《复合材料 Composites》课程教学资源（学习资料）第二章 增强体_glass fiber-17 Perspectives on the History of Glass Composition

ournal J Am Ceram Soc. s -813(1998) Perspectives on the History of Glass Composition Charles r. Kurkiian Bell Communications Research(Bellcore), Morristown, New Jersey 07960 William R. Prindle,f Santa Barbara, California 93105 The 100th anniversary of The American Ceramic s (see Fig. 1).Up to this time, very little real glass science had corresponds approximately with the 100th anniversary of been done, although, with the limited tools at their disposal what might be considered the start of the age of glass sci- earlier workers did quite remarkable things. Most work was nce, i.e the publication, in germany, in 1886, of the cata- done in an attempt to understand what soda-lime-silica glasse. og of Schott und Genossen, containing 44 optical glass were and to improve their quality. Schott- conducted detailee compositions. The American Ceramic Society centennial studies of the effects of various additions and substitutions to seems, accordingly, to be an appropriate occasion to exam- the basic soda-lime glass composition. He and winkelmann, ine the history of glass composition that both preceded and were the first to attempt to model glass behavior development followed the seminal work of Schott and to survey some of by means of a set of factors with which properties could be the major discoveries and changes in glass composition as ted to odest task ust described. The history of glass structure theories is it has continued to be so with only slight changes. Variations in considered, particularly with regard to the effects of com- roduction techniques and specific use requi osition on structure, and how these relate to glass pro to the deliberate addition of a variety of other oxides, so that erties. The article then continues with a discussion of recent most commercial"soda-lime"glasses now contain six or special glasses and concludes with a description of light more constituents. Over the years, the bulk of commercial guide glasses, the discovery of which has changed the na lasses for most purposes has continued to be based on silica as ture of glass science and the glass industry the primary glass former Research(by X-ray technologies, optical spectroscopy L. Introduction physical property measurements, etc. )during the 20th century wl corresponds approximately with the 100th anniversary of stand their structure and properties well enough to predip.o has been conducted on simple glass compositions to attempt to E 100th anniversary of The American Ceramic Society understand glasses as materials as well as to attempt to t might be considered the start of the age of glass science erties f the disclosure. in 1886. of the work of otto schott and ernst requirements. Although glasses with rather remarkable prope Abbe in Germany. This was the publication of the catalog of ties ranging from infrared transmission and superionic conduc- the"Glastechnisches Laboratorium Schott und genossen tivity to biological activity have been discovered, it is probably not entirely accurate to say that we can design a glass for a iven purpose. Available commercial silicate glasses do their job quite admirably, but they are rather complicated glasses H. A. Anderson--contributing editor that fulfill rather simple tasks. In 1970, the di a simple(titania-silica-silica compound glass fiber could con duct light over rather long distances without requiring ampli- fication has resulted in a"new glass industry"-the"light script No. 190479. Received December 30, 1997; approved February 16, guide industry. Since then, in somewhat of a turnabout, ber, American Ceramic Society scientists have discovered that these simple glasses display a ed from Corning Incorporated, Corning, NY wide range of unexpected, new, complicated, and often incom centennialfeature

Perspectives on the History of Glass Composition Charles R. Kurkjian* Bell Communications Research (Bellcore), Morristown, New Jersey 07960 William R. Prindle*,† Santa Barbara, California 93105 The 100th anniversary of The American Ceramic Society corresponds approximately with the 100th anniversary of what might be considered the start of the age of glass sci￾ence, i.e., the publication, in Germany, in 1886, of the cata￾log of Schott und Genossen, containing 44 optical glass compositions. The American Ceramic Society centennial seems, accordingly, to be an appropriate occasion to exam￾ine the history of glass composition that both preceded and followed the seminal work of Schott and to survey some of the major discoveries and changes in glass composition as well as the reasons that led to them. Although it is certainly of interest to consider a more complete history of the glass industry, we have opted to attempt the more modest task just described. The history of glass structure theories is considered, particularly with regard to the effects of com￾position on structure, and how these relate to glass prop￾erties. The article then continues with a discussion of recent special glasses and concludes with a description of light￾guide glasses, the discovery of which has changed the na￾ture of glass science and the glass industry. I. Introduction THE 100th anniversary of The American Ceramic Society corresponds approximately with the 100th anniversary of what might be considered the start of the age of glass science— the disclosure, in 1886, of the work of Otto Schott and Ernst Abbe in Germany. This was the publication of the catalog of the ‘‘Glastechnisches Laboratorium, Schott und Genossen’’ (see Fig. 1).1 Up to this time, very little real glass science had been done, although, with the limited tools at their disposal, earlier workers did quite remarkable things. Most work was done in an attempt to understand what soda–lime–silica glasses were and to improve their quality. Schott2 conducted detailed studies of the effects of various additions and substitutions to the basic soda–lime glass composition. He and Winkelmann3,4 were the first to attempt to model glass behavior development by means of a set of factors with which properties could be calculated. As a result of the coincidental natural occurrence of alkali, alkaline-earth ‘‘impurities,’’ and sand, soda–lime–silica glass became the ‘‘staple’’ glass composition very early in time, and it has continued to be so with only slight changes. Variations in production techniques and specific use requirements have led to the deliberate addition of a variety of other oxides, so that most commercial ‘‘soda–lime’’ glasses now contain six or more constituents. Over the years, the bulk of commercial glasses for most purposes has continued to be based on silica as the primary glass former. Research (by X-ray technologies, optical spectroscopy, physical property measurements, etc.) during the 20th century has been conducted on simple glass compositions to attempt to understand glasses as materials as well as to attempt to under￾stand their structure and properties well enough to predict prop￾erties from composition and to design a glass from a list of requirements. Although glasses with rather remarkable proper￾ties ranging from infrared transmission and superionic conduc￾tivity to biological activity have been discovered, it is probably not entirely accurate to say that we can design a glass for a given purpose. Available commercial silicate glasses do their job quite admirably, but they are rather complicated glasses that fulfill rather simple tasks. In 1970, the discovery that a simple (titania–silica)–silica compound glass fiber could con￾duct light over rather long distances without requiring ampli￾fication has resulted in a ‘‘new glass industry’’—the ‘‘light￾guide industry.’’ Since then, in somewhat of a turnabout, scientists have discovered that these simple glasses display a wide range of unexpected, new, complicated, and often incom￾H. A. Anderson—contributing editor Manuscript No. 190479. Received December 30, 1997; approved February 16, 1998. *Member, American Ceramic Society. † Retired from Corning Incorporated, Corning, NY. J. Am. Ceram. Soc., 81 [4] 795–813 (1998) Journal centennialfeature 795

Journal of the American Ceramic SocietyKurkjian and Prindle Vol 8I. No 4 Glasschmelzerei for optische und andere wisseaschaftliche Zwocke ATDwr 13解00t78 Glastechnisches Laboratorium 6.1 0o4|,g Schott d Gen JENA 8.7Borwf-Ftind 180b443 D a IM Ielts saliad-Flat a e. sat- Flat it watis J111s 1404s m o, 1sa Lee samt-Flix 810 hitra Wml.plant.,19p自 Fig 1. Photograph of Otto Schott and pages from glass catalog pletely explained properties. We attempt in this review to Provide a brief review of the history of glass structure and lustrate some of the interesting events in this long property relations In this article we Bring the history up-to-date by discussing some new speci Provide a brief review of the early history of glass: glasses and the new era of optical fibers. Review the work of Abbe and Schott, i. e the start of glass Our purpose here is to provide an overview of the very large science, field of inorganic glasses for the benefit, perhaps, of a re- Review the development of more-modern glass compo searcher new to glass. We attempt to provide a sense of the

pletely explained properties. We attempt in this review to il￾lustrate some of the interesting events in this long history. In this article we ● Provide a brief review of the early history of glass; ● Review the work of Abbe and Schott, i.e., the start of glass science; ● Review the development of more-modern glass composi￾tions; ● Provide a brief review of the history of glass structure and property relations; ● Bring the history up-to-date by discussing some new special glasses and the new era of optical fibers. Our purpose here is to provide an overview of the very large field of inorganic glasses for the benefit, perhaps, of a re￾searcher new to glass. We attempt to provide a sense of the present and future of glasses–properties–understanding as well Fig. 1. Photograph of Otto Schott and pages from glass catalog. 796 Journal of the American Ceramic Society—Kurkjian and Prindle Vol. 81, No. 4

April 1998 Perspectives on the History of Glass Composition s why and how we arrived at this position. Because of the priate colorants, such as copper, manganese, and iron salts many glasses that have been studied, we are forced to limit our There was no demonstrated interest in transparency at this omments to compositions that illustrate major discoveries or time. Beads also were made, and, later, small vessels were es;accordingly, some important glass compositions are constructed by coating sand cores with a glassy skin-the cores not discussed were removed after forming Besides the apparent limitations imposed by practical con The earlier and sometimes parallel development of cerami siderations and economics, physics appears to impose a real and metallurgical processes undoubtedly influenced and aided imitation to the variation of properties available in materials the growth of early glass technology, some furnac that lack a periodic crystalline lattice Inorganic glasses are ments and raw materials were applicable to glassmak extensive Egyptia making als less colorants are added; chemically durable and, therefore, had an effect, contributing knowledge of raw mate hemically inert; and brittle sintering techniques These general properties, however, are constrained only in rs ago, the blowing of glass articles with a those glasses that are normally thought of when we think of pipe was invented, probably in Syria, and this advance in tech- lasses. If we broaden our chemical viewpoint to include chal- nology was followed by a rapid increase in the use of glas cogenide, halide, and, especially, metallic glasses, a wide va ware. Glassblowing spread quickly through the roman empire riety of properties becomes available. Although the lack of a and soon glass bowls and drinking vessels were in use through crystalline lattice appears to impose a rather severe constraint out society, in both ordinary households and among the ruling with regard to some properties at the moment, in most cases we are not in a position to state unequivocally whether these this remarkable growth of blown glass production. Accord- constraints are absolute. For instance it had been thought to be ing sible to make bulk metallic glasses because their hard gly, strong efforts were directed toward the elimination of sphere structure results in rather simple dense packing, which glassware is, in itself, not conducive to extensive supercooling. However, this recently has been shown to be untrue. Also, it normally is (2) Raw-Material Preparation-The Search for considered that the lack of a crystalline lattice means that plas tic flow is not possible because the dislocations that result in Early glasses in the western world were almost all soda- stic flow cannot form. We have lime-silica compositions that varied depending upon the avail- this is completely true, or if it can be sensibly modified. ability of raw materials, but generally differed little from pres- There were few modern books in English on glass until the ent-day commercial glasses (Ta publication of George Morey's book, The Properties ofGlass, source of alkali were typical ingredients, with both the sand in 1938. After World War Il, and following the publication of nd the alkali me or magnesia to give the second edition of Morey in 1954, many other books ap- chemical durability adequate of the time. In peared. Recently, many edited bo the case of the sand, framer some have appeared regularly 6-12 The more general books usually and plant ash generally brou long with the present a short history of glass, a definition and description o soda and potash glass, and chapters that present properties and compositions of Two different sources of alkali affected the composition of simple glasses, where the chapters are arranged either by prod avated Na, CO3 )was usually the favored alkali, because it w erty or by glass composition. These books are important useful, especially as texts on the science and technology of avilla om norther Egypt(see, e.g., glas glass. There also have been many excellent review articles and Further east, in Mesopotamia and Persia, the alkali was usually book chapters that present special subjects. Examples are the provided by plant ash that contained more K,O(2%4%)and two excellent series by doremus and Tomozawa 2 and Uhl MgO(2%-6%)(see, e.g., glass 3 in Table 1). 21a The alkali mann and Kreidl. 3 In particular, in the Uhlmann and Kreidl content of the ash was influenced by the soil in which the plants ies, the Kreidl chapter on glass-forming systems is very rew. plants that grew in salty soil or near the sea were high in useful. It historically, scientifically, and technologically dis- soda, whereas those that grew inland had higher potash con usses almost every known glass-forming system. Here we tents.22 Agricola(1556)2 refers to the use of salts made from Attempt, by perhaps rather extreme simplification, to illustrate the ashes of salty herbs as well as to natron and"rock-salt. some of the issues having to do with property-composition When these were not available, he suggested the ashes of oak development. We present our simplified and personal view of could be used, or, as a last resort, the ashes of beech or pine some glass compositions-structures in order to make some The practice of using natron to produce higher-soda glasses simple generalizations. This hopefully leads to a better general continued in the Mediterranean region through early and me- understanding of what has been done, in many cases, empiri- dieval times. However, there was a surge in the use of potash cally, and hopefully leads to the possibility of predicting what in glassmaking during the 9th through 13th centuries, before remains possible. Such predictions were attempted at a meeting soda again became the predominant alkali. 24 to celebrate Kreidl's 80th birthday 14 Much glass made in the Middle Ages was dark green, dark The sections that follow immediately have to do with the brown, or almost black as a result of the impurities present early history of glass. The reader is directed to the papers of This"waldglas, or forest glass, often was used for bottles and Cables-l7 and symposia arranged by Kingery, 9 for other drinking vessels, but interest grew in preparing clearer, more- interesting insights into this history transparent glass. Although little is known about glass technol- ogy in the middle ages, we do know that some attention was IL. Early Glasses given to the purification of raw materials. One of the major sources of glass technology information in this period comes from L'Arte Vetraria,s written by Antonio Neri, an Italian ( Middle Eastern Origins and Roman Growth priest and glassworker, in 1612, and translated to English in The earliest known synthetic glasses were created in Asia 1662 by Christopher Merrett, an English physician and one of Minor several millennia ago. Some isolated examples may be the founders of the Royal Society. (It also was translated by as early as 7000 BC, but it is clear that, by 2500 BC, there were Johann Kunckel in 1679; both Merrett and Kunckel added lany sources, probably first in Mesopotamia, then in Egypt valuable personal observations on glassmaking Agricola and The first glassmakers were motivated to create decorative ob- Neri devoted considerable space to raw-material preparation, jects, possibly to simulate gems and semiprecious stones, using discussing the careful selection of crystals(quartz) and clean sintered bodies of silica and desert soda(natron)with appro- white stones free of black or yellow veins''to be used in

as why and how we arrived at this position. Because of the many glasses that have been studied, we are forced to limit our comments to compositions that illustrate major discoveries or changes; accordingly, some important glass compositions are not discussed. Besides the apparent limitations imposed by practical con￾siderations and economics, physics appears to impose a real limitation to the variation of properties available in materials that lack a periodic crystalline lattice. Inorganic glasses are generally considered to be isotropic; dielectric; transparent, un￾less colorants are added; chemically durable and, therefore, chemically inert; and brittle. These general properties, however, are constrained only in those glasses that are normally thought of when we think of glasses. If we broaden our chemical viewpoint to include chal￾cogenide, halide, and, especially, metallic glasses, a wide va￾riety of properties becomes available. Although the lack of a crystalline lattice appears to impose a rather severe constraint with regard to some properties at the moment, in most cases, we are not in a position to state unequivocally whether these constraints are absolute. For instance, it had been thought to be impossible to make bulk metallic glasses because their hard sphere structure results in rather simple dense packing, which is, in itself, not conducive to extensive supercooling. However, this recently has been shown to be untrue. Also, it normally is considered that the lack of a crystalline lattice means that plas￾tic flow is not possible because the dislocations that result in plastic flow cannot form. We have yet to determine whether this is completely true, or if it can be sensibly modified. There were few modern books in English on glass until the publication of George Morey’s book, The Properties of Glass,5 in 1938. After World War II, and following the publication of the second edition of Morey in 1954, many other books ap￾peared. Recently, many edited books and edited proceedings have appeared regularly.6–12 The more general books usually present a short history of glass, a definition and description of glass, and chapters that present properties and compositions of simple glasses, where the chapters are arranged either by prop￾erty or by glass composition. These books are important and useful, especially as texts on the science and technology of glass. There also have been many excellent review articles and book chapters that present special subjects. Examples are the two excellent series by Doremus and Tomozawa12 and Uhl￾mann and Kreidl.13 In particular, in the Uhlmann and Kreidl series, the Kreidl chapter on glass-forming systems is very useful. It historically, scientifically, and technologically dis￾cusses almost every known glass-forming system. Here we attempt, by perhaps rather extreme simplification, to illustrate some of the issues having to do with property–composition development. We present our simplified and personal view of some glass compositions–structures in order to make some simple generalizations. This hopefully leads to a better general understanding of what has been done, in many cases, empiri￾cally, and hopefully leads to the possibility of predicting what remains possible. Such predictions were attempted at a meeting to celebrate Kreidl’s 80th birthday.14 The sections that follow immediately have to do with the early history of glass. The reader is directed to the papers of Cable15–17 and symposia arranged by Kingery18,19 for other interesting insights into this history. II. Early Glasses (1) Middle Eastern Origins and Roman Growth The earliest known synthetic glasses were created in Asia Minor several millennia ago. Some isolated examples may be as early as 7000 BC, but it is clear that, by 2500 BC, there were many sources, probably first in Mesopotamia, then in Egypt. The first glassmakers were motivated to create decorative ob￾jects, possibly to simulate gems and semiprecious stones, using sintered bodies of silica and desert soda (natron) with appro￾priate colorants, such as copper, manganese, and iron salts. There was no demonstrated interest in transparency at this time. Beads also were made, and, later, small vessels were constructed by coating sand cores with a glassy skin—the cores were removed after forming. The earlier and sometimes parallel development of ceramic and metallurgical processes undoubtedly influenced and aided the growth of early glass technology; some furnace improve￾ments and raw materials were applicable to glassmaking. The extensive Egyptian tradition of faience making also must have had an effect, contributing knowledge of raw materials and sintering techniques. About 2000 years ago, the blowing of glass articles with a pipe was invented, probably in Syria, and this advance in tech￾nology was followed by a rapid increase in the use of glass￾ware. Glassblowing spread quickly through the Roman Empire, and soon glass bowls and drinking vessels were in use through￾out society, in both ordinary households and among the ruling classes. A desire for clear and transparent vessels came with this remarkable growth of blown glass production. Accord￾ingly, strong efforts were directed toward the elimination of iron and other contaminants, particularly for the higher-quality glassware.5 (2) Raw-Material Preparation—The Search for Transparency Early glasses in the western world were almost all soda– lime–silica compositions that varied depending upon the avail￾ability of raw materials, but generally differed little from pres￾ent-day commercial glasses (Table I). Beach sand and a crude source of alkali were typical ingredients, with both the sand and the alkali containing enough lime or magnesia to give chemical durability adequate for the purposes of the time. In the case of the sand, fragments of shells provided some lime, and plant ash generally brought some magnesia along with the soda and potash. Two different sources of alkali affected the composition of early glasses. On the Eastern Mediterranean littoral natron (hy￾drated Na2CO3) was usually the favored alkali, because it was available from northern Egypt (see, e.g., glass 2 in Table I).20 Further east, in Mesopotamia and Persia, the alkali was usually provided by plant ash that contained more K2O (2%–4%) and MgO (2%–6%) (see, e.g., glass 3 in Table I).21a The alkali content of the ash was influenced by the soil in which the plants grew: plants that grew in salty soil or near the sea were high in soda, whereas those that grew inland had higher potash con￾tents.22 Agricola (1556)23 refers to the use of salts made from the ashes of salty herbs as well as to natron and ‘‘rock-salt.’’ When these were not available, he suggested the ashes of oak could be used, or, as a last resort, the ashes of beech or pine. The practice of using natron to produce higher-soda glasses continued in the Mediterranean region through early and me￾dieval times. However, there was a surge in the use of potash in glassmaking during the 9th through 13th centuries, before soda again became the predominant alkali.24 Much glass made in the Middle Ages was dark green, dark brown, or almost black as a result of the impurities present. This ‘‘waldglas,’’ or forest glass, often was used for bottles and drinking vessels, but interest grew in preparing clearer, more￾transparent glass. Although little is known about glass technol￾ogy in the middle ages, we do know that some attention was given to the purification of raw materials. One of the major sources of glass technology information in this period comes from L’Arte Vetraria,25 written by Antonio Neri, an Italian priest and glassworker, in 1612, and translated to English in 1662 by Christopher Merrett, an English physician and one of the founders of the Royal Society. (It also was translated by Johann Kunckel in 1679; both Merrett and Kunckel added valuable personal observations on glassmaking.) Agricola and Neri devoted considerable space to raw-material preparation, discussing the careful selection of crystals (quartz) and clean ‘‘white stones free of black or yellow veins’’ to be used in April 1998 Perspectives on the History of Glass Composition 797

Journal of the American Ceramic SocietyKurkjian and Prindle Vol 81. No 4 Table 1. Glass Compositions Oxide content(wt%) Glasst SiO, BO3 Na,O ,O Cao Mgo AlO Fe2O3 (1) Egypt, 1500 BC 678 3.8 3.22 (2)Palestine, 4th Centur ()Sudan, 3rd century (4)Italy, 9th-10th centurie 77.8 8.7 0.7 ()Container glass, 1980 (6)1: 1: 6 soda-lime-silica 15 (9)Schott thermometer glass 12.0 II msil glass I 1)Schott Welsbach chimney 47000602 0.3 1.8 7.0 3.3 12)Nonex' 0.4 (14)E-glass, typical 54.0 17.5 high sodium); (3)Brill, calculate materials.Glass contains other oxides:(I (x708902:1m place of sand if high clarity was desired. The stones were light by small gold or copper crystals(-50 nm in diameter) that reduced to fine particles by pounding in a mortar, and the silica are formed by the precipitation of the metals in their atomic owder then often was fritted with the alkali salts. Neri gave state. The formation of the metal crystals is enhanced by re- onsiderable attention to alkali preparation, discussing in some heating the glass ("striking")and by the presence of reducing detail the washing of various plant ashes to prepare alkali salts agents, e.g., stannous chloride. The red glasses found in old for clear crystal glass. The purification process consisted of church windows are most likely copper reds, either coppe repeated sieving of the raw salt, dissolving it in boiling water, rubies, suspensions of cuprous oxide, or copper stains, because filtering, and evaporating. Thus the impurities causing color, gold rubies do not seem to have been made with any certainty such as iron compounds, were left behind Unfortunately, much of the alkaline-earth and alumina of the Opaque glasses colored by suspensions of relatively large shes were left behind as well; therefore, many clear glasses crystals(with diameters in the micrometer range), where the prepared from the purified raw materials had relatively poor crystals behave essentially as color pigments, have been known resistance to attack by moisture. The much-admired clear since antiquity. The pigments are generally insoluble or of cristallo"glass ed in Venice-Murano in the early limited solubility in the matrix glass. Some of the opaque 1500s suffered from low lime and magnesia content. As a ors formed in this way are white glasses containing suspensions of tin oxide, arsenic pentoxide, or calcium antimonate, and lass of that period now in museums have developed surface yellow glasses colored by lead antimonate. Opaque blue crizzling(a multitude of fine surface fractures) because of their glasses colored by copper calcium silicate or cobalt alumi- poor chemical durability; some extreme examples are sticky to nate, green glasses colored by chromic oxide, and brown or the touch and appear to sweat. 26 These cristallo glasses provide red-browns from iron or iron-manganese oxide mixtures also an example of an unintended consequence of the desire to re used optimize one glass property, colorless clarity in this case, caus- The most dramatic examples of colored glass are probably ng a deterioration in another property, durability the church windows of the middle with the greatest ( Colored Glasses created during the 10th through 14th centuries. Most of these windows also contain much stained glass, wherein a colorant is Although the preceding section described colorless glasses diffused into the glass surface at temperatures well below that purposely made free of unwanted color, other glasses were of molten glass. Copper reds and silver yellows are perhaps the colored purposely for decoration since the earliest days of best-known examples of surface stains glassmaking. Glassworkers in Egypt, the Middle East, and the Roman Empire knew that small amounts of certain salts could (4) Lead Glasses be incorporated in the melt to produce strongly colored glasses, The first major departure from alkali-lime-silica glasses probably the first example ue. This addition of colorants was came during the 17th century with the commercial introduction some transparent, some opac of the use of minor ingredients to of lead flint glasses. Lead had long been a minor constituent in change glass properties to produce a desired effect glazes, mosaics, and artificial gems. It was introduced as cal- The earliest and most widely used solution colorants were cined lead or lead oxide, primarily for its fluxing effect. Neri salts of copper(blue-green from the presence of Cu), iron discussed lead glasses at some length in L'Arte Vetraria and (blue to green from Fe2*, yellow to brown from Fe+), and emphasized that great care must be taken to thoroughly calcine manganese(amethyst or purple from Mn+).27 The use of small the lead to avoid the formation of molten lead because"the quantities of manganese as a decolorizer to compensate for iron least lead remaining breaks out the bottom of the pots and lets colors, also known in the Middle Ages, was referred to by all the metall run into the fire. "25 Agricola and Neri and was used by the Venetians in the pro- Shortly after the publication of Merrett's English translation duction of cristallo. Cobalt was first used in the 14th century of Neri's work in 1662, George Ravenscroft, an English glass BC (deep blue from Co). The use of chromium as a solution merchant, turned glassmaker to develop a clear glass based colorant probably began early in the 19th century English ingredients.29, 30 This latter requirement was motivated Copper and gold ruby glasses were prized highly for their by the difficulty English glassmakers were experiencing beauty and for their scarcity, the latter a result of the difficulty obtaining raw materials at acceptable cost, because a monopoly of producing these colloidal colors. Both glasses presented se- controlled the import of plant ashes for soda. 31 The glass mer rious challenges to the glassmaker because of their sensitivity chants also were struggling with unresponsive to composition, melting conditions, and subsequent thermal ers, much breakage in transit, and oppresduced history. The ruby color is caused by the selective absorption of series of experiments, Ravenscroft int

place of sand if high clarity was desired. The stones were reduced to fine particles by pounding in a mortar, and the silica powder then often was fritted with the alkali salts. Neri gave considerable attention to alkali preparation, discussing in some detail the washing of various plant ashes to prepare alkali salts for clear crystal glass. The purification process consisted of repeated sieving of the raw salt, dissolving it in boiling water, filtering, and evaporating. Thus the impurities causing color, such as iron compounds, were left behind. Unfortunately, much of the alkaline-earth and alumina of the ashes were left behind as well; therefore, many clear glasses prepared from the purified raw materials had relatively poor resistance to attack by moisture. The much-admired clear ‘‘cristallo’’ glass produced in Venice–Murano in the early 1500s suffered from low lime and magnesia content. As a result, many of the elegant examples of the elaborate Venetian glass of that period now in museums have developed surface crizzling (a multitude of fine surface fractures) because of their poor chemical durability; some extreme examples are sticky to the touch and appear to sweat.26 These cristallo glasses provide an example of an unintended consequence of the desire to optimize one glass property, colorless clarity in this case, caus￾ing a deterioration in another property, durability. (3) Colored Glasses Although the preceding section described colorless glasses purposely made free of unwanted color, other glasses were colored purposely for decoration since the earliest days of glassmaking. Glassworkers in Egypt, the Middle East, and the Roman Empire knew that small amounts of certain salts could be incorporated in the melt to produce strongly colored glasses, some transparent, some opaque. This addition of colorants was probably the first example of the use of minor ingredients to change glass properties to produce a desired effect. The earliest and most widely used solution colorants were salts of copper (blue-green from the presence of Cu2+), iron (blue to green from Fe2+, yellow to brown from Fe3+), and manganese (amethyst or purple from Mn3+).27 The use of small quantities of manganese as a decolorizer to compensate for iron colors, also known in the Middle Ages, was referred to by Agricola and Neri and was used by the Venetians in the pro￾duction of cristallo. Cobalt was first used in the 14th century BC (deep blue from Co2+). The use of chromium as a solution colorant probably began early in the 19th century.27 Copper and gold ruby glasses were prized highly for their beauty and for their scarcity, the latter a result of the difficulty of producing these colloidal colors. Both glasses presented se￾rious challenges to the glassmaker because of their sensitivity to composition, melting conditions, and subsequent thermal history. The ruby color is caused by the selective absorption of light by small gold or copper crystals (∼50 nm in diameter) that are formed by the precipitation of the metals in their atomic state. The formation of the metal crystals is enhanced by re￾heating the glass (‘‘striking’’) and by the presence of reducing agents, e.g., stannous chloride. The red glasses found in old church windows are most likely copper reds, either copper rubies, suspensions of cuprous oxide, or copper stains, because gold rubies do not seem to have been made with any certainty until the 17th century.25,28 Opaque glasses colored by suspensions of relatively large crystals (with diameters in the micrometer range), where the crystals behave essentially as color pigments, have been known since antiquity. The pigments are generally insoluble or of limited solubility in the matrix glass. Some of the opaque col￾ors formed in this way are white glasses containing suspensions of tin oxide, arsenic pentoxide, or calcium antimonate, and yellow glasses colored by lead antimonate. Opaque blue glasses colored by copper calcium silicate or cobalt alumi￾nate, green glasses colored by chromic oxide, and brown or red-browns from iron or iron-manganese oxide mixtures also are used. The most dramatic examples of colored glass are probably the church windows of the Middle Ages, with the greatest created during the 10th through 14th centuries. Most of these windows also contain much stained glass, wherein a colorant is diffused into the glass surface at temperatures well below that of molten glass. Copper reds and silver yellows are perhaps the best-known examples of surface stains. (4) Lead Glasses The first major departure from alkali–lime–silica glasses came during the 17th century with the commercial introduction of lead flint glasses. Lead had long been a minor constituent in glazes, mosaics, and artificial gems. It was introduced as cal￾cined lead or lead oxide, primarily for its fluxing effect. Neri discussed lead glasses at some length in L’Arte Vetraria and emphasized that great care must be taken to thoroughly calcine the lead to avoid the formation of molten lead because ‘‘the least lead remaining breaks out the bottom of the pots and lets all the metall run into the fire.’’25 Shortly after the publication of Merrett’s English translation of Neri’s work in 1662, George Ravenscroft, an English glass merchant, turned glassmaker to develop a clear glass based on English ingredients.29,30 This latter requirement was motivated by the difficulty English glassmakers were experiencing in obtaining raw materials at acceptable cost, because a monopoly controlled the import of plant ashes for soda.31 The glass mer￾chants also were struggling with unresponsive foreign suppli￾ers, much breakage in transit, and oppressive tariffs.32 After a series of experiments, Ravenscroft introduced a clear potash Table I. Glass Compositions Glass† Oxide content (wt%) SiO2 B2O3 Na2O K2O CaO MgO Al2O3 Fe2O3 (1) Egypt, 1500 BC‡ 67.8 16.08 2.08 3.8 2.89 3.22 0.92 (2) Palestine, 4th Century 70.5 15.7 0.8 8.7 0.6 2.7 0.4 (3) Sudan, 3rd century 64.2 15.9 2.65 10.2 2.73 2.06 2.3 (4) Italy, 9th–10th centuries 77.8 6.4 8.7 2.1 0.7 2.2 0.8 (5) Container glass, 1980 73.0 13.7 0.4 10.6 0.3 1.8 (6) 1:1:6 soda–lime–silica 75.3 13.0 11.7 (7) Faraday ‘‘heavy glass’’‡ 10.6 15.6 (8) ‘‘Jena Standard Glass’’‡ 67.2 2.0 14.0 7.0 2.5 (9) Schott thermometer glass 72.0 12.0 11.0 5.0 (10) Schott utensil glass 73.7 6.2 6.6 5.5 3.3 (11) Schott Welsbach chimney‡ 75.8 15.2 4.0 (12) Nonex‡ 73.0 16.5 4.25 (13) Pyrex 80.5 12.9 3.8 0.4 2.2 (14) E-glass, typical 54.0 10.0 17.5 4.5 14.0 † (1) Morey,5 Table I-1 (10); (2) Brill,20 Jalame glass, (low potassium, high sodium); (3) Brill,21a Sedeinga tomb glass, (high potassium, high magnesium); (4) Brill,21b Frattesina glass, (mixed alkali); (5) Ryder and Poole43; (6) by calculation; (7) Faraday;37 (8) Hovestadt,40 Jena glass 16III, 1884; (9) Hovestadt,40 p. 246, Jena glass 59III, 1889, ‘‘ideal thermometer glass’’; (10) Steiner,42 p. 172, Jena glass 202III, 1893, recalculated from batch; (11) Steiner,42 p. 172, Auer von Welsbach gas light chimney, Jena glass 276III, 1895, recalculated from batch; (12) Corning code 7720; (13) Corning code 7740, Morey;5 (14) Aubourg and Wolf,46 typical composition, can vary, depending upon manufacturer and materials. ‡ Glass contains other oxides: (1) 0.54% Mn2O3, 1.51% CuO, and 1.0% SO3; (7) 70% PbO; (8) 7.0% ZnO; (11) 4.0% Sb2O3 and 0.9% As2O3; (12) 6.25% PbO. 798 Journal of the American Ceramic Society—Kurkjian and Prindle Vol. 81, No. 4

April 1998 Perspectives on the History of Glass Composition lead glass that was the ancestor of English lead crystal. The "Deceptively like a Solid ald Hoffman ognized the potential of Ravenscr ofts invention and negotiated to buy his entire production. The first glasses suf- The conference is on Glass, in Montreal. Wintry light declines fered from poor chemical durability and crizzling, and it was a to penetrate windows, and soon will be lit glass-enclosed glows that we m lk into the night(fortified by bot few years before a truly moisture-resistant lead crystal was mineral waters metric of order trespassing on prevailing produced. The glass was called"crystal, " and the fact that lead chaos that giv was the key ingredient was kept secret by Ravenscroft and his its viscious. tra immediate successors. These glasses also were called flint The beginning was, is silica, this peon stuff glasses, because they were based on high-purity silica from the of the earth, in quartz, cristobalite, coesite flint nodules found commonly in the Cretaceous chalk deposits stishovite. Pristine marching bands of atoms of southeast England, plus calcined lead oxide, niter(potassium (surpassing the names we give them) nitrate), and potash from wood ashes (good quality potash had build crystalline lattices from chains, rings, of St become more readily available in the latter part of the 17th alternating with oxygen, each silicon tetrhedrally century). A substantial business grew in the manufacture of coordinated by Os, each oxygen lead crystal articles that took advantage of the higher refractive ion, so different from the life-giving, inflaming index and the ease of cutting and polishing of the lead flint to tomic gas, joining two silicons; on to rings create sparkling goblets, bowls, and vases in diamondoid perfection in cristobalite The 17th century also was a period of growing interest in helical O-Si-O chains in quartz, handed ing, mirror images of each other, hard, ionic SiO science, and glass improvements became driven by scientists seeking better optical instruments, particularly telesc lileo and Kepler made a number of discoveries in optics that time lent to the earth: then lava flowed, the air blew thicker, still no compound or simple eye to made possible considerable improvement in telescopes, using fret defect into the unliquid from which silica the soda-lime-silica crown glasses of the time. Crown glas crystallized. But in time we did come, handy was the name given to window glass of the period that was set to garner sand, limestone, soda ash, to break made by the crown process, wherein a large blown bubble of the still witness of silica. Heat disrupts. Not the glass was transferred to a pontil, opened, and spun into a cir warmth of Alabama midsummer evenings. not cular disk by centrifugal force. )However, later optical physi our hand but formless wonder of prolonged fire, cists and astronomers found themselves increasingly frustrated he blast of air drawn in, controlled fire storms. Sand, which is silica, melts. To a liquid, where by poor glass quality and by the difficulty imposed by chro- matic aberration in obtaining a clear, sharp focus. After New order is local but not long-range. Atoms wander from their places, bonds break, tetrahedra in a ton explained the refraction of light by prisms, he examined tizzy, juxtapose, chains tilt, bump and stretch- many glasses and studied their dispersion( the variation in re- Jaggerwalky ractive index with wavelength ). Because the glasses The restive structures in microscopic turmoil probably all reasonably similar in composition, given the lim- meld to gross flow, bubbling eddies of the melt. ited variety of glasses available, he concluded, incorrectly, that all glasses had the same dispersion, and, therefore, that chro- Peace in crystal meshes matic aberration was an uncorrectable fault in lenses. Accord- n hot yellow flux. But the gloved gly, Newton then decided that it was useless to attempt to men who hold the ladies get nervy volca anoes on their minds. So-tilt, pour .. douse, build a better refracting telescope and switched his energies to o quench, freeze in that micro lurch reflecting telescopes. Others did the same, and refracting tele- Glass forms and who would have thought it clear? scopes went into ecl During the early 1730s, Chester Moor Hall, an English law- We posit that the chanced, in its innards so upset, er with an amateur interest in telescopes, recognized that lead ught not be transparent. Light scattered from entangled polymer blocks, adventitious dirt, flint glasses had higher dispersion than soda-lime crown owes it to us-oh, we see it so clearly--to lasses. He reasoned that chromatic aberration could be cor- sh in black or at least rected by an objective lens with two elements: a convex crown in the muddy browns of spring run-off, another element and a concave flint element (Crown"'and"flint But light's submicroscopic tap dance is done in became the terms used to describe, respectively, low refractive The crossed fields shimmer, resonant, they plink index(low dispersion) and high refractive index(high disper- sion)optical glasses, respectively. This doublet worked, and toms matter, their neighbors less, the tangle of the locked-in some telescopes were built using this first achromatic lens. The iquid irrelevant in the birthing of color, or lack of it. invention was not patented or publicized, however, and was Optical fibers Crystal Palace rediscovered by John Dollond, who patented it in 1758. Dol- The Worshipful Company of Glass Sellers lond and his son Peter were skillful, well-known opticians, and recycled Millefiori they were quite successful in marketing the achromats. These Prince Ruperts drops doublets were largely successful in bringing the red light and Chartres. Rouen. Amiens blue light to focus in a common image, although a secondary spectrum remained. This improvement should have encouraged network modifiers the palomar mirror moked for viewing e nvestigations of the effects of composition on the optical properties of glass, but progress was slow because of the prob- etched with hydrofluor lems of making homogeneous glass. Poor-quality optical glass annealed persisted until stirring of the melt was introduced by Pierre softening point Louis Guinand and his successors in the beginning of the 19th y Joseph Fraunhofer entered optical physics from the practical e, working for a time in an optical institute where Guinand was employed both as a glassmaker and as an optician grinding and polishing lenses. Fraunhofer made some excellent achro- From The Metamict State, pp. 44-48 University of Central Florida Press, Orlando, FL, 1987 mats, which helped revive refracting telescopes In the proces he experimented with glass compositions and recogn re choices were needed in refractive index and dispersion

lead glass that was the ancestor of English lead crystal. The Worshipful Company of Glass Sellers of London, a trade guild, quickly recognized the potential of Ravenscroft’s invention and negotiated to buy his entire production. The first glasses suf￾fered from poor chemical durability and crizzling, and it was a few years before a truly moisture-resistant lead crystal was produced. The glass was called ‘‘crystal,’’ and the fact that lead was the key ingredient was kept secret by Ravenscroft and his immediate successors. These glasses also were called flint glasses, because they were based on high-purity silica from the flint nodules found commonly in the Cretaceous chalk deposits of southeast England, plus calcined lead oxide, niter (potassium nitrate), and potash from wood ashes (good quality potash had become more readily available in the latter part of the 17th century). A substantial business grew in the manufacture of lead crystal articles that took advantage of the higher refractive index and the ease of cutting and polishing of the lead flint to create sparkling goblets, bowls, and vases. The 17th century also was a period of growing interest in science, and glass improvements became driven by scientists seeking better optical instruments, particularly telescopes. Ga￾lileo and Kepler made a number of discoveries in optics that made possible considerable improvement in telescopes, using the soda–lime–silica crown glasses of the time. (Crown glass was the name given to window glass of the period that was made by the crown process, wherein a large blown bubble of glass was transferred to a pontil, opened, and spun into a cir￾cular disk by centrifugal force.) However, later optical physi￾cists and astronomers found themselves increasingly frustrated by poor glass quality and by the difficulty imposed by chro￾matic aberration in obtaining a clear, sharp focus. After New￾ton explained the refraction of light by prisms, he examined many glasses and studied their dispersion (the variation in re￾fractive index with wavelength). Because the glasses were probably all reasonably similar in composition, given the lim￾ited variety of glasses available, he concluded, incorrectly, that all glasses had the same dispersion, and, therefore, that chro￾matic aberration was an uncorrectable fault in lenses. Accord￾ingly, Newton then decided that it was useless to attempt to build a better refracting telescope and switched his energies to reflecting telescopes. Others did the same, and refracting tele￾scopes went into eclipse until well into the 18th century.33 During the early 1730s, Chester Moor Hall, an English law￾yer with an amateur interest in telescopes, recognized that lead flint glasses had higher dispersion than soda–lime crown glasses. He reasoned that chromatic aberration could be cor￾rected by an objective lens with two elements: a convex crown element and a concave flint element. (‘‘Crown’’ and ‘‘flint’’ became the terms used to describe, respectively, low refractive index (low dispersion) and high refractive index (high disper￾sion) optical glasses, respectively.) This doublet worked, and some telescopes were built using this first achromatic lens. The invention was not patented or publicized, however, and was rediscovered by John Dollond, who patented it in 1758. Dol￾lond and his son Peter were skillful, well-known opticians, and they were quite successful in marketing the achromats.34 These doublets were largely successful in bringing the red light and blue light to focus in a common image, although a secondary spectrum remained. This improvement should have encouraged investigations of the effects of composition on the optical properties of glass, but progress was slow because of the prob￾lems of making homogeneous glass. Poor-quality optical glass persisted until stirring of the melt was introduced by Pierre Louis Guinand and his successors in the beginning of the 19th century. Joseph Fraunhofer entered optical physics from the practical side, working for a time in an optical institute where Guinand was employed both as a glassmaker and as an optician grinding and polishing lenses. Fraunhofer made some excellent achro￾mats, which helped revive refracting telescopes. In the process, he experimented with glass compositions and recognized that more choices were needed in refractive index and dispersion ‘‘Deceptively like a Solid’’ Roald Hoffman The conference is on Glass, in Montreal. Wintry light declines to penetrate windows, and soon will be lit glass-enclosed glows so that we may talk, talk into the night (fortified by bottled mineral waters), of the metric of order trespassing on prevailing chaos that gives this warder of our warmed up air, clinker, its viscious, transparent strength. The beginning was, is silica, this peon stuff of the earth, in quartz, cristobalite, coesite, stishovite. Pristine marching bands of atoms (surpassing the names we give them) build crystalline lattices from chains, rings, of Si alternating with oxygen, each silicon tetrhedrally coordinated by O’s, each oxygen ion, so different from the life-giving, inflaming diatomic gas, joining two silicons; on to rings in diamondoid perfection in cristobalite; helical O-Si-O chains in quartz, handed in coiling, mirror images of each other, hard, ionic SiO2. There must be reasons for such perfection— time lent to the earth: then lava flowed, the air blew thicker, still no compound or simple eye to fret defect into the unliquid from which silica crystallized. But in time we did come, handy, set to garner sand, limestone, soda ash, to break the still witness of silica. Heat disrupts. Not the warmth of Alabama midsummer evenings, not your hand but formless wonder of prolonged fire, the blast of air drawn in, controlled fire storms. Sand, which is silica, melts. To a liquid, where order is local but not long-range. Atoms wander from their places, bonds break, tetrahedra in a tizzy, juxtapose, chains tilt, bump and stretch— Jaggerwalky. The restive structures in microscopic turmoil meld to gross flow, bubbling eddies of the melt. Peace in crystal meshes, peace in hot yellow flux. But the gloved men who hold the ladies get nervy volcanoes on their minds. So—tilt, pour . . . douse, so quench, freeze in that micro lurch. Glass forms, and who would have thought it clear? We posit that the chanced, in its innards so upset, ought not be transparent. Light scattered from entangled polymer blocks, adventitious dirt, owes it to us— oh, we see it so clearly—to lose its way, come awash in black or at least in the muddy browns of spring run-off, another flux. But light’s submicroscopic tap dance is done in place. The crossed fields shimmer, resonant, they plink electron orbits of O and Si. Atoms matter, their neighbors less, the tangle of the locked-in liquid irrelevant in the birthing of color, or lack of it. Optical fibers Crystal Palace The Worshipful Company of Glass Sellers recycled Millefiori prone to shattering Prince Rupert’s drops Chartres, Rouen, Amiens float Pyrex Vycor glass wool network modifiers the Palomar mirror smoked for viewing eclipses thermos lead glass microcrack etched with hydrofluoric acid spun frustration bull’s eyes annealed borosilicate softening point High winds on Etna or Kilauea spin off the surface of a lava lake thin fibers. Pele’s hair. The Goddesses’ hair, here black. From The Metamict State; pp. 44–48. University of Central Florida Press, Orlando, FL, 1987. April 1998 Perspectives on the History of Glass Composition 799