Tartar Salt

So-called "wine diamonds," (harmless)

Potassium bitartrate deposits which can accumulate

in bottles and barrels of wine

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

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

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

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

The first step in making Neri's purified tartar salt is to obtain the raw "gruma, from barrels of red wine in which it forms large lumps." Next, he gently roasts it in terracotta pots "until it becomes calcined black and all its sliminess is roasted away. It then will begin to whiten, but do not let it become white, because if you do the salt will be no good." Now, he boils it in water for two hours, evaporating off three-quarters of the liquid. After filtering, he lets the remaining liquid "lye" cool in pans, allowing any sediment to settle to the bottom. He gently pours off  (decants)  the liquid which is further processed on the stove, this time in glass containers. The result, after full evaporation over a slow fire is a “white salt” left in the vessel. He dissolves this in hot water, filters it again and allows more sediment to settle out for a period of two days. Again, the liquid is decanted and evaporated in a glass container. The filtering and evaporation process is repeated four times, resulting in a product that is "whiter than snow."

Neri's final remarks for this chapter are as follows:

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

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

* This post first appeared here on 5 Sept. 2014.

A Glassmaker's Birthday

Relief portrait of Antonio Neri,

artist unknown, La Specola Museum,

Florence.

Alchemist, Glassmaker, and Priest Antonio Neri was born in Florence, Italy on 29 February 1576. From his baptismal record, we know the exact time of birth: "three hours and 25 minutes past sunset." In terms of current timekeeping conventions, sunset occurred on that particular Thursday at about 6:15 pm (local time) so the big event happened at 9:40 pm.

It might seem a bit odd to have such accurate records -- almost as if an astronomical event were being recorded. Actually, that is exactly what was being done; astrology of the sixteenth century drew a strong correspondence between 'macroscopic' events in the heavens and more earthly matters. To have an exact time of birth was seen as a way to gain greater insights into the events of ones personal life and to plan in a way that was more in harmony with the natural order of things.

Of all the days to be born, 29 February was considered among the least auspicious. A dire Northern Italian folk proverb states "An bisesti, o la mama o 'l bambi" predicting that, born on this day, a child or its mother was fated to die by year's end. Indeed, the Italian word naming the day, bisestile, had become a synonym for misfortune or calamity and is still the case for the French cognate bissêtre. Whatever stock the family put into ancient superstitions, happily this prophecy did not come true for Dianora or her fourth child Antonio.

Although his was a February birth, it was perhaps not as deep into winter as one might assume. Due to a discrepancy in the Julian calendar, which was in force then, the Spring equinox of Neri's birth year happened much earlier in the calendar than today, around 10 March, in fact. 

Infant mortality was not uncommon and for a child to die unbaptized only magnified a family's trauma. Church theologians had debated since the fourth century on the fate of the souls of such children. Most Catholic families baptized infants as soon as humanly possible, in Antonio's case the very next morning. Births occurring within Florence were officially registered at a central baptistery, San Giovanni, the ancient octagonal basilica standing directly in front of Florence's main Cathedral. 

The full baptistery record, in translation, for Antonio Neri reads:

Thursday, 1 March 1575:  Antonio Lodovico was born to Mr. Neri di Jacopo and Dianora di Francesco Parenti, residents of San Pier Maggiore parish. The time of birth was 29 February, at 3 hours 25 minutes past sunset. The godparents are Francesco di Girolamo Lenzoni and Ginevra di Federigo Sassetti.

The year is recorded as 1575 because in those days, Florentines celebrated the New Year on 25 March. Today we consider January, February and March to be part of the new year. 

Antonio joined a growing family that already contained siblings Lessandra, Jacopo and Francesco, and later would number ten children.  His father was thirty-six year-old Neri di Jacopo Neri, (Neri Neri to his friends) and his mother was twenty-one year-old Dianora Parenti. Neri Neri was a prominent doctor and later was appointed to be the personal physician to Grand Duke Ferdinando. Dianora was the daughter of Francesco Parenti, Michelangelo's lawyer. 

Tradition dictated that births were celebrated with a house party open to friends and neighbors. Thirty-four year-old Francesco Lenzoni, Antonio's godfather, would certainly have done his best to attend. His family included Florentine senators and Francesco himself would later become Tuscan ambassador to Spain. Godmother Ginevra Sassetti, in her late fifties, was also from a prominent family. Her nephew Filippo would send plant specimens back from India to be inspected by Neri Neri and their mutual friend Baccio Valori who would become director of the Laurentian Library in Florence.

Antonio Neri, would go on to learn the finer points of alchemy and glassmaking, developing new formulas and techniques that would be applied throughout Europe. In 1612, he published the world's first book entirely devoted to formulating glass, L'Arte Vetraria. It seems especially appropriate that we pause and raise a toast (in glass, of course) to his accomplishment and to the end of February, looking forward to warmer days ahead. Buon compleanno Antonio!

A Glassmaker's Birthday

Relief portrait of Antonio Neri,

artist unknown, La Specola Museum,

Florence.

Alchemist, Glassmaker, and Priest Antonio Neri was born in Florence, Italy on 29 February 1576. From his baptismal record, we know the exact time of birth: "three hours and 25 minutes past sunset." In terms of current timekeeping conventions, sunset occurred on that particular Thursday at about 6:15 pm (local time) so the big event happened at 9:40 pm.

It might seem a bit odd to have such accurate records -- almost as if an astronomical event were being recorded. Actually, that is exactly what was being done; astrology of the sixteenth century drew a strong correspondence between 'macroscopic' events in the heavens and more earthly matters. To have an exact time of birth was seen as a way to gain greater insights into the events of ones personal life and to plan in a way that was more in harmony with the natural order of things.

Of all the days to be born, 29 February was considered among the least auspicious. A dire Northern Italian folk proverb states "An bisesti, o la mama o 'l bambi" predicting that, born on this day, a child or its mother was fated to die by year's end. Indeed, the Italian word naming the day, bisestile, had become a synonym for misfortune or calamity and is still the case for the French cognate bissêtre. Whatever stock the family put into ancient superstitions, happily this prophecy did not come true for Dianora or her fourth child Antonio.

Although his was a February birth, it was perhaps not as deep into winter as one might assume. Due to a discrepancy in the Julian calendar, which was in force then, the Spring equinox of Neri's birth year happened much earlier in the calendar than today, around 10 March, in fact. 

Infant mortality was not uncommon and for a child to die unbaptized only magnified a family's trauma. Church theologians had debated since the fourth century on the fate of the souls of such children. Most Catholic families baptized infants as soon as humanly possible, in Antonio's case the very next morning. Births occurring within Florence were officially registered at a central baptistery, San Giovanni, the ancient octagonal basilica standing directly in front of Florence's main Cathedral. 

The full baptistery record, in translation, for Antonio Neri reads:

Thursday, 1 March 1575:  Antonio Lodovico was born to Mr. Neri di Jacopo and Dianora di Francesco Parenti, residents of San Pier Maggiore parish. The time of birth was 29 February, at 3 hours 25 minutes past sunset. The godparents are Francesco di Girolamo Lenzoni and Ginevra di Federigo Sassetti.

The year is recorded as 1575 because in those days, Florentines celebrated the New Year on 25 March. Today we consider January, February and March to be part of the new year. 

Antonio joined a growing family that already contained siblings Lessandra, Jacopo and Francesco, and later would number ten children.  His father was thirty-six year-old Neri di Jacopo Neri, (Neri Neri to his friends) and his mother was twenty-one year-old Dianora Parenti. Neri Neri was a prominent doctor and later was appointed to be the personal physician to Grand Duke Ferdinando. Dianora was the daughter of Francesco Parenti, Michelangelo's lawyer. 

Tradition dictated that births were celebrated with a house party open to friends and neighbors. Thirty-four year-old Francesco Lenzoni, Antonio's godfather, would certainly have done his best to attend. His family included Florentine senators and Francesco himself would later become Tuscan ambassador to Spain. Godmother Ginevra Sassetti, in her late fifties, was also from a prominent family. Her nephew Filippo would send plant specimens back from India to be inspected by Neri Neri and their mutual friend Baccio Valori who would become director of the Laurentian Library in Florence.

Antonio Neri, would go on to learn the finer points of alchemy and glassmaking, developing new formulas and techniques that would be applied throughout Europe. In 1612, he published the world's first book entirely devoted to formulating glass, L'Arte Vetraria. It seems especially appropriate that we pause and raise a toast (in glass, of course) to his accomplishment and to the end of February, looking forward to warmer days ahead. Buon compleanno Antonio!

Sal Ammoniac

Alchemical symbols used to denote sal ammoniac.

Today we will examine "sal ammoniac," a common alchemical ingredient used by Antonio Neri in many of his preparations. In its pure form, it is a colorless crystalline material and is known to chemists as ammonium chloride. It does occur as a (rare) natural mineral, but it was also manufactured as early as the thirteenth century, as noted by alchemist Albertus Magnus in his De alchymia.[1] Neither he nor Neri provides a recipe for sal ammoniac, but other sources indicate that it was made by allowing urine to putrefy with common salt. French investigators documented another method used in Egypt in the eighteenth century. This scheme involved burning the dung of animals who fed on spring grasses and then sublimating the ammoniac out of the resulting soot. Sublimation occurs when a heated material goes directly from a solid to a gaseous state without ever becoming liquid. Sal ammoniac has this property; when heated it turns to a gas and upon cooling, turns back to a solid.

Sal Ammoniac,
natural formation

The usefulness of sal ammoniac in alchemy stems from the fact that when dissolved in water, which it does easily, it immediately dissociates into equal parts of ammonia and hydrochloric acid, which in turn will dissolve some metals, including tin, zinc, iron and (reluctantly) lead. Its most famous use was as an additive to the stronger acid aqua fortis (nitric acid). Together the two formed aqua regis which was strong enough to dissolve gold. At the time that Neri was working, the only known way to dissolve the most 'noble' of metals (gold) was with the 'king' of acids (aqua regis). Neri puts this knowledge to use in his recipe for ruby-red colored glass made with pure gold. His description is light on details, but he does clearly direct the reader to dissolve the precious metal in aqua regis, then gently evaporate away the acid to obtain the red pigment.

Elsewhere in Neri's glassmaking book, L'Arte Vetraria,[2] he uses sal ammoniac in the production of "alemagna blue" paint and in the tinting of natural rock crystal. 

Another of Neri's creations requiring sal ammoniac was Chalcedony glass. It had swirls of every color the glassmaker could produce. He achieved this feat by making extensive use of aqua regis to dissolve each of a long list of metals. He then gently evaporated off the acid, leaving ultrafine powdered metals, which he added as pigments to the glass melt. 

With this powder, I made a chalcedony in a glass furnace in Antwerp that was then run by a most courteous gentleman; Mr. Filippo Gridolfi. This chalcedony gave rise to work so nice and graceful, that it emulated true oriental agate, and in beauty and delightful colors by far exceeded it.

Today, chemical factories produce vast quantities of the materials used by Neri in his glassmaking exploits and in far higher purities. Having unlimited quantities of every conceivable chemical compound at our fingertips makes it difficult to appreciate the physical labor involved by seventeenth century alchemists, both in the preparation of the glass and in the production of the individual ingredients. The chalcedony glass recipe cited above must have taken workers many, many hours to produce and must have cost a small fortune. 

[1] Magnus 1958.
[2] Neri 1612.
[3] Glauber and others used the term 'sal ammoniac' to describe a related chemical (NH4)2SO4. When mixed with aqua fortis this forms a nitric-sulfuric acid solution, which does not form aqua regis, and does not dissolve gold.
* This post first appeared here on 22 August 2014.

Antonio Neri's Birthday

Relief portrait of Antonio Neri,

artist unknown, La Specola Museum,

Florence.

Glassmaker Antonio Neri was born in Florence, Italy on 29 February 1576. Because he was a "leap year baby" we celebrate the actual day of his birth only every fourth year. From his baptismal record, we know the exact time of birth: "three hours and 25 minutes past sunset." In terms of current timekeeping conventions, sunset occurred on that particular Thursday at about 6:15 pm CET (local time), so the big event happened at 9:40 pm.

It might seem a bit odd to have such accurate records -- almost as if an astronomical event were being recorded. Actually, that is exactly what was being done; astrology of the sixteenth century drew a strong correspondence between 'macroscopic' events in the heavens and more earthly matters. To have an exact time of birth was seen as a way to gain greater insights into the events of ones personal life and to plan in a way that was more in harmony with the natural order of things.

Of all the days to be born, 29 February was considered among the least auspicious. A dire Northern Italian folk proverb states "An bisesti, o la mama o 'l bambi" predicting that, born on this day, a child or its mother was fated to die by year's end. Indeed, the Italian word naming the day, bisestile, had become a synonym for misfortune or calamity and is still the case for the French cognate bissêtre. Whatever stock the family put into ancient superstitions, happily this prophecy did not come true for Dianora or her fourth child Antonio.

Although his was a February birth, it was perhaps not as deep into winter as one might assume. Due to a discrepancy in the Julian calendar, which was in force then, the Spring equinox of Neri's birth year happened much earlier in the calendar than today, around 10 March, in fact. 

Infant mortality was not uncommon and for a child to die unbaptized only magnified a family's trauma. Church theologians had debated since the fourth century on the fate of the souls of such children. Most Catholic families baptized infants as soon as humanly possible, in Antonio's case the very next morning. Births occurring within Florence were officially registered at a central baptistery, San Giovanni, the ancient octagonal basilica standing directly in front of Florence's main Cathedral. 

The full baptistery record, in translation, for Antonio Neri reads:

Thursday, 1 March 1575:  Antonio Lodovico was born to Mr. Neri di Jacopo and Dianora di Francesco Parenti, residents of San Pier Maggiore parish. The time of birth was 29 February, at 3 hours 25 minutes past sunset. The godparents are Francesco di Girolamo Lenzoni and Ginevra di Federigo Sassetti.

The year is recorded as 1575 because in those days, Florentines celebrated the New Year on 25 March. Today we consider January, February and March to be part of the new year. 

Antonio joined a growing family that already contained siblings Lessandra, Jacopo and Francesco, and later would number ten children.  His father was thirty-six year-old Neri di Jacopo Neri, (Neri Neri to his friends) and his mother was twenty-one year-old Dianora Parenti. Neri Neri was a prominent doctor and later was appointed to be the personal physician to Grand Duke Ferdinando. Dianora was the daughter of Francesco Parenti, Michelangelo's lawyer. 

Tradition dictated that births were celebrated with a house party open to friends and neighbors. Thirty-four year-old Francesco Lenzoni, Antonio's godfather, would certainly have done his best to attend. His family included Florentine senators and Francesco himself would later become Tuscan ambassador to Spain. Godmother Ginevra Sassetti, in her late fifties, was also from a prominent family. Her nephew Filippo would send plant specimens back from India to be inspected by Neri Neri and their mutual friend Baccio Valori who would become director of the Laurentian Library in Florence.

Antonio Neri, would go on to learn the finer points of alchemy and glassmaking, developing new formulas and techniques that would be applied throughout Europe. In 1612, he published the world's first book entirely devoted to formulating glass, L'Arte Vetraria. It seems especially appropriate that we pause and raise a toast (in glass, of course) to his accomplishment and to the end of February, looking forward to warmer days ahead. Buon compleanno Antonio!

Sal Ammoniac

Alchemical symbols used to denote sal ammoniac.

Today we will examine "sal ammoniac," a common alchemical ingredient used by Antonio Neri in many of his preparations. In its pure form, it is a colorless crystalline material and is known to chemists as ammonium chloride. It does occur as a (rare) natural mineral, but it was also manufactured as early as the thirteenth century, as noted by alchemist Albertus Magnus in his De alchymia.[1] Neither he nor Neri provides a recipe for sal ammoniac, but other sources indicate that it was made by allowing urine to putrefy with common salt. French investigators documented another method used in Egypt in the eighteenth century. This scheme involved burning the dung of animals who fed on spring grasses and then sublimating the ammoniac out of the resulting soot. Sublimation occurs when a heated material goes directly from a solid to a gaseous state without ever becoming liquid. Sal ammoniac has this property; when heated it turns to a gas and upon cooling, turns back to a solid.

Sal Ammoniac,
natural formation

The usefulness of sal ammoniac in alchemy stems from the fact that when dissolved in water, which it does easily, it immediately dissociates into equal parts of ammonia and hydrochloric acid, which in turn will dissolve some metals, including tin, zinc, iron and (reluctantly) lead. Its most famous use was as an additive to the stronger acid aqua fortis (nitric acid). Together the two formed aqua regis which was strong enough to dissolve gold. At the time that Neri was working, the only known way to dissolve the most 'noble' of metals (gold) was with the 'king' of acids (aqua regis). Neri puts this knowledge to use in his recipe for ruby-red colored glass made with pure gold. His description is light on details, but he does clearly direct the reader to dissolve the precious metal in aqua regis, then gently evaporate away the acid to obtain the red pigment.

Elsewhere in Neri's glassmaking book, L'Arte Vetraria,[2] he uses sal ammoniac in the production of "alemagna blue" paint and in the tinting of natural rock crystal. 

Another of Neri's creations requiring sal ammoniac was Chalcedony glass. It had swirls of every color the glassmaker could produce. He achieved this feat by making extensive use of aqua regis to dissolve each of a long list of metals. He then gently evaporated off the acid, leaving ultrafine powdered metals, which he added as pigments to the glass melt. 

With this powder, I made a chalcedony in a glass furnace in Antwerp that was then run by a most courteous gentleman; Mr. Filippo Gridolfi. This chalcedony gave rise to work so nice and graceful, that it emulated true oriental agate, and in beauty and delightful colors by far exceeded it.

Today, chemical factories produce vast quantities of the materials used by Neri in his glassmaking exploits and in far higher purities. Having unlimited quantities of every conceivable chemical compound at our fingertips makes it difficult to appreciate the physical labor involved by seventeenth century alchemists, both in the preparation of the glass and in the production of the individual ingredients. The chalcedony glass recipe cited above must have taken workers many, many hours to produce and must have cost a small fortune. 

[1] Magnus 1958.
[2] Neri 1612.
[3] Glauber and others used the term 'sal ammoniac' to describe a related chemical (NH4)2SO4. When mixed with aqua fortis this forms a nitric-sulfuric acid solution, which does not form aqua regis, and does not dissolve gold.
* This post first appeared here on 22 August 2014.

Antonio Neri's Birthday

Relief portrait of Antonio Neri,

artist unknown, La Specola Museum,

Florence.

Glassmaker Antonio Neri was born in Florence, Italy on 29 February 1576. Because he was a "leap year baby" we celebrate the actual day of his birth only every fourth year. From his baptismal record, we actually know the exact time of birth: "three hours and 25 minutes past sunset." In terms of current timekeeping conventions, sunset occurred on that particular Thursday at about 6:15 pm CET (local time), so the big event happened at 9:40 pm.

It might seem a bit odd to have such accurate records -- almost as if an astronomical event were being recorded. Actually, that is exactly what was being done; astrology of the sixteenth century drew a strong correspondence between 'macroscopic' events in the heavens and more earthly matters. To have an exact time of birth was seen as a way to gain greater insights into the events of ones personal life and to plan in a way that was more in harmony with the natural order of things.

Of all the days to be born, 29 February was considered among the least auspicious. A dire Northern Italian folk proverb states "An bisesti, o la mama o 'l bambi" predicting that, born on this day, a child or its mother was fated to die by year's end. Indeed, the Italian word naming the day, bisestile, had become a synonym for misfortune or calamity and is still the case for the French cognate bissêtre. Whatever stock the family put into ancient superstitions, happily this prophecy did not come true for Dianora or her fourth child Antonio.

Although his was a February birth, it was perhaps not as deep into winter as one might assume. Due to a discrepancy in the Julian calendar, which was in force then, the Spring equinox of Neri's birth year happened much earlier in the calendar than today, around 10 March, in fact. 

Infant mortality was not uncommon and for a child to die unbaptized only magnified a family's trauma. Church theologians had debated since the fourth century on the fate of the souls of such children. Most Catholic families baptized infants as soon as humanly possible, in Antonio's case the very next morning. Births occurring within Florence were officially registered at a central baptistery, San Giovanni, the ancient octagonal basilica standing directly in front of Florence's main Cathedral. 

The full baptistery record, in translation, for Antonio Neri reads:

Thursday, 1 March 1575:  Antonio Lodovico was born to Mr. Neri di Jacopo and Dianora di Francesco Parenti, residents of San Pier Maggiore parish. The time of birth was 29 February, at 3 hours 25 minutes past sunset. The godparents are Francesco di Girolamo Lenzoni and Ginevra di Federigo Sassetti.

The year is recorded as 1575 because in those days, Florentines celebrated the New Year on 25 March. Today we consider January, February and March to be part of the new year. 

Antonio joined a growing family that already contained siblings Lessandra, Jacopo and Francesco, and later would number ten children.  His father was thirty-six year-old Neri di Jacopo Neri, (Neri Neri to his friends) and his mother was twenty-one year-old Dianora Parenti. Neri Neri was a prominent doctor and later was appointed to be the personal physician to Grand Duke Ferdinando. Dianora was the daughter of Francesco Parenti, Michelangelo's lawyer. 

Tradition dictated that births were celebrated with a house party open to friends and neighbors. Thirty-four year-old Francesco Lenzoni, Antonio's godfather, would certainly have done his best to attend. His family included Florentine senators and Francesco himself would later become Tuscan ambassador to Spain. Godmother Ginevra Sassetti, in her late fifties, was also from a prominent family. Her nephew Filippo would send plant specimens back from India to be inspected by Neri Neri and their mutual friend Baccio Valori who would become director of the Laurentian Library in Florence.

Antonio Neri, would go on to learn the finer points of alchemy and glassmaking, developing new formulas and techniques that would be applied throughout Europe. In 1612, he published the world's first book entirely devoted to formulating glass, L'Arte Vetraria. It seems especially appropriate that we pause and raise a toast (in glass, of course) to his accomplishment and to the end of February, looking forward to warmer days ahead.

Sal Ammoniac

Alchemical symbols used to denote sal ammoniac.

Today we will examine "sal ammoniac," a common alchemical ingredient used by Antonio Neri in many of his preparations. In its pure form, it is a colorless crystalline material and is known to chemists as ammonium chloride. It does occur as a (rare) natural mineral, but it was also manufactured as early as the thirteenth century, as noted by alchemist Albertus Magnus in his De alchymia.[1] Neither he nor Neri provides a recipe for sal ammoniac, but other sources indicate that it was made by allowing urine to putrefy with common salt. French investigators documented another method used in Egypt in the eighteenth century. This scheme involved burning the dung of animals who fed on spring grasses and then sublimating the ammoniac out of the resulting soot. Sublimation occurs when a heated material goes directly from a solid to a gaseous state without ever becoming liquid. Sal ammoniac has this property; when heated it turns to a gas and upon cooling, turns back to a solid.

The usefulness of sal ammoniac in alchemy stems from the fact that when dissolved in water, which it does easily, it immediately dissociates into equal parts of ammonia and hydrochloric acid, which in turn will dissolve some metals, including tin, zinc, iron and (reluctantly) lead. Its most famous use was as an additive to the stronger acid aqua fortis (nitric acid). Together the two formed aqua regis which was strong enough to dissolve gold. At the time that Neri was working, the only known way to dissolve the most 'noble' of metals (gold) was with the 'king' of acids (aqua regis). Neri puts this knowledge to use in his recipe for ruby-red colored glass made with pure gold. His description is light on details, but he does clearly direct the reader to dissolve the precious metal in aqua regis, then gently evaporate away the acid to obtain the red pigment.

Elsewhere in Neri's glassmaking book, L'Arte Vetraria,[2] he uses sal ammoniac in the production of "alemagna blue" paint and in the tinting of natural rock crystal. 

Another of Neri's creations requiring sal ammoniac was Chalcedony glass. It had swirls of every color the glassmaker could produce. He achieved this feat by making extensive use of aqua regis to dissolve each of a long list of metals. He then gently evaporated off the acid, leaving ultrafine powdered metals, which he added as pigments to the glass melt. 

With this powder, I made a chalcedony in a glass furnace in Antwerp that was then run by a most courteous gentleman; Mr. Filippo Gridolfi. This chalcedony gave rise to work so nice and graceful, that it emulated true oriental agate, and in beauty and delightful colors by far exceeded it.

Today, chemical factories produce vast quantities of the materials used by Neri in his glassmaking exploits and in far higher purities. Having unlimited quantities of every conceivable chemical compound at our fingertips makes it difficult to appreciate the physical labor involved by seventeenth century alchemists, both in the preparation of the glass and in the production of the individual ingredients. The chalcedony glass recipe cited above must have taken workers many, many hours to produce and must have cost a small fortune. 

[1] Magnus 1958.
[2] Neri 1612.
[3] Glauber and others used the term 'sal ammoniac' to describe a related chemical (NH4)2SO4. When mixed with aqua fortis this forms a nitric-sulfuric acid solution, which does not form aqua regis, and does not dissolve gold.
* This post first appeared here on 22 August 2014.

Antonio Neri's Birthday

Relief portrait of Antonio Neri,
artist unknown, La Specola Museum,
Florence.

Glassmaker Antonio Neri was born in Florence, Italy on 29 February 1576. Because he was a "leap year baby" we celebrate on 1 March in off years. From his baptismal record, we actually know the exact time of birth: "three hours and 25 minutes past sunset." In terms of current timekeeping conventions, sunset occurred on that particular Thursday at about 6:15 pm CET (local time), so the big event happened at 9:40 pm.

It might seem a bit odd to have such accurate records -- almost as if an astronomical event were being recorded. Actually, that is exactly what was being done; astrology of the sixteenth century drew a strong correspondence between 'macroscopic' events in the heavens and more earthly matters. To have an exact time of birth was seen as a way to gain greater insights into the events of ones personal life and to plan in a way that was more in harmony with the natural order of things.

Of all the days to be born, 29 February was considered among the least auspicious. A dire Northern Italian folk proverb states "An bisesti, o la mama o 'l bambi" predicting that, born on this day, a child or its mother was fated to die by year's end. Indeed, the Italian word naming the day, bisestile, had become a synonym for misfortune or calamity and is still the case for the French cognate bissêtre. Whatever stock the family put into ancient superstitions, happily this prophecy did not come true for Dianora or her fourth child Antonio.

Although his was a February birth, it was perhaps not as deep into winter as one might assume. Due to a discrepancy in the Julian calendar, which was in force then, the Spring equinox of Neri's birth year happened much earlier in the calendar than today, around 10 March, in fact. 

Infant mortality was not uncommon and for a child to die unbaptized only magnified a family's trauma. Church theologians had debated since the fourth century on the fate of the souls of such children. Most Catholic families baptized infants as soon as humanly possible, in Antonio's case the very next morning. Births occurring within Florence were officially registered at a central baptistery, San Giovanni, the ancient octagonal basilica standing directly in front of Florence's main Cathedral. 

The full baptistery record, in translation, for Antonio Neri reads:

Thursday, 1 March 1575:  Antonio Lodovico was born to Mr. Neri di Jacopo and Dianora di Francesco Parenti, residents of San Pier Maggiore parish. The time of birth was 29 February, at 3 hours 25 minutes past sunset. The godparents are Francesco di Girolamo Lenzoni and Ginevra di Federigo Sassetti.

The year is recorded as 1575 because in those days, Florentines celebrated the New Year on 25 March. Today we consider January, February and March to be part of the new year. 

Antonio joined a growing family that already contained siblings Lessandra, Jacopo and Francesco, and later would number ten children.  His father was thirty-six year-old Neri di Jacopo Neri, (Neri Neri to his friends) and his mother was twenty-one year-old Dianora Parenti. Neri Neri was a prominent doctor and later was appointed to be the personal physician to Grand Duke Ferdinando. Dianora was the daughter of Francesco Parenti, Michelangelo's lawyer. 

Tradition dictated that births were celebrated with a house party open to friends and neighbors. Thirty-four year-old Francesco Lenzoni, Antonio's godfather, would certainly have done his best to attend. His family included Florentine senators and Francesco himself would later become Tuscan ambassador to Spain. Godmother Ginevra Sassetti, in her late fifties, was also from a prominent family. Her nephew Filippo would send plant specimens back from India to be inspected by Neri Neri and their mutual friend Baccio Valori who would become director of the Laurentian Library in Florence.

Antonio Neri, would go on to learn the finer points of alchemy and glassmaking, developing new formulas and techniques that would be applied throughout Europe. In 1612, he published the world's first book entirely devoted to formulating glass, L'Arte Vetraria. It seems especially appropriate that we pause and raise a toast (in glass, of course) to his accomplishment and to the end of February, looking forward to warmer days ahead.