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 dispersionlead 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