1600s Glass Furnace

 

From "De re metallica" 

Agricola (Georg Bauer) 1556.

In the seventeenth century, glass furnaces represented a pinnacle of technology. True, the ability to achieve the high temperatures required to melt glass had been around for centuries – high enough to melt gold, silver and copper as well. What made the glass furnace remarkable was its refinement. It made efficient use of its hardwood fuel and was able to maintain a controlled, even temperature long before any thermometer could measure it. In fact, in the early seventeenth century, Galileo was only just beginning to use glass bulbs and tubes to measure differences in ambient room temperatures.

In Florence, the construction used was typical of the time throughout Europe, called a "beehive" furnace because its shape resembled the classic elongated dome of a beehive. A double wall, built of fire resistant bricks, provided further insulation, trapping heat inside. Vertically, the furnace was divided into three levels, each forming a wide open chamber. The bottom space was used to build the fire, and had one or two openings to the outside, used to add wood fuel, rake the coals, or shovel out ash. The second, central level was where the pots of glass resided. A central hole or "eye" on the floor directly exposed the fire pit below. The space directly next to the eye was the hottest, and temperature could be further controlled by moving the crucibles farther away or closer to the eye. A number of openings in the wall allowed gaffers access to the glass pots, and at least one larger opening was used to place new crucibles, or rearrange the existing ones. The upper chamber was used to control the draft, and sometimes for annealing. Again, a central hole in the floor of this (top) level allowed exhaust gasses to leave the glass chamber and an opening to one side vented the exhaust.

In his 1612 book, L’Arte Vetraria, Neri is careful to stress that only dry oak or other hardwood should be used because it burns cleanly, and will not deposit ash or creosote in the glass.

The furnace should have dry wood, hard wood of oak because soft wood tinges the furnace and does no good. Stoke it steadily and continuously so that the flame is always clear, and there is never any smoke, which is very important in order to make a beautiful cristallo.

Once a finished piece of glassware is made, it must be allowed to cool slowly, over a period of many hours. This was often accomplished by building a long enclosed horizontal trough that connected to the furnace. A draft opening at the far end allowed heat from the furnace to be drawn in, and finished pieces were placed in a pan at the furnace end and then slowly pulled by a chain further and further down the trough toward the cooler end. This "annealing" process ensured the glass would not develop stresses and crack as it cooled.

Although Neri does not concern himself with the vagaries of furnace construction in the book, it is clear that he did possess considerable knowledge on the subject. Several of his unconventional methods for making pigments for glass involve taking bricks out of the furnace wall to stash chemicals for long term exposure to the heat.

Take small pieces of copper and put them inside the arches of the furnace. In that place, they will be within the walls. Leave them that way until each piece of copper is well calcined, using a simple fire.

While it is true that artisans of the early seventeenth century did not possess the same understanding of nature that we now enjoy, they did have a working knowledge that served them very well. It was backed by a theoretical framework that was quite sophisticated and was consistent with what could be observed and measured at the time. This is no different from our own modern understanding of nature: sophisticated and consistent with what we can observe and measure.

*This post first appeared here 24 January 2014

Early Modern Glass Furnace

From "De re metallica" 

Agricola (Georg Bauer) 1556.

In the seventeenth century, glass furnaces represented a pinnacle of technology. True, the ability to achieve the high temperatures required to melt glass had been around for centuries – high enough to melt gold, silver and copper as well. What made the glass furnace remarkable was its refinement. It made efficient use of its hardwood fuel and was able to maintain a controlled, even temperature long before any thermometer could measure it. In fact, in the early seventeenth century, Galileo was only just beginning to use glass bulbs and tubes to measure differences in ambient room temperatures.

In Florence, the construction used was typical of the time throughout Europe, called a "beehive" furnace because its shape resembled the classic elongated dome of a beehive. A double wall, built of fire resistant bricks, provided further insulation, trapping heat inside. Vertically, the furnace was divided into three levels, each forming a wide open chamber. The bottom space was used to build the fire, and had one or two openings to the outside, used to add wood fuel, rake the coals, or shovel out ash. The second, central level was where the pots of glass resided. A central hole or "eye" on the floor directly exposed the fire pit below. The space directly next to the eye was the hottest, and temperature could be further controlled by moving the crucibles farther away or closer to the eye. A number of openings in the wall allowed gaffers access to the glass pots, and at least one larger opening was used to place new crucibles, or rearrange the existing ones. The upper chamber was used to control the draft, and sometimes for annealing. Again, a central hole in the floor of this (top) level allowed exhaust gasses to leave the glass chamber and an opening to one side vented the exhaust.

In his 1612 book, L’Arte Vetraria, Neri is careful to stress that only dry oak or other hardwood should be used because it burns cleanly, and will not deposit ash or creosote in the glass.

The furnace should have dry wood, hard wood of oak because soft wood tinges the furnace and does no good. Stoke it steadily and continuously so that the flame is always clear, and there is never any smoke, which is very important in order to make a beautiful cristallo.

Once a finished piece of glassware is made, it must be allowed to cool slowly, over a period of many hours. This was often accomplished by building a long enclosed horizontal trough that connected to the furnace. A draft opening at the far end allowed heat from the furnace to be drawn in, and finished pieces were placed in a pan at the furnace end and then slowly pulled by a chain further and further down the trough toward the cooler end. This "annealing" process ensured the glass would not develop stresses and crack as it cooled.

Although Neri does not concern himself with the vagaries of furnace construction in the book, it is clear that he did possess considerable knowledge on the subject. Several of his unconventional methods for making pigments for glass involve taking bricks out of the furnace wall to stash chemicals for long term exposure to the heat.

Take small pieces of copper and put them inside the arches of the furnace. In that place, they will be within the walls. Leave them that way until each piece of copper is well calcined, using a simple fire.

While it is true that artisans of the early seventeenth century did not possess the same understanding of nature that we now enjoy, they did have a working knowledge that served them very well. It was backed by a theoretical framework that was quite sophisticated and was consistent with what could be observed and measured at the time. This is no different from our own modern understanding of nature: sophisticated and consistent with what we can observe and measure.

*This post first appeared here 24 January 2014

The Purse of Envy

Antonio Neri, "The Mineral Gold" Tesoro del Mondo,
(MS Ferguson 67, GB 0247,
Glasgow University Library, Special Collections,
1598-1600), f. 5r.

As a young alchemist, Antonio Neri faced a decision that had confronted virtually all accomplished artisans since the dawn of time and continues to do so today; whether or not to freely share hard-won technical knowledge with others. The indications are that Neri's thinking on the subject evolved over his lifetime. Testimony given by Florentine metals refiner Guido Melani indicate that as a twenty-year-old, Neri was willing to share his most precious secrets, albeit reluctantly.

Melani reported that in July 1596, Neri performed a transmutation of base metal into "twenty-four carat" gold. Upon being pressed, Neri confided that he had learned the secret from a German, who performed the gold transmutation with a "tablet of medicine." The German told him the medicine was nothing but the simple quintessence of green vitriol and the method to produce it was described by Paracelsus.[1] (In reality, an ion exchange reaction that we now know takes up iron and deposits copper in its place).

The motivations for keeping techniques secret are obvious; potential monetary reward and personal prestige. Aside from the immediate gratitude of confidants, the motivation for sharing technical secrets can be more subtle; the satisfaction of serving a greater good by advancing the art. It is indeed an ancient and very human dilemma. Five centuries before Neri, in the early 1100s a glassmaking Benedictine monk wrote on the subject. In Hesse, Germany, Theophilus Presbyter penned these lines in his De Diversis Artibus [On Various Arts]. "Do not hide His [God's] gifts in the purse of envy, nor conceal them in the storeroom of a selfish heart" and "Do not hide away the talent given to you by God, but, working and teaching openly and with humility, … faithfully reveal it to those who desire to learn."[2] Although it is doubtful that this particular writing was ever seen by Neri, his access to the most extensive libraries in Italy, along with his knowledge of Latin and the writings of other alchemists ensured a comprehensive understanding of his subject and the politics surrounding it.

Two centuries after Neri's death, historian Francesco Inghirami published details of an incident, which if true, might have contributed to a change of heart with our priest:

He [Neri] claimed he had found the secret of making the famous philosopher's stone and it was said he had discovered it among some of his confidants.  Some thugs learnt of this and attacked him at night, in order to obtain the secret by force. He shrewdly gave them a certain recipe he had in his pocket and explained the figures written on it, claiming it to be the secret oil required. But that night, Neri left Florence and traveled to various parts of Europe.[3]

Nevertheless, in his travels to Antwerp it is clear that Priest Neri continued to share his knowledge of glassmaking, in the shop of Filippo Gridolfi, and of course, upon his return to Florence seven years later in the publication of his famous book, L' Arte Vetraria.[4] In contrast, on the subject of transmuting gold and silver, Neri had decided to take his secrets with him to the grave, a decision that he justifies in a manuscript, Discorso, which he completed shortly before his death:

We must also consider the danger to its possessor if it became known to others and particularly to the princes. For that reason even if someone knows and practices this art, he is obliged to keep it hidden and to conceal it; and I know of what I speak.[5]

Neri outlines his fears that such a momentous discovery, if generally known could lead to abuse of power, a collapse of the monetary system, and general chaos in society. In spite of his deep reservations, we see a final glimmer of his innate desire to share. He did, in fact, leave behind his recipe for the philosopher's stone, but in coded, obscure language that has never to this day been deciphered. As he put it: "I wrote the words so strangers will not understand." 

[1]  Galluzzi 1982, p. 53; Grazzini 1983, pp. 214–216. 
[2]  For modern English translation see Theophilus 1979. 
[3]  Inghirami 1841–44, v. 13, pp. 457–458. 
[4]  Neri 1612.
[5]  Grazzini 2012, pp. 329, 356.
*This post first appeared here on 6 November 2013.

1600s Glass Furnace

From "De re metallica" 

Agricola (Georg Bauer) 1556.

In the seventeenth century, glass furnaces represented a pinnacle of technology. True, the ability to achieve the high temperatures required to melt glass had been around for centuries – high enough to melt gold, silver and copper as well. What made the glass furnace remarkable was its refinement. It made efficient use of its hardwood fuel and was able to maintain a controlled, even temperature long before any thermometer could measure it. In fact, in the early seventeenth century, Galileo was only just beginning to use glass bulbs and tubes to measure differences in ambient room temperatures.

In Florence, the construction used was typical of the time throughout Europe, called a "beehive" furnace because its shape resembled the classic elongated dome of a beehive. A double wall, built of fire resistant bricks, provided further insulation, trapping heat inside. Vertically, the furnace was divided into three levels, each forming a wide open chamber. The bottom space was used to build the fire, and had one or two openings to the outside, used to add wood fuel, rake the coals, or shovel out ash. The second, central level was where the pots of glass resided. A central hole or "eye" on the floor directly exposed the fire pit below. The space directly next to the eye was the hottest, and temperature could be further controlled by moving the crucibles farther away or closer to the eye. A number of openings in the wall allowed gaffers access to the glass pots, and at least one larger opening was used to place new crucibles, or rearrange the existing ones. The upper chamber was used to control the draft, and sometimes for annealing. Again, a central hole in the floor of this (top) level allowed exhaust gasses to leave the glass chamber and an opening to one side vented the exhaust.

In his 1612 book, L’Arte Vetraria, Neri is careful to stress that only dry oak or other hardwood should be used because it burns cleanly, and will not deposit ash or creosote in the glass.

The furnace should have dry wood, hard wood of oak because soft wood tinges the furnace and does no good. Stoke it steadily and continuously so that the flame is always clear, and there is never any smoke, which is very important in order to make a beautiful cristallo.

Once a finished piece of glassware is made, it must be allowed to cool slowly, over a period of many hours. This was often accomplished by building a long enclosed horizontal trough that connected to the furnace. A draft opening at the far end allowed heat from the furnace to be drawn in, and finished pieces were placed in a pan at the furnace end and then slowly pulled by a chain further and further down the trough toward the cooler end. This "annealing" process ensured the glass would not develop stresses and crack as it cooled.

Although Neri does not concern himself with the vagaries of furnace construction in the book, it is clear that he did possess considerable knowledge on the subject. Several of his unconventional methods for making pigments for glass involve taking bricks out of the furnace wall to stash chemicals for long term exposure to the heat.

Take small pieces of copper and put them inside the arches of the furnace. In that place, they will be within the walls. Leave them that way until each piece of copper is well calcined, using a simple fire.

While it is true that artisans of the early seventeenth century did not possess the same understanding of nature that we now enjoy, they did have a working knowledge that served them very well. It was backed by a theoretical framework that was quite sophisticated and was consistent with what could be observed and measured at the time. This is no different from our own modern understanding of nature: sophisticated and consistent with what we can observe and measure.

*This post first appeared here 24 January 2014

A Reluctant Glassmaker

The Sun, Robert Fludd

from Utriusque Cosmi (1617),v. 2, p. 19.
(alchemical symbol for gold)

Today, Antonio Neri is best known for his 1612 book, L'Arte Vetraria, in which he exposes the secrets of the art of making glass. In publishing his volume, he helped to fuel new discoveries in chemistry and medicine simply by making glass apparatus more available to experimenters. In fact, chemistry and medicine were areas for which he expressed the highest regard. A 1662 translation of his book into English at the behest of Robert Boyle was one of the first acts undertaken by the newly formed Royal Society in London. Neri himself lived for only two years after his book went to press in his native Florence, and he never saw the seeds of his labor come to fruition. If he had lived, he might well be surprised that his legacy is in glassmaking and not in the subjects that he himself held most dear.

In his death at the age of thirty-eight, Neri missed a rapid advancement in our basic understanding of nature. In the space of only a few decades the face of science and medicine would start to change irrevocably. Soon, experimenters were finding new chemical elements and began to map out the periodic table, often with apparatus made of glass. For centuries, the ancient Aristotelian concept of air, earth, water and fire as the basic building blocks of the universe had endured. By the end of the seventeenth century, the inadequacies of the old model were becoming clear. 

But Neri was not privy to any of this. In his time, any cracks in the Aristotelian model were minor. Like his sponsor, Medici prince Don Antonio, Neri was an adherent of new doctrines of the physician Paracelsus, who rebelled against the old system, but was still very much a product of it. First and foremost, Neri thought of himself as an alchemist. While history has not generally been kind to his ilk, a true understanding of early modern science rests on the methods and reasoning developed by alchemists like Neri. 

Although alchemy covered a wide range of activities, it will forever be associated most closely with the mistaken notion that base metals such as lead or iron could be transmuted into gold. Once science had established this idea as specious, the race was on to separate "new science" from the old. It became fashionable to cast alchemists into the mold of charlatans, tricksters and self-deceived fools. While many such characters did exist, Neri was not one of them; his work was based on careful reasoning and experimentation. The final irony is that through the kind of advancements that he himself helped to pioneer, the majority of his life's work has fallen by the wayside. What has endured the test of modern science is his treatise on glassmaking.

As early as the age of twenty, Neri was presenting  transmutation experiments to expert gold refiners. As late as the year before his death he was writing authoritatively and coherently on the subject. To understand how this is possible – to be rational and methodical, and at the same time completely wrong – is to get a sense of the true difficulties involved in science. Based on what he was taught, what he read, and his own experimentation, Neri thought metals and other materials "matured" over time. He thought that more "imperfect" metals like lead and iron were part of a continuum that ended with the "perfect" metal gold. Furthermore, he thought that primordial "seeds of gold" left over from the creation of the earth could be mined and isolated. Like wheat and other plants, given the correct nurturing, and conditions, this seed material could be encouraged to mature into vast quantities of gold. Writing in his 1613 manuscript Discorso, Neri says,

The response is that the chemical art lets the gold proceed from that present and immediate cause, because this is the seed of gold, which acts naturally when art cooperates. The chemist does nothing but extract the seed from gold and apply it to suitable bodies, with which it is united to render the fruit multiplied in the same way that the farmer does. He does not produce the fruit, but provides and prepares the earth and the seed, uniting them in such a way so that they bear fruit.*

Neri thought that ultimately, for gold transmutation to be successful one needed the blessing of the Creator. He documented his process in a heavily coded (and incomprehensible) recipe he called "Donum Dei" (the most precious gift of God). This series of chemical transformations traces to alchemical writings from as early as the fifteenth century. Neri maintained that those who might harm society with this knowledge or wished to profit personally or swindle others would be denied the blessing and therefore be unsuccessful. 

The remarkable thing here is that Neri's understanding of chemistry was supported at every turn by experimentation. His recorded methods, for transforming lesser metals into one-another, were repeatable and stood the test of scrutiny by contemporary experts. In the light of modern chemistry, these transformations depended on subtle physical processes and chemical reactions that would not be understood for another century or more. By performing these experiments under controlled conditions, he was taking the first steps in what would become modern science. Eventually, it would be understood that while chemical compounds can be created and destroyed by various manipulations, individual elements cannot. Today we know that iron, lead and gold were formed in the cores of ancient stars, not too different from our sun. Lighter elements are successively transformed into heavier ones under a star's "nurturing" conditions. While he lived in a period in which he had little chance of getting the particular details correct, in a poetic sense Neri was not far from the truth.

* See Maria Grazia Grazzini, “Discorso sopra la Chimica: The Paracelsian Philosophy of Antonio Neri” Nuncius 27 (2012) 311–367.

The Purse of Envy

Antonio Neri, "The Mineral Gold" Tesoro del Mondo,
(MS Ferguson 67, GB 0247,
Glasgow University Library, Special Collections,
1598-1600), f. 5r.

As a young alchemist, Antonio Neri faced a decision that had confronted virtually all accomplished artisans since the dawn of time and continues to do so today; whether or not to freely share hard-won technical knowledge with others. The indications are that Neri's thinking on the subject evolved over his lifetime. Testimony given by Florentine metals refiner Guido Melani indicate that as a twenty-year-old, Neri was willing to share his most precious secrets, albeit reluctantly.

Melani reported that in July 1596, Neri performed a transmutation of base metal into "twenty-four carat" gold. Upon being pressed, Neri confided that he had learned the secret from a German, who performed the gold transmutation with a "tablet of medicine." The German told him the medicine was nothing but the simple quintessence of green vitriol and the method to produce it was described by Paracelsus.[1] (An ion exchange reaction that we now know takes up iron and deposits copper in its place).

The motivations for keeping techniques secret are obvious; potential monetary reward and personal prestige. Aside from the immediate gratitude of confidants, the motivation for sharing technical secrets can be more subtle; the satisfaction of serving a greater good by advancing the art. It is indeed an ancient and very human dilemma. Five centuries before Neri, in the early 1100s a glassmaking Benedictine monk wrote on the subject. In Hesse, Germany, Theophilus Presbyter penned these lines in his De Diversis Artibus [On Various Arts]. "Do not hide His [God's] gifts in the purse of envy, nor conceal them in the storeroom of a selfish heart" and "Do not hide away the talent given to you by God, but, working and teaching openly and with humility, … faithfully reveal it to those who desire to learn."[2] Although it is doubtful that this particular writing was ever seen by Neri, his access to the most extensive libraries in Italy, along with his knowledge of Latin and the writings of other alchemists ensured a comprehensive understanding of his subject and the politics surrounding it.

Two centuries after Neri's death, historian Francesco Inghirami published details of an incident, which if true, might have contributed to a change of heart with our priest:

He [Neri] claimed he had found the secret of making the famous philosopher's stone and it was said he had discovered it among some of his confidants.  Some thugs learnt of this and attacked him at night, in order to obtain the secret by force. He shrewdly gave them a certain recipe he had in his pocket and explained the figures written on it, claiming it to be the secret oil required. But that night, Neri left Florence and traveled to various parts of Europe.[3]

Nevertheless, in his travels to Antwerp it is clear that Priest Neri continued to share his knowledge of glassmaking, in the shop of Filippo Gridolfi, and of course, upon his return to Florence seven years later in the publication of his famous book, L' Arte Vetraria.[4] In contrast, on the subject of transmuting gold and silver, Neri had decided to take his secrets with him to the grave, a decision that he justifies in a manuscript, Discorso, which he completed shortly before his death:

We must also consider the danger to its possessor if it became known to others and particularly to the princes. For that reason even if someone knows and practices this art, he is obliged to keep it hidden and to conceal it; and I know of what I speak.[5]

Neri outlines his fears that such a momentous discovery, if generally known could lead to abuse of power, a collapse of the monetary system, and general chaos in society. In spite of his deep reservations, we see a final glimmer of his innate desire to share. He did, in fact, leave behind his recipe for the philosopher's stone, but in coded, obscure language that has never to this day been deciphered. As he put it: "I wrote the words so strangers will not understand." 

[1]  Galluzzi 1982, p. 53; Grazzini 1983, pp. 214–216. 
[2]  For modern English translation see Theophilus 1979. 
[3]  Inghirami 1841–44, v. 13, pp. 457–458. 
[4]  Neri 1612.
[5]  Grazzini 2012, pp. 329, 356.
*This post first appeared here on 6 November 2013.

Neri's Glass Furnace

From "De re metallica" 

Agricola (Georg Bauer) 1556.

In the seventeenth century, glass furnaces represented a pinnacle of technology. True, the ability to achieve the high temperatures required to melt glass had been around for centuries – high enough to melt gold, silver and copper as well. What made the glass furnace remarkable was its refinement. It made efficient use of its hardwood fuel and was able to maintain a controlled, even temperature long before any thermometer could measure it. In fact, in the early seventeenth century, Galileo was only just beginning to use glass bulbs and tubes to measure differences in ambient room temperatures.

In Florence, the construction used was typical of the time throughout Europe, called a "beehive" furnace because its shape resembled the classic elongated dome of a beehive. A double wall, built of fire resistant bricks, provided further insulation, trapping heat inside. Vertically, the furnace was divided into three levels, each forming a wide open chamber. The bottom space was used to build the fire, and had one or two openings to the outside, used to add wood fuel, rake the coals, or shovel out ash. The second, central level was where the pots of glass resided. A central hole or "eye" on the floor directly exposed the fire pit below. The space directly next to the eye was the hottest, and temperature could be further controlled by moving the crucibles farther away or closer to the eye. A number of openings in the wall allowed gaffers access to the glass pots, and at least one larger opening was used to place new crucibles, or rearrange the existing ones. The upper chamber was used to control the draft, and sometimes for annealing. Again, a central hole in the floor of this (top) level allowed exhaust gasses to leave the glass chamber and an opening to one side vented the exhaust.

In his 1612 book, L’Arte Vetraria, Neri is careful to stress that only dry oak or other hardwood should be used because it burns cleanly, and will not deposit ash or creosote in the glass.

The furnace should have dry wood, hard wood of oak because soft wood tinges the furnace and does no good. Stoke it steadily and continuously so that the flame is always clear, and there is never any smoke, which is very important in order to make a beautiful cristallo.

Once a finished piece of glassware is made, it must be allowed to cool slowly, over a period of many hours. This was often accomplished by building a long enclosed horizontal trough that connected to the furnace. A draft opening at the far end allowed heat from the furnace to be drawn in, and finished pieces were placed in a pan at the furnace end and then slowly pulled by a chain further and further down the trough toward the cooler end. This "annealing" process ensured the glass would not develop stresses and crack as it cooled.

Although Neri does not concern himself with the vagaries of furnace construction in the book, it is clear that he did possess considerable knowledge on the subject. Several of his unconventional methods for making pigments for glass involve taking bricks out of the furnace wall to stash chemicals for long term exposure to the heat.

Take small pieces of copper and put them inside the arches of the furnace. In that place, they will be within the walls. Leave them that way until each piece of copper is well calcined, using a simple fire.

While it is true that artisans of the early seventeenth century did not possess the same understanding of nature that we now enjoy, they did have a working knowledge that served them very well. It was backed by a theoretical framework that was quite sophisticated and was consistent with what could be observed and measured at the time. This is no different from our own modern understanding of nature: sophisticated and consistent with what we can observe and measure.

*This post first appeared here 24 January 2014

A Reluctant Glassmaker

The Sun, Robert Fludd

from Utriusque Cosmi (1617),v. 2, p. 19.
(alchemical symbol for gold)

Today, Antonio Neri is best known for his 1612 book, L'Arte Vetraria, in which he exposes the secrets of the art of making glass. In publishing his volume, he helped to fuel new discoveries in chemistry and medicine simply by making glass apparatus more available to experimenters. A 1662 translation of his book into English was one of the first acts undertaken by the newly formed Royal Society in London, at the behest of Robert Boyle. Neri himself lived for only two years after his book went to press, in his native Florence, and never saw the seeds of his labor come to fruition. If he had lived, he might well be surprised that his legacy is in glassmaking, and not in the subjects that he himself held most dear.

In his death at the age of thirty-eight, Neri missed a rapid advancement in our basic understanding of nature. In the space of only a few decades the face of science and medicine would start to change irrevocably. Soon, experimenters were finding new chemical elements and began to map out the periodic table, often with apparatus made of glass. For centuries, the ancient Aristotelian concept of air, earth, water and fire as the basic building blocks of the universe had endured. By the end of the seventeenth century, the inadequacies of the old model were becoming clear. 

But Neri was not privy to any of this. In his time, any cracks in the Aristotelian model were minor. Like his sponsor, Medici prince Don Antonio, Neri was an adherent of new doctrines of the physician Paracelsus, who rebelled against the old system, but was still very much a product of it. First and foremost, Neri thought of himself as an alchemist. While history has not generally been kind to his ilk, a true understanding of early modern science rests on the methods and reasoning developed by alchemists like Neri. 

Although alchemy covered a wide range of activities, it will forever be associated most closely with the mistaken notion that base metals such as lead or iron could be transmuted into gold. Once science had established this idea as specious, the race was on to separate "new science" from the old. It became fashionable to cast alchemists into the mold of charlatans, tricksters and self-deceived fools. While many such characters did exist, Neri was not one of them; his work was based on careful reasoning and experimentation. The final irony is that through the kind of advancements that he himself helped to pioneer, the majority of his life's work has fallen by the wayside. What has endured the test of modern science is his treatise on glassmaking.

As early as the age of twenty, Neri was demonstrating transmutation to expert gold refiners. As late as the year before his death he was writing authoritatively and coherently on the subject. To understand how this is possible – to be rational and methodical, and at the same time completely wrong – is to get a sense of the true difficulties involved in science. Based on what he was taught, what he read, and his own experimentation, Neri thought metals and other materials "matured" over time. He thought that more "imperfect" metals like lead and iron were part of a continuum that ended with the "perfect" metal gold. Furthermore, he thought that primordial "seeds of gold" left over from the creation of the earth could be mined and isolated. Like wheat and other plants, given the correct nurturing, and conditions, this seed material could be encouraged to mature into vast quantities of gold. Writing in his 1613 manuscript Discorso, he says,

The response is that the chemical art lets the gold proceed from that present and immediate cause, because this is the seed of gold, which acts naturally when art cooperates. The chemist does nothing but extract the seed from gold and apply it to suitable bodies, with which it is united to render the fruit multiplied in the same way that the farmer does. He does not produce the fruit, but provides and prepares the earth and the seed, uniting them in such a way so that they bear fruit.*

Neri thought that ultimately, for gold transmutation to be successful one needed the blessing of the Creator. He documented his process in a heavily coded (and incomprehensible) recipe he called "Donum Dei" (the most precious gift of God). This name traces to alchemical writings from as early as the fifteenth century. He maintained that those who might harm society with this knowledge or wished to profit personally or swindle others would be denied the blessing and therefore be unsuccessful. 

The remarkable thing here is that Neri's understanding of chemistry was supported at every turn by experimentation. His recorded methods, for transforming lesser metals into one-another, were repeatable and stood the test of scrutiny by contemporary experts. In the light of modern chemistry, these transformations depended on subtle physical processes and chemical reactions that would not be understood for another century or more. By performing these experiments under controlled conditions, he was taking the first steps in what would become modern science. Eventually, it would be understood that while chemical compounds can be created and destroyed by various manipulations, individual elements cannot. Today we know that iron, lead and gold were formed in the cores of ancient stars, not too different from our sun. Lighter elements are successively transformed into heavier ones under a star's "nurturing" conditions. While he lived in a period in which he had no chance of getting the particular details correct, in a poetic sense Neri was not far from the truth.

* See Maria Grazia Grazzini, “Discorso sopra la Chimica: The Paracelsian Philosophy of Antonio Neri” Nuncius 27 (2012) 311–367.

The Purse of Envy

Antonio Neri, "The Mineral Gold" Tesoro del Mondo,
(MS Ferguson 67, GB 0247,
Glasgow University Library, Special Collections,
1598-1600), f. 5r.

As a young alchemist, Antonio Neri faced a decision that had confronted virtually all accomplished artisans since the dawn of time and continues to do so today; whether or not to freely share hard-won technical knowledge with others. The indications are that Neri's thinking on the subject evolved over his lifetime. Testimony given by Florentine metals refiner Guido Melani indicate that as a twenty-year-old, Neri was willing to share his most precious secrets, albeit reluctantly.

Melani reported that in July 1596, Neri performed a transmutation of base metal into "twenty-four carat" gold. Upon being pressed, Neri confided that he had learned the secret from a German, who performed the gold transmutation with a "tablet of medicine." The German told him the medicine was nothing but the simple quintessence of green vitriol and the method to produce it was described by Paracelsus.[1] (An ion exchange reaction that we now know takes up iron and deposits copper in its place).

The motivations for keeping techniques secret are obvious; potential monetary reward and personal prestige. Aside from the immediate gratitude of confidants, the motivation for sharing technical secrets can be more subtle; the satisfaction of serving a greater good by advancing the art. It is indeed an ancient and very human dilemma. Five centuries before Neri, in the early 1100s a glassmaking Benedictine monk wrote on the subject. In Hesse, Germany, Theophilus Presbyter penned these lines in his De Diversis Artibus [On Various Arts]. "Do not hide His [God's] gifts in the purse of envy, nor conceal them in the storeroom of a selfish heart" and "Do not hide away the talent given to you by God, but, working and teaching openly and with humility, … faithfully reveal it to those who desire to learn."[2] Although it is doubtful that this particular writing was ever seen by Neri, his access to the most extensive libraries in Italy, along with his knowledge of Latin and the writings of other alchemists ensured a comprehensive understanding of his subject and the politics surrounding it.

Two centuries after Neri's death, historian Francesco Inghirami published details of an incident, which if true, might have contributed to a change of heart with our priest:

He [Neri] claimed he had found the secret of making the famous philosopher's stone and it was said he had discovered it among some of his confidants.  Some thugs learnt of this and attacked him at night, in order to obtain the secret by force. He shrewdly gave them a certain recipe he had in his pocket and explained the figures written on it, claiming it to be the secret oil required. But that night, Neri left Florence and traveled to various parts of Europe.[3]

Nevertheless, in his travels to Antwerp it is clear that Priest Neri continued to share his knowledge of glassmaking, in the shop of Filippo Gridolfi, and of course, upon his return to Florence seven years later in the publication of his famous book, L' Arte Vetraria.[4] In contrast, on the subject of transmuting gold and silver, Neri had decided to take his secrets with him to the grave, a decision that he justifies in a manuscript, Discorso, which he completed shortly before his death:

We must also consider the danger to its possessor if it became known to others and particularly to the princes. For that reason even if someone knows and practices this art, he is obliged to keep it hidden and to conceal it; and I know of what I speak.[5]

Neri outlines his fears that such a momentous discovery, if generally known could lead to abuse of power, a collapse of the monetary system, and general chaos in society. In spite of his deep reservations, we see a final glimmer of his innate desire to share. He did, in fact, leave behind his recipe for the philosopher's stone, but in coded, obscure language that has never to this day been deciphered. As he put it: "I wrote the words so strangers will not understand." 

[1]  Galluzzi 1982, p. 53; Grazzini 1983, pp. 214–216. 
[2]  For modern English translation see Theophilus 1979. 
[3]  Inghirami 1841–44, v. 13, pp. 457–458. 
[4]  Neri 1612.
[5]  Grazzini 2012, pp. 329, 356.
*This post first appeared here on 6 November 2013.

Early Modern Glass Furnace

From "De re metallica" 

Agricola (Georg Bauer) 1556.

In the seventeenth century, glass furnaces represented a pinnacle of technology. True, the ability to achieve the high temperatures required to melt glass had been around for centuries – high enough to melt gold, silver and copper as well. What made the glass furnace remarkable was its refinement. It made efficient use of its hardwood fuel and was able to maintain a controlled, even temperature long before any thermometer could measure it. In fact, in the early seventeenth century, Galileo was only just beginning to use glass bulbs and tubes to measure differences in ambient room temperatures.

In Florence, the construction used was typical of the time throughout Europe, called a "beehive" furnace because its shape resembled the elongated dome of a beehive. A double wall, built of fire resistant bricks, provided further insulation, trapping heat inside. Vertically, the furnace was divided into three levels, each forming a wide open chamber. The bottom space was used to build the fire, and had one or two openings to the outside, used to add wood fuel, rake the coals, or shovel out ash. The second, central level was where the pots of glass resided. A central hole or "eye" on the floor directly exposed the fire pit below. The space directly next to the eye was the hottest, and temperature could be further controlled by moving the crucibles farther away or closer to the eye. A number of openings in the wall allowed gaffers access to the glass pots, and at least one larger opening was used to place new crucibles, or rearrange the existing ones. The upper chamber was used to control the draft, and sometimes for annealing. Again, a central hole in the floor of this (top) level allowed exhaust gasses to leave the glass chamber and an opening to one side vented the exhaust.

In his book, L’Arte Vetraria, Neri is careful to stress that only dry oak or other hardwood should be used because it burns cleanly, and will not deposit ash or creosote in the glass.

The furnace should have dry wood, hard wood of oak because soft wood tinges the furnace and does no good. Stoke it steadily and continuously so that the flame is always clear, and there is never any smoke, which is very important in order to make a beautiful cristallo.

Once a finished piece of glassware is made, it must be allowed to cool slowly, over a period of many hours. This was often accomplished by building a long enclosed horizontal trough that connected to the furnace. A draft opening at the far end allowed heat from the furnace to be drawn in, and finished pieces were placed in a pan at the furnace end and then slowly pulled by a chain further and further down the trough toward the cooler end. This "annealing" process ensured the glass would not develop stresses and crack as it cooled.

Although Neri does not concern himself with the vagaries of furnace construction in the book, it is clear that he did possess considerable knowledge on the subject. Several of his unconventional methods for making pigments for glass involve taking bricks out of the furnace wall to stash chemicals for long term exposure to the heat.

Take small pieces of copper and put them inside the arches of the furnace. In that place, they will be within the walls. Leave them that way until each piece of copper is well calcined, using a simple fire.

While it is true that artisans of the early seventeenth century did not possess the same understanding of nature that we now enjoy, they did have a working knowledge that served them very well. It was backed by a theoretical framework that was quite sophisticated and was consistent with what could be observed and measured at the time. This is no different from our own modern understanding of nature: sophisticated and consistent with what we can observe and measure.

*This post first appeared here 24 January 2014

The Reluctant Glassmaker

The Sun, Robert Fludd

from Utriusque Cosmi (1617),v. 2, p. 19.
(alchemical symbol for gold)

Today, Antonio Neri is best known for his 1612 book, L'Arte Vetraria, in which he exposes the secrets of the art of making glass. In publishing his volume, he helped to fuel new discoveries in chemistry and medicine simply by making glass apparatus more available to experimenters. A 1662 translation of his book into English was one of the first acts undertaken by the newly formed Royal Society in London, at the behest of Robert Boyle. Neri himself lived for only two years after his book went to press, in his native Florence, and never saw the seeds of his labor come to fruition. If he had lived, he might well be surprised that his legacy is in glassmaking, and not in the subjects that he himself held most dear.

In his death at the age of thirty-eight, Neri missed a rapid advancement in our basic understanding of nature. In the space of only a few decades the face of science and medicine would start to change irrevocably. Soon, experimenters were finding new chemical elements and began to map out the periodic table, often with apparatus made of glass. For centuries, the ancient Aristotelian concept of air, earth, water and fire as the basic building blocks of the universe had endured. By the end of the seventeenth century, the inadequacies of the old model were becoming clear. 

But Neri was not privy to any of this. In his time, any cracks in the Aristotelian model were minor. Like his sponsor, Medici prince Don Antonio, Neri was an adherent of new doctrines of the physician Paracelsus, who rebelled against the old system, but was still very much a product of it. First and foremost, Neri thought of himself as an alchemist. While history has not generally been kind to his ilk, a true understanding of early modern science rests on the methods and reasoning developed by alchemists like Neri. 

Although alchemy covered a wide range of activities, it will forever be associated most closely with the mistaken notion that base metals such as lead or iron could be transmuted into gold. Once science had established this idea as specious, the race was on to separate "new science" from the old. It became fashionable to cast alchemists into the mold of charlatans, tricksters and self-deceived fools. While many such characters did exist, Neri was not one of them; his work was based on careful reasoning and experimentation. The final irony is that through the kind of advancements that he himself helped to pioneer, the majority of his life's work has fallen by the wayside. What has endured the test of modern science is his treatise on glassmaking.

As early as the age of twenty, Neri was demonstrating transmutation to expert gold refiners. As late as the year before his death he was writing authoritatively and coherently on the subject. To understand how this is possible – to be rational and methodical, and at the same time completely wrong – is to get a sense of the true difficulties involved in science. Based on what he was taught, what he read, and his own experimentation, Neri thought metals and other materials "matured" over time. He thought that more "imperfect" metals like lead and iron were part of a continuum that ended with the "perfect" metal gold. Furthermore, he thought that primordial "seeds of gold" left over from the creation of the earth could be mined and isolated. Like wheat and other plants, given the correct nurturing, and conditions, this seed material could be encouraged to mature into vast quantities of gold. Writing in his 1613 manuscript Discorso, he says,

The response is that the chemical art lets the gold proceed from that present and immediate cause, because this is the seed of gold, which acts naturally when art cooperates. The chemist does nothing but extract the seed from gold and apply it to suitable bodies, with which it is united to render the fruit multiplied in the same way that the farmer does. He does not produce the fruit, but provides and prepares the earth and the seed, uniting them in such a way so that they bear fruit.*

Neri thought that ultimately, for gold transmutation to be successful one needed the blessing of the Creator. He documented his process in a heavily coded (and incomprehensible) recipe he called "Donum Dei" (the most precious gift of God). This name traces to alchemical writings from as early as the fifteenth century. He maintained that those who might harm society with this knowledge or wished to profit personally or swindle others would be denied the blessing and therefore be unsuccessful. 

The remarkable thing here is that Neri's understanding of chemistry was supported at every turn by experimentation. His recorded methods, for transforming lesser metals into one-another, were repeatable and stood the test of scrutiny by contemporary experts. In the light of modern chemistry, these transformations depended on subtle physical processes and chemical reactions that would not be understood for another century or more. By performing these experiments under controlled conditions, he was taking the first steps in what would become modern science. Eventually, it would be understood that while chemical compounds can be created and destroyed by various manipulations, individual elements cannot. Today we know that iron, lead and gold were formed in the cores of ancient stars, not too different from our sun. Lighter elements are successively transformed into heavier ones under a star's "nurturing" conditions. While he lived in a period in which he had no chance of getting the particular details correct, in a poetic sense Neri was not far from the truth.

* See Maria Grazia Grazzini, “Discorso sopra la Chimica: The Paracelsian Philosophy of Antonio Neri” Nuncius 27 (2012) 311–367.

The Purse of Envy

Antonio Neri, "The Mineral Gold" Tesoro del Mondo,
(MS Ferguson 67, GB 0247,
Glasgow University Library, Special Collections,
1598-1600), f. 5r.

As a young alchemist, Antonio Neri faced a decision that had confronted virtually all accomplished artisans since the dawn of time and continues to do so today; whether or not to freely share hard-won technical knowledge with others. The indications are that Neri's thinking on the subject evolved over his lifetime. Testimony given by Florentine metals refiner Guido Melani indicate that as a twenty-year-old, Neri was willing to share his most precious secrets, albeit reluctantly.

Melani reported that in July 1596, Neri performed a transmutation of base metal into "twenty-four carat" gold. Upon being pressed, Neri confided that he had learned the secret from a German, who performed the gold transmutation with a "tablet of medicine." The German told him the medicine was nothing but the simple quintessence of green vitriol and the method to produce it was described by Paracelsus.[1] (An ion exchange reaction that we now know takes up iron and deposits copper in its place).

The motivations for keeping techniques secret are obvious; potential monetary reward and personal prestige. Aside from the immediate gratitude of confidants, the motivation for sharing technical secrets can be more subtle; the satisfaction of serving a greater good by advancing the art. It is indeed an ancient and very human dilemma. Five centuries before Neri, in the early 1100s a glassmaking Benedictine monk wrote on the subject. In Hesse, Germany, Theophilus Presbyter penned these lines in his De Diversis Artibus [On Various Arts]. "Do not hide His [God's] gifts in the purse of envy, nor conceal them in the storeroom of a selfish heart" and "Do not hide away the talent given to you by God, but, working and teaching openly and with humility, … faithfully reveal it to those who desire to learn."[2] Although it is doubtful that this particular writing was ever seen by Neri, his access to the most extensive libraries in Italy, along with his knowledge of Latin and the writings of other alchemists ensured a comprehensive understanding of his subject and the politics surrounding it.

Two centuries after Neri's death, historian Francesco Inghirami published details of an incident, which if true, might have contributed to a change of heart with our priest:

He [Neri] claimed he had found the secret of making the famous philosopher's stone and it was said he had discovered it among some of his confidants.  Some thugs learnt of this and attacked him at night, in order to obtain the secret by force. He shrewdly gave them a certain recipe he had in his pocket and explained the figures written on it, claiming it to be the secret oil required. But that night, Neri left Florence and traveled to various parts of Europe.[3]

Nevertheless, in his travels to Antwerp it is clear that Priest Neri continued to share his knowledge of glassmaking, in the shop of Filippo Gridolfi, and of course, upon his return to Florence seven years later in the publication of his famous book, L' Arte Vetraria.[4] In contrast, on the subject of transmuting gold and silver, Neri had decided to take his secrets with him to the grave, a decision that he justifies in a manuscript, Discorso, which he completed shortly before his death:

We must also consider the danger to its possessor if it became known to others and particularly to the princes. For that reason even if someone knows and practices this art, he is obliged to keep it hidden and to conceal it; and I know of what I speak.[5]

Neri outlines his fears that such a momentous discovery, if generally known could lead to abuse of power, a collapse of the monetary system, and general chaos in society. In spite of his deep reservations, we see a final glimmer of his innate desire to share. He did, in fact, leave behind his recipe for the philosopher's stone, but in coded, obscure language that has never to this day been deciphered. As he put it: "I wrote the words so strangers will not understand." 

[1]  Galluzzi 1982, p. 53; Grazzini 1983, pp. 214–216. 
[2]  For modern English translation see Theophilus 1979. 
[3]  Inghirami 1841–44, v. 13, pp. 457–458. 
[4]  Neri 1612.
[5]  Grazzini 2012, pp. 329, 356.
*This post first appeared here on 6 November 2013.

The Art of Metals

Fig. 1: Antonio Neri, "Ars Preparatio Metallor[um]"

in Tesoro del Mondo, f. 8r.

Recently we examined another of a set of four illustrations drawn by priest Antonio Neri in a manuscript started in 1598.[1] They show various "arts" being practiced involving items found in nature; plants, animals, stone and today's subject: metals. 

Metals and their chemical manipulation concern Neri's work both as a glassmaker and as an alchemist. Most of the colorful pigments he uses in his glassmaking derive from metals; white from tin, green from iron, red from copper and gold, blue from cobalt, although Neri knew this last one only as a mineral called "zaffer." As an alchemist, metals were the subject of medicinal cures and of course were the focus of transmutation—the quest to turn one metal into another. In another manuscript written towards the end of his life, he indicates that he spent time in mines, where it was thought that metals "grew" underground as "veins" which nourished the earth. [2]

After an examination of Neri's "Art of Preparing Metals" we will take a look at another picture on the same subject, this time a painting titled the "Goldsmith's Workshop" by Alessandro Fei. It was executed a few years before Antonio was born, but bears some remarkable similarities in subject matter.

First, the manuscript illustration (fig. 1): At center left, we see a special furnace construction which the label tells us is for "reverberation and calcination." Two crucibles sit inside, exposed to the heat. These are both procedures with which Neri was quite familiar. In the recipes of his glassmaking book, L'Arte Vetraria, [3] he speaks numerous times about what was called "calcination"—the conversion of a metal into what is usually a powdered oxide form. [4] This was a fundamental operation in producing the pigments for glass. "Reverberation" was exposing a material to secondary heat reflected from the inner walls of the furnace chamber; it was a more even heat than that produced by a direct flame.

Above the reverberation furnace is a foundry furnace, used for melting metals. Because of the high temperatures that needed to be achieved, it has a large bellows attached to force air into the fire causing a "blast" effect, which causes the fire to burn faster and hotter. Resting on the hearth is a long pair of pincers used to insert and remove crucibles of molten metal.

To the right, we see a curious arrangement of two glass retorts, each feeding into the other. They sit on purpose built stoves. The chimneys are capped by dome shaped dampers to control the draft and paddle mechanisms in front regulate heat under the glassware. A worker tends the apparatus, and the caption below reads "for extraction of the quintessence." Neri's other writing makes plain that this "quintessence" was a material that exhibits such a harmonious blending of the four essences: air, water, fire and earth that a new fifth essence (supposedly) emerged with extraordinary properties. To the right is a similar stove set-up with a single retort which is labeled "distilling." This station might have been used in preparation of the acids needed to purify metals.

At lower right, a blacksmith is hammering a piece of iron into a sword on an anvil. High-carbon "steel" was being made and used in the Medici court at the time, and that may well be what the smith is working with. Around him are several examples of his art, including two finished swords, a large copper bowl or cauldron, and a covered drinking stein made of tin.

To his left, we find a goldsmith, also hammering on an anvil, fashioning a silver platter. Displayed behind him are a variety of his handiwork, including more platters, gold necklaces and crosses and other ornamentation. A number of tools hang along the bottom of the anvil station, and behind it a small dog is curled up on the floor. 

Fig 2: Alessandro Fei (Barbieri)
"Goldsmith's Workshop" c. 1572.

About twenty-five years before Neri wrote his manuscript, Alessandro Fei painted a similar picture (fig. 2). Here we are treated to a view of a royal foundry housed in the yet to be completed Uffizi palace. [5] There is a remarkable concordance between this painting and Neri's illustration, right down to a small dog, hanging around the goldsmith's bench. 

The central figure of the painting is  Francesco de' Medici, seated in the foreground, inspecting his father's gold crown at a workbench. The dog is playfully engaging with the future Grand Duke, while on the opposite side of the bench, two other men are amiably discussing their work, perhaps silver chasing.To the left of Francesco, a younger man examines a gold ewer in the company of an older goldsmith seated across the table. The artisan is wearing spectacles and (although it is hard to see) he holds a small hammer in his hand. A worker to Francesco’s right is also intently engaged in his work. In the right mid-ground we find a small furnace with a tall chimney leading upward. On the mantle are displayed a number of gold and silver items, including platters, vessels and chains or necklaces. To the left, four men are busy seated around a large workbench. Behind that group, toward the center of the picture, are two men working at an anvil and three more at another bench on the right, accompanied by a second small dog. In an enclosed area in the background we see two large open furnace hearths, with their fireboxes glowing from underneath and men working in close proximity. In the far left background is a group entering the work area, including a figure in a yellow cape accompanied by a third dog.

The one element present in Neri's illustration that is missing in the painting is the glassware. Metalwork was a venerated and mature art long before Neri's era, which is underlined by the similarity of the two scenes, even though they are a quarter century apart, the tools, equipment and work methods are identical for all intents and purposes. There is no doubt that chemistry and distillation apparatus were used by the earlier metals artisans, the fact that Neri chose to emphasize this aspect of the work is a clear indication of his own interest and a foreshadowing of his future involvement in the production of the glass itself.

[1] Neri 1598-1600.
[2] Neri 1613, Grazzini 2012. 
[3] Neri 1612.
[4] In several of Neri's glass recipes the result of "calcination" is a sulfide.
[5] Beretta, 2014.

(Bibliography)
*This post first appeared here on 17 September 2014.