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.

The Art of Metals

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

in Tesoro del Mondo, f. 8r.
(click to enlarge)

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 reduction 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.

The Art of Metals

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

in Tesoro del Mondo, f. 8r.
(click to enlarge)

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 reduction 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.

The Art of Metals

Fig. 1: Antonio Neri, "Ars Preparatio Metallor[um]"
in Tesoro del Mondo, f. 8r.

Recently we examined three 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, click to enlarge): 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 reduction 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)

Spanish Ferretto

Covered crucible similar to
Neri's Stratification of copper.
lchemistische Gefäße, (1681)
u.a. Destillierhelm, Retorte (detail)

In his 1612 book on glassmaking, L'Arte Vetraria, Antonio Neri describes how to prepare a variety of metal pigments for glass. Among them is "Spanish ferretto," a copper based pigment. Neri describes the process in plain language, but definitely through the eyes of an alchemist. He writes:

To make ferretto requires nothing more than a simple calcination of copper, where the metal is opened so it can impart its pigment to the glass. When this calcination is done well there is no doubt to anyone that a very interesting diversity of colors appear in the glass. This calcination may be done many ways, but I will put down two that are not only easy, but have been used by me many times for a variety of beautiful effects in the glass. The first method follows here. 

For Neri, "calcination" is the process of breaking a metal down into a powdered form using heat. Notice that he says the copper must be "opened" so that it can color the glass. The thinking here is that the colors are normally hidden inside the metal and that by roasting it in the furnace, the metal is "opened" and those hidden colors become exposed and available to tint the glass. Elsewhere, Neri implies that all the colors of the rainbow are hidden in the glass itself, and that metal pigments cause certain of them to be revealed. 

You should get thin shims of copper the size of a florin [coin] and have one or more goldsmith's crucibles ready. In the bottom of them, you should make a layer of pulverized sulfur, then a layer of the shims, and over them another layer of pulverized sulfur, and one of copper shims, and so on. With this method, fill the crucible in what is otherwise called a stratification. Cover the crucibles, coat them well with refractory clay, dry and place in an open oven to vent amongst burning coals and put a strong fire to them for two hours. Allow them to cool and you will find calcined copper, which will come apart with the fingers, as if it were dry earth. It will rise in color to a blackish-reddishness; this copper should be ground fine, passed through a sieve and kept well secure for use in coloring glass.

To Neri's mind, the result is copper that has been transformed into an "opened" state, ready to impart its color to the glass. To a modern chemist the result could be analyzed and would most likely show a mixture of copper sulfides, copper oxides and perhaps some unreacted sulfur and copper. Through a simple process he has produced a cocktail of different materials. In a very hot furnace, sulfur would tend to be driven off as  toxic, smelly, sulfur dioxide gas, leaving behind copper oxides. The two prevalent copper oxides are red and black in color, as suggested by Neri's statement: "It will rise in color to a blackish-reddishness." How they would tint glass would depend on further preparation of the glass and on what temperatures were achieved in the furnace. 

This second way to make ferretto is much more laborious than the first; nonetheless, it will produce extraordinary effects in the glass. Instead of stratifying the copper in the crucible with sulfur, stratify it with vitriol. Now calcine it, leaving it in the furnace chamber,  near the eye for three days. Remove it, stratify it again with new vitriol and leave it to reverberate as above. Repeat this calcination with the vitriol six times at which point you will have a most noble ferretto whose colors will produce extraordinary effects.

"Vitriol" is a caustic sulfur compound that comes in two varieties: blue and green. When added to water, they can be described essentially as copper or iron dissolved in a sulfuric acid solution (copper for blue, iron for green). Neri does not specify which to use, green vitriol would add iron to the recipe while blue vitriol would simply increase the amount of copper. He then says to leave the preparation "near the eye for three days." The "eye" was a central hole in the furnace floor exposing the flames of the combustion chamber below; it was the hottest part of the furnace, the pots of hot glass were usually arranged around it in a circle. "Reverberation" was a term for indirect heating; in other words not directly exposed to the flames.

Copper oxide in glass can produce a sky blue, a green or a vibrant red. Pure copper can make a dark ruby red color. Iron oxide creates a blue-green and, Neri claims, also a blood red. Sulfur in combination with iron makes a yellowish to amber color. Many of these colors depend not only on the glass formulation, but on the artisan who makes the finished piece. How the glass is "struck," that is: heated, cooled and reheated, can affect the color dramatically. Even today, the only sure way to see what colors are possible with this recipe is to reproduce it and experiment. Through a simple recipe for copper pigment we see just how complex glassmaking could be. Neri’s explanation of metals being "opened" to expose hidden colors is elegant. It was based on observation and it guided him and artisans to make glass creations in a wonderful range of colors. The fact that Neri’s understanding of four-hundred years ago was less accurate than our understanding today is hardly surprising. We should not be surprised at the same outcome four-hundred years from now.