furniture, New Haven: Yale Univ. Press, p. 37. For the Freemason reference, see The Pennsylvania Gazette, June 25, 1741. Franklin was the chapter’s grand master by 1734.
[3] Letter to Joseph Leacock and Robert Towers from BF, London dated 22 Aug 1772. See The Papers of Benjamin Franklin (1959–) New Haven: Yale Univ. Press, v. 19, p. 282. Also, see 
[4] Henry William Stiegel (1729-83) owned three glasshouses, in Lancaster County Pa. See letter from Richard Bache to Franklin, dated 16 May 1772 (Bache was Franklin’s son-in-law).
[5] Letter from sons of Herman Heyman, Bremen to BF, Passay, dated 31 July 1783. Op. cit. Papers of BF, v. 40, p. 143.
[6] Letter from Mr. Sutter to BF, Passay, dated 29 October 1783. Op. cit., Papers of BF, v. 41, p. 548.
[7] Letter from Herman Heyman Jr., Bremen to BF, Passay, dated 19 January 1784. Op. cit., Papers of BF, v. 41, p. 489–90.
[8] Op. Cit., Papers of BF, v. 41, p. 552.
[9] Note to Dr. Franklin, from David Rittenhouse, Monday noon [c. 1787]. Op. cit. Papers of BF, (forthcoming).
[10] Kevin Keim, Peter Keim, (2007). A Grand Old Flag, a History of the United States through Its Flags. New York, New York: Dorling Kindersley Ltd. p. 43.

[11] BF (1736), Poor Richard’s Almanack, Philadelphia, August 1736, (v. 2, p. 141), see

Monday, August 7, 2017

Tartar Salt

So-called "wine diamonds," (harmless)
Potassium bitartrate deposits which can accumulate
in bottles and barrels of wine
Tartar salt is an example of an alchemist's chemical that is a byproduct of another process, in this case winemaking. In his book L'Arte Vetraria, [1] Antonio Neri uses it in his glassmaking for two very different effects. The first application is to improve the appearance of the glass and the other is to modify colors. In addition to uses in glass, tartar also finds its way into his recipes for red paint made from the dried kermes insect [2] and for cast bronze mirrors, as a flux. (In foundries, a flux keeps the metal bright and shiny while in a molten state). [3]

Neri notes that tartar also went by the name of "gruma" to which we can add the synonyms greppola and argol. He warns readers several times to "leave behind the [dried] powder of the [raw] tartar, which is no good" and that "you should have tartar, from the dregs of red wine, which is better than white wine." [4] Nevertheless, he does specifically use white wine tartar in his recipes for rosichiero, a transparent dark red enamel. [5] In his recipe for producing tartar salt [6] he directs the reader to obtain the raw material from emptied wine barrels, but elsewhere in the book he seems to prefer to use the large crystals of tartar that have “vitrified naturally in bottles of wine.” [7] Chemically, tartar is a potassium compound formed through a reaction with tartaric acid, a major constituent of grape juice. [8] 

The effect of tartar in improving the appearance of glass can be readily explained. Most of the glass that was made in Italy in the seventeenth century used sodium-based additives to lower the melting temperature of finely ground quartz powder; these formulations are known as soda-based glasses. Using potassium compounds can have the same effect and these 'potash' based glasses were predominantly produced in northern Europe where trees and plants rich in potassium were used in glass. Potassium is a heavier element and it produces a denser, more refractive glass, giving it more sparkle, although not as much as lead imparts to crystal. Unfortunately, potassium also makes the glass harder to work for the artisan. Potash glass stiffens more quickly as it cools, whereas soda glass remains workable for a longer time before requiring reheating in the furnace. Many of Neri's recipes blend the two additives, which we can imagine gives some of the advantages of both.

Neri also used tartar to modify color in glass. The effects of tartar are exemplified in a number of passages throughout the book. He uses it as the sole pigment in his recipe for pearl colored glass, but he warns, "Once obtained, you must work the color quickly, because it will dissipate." [9] Conversely, he also uses tartar to produce a black colored enamel, combining it with manganese [oxide], which by itself imparts a magenta color. [10] 

The first step in making Neri's purified tartar salt is to obtain the raw "gruma, from barrels of red wine in which it forms large lumps." Next, he gently roasts it in terracotta pots "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." Now, he boils it in water for two hours, evaporating off three-quarters of the liquid. After filtering, he lets the remaining liquid "lye" cool in pans, allowing any sediment to settle to the bottom. He gently pours off  (decants)  the liquid which is further processed on the stove, this time in glass containers. The result, after full evaporation over a slow fire is a “white salt” left in the vessel. He dissolves this in hot water, filters it again and allows more sediment to settle out for a period of two days. Again, the liquid is decanted and evaporated in a glass container. The filtering and evaporation process is repeated four times, resulting in a product that is "whiter than snow."

Neri's final remarks for this chapter are as follows:
“When mixed with sifted polverino, or rocchetta, with its doses of tarso or sand, this salt will make a frit that in crucibles will produce the most beautiful cristallino and common glass, which one cannot make without the accompaniment of tartar salt. Without it, good fine cristallino can be made, nevertheless with it, it will be the absolute most beautiful.” [11]

[1] Neri 1612.
[2] Ibid, ch 116, 117.
[3] Ibid, ch 113. Note that in glassmaking, the term 'flux' has a different meaning than in metallurgy.
[4] Ibid,  ch 41. 
[5] Ibid, ch 125.
[6] Ibid, ch 11.
[7] Ibid. ch 46.
[8] Pure tartar takes the form potassium bitartrate KHC4H4O6.
[9] Neri 1612, ch 60.
[10] Ibid, ch 102.
[11] Ibid, ch 11. Polverino and rocchetta are thought to be forms of dried Salsola Kali plants. Tarso is Neri's term for white quartz river stones. Cristallino was a Venetian style glass that in quality fell between common glass and the premium cristallo, for which Murano became famous.
* This post first appeared here on 5 Sept. 2014.

Friday, August 4, 2017

Vitriol of Venus

Crystals of Copper Sulfate Pentahydrate
(Vitriol of Venus)
Vitriol of Venus was one of the most cherished items in Antonio Neri’s chemical library. In his book, L'Arte Vetraria, he describes its effect in glass this way:
To your great contentment, you will be astonished at what you see. I do not know of anybody else who has tried it this way and I Priest Antonio Neri trying it found it most marvelous, as said above, and it is of my own invention. [1]
To be clear, Neri is claiming a novel preparation technique for a chemical substance that was known since antiquity. I think it is quite reasonable to say that a particular personality trait led him down this path of discovery; his almost maniacal drive for purification. For a seventeenth century alchemist, it is a trait that served him well. Where other practitioners were content to use contaminated or substitute ingredients in their formulations, Neri always goes the extra mile in verifying his ingredients and using any extra filtering steps that might be warranted, no matter how time consuming. More than anything else this is what led him to such success in glass formulation, the assurance of exceptionally clear product and bright colors.

He is so proud of his creation that he spreads the description of his method over four full chapters of the book, going into a level of meticulous detail that is extreme, even for Neri. Rest assured, dear readers, that I have taken the liberty of distilling said description down to a more manageable form for your reading pleasure. Nevertheless, our priest-alchemist clearly puts great stock in this preparation, going so far as to drop hints that this material has uses that go far beyond glassmaking: "Many things could be said here, which are omitted as not being pertinent to the art of glassmaking, which perhaps upon another occasion you will be able to judge." [2]

Before starting, he gives some general advice:
You should make the sulfurs, vitriols, ammoniac salts, and similar materials slowly, over a low fire, so they are well prepared and well opened, because a violent fire will cause great damage to them.[3]
To begin, Neri cuts thin copper sheet into small pieces half the size of a small coin. filling a crucible, he layers the copper pieces with common sulfur (known as brimstone).  He cements the vessel shut with a lid and then buries it in the hot coals of a drafted furnace for two hours.

The dark purple contents are then ground and sifted through a fine screen, mixed with six ounces of pulverized sulfur per pound and then heated in a round terracotta pan, which is sitting in the hot coals. When the sulfur starts to burn, he stirs the mixture, rolling it into balls with an iron hook so it does not stick to the pan, continuing until it stops smoking. He removes the mixture from the heat, grinds it finely, adds more sulfur and repeats the entire process three times.

Neri grinds the resulting reddish tawny colored material into powder, putting a pound of it into a large glass vessel containing six pounds of clean water and gently evaporate away a third of the water. The liquid is carefully poured off and saved. The residual solids are dried and recycled in the process. Now more solids are allowed to settle out of the "beautiful blue" liquid over a two-day period and then the liquid is filtered through a felt cone.

He heats the liquid again, this time evaporating two thirds and then puts the remaining third into glazed terracotta pans, and leaves them in a cold damp place overnight. "You will find the vitriol of copper has formed into crystalline points that mimic true oriental emeralds." The crystals are removed, dried and the liquid is further evaporated in order to obtain more crystals. To the chemist, this material is copper sulfate pentahydrate [4]; today it is sold inexpensively as a fungicide for swimming pools. One reason it was so valuable to alchemists is that when gently heated or added to water this chemical forms a sulfuric acid solution. 
This is the true flaming azure blue [tincture], with which marvelous things are made. It is most potent, and as sharp as anything known in nature today, as can easily be perceived from its odor.
However important this was in other areas of alchemy, those applications do not have any particular relevance to the blue-green tint it imparts to glass, which he does make use of throughout the book. The full recipe was so long that he continued it several times and finished as the final chapter of L'Arte Vetraria. Here are the closing words to the book:
Although I have placed here the way to make this powder with much clarity, do not presuppose that I have described a way to make something ordinary, but rather a true treasure of nature, and this for the delight of kind and curious spirits.[5]
[1] Neri 1612, ch. 31.
[2] Ibid, ch. 133.
[3] Ibid, ch. 37.
[4] CuSO4•5H2O
[5] Ibid, ch 133.
* This post first appeared here on 29 Aug 2014.

Wednesday, August 2, 2017

Sulfur of Saturn

The Roman Goddess Ops, 'sweet'-heart (and wife)
of Saturn, Peter Paul Rubens c. 1630,
“Abundance (Abundantia).” [1]
Antonio Neri’s book on glassmaking, L'Arte Vetraria, devotes an entire chapter to making artificial gems. These are made with an especially dense, refractive form of lead glass—what today would be called lead crystal. He made it in small batches, in sealed ceramic vessels; each infused with various metal oxide pigments to give characteristic jewel tone colors.  His secret ingredient for making the finest artificial gems was a material known as "sulfur of Saturn." He writes:
You will have jewels of marvelous beauty in every color, which by far surpass those described above, made with ordinary minium. Because with this true sulfur of Saturn, they will surpass all others by far more than I can write here, as I have seen and made many times in Antwerp.[2]
This "ordinary minium" that he speaks of is one of several oxide forms of lead, also known as 'red lead,' it is bright red or orange in color. As a stable red pigment it was well known to ancient Byzantine and Persian illuminators. [3] It was so popular, in fact, that the word used to describe small intricate pictures 'miniature,' is derived directly from 'minium.' [4] The intricate embellishments in manuscripts ultimately took on the name of the scribes' favorite color.  In glass, minium does not impart red or any other color on its own, but does add 'sparkle' and made Neri's jewels highly refractive to light. 

In the recipe, he uses white vinegar and he reacts it with finely ground minium through a laborious process. The acetic acid in vinegar chemically combines with the minium to form lead acetate, which alchemists called "sugar of Saturn" because it had a distinctively sweet taste (more on that later). [5] Lead (Saturn) could be added to the melt in a number of different forms including acetate, carbonate and various oxides. The heat of the furnace reduces them all and the result is essentially identical glass from any of these sources. The lead acetate has one major advantage that set it apart from the others. Lead acetate is soluble in water and therefore it can easily be purified of contaminants and to a much higher degree. It can be filtered, allowed to stand and decanted after any insoluble impurities settle out.

In other references "sugar of Saturn" and "sulfur of Saturn" are considered synonyms. This is not the case with Neri, for him they are two different substances; the 'sugar' is a precursor for his final product, sulfur of Saturn:
Left in the bottom will be a salt as white as snow, and as sweet as sugar. Repeat the dissolution, and filtering, and evaporation with common water three times. This is the required sugar of Saturn. 
Keep it to calcine in sand in a glass flask or ball in a furnace over a moderated fire for many days. It will further calcine to a color that is much redder than cinnabar, and more finely impalpable than sifted grain flour. This is the required true sulfur of Saturn; purified from the sediment, foulness and blackness that were upon the lead at first. [6]
It would be a reasonable guess that by heating the acetate for "many days" he is reducing it back to minium, its more basic, bright red oxide state, but this time in a greatly purified form.

Unfortunately for his health, in this recipe for sulfur of Saturn, Antonio makes extensive use of heating and evaporation. Even more unfortunate is that in a number of steps he judges the potency of his product by taste. Lead acetate is highly toxic; because it is soluble in water, it enters the bloodstream easily. It attacks the nervous system, accumulates in the bones and can cause organ failure. It is quite likely that by breathing the fumes and tasting crystals of sugar of Saturn, Neri was contributing to his own demise at the relatively young age of thirty-eight. Lead acetate was not the only toxic substance he handled regularly, but it was certainly one of the worst for his health. 

 It does not follow that he was totally ignorant of the risks he was taking. The dangers of heavy metals were recognized from early times. Pliny speaks of the noxious fumes from lead furnaces, and Plutarch opined that lead and mercury mines were "unwholesome and pestilent places." Neri’s own father followed the work of Dioscorides, who wrote that ceruse (lead carbonate), taken internally, could be fatal and that certain sweet wines could adversely affect the abdomen and the nerves.

Ancient Romans discovered that when wine started to turn to vinegar, it could be boiled down in lead lined pots to produce a highly sweet syrup called sapa. A late Roman cookbook made extensive use of sapa, which presumably contained considerable lead acetate. [7] It has been conjectured that  lead laced sapa contributed to poisoning among the Roman aristocracy. While lead acetate is a deadly poison, it is a step too far to imply that it contributed to the fall of the Roman Empire.

[1] Alchemical tradition does provide for an association between the metal lead and the Roman god Saturn. However, there is no such association between 'sugar of Saturn' and either of his consorts Ops or Lua, although Ops, the goddess of abundance (opulence) does rather nicely represent the chemical that made Neri's most opulent artificial gems possible.
[2] Neri 1612, ch. 91.
[3] Chemically, this is Pb3O4, also known as Lead (II,IV) oxide, triplumbic tetroxide. Historically, it was called minium and red lead.
[4] The accepted etymology of ‘miniature’ is from ‘minium,’ but may have been influenced by similar Latin terms such as  minor, minimus, minutus, etc.
[5] Lead acetate comes in two forms; Pb (C2H3O2)4 and Pb (C2H3O2)2, both are toxic; the later variety is soluble in water.
[6] Neri 1612, ch. 91.
[7] “Saba” endures today as a popular grape syrup, albeit without the lead.

* This post forst appeared here on 12 September 2014.