most diverse shapes and sizes possible, produces optical isotropy, gives much flexibility in terms of raw materials and coloring elements thanks to the almost limitless extent of its solid solutions, and is at the source of mechanical properties in principle limited only by the strength of interatomic bonds thanks to the lack of weak grain boundaries.
How was it figured out that glass could completely lose its vivid colors, which first attracted man's interest, we do not know. The transparency now so closely associated with glass was first achieved for very special pieces such as cups made in Achaemenid Persia in the fifth century BCE (Chapter 10.0, Figure 1a). But it took several more centuries before transparency became common. The existence of pure, natural carbonates commonly termed natron was the key ingredient to achieve it at a large scale at the beginning of our era [11]. Especially in the Levant, the competitive edge acquired by glassmakers thanks to this substance was such that it led to the establishment of a world market: finished items and glass ingots were traded along well‐established commercial routes to be exported as far as East Africa and India [12], the ingots to be shaped locally in small workshops (Chapter 10.3). A first glimpse at globalization?
1.3 A Multifaceted Material
Glass has always aroused much curiosity by its virtue of embodying almost unlimited possibilities for transforming matter. Until the end of the nineteenth century, industrial illustrations of such transformations were the metamorphoses undergone by the large glass pieces that were first blown before being opened and flattened to yield flat panes with the neat fire finish required for transparency (Chapter 10.8). Nowadays, who has never been captivated by the work of a blower, by the action of a delicately controlled fire that gives birth to the most surprising shapes and, in a way, makes the material living for an instant? Even the proverbial brittleness of glass is part of this powerful imaginative world: its fracture indeed seems as unpredictable as it is dramatic, as illustrated by a tempered drinking glass suddenly exploding after several bounces when falling onto the ground.
To this kind of amazement also contributed early the miracles wrought by glass ever since it first restored sight to visually impaired people in the thirteenth century (Chapter 10.10). It is thus no wonder that Leonardo da Vinci (1452–1519) devoted efforts to design a device for machining eyeglasses. Shortly after, the transparent glazing of windows opened houses on the outside world at about the same time as the telescope and the microscope led to the discovery of the universe from the infinitely large to the infinitely small (Chapter 10.10). Grinding of optical lenses was then extensively practiced by Galileo Galilei (1564–1642) himself and considered a trade worth earning a living by the eminent philosopher Baruch Spinoza (1632–1677). That glassmaking had something special is actually indicated by the fact that, in France, it was long the only trade that the nobility could practice as gentlemen glassmakers without losing its special status.
To acknowledge all what civilization was owing to this material, the polymath and glassmaker Mikhail Vasilyevich Lomonosov (1711–1765) wrote in Russia a long poem entitled Letter on the use of Glass. “A whole year would hardly suffice me to reach the end of worthy praise for Glass” [13], Lomonosov thus claimed when mentioning not only the telescope, the microscope, or the barometer, but also the thrilling electrical researches of his time based on the accumulation of charges on the glass disks of electrostatic machines (Chapter 10.10). Such was the interest raised by the vitreous (positive) and resinous (negative) electricities “that people of all genders and ranks were then begging for the favor of being subjected to electric shock, to the point that the noble and courageous Professor Georg Matthias Bose (1710–1761) said with philosophical heroism: I would not regret dying of an electric shock, since the account of my death would provide the subject of an article in the Memoirs of the Royal Academy of Sciences of Paris” [14]. Could this admirable philosophical heroism have been elicited by a material other than glass?
At the same period, glass became the source of another kind of emotions when the famous Benjamin Franklin (1706–1790) was inspired by “the sweet tone that is drawn from a drinking glass, by passing a wet finger around the rim” [15] to design in 1761 the glass armonica whereby it was a set of overlapping wet glass cones of different sizes that was rotating to emit a sweet, ethereal, or pathetic tone through the friction of fingers. The instrument met with rapid success such that, beginning with Wolfgang Amadeus Mozart (1756–1791) [16], quite a few great composers wrote short pieces for it. The fashion for glass was such that a German living in Paris named Beyer presented in 1785 to the Académie des Sciences his forte‐piano with glass plates, acted upon by wool‐covered hammers, which Franklin christened glass‐cord [17]. And it was a flute made from lead‐crystal glass that the Parisian instrument maker Claude Laurent (d. 1848) patented in 1806 and produced in white, cobalt‐blue, and uranium‐green hues; in spite of its weight, its musical qualities and reduced temperature‐induced pitch changes ensured its popularity for several decades [18].
This select series of anecdotes probably makes it unnecessary to emphasize again the importance of glass in daily and social life stressed above by Bontemps and Figuier. It might in contrast be useful to mention that the antique tradition or ornamental glass was revived at the same period by Georges Frédéric Strass (1701–1773), who became the French King's jeweler, when he invented strass, or rhinestone, a high‐lead crystal glass bearing various metal oxides that is still made today to imitate precious stones.
1.4 The Silica Paradoxes
1.4.1 Biogenic Silica vs. Flint
Historically, glass owes its importance to silicates. But what substances could have replaced silicate glasses in their diversity of uses on a silicon‐free planet? The question would be moot if carbon – the next of kin of silicon in the Periodic Table – and, therefore, life and human beings would have also been lacking. More seriously, however, reflecting on the origin of the silica sources used in glassmaking is not a futile exercise.
It is not widely known that 15 billion tons of biogenic silica glass are yearly produced in seawater by diatoms, sponges, and some other living organisms. Such a biological production has major effects on the Earth's global ecosystem and has now become a biomimetic source of inspiration for designing wholly new materials (Chapter 8.1). Interestingly, biogenic silica also had noteworthy implications for glassmaking because of its recycling into the opal or microcrystalline quartz of flint. Flint, or chert as it is called in geology, is commonly found as abundant nodules horizontally embedded in limestone (Figure 4). Its deposition thus requires carbonate dissolution followed by silica precipitation and, thus, percolating waters undersaturated with respect to calcium carbonates but oversaturated with respect to silica. Without going into the details of the process and of its control by pH and geological context [19, 20], it will suffice here to state that biogenic silica accumulating at the bottom of the sea is the source of the dissolved silica that reprecipitates as flint. And it happens that flint was the raw material used in England from the seventeenth century to remedy the lack of sand pure enough for making optical glass and luxury ware (Chapter 10.10).
