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.

A Very Good Run

The title page of Antonio Neri's 1612 book
L'Arte Vetraria.

For most of the past five thousand years, the techniques of glassmaking were passed only in strict confidence from master to apprentice. When artisans did commit methods to writing, they were held close as precious possessions, often passed down within families. Inevitably though, some glass recipe compilations did become public, a few were even purposefully shared. But before the advent of printed books and some time after, a manuscript was typically propagated through the laborious and often error-prone process of writing copies out by hand. Even at the beginning of the seventeenth century, a mere four hundred years ago, glassmaking techniques and materials were passed primarily through the apprentice system. 

All of that changed forever, in 1612, when a Florentine priest named Antonio Neri published the first printed book devoted to the ‘art of glassmaking’. In fact, the title he chose was exactly that: L’Arte Vetraria. [1] Neri’s volume was noticed almost immediately by technical types; Galileo owned a copy and supplied one to his friend Federico Cesi, founder of an early scientific society called the Lincei [lynxes]. In his introduction, Neri specifically invites anyone curious and willing to apply themselves to give glassmaking a try, saying, “Unless you purposely foul-up, it will be impossible to fail”. However, the book did not exactly catch fire with the general public. Slowly but surely, copies found their way to the hands of early scientific investigators and also to the hands of glassmakers throughout Europe. As Italian artisans migrated to northern Europe, Neri’s book came with them.

In 1661, a reprint of L’Arte Vetraria was issued in the priest’s native Florence, the next year an English translation was published in London for the Royal Society and the year after that a Venetian edition appeared. Within ten years, illustrated Latin and German translations were published and French and Spanish versions were not far behind. By the year 1800 over two dozen editions circulated around Europe. It had become the de facto bible of glassmakers throughout. There is precious little personal information in the book about Neri, but it does make clear that he started his career at the Medici court, in the laboratory of prince Don Antonio de’ Medici. He went on to work in a glass house in Pisa – one that supplied fine glassware to the Vatican – and then spent the bulk of his career, seven years, in Antwerp. 

Neri’s book, L’Arte Vetraria, shined brightest in the hands of an artisan. Neri has the rare ability to translate non-verbal skills into written words. Where exact amounts could not be given, he urges the glassmaker to develop an eye for the right color and to take the final intended purpose into account. He warns against the pitfalls of roasting a chemical too much or not purifying an ingredient enough. His book became a platform upon which later glass experimenters added their own findings and it became a kind of working document. This started with the 1662 English translation by London physician Christopher Merrett. Not particularly familiar with glassmaking himself, Merrett canvassed experienced artisans in England and made extensive notes that he appended to Neri’s original. Merrett also rearranged Neri’s text in a format that he felt more appropriate. The Latin edition by Frisius, in Amsterdam, restored Neri’s original format, but also retained Merrett’s observations. In 1679, Johann Kunckel made a German translation that added his own extensive knowledge, producing what is perhaps the most authoritative edition that the book attained.

In 1697, Jean Haudicquer de Blancourt translated Merrett’s English edition into French, but he gave no acknowledgment to Neri or Merrett. Blancourt plagiarized the work, putting his own name as the sole author. He greatly expanded the page count, but added little or no new material. Where Neri stipulated, for instance, that artificial gems of all colors could be made by adding previously discussed pigments to a basic lead glass formula, Blancourt turned each of these into a separate recipe. In doing this, that one particular section grew larger than the entirety of Neri’s original book. Two years later, in 1699, Daniel Brown translated Blancourt’s English-to-French rendition back into English. From there, the formulas – especially the artificial gem recipes – started to appear un-attributed in popular craft encyclopedias; the Neri provenance of these recipes was now erased, but they continued to influence artisans through the nineteenth century.

Meanwhile, new translations with correct attribution were published and the book flourished in popularity. Authors built on each other’s annotations; from Neri to Merrett to Kunckel. In 1752, Paul Thiry d’Holbach published a proper French edition that included the accumulated comments of the three annotators. In 1780, Suárez and Núñez completed their Spanish edition, based on Holbach.[2] And the tradition continues today; in 2007, Holbach’s edition was used as the basis for the first ever Japanese translation by Sakata and Ikeda. [3]  

On one hand, this particular lineage of the book is remarkable for the tour of languages; Italian, English, German, French, Spanish and Japanese. On the other hand, it spans a remarkable period in history, starting with alchemy and progressing through the volumes to modern science. With each new set of annotations Neri's book starts with a purely empirical set of recipes, using classical alchemy. By Kunckel’s edition, experimentation was more formalized and rigorous; the chemistry behind pigments for coloring glass became an intense subject of scrutiny. By Holbach’s edition, the physical and mechanical properties of glass were being investigated and in turn, glass played an ever-critical role in instrumentation like thermometers, barometers, microscopes, telescopes and a newly invented electrical device called a Leiden jar.

Antoine Lavoisier is considered by many to be the ‘father of modern chemistry’. For all practical purposes, his isolation of oxygen as a discrete element, in 1778, rang the death knell for classical alchemy. About 1799, Lavoisier’s good friend Pierre Loysel wrote what was to be the successor to Neri’s book on glassmaking, Essai sur l’art de la verrerie [Essays on the art of Glassmaking]. [4] While it never attained the fame or currency of Neri’s contribution, it did mark the passing of the mantle to new techniques and a better understanding of the materials. [5] For nearly two centuries before Loysel, Neri’s book and its derivatives held the floor as the authoritative reference for glassmakers throughout Europe and beyond. 187 years is a remarkable run for any book, even more so for a volume devoted to technical advice and recipes. Antonio Neri would have probably preferred to be remembered for his work on alchemical transmutation and medicinal cures, but in the end it was his sensible book on glass formulation that continues to endear him to anyone interested in the art of glass.

[1] Antonio Neri, L’Arte vetraria, distinta in libri sette, del R.[everendo] P.[rete/ padre] Antonio Neri fiorentino. Ne quali si scoprono, effetti maravigliosi, & insegnano segreti bellissimi, del vetro nel fuoco & altre cose curiose. All’Illvst.mo et eccell.mo Sig., Il Sig, Don Antonio Medici (Florence: Giunti 1612).

[2] “Sobre el Vidrio Y Los Esmaltes” and “Continuacion Del Arte De Vidrieria” in Memorias instructivas, y curiosas sobre agricultura, comercio, industria, economía, chymica, botanica, historia natural, &c, ... Miguel Gerónimo Suárez y Núñez, ed., tr. (Madrid: Dom Pedro Marin, 1780) v. 4., pp. 185–224 (Mem. 50, prolog); 225–470

[3] L’Arte Vetraria by Antonio Neri, Japanese Translation, Hironobu Sakata, Mayumi Ikeda eds., tr. (Yokohama: Shunpusha, 2007), a translation of Neri 1759 (Holbach).
[4]Pierre Loysel, Essai sur l’art de la verrerie (Paris, 1799/1800).
[5] For more on Loysel and his book see Marco Beretta, “Unveiling Glass’s Mysteries Lavoisier, Loysel and the First Chemical Treatise on Glass (1765–1799),” in Objects of Chemical Inquiry ed. by Ursula Klein and Carsten Reinhardt (Sagamore Beach: Science History Publications/USA, 2014)

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.

A Very Good Run

The title page of Antonio Neri's 1612 book

L'Arte Vetraria.

For most of the past five thousand years, the techniques of glassmaking were passed only in strict confidence from master to apprentice. When artisans did commit methods to writing, they were held close as precious possessions, often passed down within families. Inevitably though, some glass recipe compilations did become public, a few were even purposefully shared. But before the advent of printed books and some time after, a manuscript was typically propagated through the laborious and often error-prone process of writing copies out by hand. Even at the beginning of the seventeenth century, a mere four hundred years ago, glassmaking techniques and materials were passed primarily through the apprentice system. 

All of that changed forever, in 1612, when a Florentine priest named Antonio Neri published the first printed book devoted to the ‘art of glassmaking’. In fact, the title he chose was exactly that: L’Arte Vetraria. [1] Neri’s volume was noticed almost immediately by technical types; Galileo owned a copy and supplied one to his friend Federico Cesi, founder of an early scientific society called the Lincei [lynxes]. In his introduction, Neri specifically invites anyone curious and willing to apply themselves to give glassmaking a try, saying, “Unless you purposely foul-up, it will be impossible to fail”. However, the book did not exactly catch fire with the general public. Slowly but surely, copies found their way to the hands of early scientific investigators and also to the hands of glassmakers throughout Europe. As Italian artisans migrated to northern Europe, Neri’s book came with them.

In 1661, a reprint of L’Arte Vetraria was issued in the priest’s native Florence, the next year an English translation was published in London for the Royal Society and the year after that a Venetian edition appeared. Within ten years, illustrated Latin and German translations were published and French and Spanish versions were not far behind. By the year 1800 over two dozen editions circulated around Europe. It had become the de facto bible of glassmakers throughout. There is precious little personal information in the book about Neri, but it does make clear that he started his career at the Medici court, in the laboratory of prince Don Antonio de’ Medici. He went on to work in a glass house in Pisa – one that supplied fine glassware to the Vatican – and then spent the bulk of his career, seven years, in Antwerp. 

Neri’s book, L’Arte Vetraria, shined brightest in the hands of an artisan. Neri has the rare ability to translate non-verbal skills into written words. Where exact amounts could not be given, he urges the glassmaker to develop an eye for the right color and to take the final intended purpose into account. He warns against the pitfalls of roasting a chemical too much or not purifying an ingredient enough. His book became a platform upon which later glass experimenters added their own findings and it became a kind of working document. This started with the 1662 English translation by London physician Christopher Merrett. Not particularly familiar with glassmaking himself, Merrett canvassed experienced artisans in England and made extensive notes that he appended to Neri’s original. Merrett also rearranged Neri’s text in a format that he felt more appropriate. The Latin edition by Frisius, in Amsterdam, restored Neri’s original format, but also retained Merrett’s observations. In 1679, Johann Kunckel made a German translation that added his own extensive knowledge, producing what is perhaps the most authoritative edition that the book attained.

In 1697, Jean Haudicquer de Blancourt translated Merrett’s English edition into French, but he gave no acknowledgment to Neri or Merrett. Blancourt plagiarized the work, putting his own name as the sole author. He greatly expanded the page count, but added little or no new material. Where Neri stipulated, for instance, that artificial gems of all colors could be made by adding previously discussed pigments to a basic lead glass formula, Blancourt turned each of these into a separate recipe. In doing this, that one particular section grew larger than the entirety of Neri’s original book. Two years later, in 1699, Daniel Brown translated Blancourt’s English-to-French rendition back into English. From there, the formulas – especially the artificial gem recipes – started to appear un-attributed in popular craft encyclopedias; the Neri provenance of these recipes was now erased, but they continued to influence artisans through the nineteenth century.

Meanwhile, new translations with correct attribution were published and the book flourished in popularity. Authors built on each other’s annotations; from Neri to Merrett to Kunckel. In 1752, Paul Thiry d’Holbach published a proper French edition that included the accumulated comments of the three annotators. In 1780, Suárez and Núñez completed their Spanish edition, based on Holbach.[2] And the tradition continues today; in 2007, Holbach’s edition was used as the basis for the first ever Japanese translation by Sakata and Ikeda. [3]  

On one hand, this particular lineage of the book is remarkable for the tour of languages; Italian, English, German, French, Spanish and Japanese. On the other hand, it spans a remarkable period in history, starting with alchemy and progressing through the volumes to modern science. With each new set of annotations Neri's book starts with a purely empirical set of recipes, using classical alchemy. By Kunckel’s edition, experimentation was more formalized and rigorous; the chemistry behind pigments for coloring glass became an intense subject of scrutiny. By Holbach’s edition, the physical and mechanical properties of glass were being investigated and in turn, glass played an ever-critical role in instrumentation like thermometers, barometers, microscopes, telescopes and a newly invented electrical device called a Leiden jar.

Antoine Lavoisier is considered by many to be the ‘father of modern chemistry’. For all practical purposes, his isolation of oxygen as a discrete element, in 1778, rang the death knell for classical alchemy. About 1799, Lavoisier’s good friend Pierre Loysel wrote what was to be the successor to Neri’s book on glassmaking, Essai sur l’art de la verrerie [Essays on the art of Glassmaking]. [4] While it never attained the fame or currency of Neri’s contribution, it did mark the passing of the mantle to new techniques and a better understanding of the materials. [5] For nearly two centuries before Loysel, Neri’s book and its derivatives held the floor as the authoritative reference for glassmakers throughout Europe and beyond. 187 years is a remarkable run for any book, even more so for a volume devoted to technical advice and recipes. Antonio Neri would have probably preferred to be remembered for his work on alchemical transmutation and medicinal cures, but in the end it was his sensible book on glass formulation that continues to endear him to anyone interested in the art of glass.

[1] Antonio Neri, L’Arte vetraria, distinta in libri sette, del R.[everendo] P.[rete/ padre] Antonio Neri fiorentino. Ne quali si scoprono, effetti maravigliosi, & insegnano segreti bellissimi, del vetro nel fuoco & altre cose curiose. All’Illvst.mo et eccell.mo Sig., Il Sig, Don Antonio Medici (Florence: Giunti 1612).

[2] “Sobre el Vidrio Y Los Esmaltes” and “Continuacion Del Arte De Vidrieria” in Memorias instructivas, y curiosas sobre agricultura, comercio, industria, economía, chymica, botanica, historia natural, &c, ... Miguel Gerónimo Suárez y Núñez, ed., tr. (Madrid: Dom Pedro Marin, 1780) v. 4., pp. 185–224 (Mem. 50, prolog); 225–470

[3] L’Arte Vetraria by Antonio Neri, Japanese Translation, Hironobu Sakata, Mayumi Ikeda eds., tr. (Yokohama: Shunpusha, 2007), a translation of Neri 1759 (Holbach).
[4]Pierre Loysel, Essai sur l’art de la verrerie (Paris, 1799/1800).
[5] For more on Loysel and his book see Marco Beretta, “Unveiling Glass’s Mysteries Lavoisier, Loysel and the First Chemical Treatise on Glass (1765–1799),” in Objects of Chemical Inquiry ed. by Ursula Klein and Carsten Reinhardt (Sagamore Beach: Science History Publications/USA, 2014)

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.

A Very Good Run

The title page of Antonio Neri's 1612 book
L'Arte Vetraria.

For most of the past five thousand years, the techniques of glassmaking were passed only in strict confidence from master to apprentice. When artisans did commit methods to writing, they were held close as precious possessions, often passed down within families. Inevitably though, some glass recipe compilations did become public, a few were even purposefully shared. But before the advent of printed books and some time after, a manuscript was typically propagated through the laborious and often error-prone process of writing copies out by hand. Even at the beginning of the seventeenth century, a mere four hundred years ago, glassmaking techniques and materials were passed primarily through the apprentice system. 

All of that changed forever, in 1612, when a Florentine priest named Antonio Neri published the first printed book devoted to the ‘art of glassmaking’. In fact, the title he chose was exactly that: L’Arte Vetraria. [1] Neri’s volume was noticed almost immediately by technical types; Galileo owned a copy and supplied one to his friend Federico Cesi, founder of an early scientific society called the Lincei [lynxes]. In his introduction, Neri specifically invites anyone curious and willing to apply themselves to give glassmaking a try, saying, “Unless you purposely foul-up, it will be impossible to fail”. However, the book did not exactly catch fire with the general public. Slowly but surely, copies found their way to the hands of early scientific investigators and also to the hands of glassmakers throughout Europe. As Italian artisans migrated to northern Europe, Neri’s book came with them.

In 1661, a reprint of L’Arte Vetraria was issued in the priest’s native Florence, the next year an English translation was published in London for the Royal Society and the year after that a Venetian edition appeared. Within ten years, illustrated Latin and German translations were published and French and Spanish versions were not far behind. By the year 1800 over two dozen editions circulated around Europe. It had become the de facto bible of glassmakers throughout. There is precious little personal information in the book about Neri, but it does make clear that he started his career at the Medici court, in the laboratory of prince Don Antonio de’ Medici. He went on to work in a glass house in Pisa – one that supplied fine glassware to the Vatican – and then spent the bulk of his career, seven years, in Antwerp. 

Neri’s book, L’Arte Vetraria, shined brightest in the hands of an artisan. Neri has the rare ability to translate non-verbal skills into written words. Where exact amounts could not be given, he urges the glassmaker to develop an eye for the right color and to take the final intended purpose into account. He warns against the pitfalls of roasting a chemical too much or not purifying an ingredient enough. His book became a platform upon which later glass experimenters added their own findings and it became a kind of working document. This started with the 1662 English translation by London physician Christopher Merrett. Not particularly familiar with glassmaking himself, Merrett canvassed experienced artisans in England and made extensive notes that he appended to Neri’s original. Merrett also rearranged Neri’s text in a format that he felt more appropriate. The Latin edition by Frisius, in Amsterdam, restored Neri’s original format, but also retained Merrett’s observations. In 1679, Johann Kunckel made a German translation that added his own extensive knowledge, producing what is perhaps the most authoritative edition that the book attained.

In 1697, Jean Haudicquer de Blancourt translated Merrett’s English edition into French, but he gave no acknowledgment to Neri or Merrett. Blancourt plagiarized the work, putting his own name as the sole author. He greatly expanded the page count, but added little or no new material. Where Neri stipulated, for instance, that artificial gems of all colors could be made by adding previously discussed pigments to a basic lead glass formula, Blancourt turned each of these into a separate recipe. In doing this, that one particular section grew larger than the entirety of Neri’s original book. Two years later, in 1699, Daniel Brown translated Blancourt’s English-to-French rendition back into English. From there, the formulas – especially the artificial gem recipes – started to appear un-attributed in popular craft encyclopedias; the Neri provenance of these recipes was now erased, but they continued to influence artisans through the nineteenth century.

Meanwhile, new translations with correct attribution were published and the book flourished in popularity. Authors built on each other’s annotations; from Neri to Merrett to Kunckel. In 1752, Paul Thiry d’Holbach published a proper French edition that included the accumulated comments of the three annotators. In 1780, Suárez and Núñez completed their Spanish edition, based on Holbach.[2] And the tradition continues today; in 2007, Holbach’s edition was used as the basis for the first ever Japanese translation by Sakata and Ikeda. [3]  

On one hand, this particular lineage of the book is remarkable for the tour of languages; Italian, English, German, French, Spanish and Japanese. On the other hand, it spans a remarkable period in history, starting with alchemy and progressing through the volumes to modern science. With each new set of annotations Neri's book starts with a purely empirical set of recipes, using classical alchemy. By Kunckel’s edition, experimentation was more formalized and rigorous; the chemistry behind pigments for coloring glass became an intense subject of scrutiny. By Holbach’s edition, the physical and mechanical properties of glass were being investigated and in turn, glass played an ever-critical role in instrumentation like thermometers, barometers, microscopes, telescopes and a newly invented electrical device called a Leiden jar.

Antoine Lavoisier is considered by many to be the ‘father of modern chemistry’. For all practical purposes, his isolation of oxygen as a discrete element, in 1778, rang the death knell for classical alchemy. About 1799, Lavoisier’s good friend Pierre Loysel wrote what was to be the successor to Neri’s book on glassmaking, Essai sur l’art de la verrerie [Essays on the art of Glassmaking]. [4] While it never attained the fame or currency of Neri’s contribution, it did mark the passing of the mantle to new techniques and a better understanding of the materials. [5] For nearly two centuries before Loysel, Neri’s book and its derivatives held the floor as the authoritative reference for glassmakers throughout Europe and beyond. 187 years is a remarkable run for any book, even more so for a volume devoted to technical advice and recipes. Antonio Neri would have probably preferred to be remembered for his work on alchemical transmutation and medicinal cures, but in the end it was his sensible book on glass formulation that continues to endear him to anyone interested in the art of glass.

[1] Antonio Neri, L’Arte vetraria, distinta in libri sette, del R.[everendo] P.[rete/ padre] Antonio Neri fiorentino. Ne quali si scoprono, effetti maravigliosi, & insegnano segreti bellissimi, del vetro nel fuoco & altre cose curiose. All’Illvst.mo et eccell.mo Sig., Il Sig, Don Antonio Medici (Florence: Giunti 1612).

[2] “Sobre el Vidrio Y Los Esmaltes” and “Continuacion Del Arte De Vidrieria” in Memorias instructivas, y curiosas sobre agricultura, comercio, industria, economía, chymica, botanica, historia natural, &c, ... Miguel Gerónimo Suárez y Núñez, ed., tr. (Madrid: Dom Pedro Marin, 1780) v. 4., pp. 185–224 (Mem. 50, prolog); 225–470

[3] L’Arte Vetraria by Antonio Neri, Japanese Translation, Hironobu Sakata, Mayumi Ikeda eds., tr. (Yokohama: Shunpusha, 2007), a translation of Neri 1759 (Holbach).
[4]Pierre Loysel, Essai sur l’art de la verrerie (Paris, 1799/1800).
[5] For more on Loysel and his book see Marco Beretta, “Unveiling Glass’s Mysteries Lavoisier, Loysel and the First Chemical Treatise on Glass (1765–1799),” in Objects of Chemical Inquiry ed. by Ursula Klein and Carsten Reinhardt (Sagamore Beach: Science History Publications/USA, 2014)