Journal of the American Ceramic SocietyKurkjian and Prindle Vol 8I. No 4 Glass is much significant advances in the discovery and isolation of new el more gentile, graceful ements, and, in the 1830s, Harcourt began investigations of the effects of many of these new elements on the optical properties long the elem and noble than any cadmium, fluorine, lithium, magnesium, molybdenum, tungsten, uranium, and vanadium. He also studied the Metall It is more effects of other elements, including antimony, arsenic, barium, boron, phosphorus, tin, and zinc, first introduced into glass by delightful, polite, and but also melted some phosphates, borates, and titanates, in part sightly than any other neous glass. He did not widely publicize his findings, but Sir George Stokes, the noted mathematician and physicist, learned of his work, collaborated with him, and helped to bring the material at this day results to the attention of the scientific community in 1871, the ear of Harcourts death. In 1874. Stokes made a small. three- known to the world omponent lens that was largely free of the secondary spectrum from some of Harcourts glasses. Therefore, even though Har Antonio neri. 1612 courts glasses were not completely homogeneous, his work demonstrated that different glassmaking ingredients did bring changes in dispersion and refractive index that could yield glasses that began to solve the optical problems of the time.16,31,39 beyond those of ordinary crown and flint glasses if better lenses were to be made that corrected the secondary spectrum. Fraun- British glass industry to investigate further the effects of dif- ferent glass constituents, it did little beyond the production of was probably the discoverer of the mixed-alkali effect, noting some standard optical crowns and flints by Chance Brothers in that glasses with mixed alkalis had superior durability. (The irmingham. Experimentation to develop new glas served in some properties when one alkali ion is gradually tions was severely constrained at that time in England by ex- substituted for another alkali ion. This phenomenon is observed orbitant taxes on all glassmelting. Therefore, Chance Brothers in properties affected by transport mechanisms, such as ele concentrated instead on improving the quality of the standare trical conductivity, dielectric loss, internal friction, and self- glasses by stirring the I nelt. Accordingly, the initiative in glass diffusion. )Later, Fraunhofer's spectral studies enabled him to composition research passed to German glassmakers, who built on the work of fraunhofer and harcourt 31 make observations on dispersion for the principal glass com- ponents of the day 17, 22,25,35,36 As is evident from the foregoing, until the late 19th century Impressed by Fraunhofer's results, the Royal Society estab- he development of new glasses was largely a matter of ar lished, in 1824, a commission consisting of Michael Faraday occasional fortuitous discovery. These early investigations, al John Herschel( the astronomer), and George Dollond(another though often motivated by a need, were not pursued of the famed clan of opticians), to study the possibility of atically, had difficulty in yielding a homogeneous prod exce on of Harcourts work, usually used the same making superior glasses for telescope objectives. Faraday be w dients hovestadt wrote. in 1900 el came interested in glassmelting and made some prolonged in ment of the art of glassmaking in response to optical require of melting glasses in platinum containers and the importance of fluxes broke the monotony of a uniform series of crowns and tiring melts to improve homogeneity. His experiments, un- flints. 740 fortunately, did not contribute much to the knowledge of glass omposition, although he did demonstrate that boron could be Ised in glassmaking to make a passable lead borosilicate flint llL Abbe and Schott lass. Faraday later(1845)conducted some experiments of which he demonstrated the Faraday effect(rotation of the plane a microscope maker at the university. Similar to the telescope of polarization of light in a magnetic field ). 15,33,35, 37,38 makers, Abbe soon realized that a wider variation in dispersion It may seem surprising today that eminent scientists and for a given refractive index was needed to remove completely intellectuals of the time were deeply interested in finding so- states,Goethe, then Prime Minister of a German duchy. in of Otto Schott, a young German chemist who had been explor- University of Jena, it would be most important to determine ing glassmelting phenomena in connection with his family' the relation of refraction and dispersion in your (barium and glassworks in Westphalia. Schott contacted Abbe and sent him strontium glasses 6 should be pleased to contribute the samples might aid Abbe in his research for glasses with dif- of a wide range of elements on the properties of glass was the laborating and thus was born one of the greatest and most Schott moved to Jena in 1882 to be closer to abbe and Zeiss Abbe(the scientist), Schott(the glassmaker), and Zeiss(the instrument builder) worked together in a synergistic manner that bore dramatic results. abbe and Schott d discuss the tThe poem on the 就运 composition changes to be made, Schott would then prepare homogeneous glass melts, and Abbe would measure the results If the properties appeared to be an improvement, Zeiss would grind and polish lenses and observe the performance of the
beyond those of ordinary crown and flint glasses if better lenses were to be made that corrected the secondary spectrum. Fraunhofer also wrote about the chemical durability of glasses and was probably the discoverer of the mixed-alkali effect, noting that glasses with mixed alkalis had superior durability. (The mixed-alkali effect is the distinctly nonlinear behavior observed in some properties when one alkali ion is gradually substituted for another alkali ion. This phenomenon is observed in properties affected by transport mechanisms, such as electrical conductivity, dielectric loss, internal friction, and selfdiffusion.) Later, Fraunhofer’s spectral studies enabled him to make observations on dispersion for the principal glass components of the day.17,22,25,35,36 Impressed by Fraunhofer’s results, the Royal Society established, in 1824, a commission consisting of Michael Faraday, John Herschel (the astronomer), and George Dollond (another of the famed clan of opticians), to study the possibility of making superior glasses for telescope objectives. Faraday became interested in glassmelting and made some prolonged investigations during 1825–1830 that demonstrated the benefits of melting glasses in platinum containers and the importance of stirring melts to improve homogeneity. His experiments, unfortunately, did not contribute much to the knowledge of glass composition, although he did demonstrate that boron could be used in glassmaking to make a passable lead borosilicate flint glass. Faraday later (1845) conducted some experiments of significance with his ‘‘heavy glass’’ (see glass 7 in Table I), in which he demonstrated the Faraday effect (rotation of the plane of polarization of light in a magnetic field).15,33,35,37,38 It may seem surprising today that eminent scientists and intellectuals of the time were deeply interested in finding solutions to glass composition problems. For example, Vogel states, ‘‘Goethe, then Prime Minister of a German duchy . . . in 1829 wrote to his friend, the noted chemist Do¨breiner at the University of Jena, ‘it would be most important to determine the relation of refraction and dispersion in your [barium and strontium] glasses . . . I should be pleased to contribute the modest funding . . .’.’’36,‡ The first, however, to make an extensive study of the effects of a wide range of elements on the properties of glass was the Rev. William Vernon Harcourt, an English clergyman. The late 18th century and the early 19th century was a period of highly significant advances in the discovery and isolation of new elements, and, in the 1830s, Harcourt began investigations of the effects of many of these new elements on the optical properties of glass. Among the elements he first used in glass were beryllium, cadmium, fluorine, lithium, magnesium, molybdenum, nickel, tungsten, uranium, and vanadium. He also studied the effects of other elements, including antimony, arsenic, barium, boron, phosphorus, tin, and zinc, first introduced into glass by others. Harcourt did not confine his studies to silicate glasses, but also melted some phosphates, borates, and titanates, in part because he found it difficult to fuse the silicates to a homogeneous glass. He did not widely publicize his findings, but Sir George Stokes, the noted mathematician and physicist, learned of his work, collaborated with him, and helped to bring the results to the attention of the scientific community in 1871, the year of Harcourt’s death. In 1874, Stokes made a small, threecomponent lens that was largely free of the secondary spectrum from some of Harcourt’s glasses. Therefore, even though Harcourt’s glasses were not completely homogeneous, his work demonstrated that different glassmaking ingredients did bring changes in dispersion and refractive index that could yield glasses that began to solve the optical problems of the time.16,31,39 Although the work of Harcourt should have encouraged the British glass industry to investigate further the effects of different glass constituents, it did little beyond the production of some standard optical crowns and flints by Chance Brothers in Birmingham. Experimentation to develop new glass compositions was severely constrained at that time in England by exorbitant taxes on all glassmelting. Therefore, Chance Brothers concentrated instead on improving the quality of the standard glasses by stirring the melt. Accordingly, the initiative in glass composition research passed to German glassmakers, who built on the work of Fraunhofer and Harcourt.31 As is evident from the foregoing, until the late 19th century, the development of new glasses was largely a matter of an occasional fortuitous discovery. These early investigations, although often motivated by a need, were not pursued systematically, had difficulty in yielding a homogeneous product, and, with the exception of Harcourt’s work, usually used the same few ingredients. Hovestadt wrote, in 1900, ‘‘. . . the development of the art of glassmaking in response to optical requirements kept, for a long time, to one narrow groove, and no new fluxes broke the monotony of a uniform series of crowns and flints.’’40 III. Abbe and Schott Ernst Abbe, professor of physics at Jena University, became interested in optical glasses through his work with Carl Zeiss, a microscope maker at the university. Similar to the telescope makers, Abbe soon realized that a wider variation in dispersion for a given refractive index was needed to remove completely the secondary spectrum from optical images. He wrote on the subject in the late 1870s, and his remarks attracted the interest of Otto Schott, a young German chemist who had been exploring glassmelting phenomena in connection with his family’s glassworks in Westphalia. Schott contacted Abbe and sent him some lithium glasses he had prepared with the thought the samples might aid Abbe in his research for glasses with different optical properties. By 1881 Abbe and Schott were collaborating and thus was born one of the greatest and most productive associations in the history of glass composition.31,40 Schott moved to Jena in 1882 to be closer to Abbe and Zeiss. Abbe (the scientist), Schott (the glassmaker), and Zeiss (the instrument builder) worked together in a synergistic manner that bore dramatic results. Abbe and Schott would discuss the composition changes to be made, Schott would then prepare homogeneous glass melts, and Abbe would measure the results. If the properties appeared to be an improvement, Zeiss would grind and polish lenses and observe the performance of the ‡ The poem on the previous page was authored by Roald Hoffman, the Nobel Laureate in chemistry in 1981 with Kenichi Fukui for ‘‘His application of molecular orbital theory to chemical reactions.’’ Also, the 1977 Nobel Prize in physics was awarded to P. W. Anderson, Sir N. F. Mott, and J. H. van Vleck for ‘‘Their fundamental theoretical investigations of the electronic structure of magnetic and disordered systems.’’ The eminent scientists continue to find glassy systems of interest. ‘‘Glass . . . is much more gentile, graceful, and noble than any Metall, . . . it is more delightful, polite, and sightly than any other material at this day known to the world,’’ Antonio Neri, 1612 800 Journal of the American Ceramic Society—Kurkjian and Prindle Vol. 81, No. 4
April 1998 Perspectives on the History of Glass Composition Schott und genossen As stated by Douglas and Frank, 31The success of the were added to the list every few years, and the effect on the firm [ Schott und Genossen] was spectacular. Its first price manufacture of optical systems was so great that Germany list of 1886 contained forty-four optical gla asses of which which had previously imported ninety percent of its optical nineteen were essentially new compositions. The first systems from England and France, started to export to these supplement of 1888 added twenty-four glasses, including countries. Thus, an industrial development which was ac- ew barium light flints which were remarkable for complished in less than ten years virtually eliminated exist mall dispersion pared with refractive index. They ng manufacturers and, for about 30 years, until the outbreak ed so little lead oxide that the usual light absorption of the World War I, Jena held an effective world monopoly by flint glasses was greatly reduced. New glasses in the manufacture of optical glass lime, and lead oxide and eventually added 28 othere/a potash, optical glasses. In the 1890s, the group at Jena analyzed the rIse of ass meters. It was noted in one of the early observations of quantities of at least 10% to produce glasses of refractive in- the mixed alkali effect that the zero rise was particularly pro- dexes and dispersions substantially different from those made nounced(more than one celsius degree) in glasses with ap- proximately equal quantities of soda and potash Glasses made The techniques used by Abbe and Schott in their studies with either only soda or only potash as the alkali suffered only were based on careful observation and measurement, although one tenth or less the secular rise as the mixed alkali glasses almost totally empirical, because no reasonable theories existed The most stable glass was found to be a borosilicate(see glass to guide their work. Additions of new minor ingredients were 9 in Table 1). 40 made to correct or offset faults in the original compositions Improved laboratory glassware also resulted from Schott's For example, Schott found that, in borate and phosphate further pursuit of boron in glass with the discovery that boro- glasses, alkalis had to be used very sparingly, if at all; other silicate glasses had exceptional resistance to attack by boiling vise surface staining resulted on exposure to air. However water. Accordingly, these glasses also made excellent boiler when alumina, zinc oxide, and barium oxide were added the gauge glasses. It also was noted that boric oxide was the most surface durability could be improved enough to make the effective addition to silicate glasses in reducing the coefficient glasses serviceable. Schott soon learned that the addition of of thermal ex and this discot some elements would have no effect on optical properties but glassware with oved resistance to thermal shock 40 would have a favorable effect on other properties In the remarkably short period from 1879 to 1886, Otto In an effort to at least make their results usable, Schott, and Schott, with the assistance of Abbe and Zeiss, created and Winkelmann developed what probably was the first composi- offered commercially a surprising array of optical glasses. Be- tion-property model. They produced a series of oxide factors sides using a systematic approach to glass composition re that allowed them to calculate the value of a property knowing search, Schott had mastered the small-scale melt-stirring pro the composition. Today, many such models are available be- cess so as to be able to make a homogeneous product. The cause of computers(see Cable) glasses also had been carefully characterized, so they were sold Early useful results were obtained with boron, barium, and with exact measured values of refractive index and dispersion fluorine, leading to families of borosilicate crowns, barium This work was a watershed in the history of glass composition flints, and fluor crowns. (The demarcation between crowns and in that it demonstrated for the first time the ability to tailor the flints is arbitrarily defined by their dispersion and is shown properties of a glass by judicious adjustments in composition in Fig. 2.)The government was quite impressed by the pI based on a composition-property model ress and made some large grants to support the work of the laboratory that became, in 1884, the Jena firm of Schott und Genossen IV. Modern Glasses The discoveries of abbe and Schott were not confined to (1) Soda-Lime-Silica Glasses Although sand and alkali were known from the earliest days of glass to be necessary ingredients, the role of lime was not Flints apparent until much later times. Lime was not recognized as an important glass constituent by early glassmakers, because ad- equate amounts of lime were generally added unknowingly as an impurity in the sand and alkali. Lime appears to have been added consciously to glass batches in Roman times, but Neri mentioned lime only casually in suggesting that small quanti ties could be added to make a very fair and beautiful Crystall. 2 Only in the 17th, 18th, and 19th centuries did the increase in chemical durability brought about by the addition of lime to alkali silicate glasses become understood. Bohemian glassmakers added lime to their fine crystal in the 17th century and, during the late 1700s, P D. Deslandes added up to 6% lime to increase the resistance of Saint-Gobain's plate glass to attack by moisture. Guinand and Fraunhofer observed that it was necessary to add lime to increase glass durability, and, in historical development of optical glasses, 34(White area within curve 1830, J.B. Dumas, a French glass technologist, noted that the presents modern glasses(Morey et al.), hatched area represents ear. chemical durability of glass was oved by adding one part lier glasses, i. e, 1880-1934( Schott et al ); and black area represents of lime to one part of soda and six parts of silica. The addition glasses before 1880.) of lime to the batch became essential in practical glassmaking
finished pieces, then feed his observations back to Abbe and Schott. In this manner they started with silica, soda, potash, lime, and lead oxide and eventually added 28 other elements in quantities of at least 10% to produce glasses of refractive indexes and dispersions substantially different from those made previously. The techniques used by Abbe and Schott in their studies were based on careful observation and measurement, although almost totally empirical, because no reasonable theories existed to guide their work. Additions of new minor ingredients were made to correct or offset faults in the original compositions. For example, Schott found that, in borate and phosphate glasses, alkalis had to be used very sparingly, if at all; otherwise surface staining resulted on exposure to air. However, when alumina, zinc oxide, and barium oxide were added, the surface durability could be improved enough to make the glasses serviceable. Schott soon learned that the addition of some elements would have no effect on optical properties but would have a favorable effect on other properties. In an effort to at least make their results usable, Schott, and Winkelmann developed what probably was the first composition–property model.4 They produced a series of oxide factors that allowed them to calculate the value of a property knowing the composition. Today, many such models are available because of computers (see Cable41). Early useful results were obtained with boron, barium, and fluorine, leading to families of borosilicate crowns, barium flints, and fluor crowns. (The demarcation between crowns and flints is arbitrarily defined by their dispersion and is shown in Fig. 2.) The government was quite impressed by the progress and made some large grants to support the work of the laboratory that became, in 1884, the Jena firm of Schott und Genossen. The discoveries of Abbe and Schott were not confined to optical glasses. In the 1890s, the group at Jena analyzed the problem of the secular rise of the zero in the aging of glass thermometers. It was noted in one of the early observations of the mixed alkali effect that the zero rise was particularly pronounced (more than one celsius degree) in glasses with approximately equal quantities of soda and potash. Glasses made with either only soda or only potash as the alkali suffered only one tenth or less the secular rise as the mixed alkali glasses. The most stable glass was found to be a borosilicate (see glass 9 in Table I).40 Improved laboratory glassware also resulted from Schott’s further pursuit of boron in glass with the discovery that borosilicate glasses had exceptional resistance to attack by boiling water. Accordingly, these glasses also made excellent boiler gauge glasses. It also was noted that boric oxide was the most effective addition to silicate glasses in reducing the coefficient of thermal expansion, and this discovery led to laboratory glassware with improved resistance to thermal shock.40 In the remarkably short period from 1879 to 1886, Otto Schott, with the assistance of Abbe and Zeiss, created and offered commercially a surprising array of optical glasses. Besides using a systematic approach to glass composition research, Schott had mastered the small-scale melt-stirring process so as to be able to make a homogeneous product. The glasses also had been carefully characterized, so they were sold with exact measured values of refractive index and dispersion. This work was a watershed in the history of glass composition in that it demonstrated for the first time the ability to tailor the properties of a glass by judicious adjustments in composition based on a composition–property model.42 IV. Modern Glasses (1) Soda–Lime–Silica Glasses Although sand and alkali were known from the earliest days of glass to be necessary ingredients, the role of lime was not apparent until much later times. Lime was not recognized as an important glass constituent by early glassmakers, because adequate amounts of lime were generally added unknowingly as an impurity in the sand and alkali. Lime appears to have been added consciously to glass batches in Roman times, but Neri mentioned lime only casually in suggesting that small quantities could be added ‘‘. . . to make a very fair and beautiful Crystall.’’12 Only in the 17th, 18th, and 19th centuries did the increase in chemical durability brought about by the addition of lime to alkali silicate glasses become understood. Bohemian glassmakers added lime to their fine crystal in the 17th century, and, during the late 1700s, P. D. Deslandes added up to 6% lime to increase the resistance of Saint-Gobain’s plate glass to attack by moisture.31 Guinand and Fraunhofer observed that it was necessary to add lime to increase glass durability, and, in 1830, J. B. Dumas, a French glass technologist, noted that the chemical durability of glass was improved by adding one part of lime to one part of soda and six parts of silica. The addition of lime to the batch became essential in practical glassmaking Schott und Genossen As stated by Douglas and Frank,31 ‘‘The success of the firm [Schott und Genossen] was spectacular. Its first price list of 1886 contained forty-four optical glasses of which nineteen were essentially new compositions. The first supplement of 1888 added twenty-four glasses, including eight new barium light flints which were remarkable for their small dispersion compared with refractive index. They contained so little lead oxide that the usual light absorption shown by flint glasses was greatly reduced. New glasses were added to the list every few years, and the effect on the manufacture of optical systems was so great that Germany, which had previously imported ninety percent of its optical systems from England and France, started to export to these countries. Thus, an industrial development which was accomplished in less than ten years virtually eliminated existing manufacturers and, for about 30 years, until the outbreak of the World War I, Jena held an effective world monopoly in the manufacture of optical glass.’’ Fig. 2. Refractive index, n, versus reciprocal dispersion, n, showing historical development of optical glasses.34 (White area within curve represents modern glasses (Morey et al.); hatched area represents earlier glasses, i.e., 1880–1934 (Schott et al.); and black area represents glasses before 1880.) April 1998 Perspectives on the History of Glass Composition 801