ways to create original materials, to satisfy the most diverse needs and even to discover the world at large.
Unlike other well‐established materials, glass has gone through more developments in the past 50 years than in two millennia from both industrial and technological standpoints. Whether overwhelming in the glazing of skyscrapers or hidden in telecommunication networks, glass has become still more ubiquitous in the modern environment than at Bontemps and Figuier's time so that claiming that we are now living in the Glass Age is not an overstatement [3, 4]. Whereas original glass compositions have, for instance, been designed for innovative lighting, screen, and display applications (Chapters 6.9 and 6.10), even the traditional products used for glazing and containers are now taking advantage of various new functionalities (Chapters 6.7 and 6.8). But what might be the most fascinating modern feature of glass is the way in which the material can be engineered to satisfy the most opposite requirements. Long celebrated for light transmission (Chapter 6.1), glass can be made opaque to a wide range of electromagnetic radiations from infrared to X‐ray wavelengths through addition of appropriately absorbing elements (Chapters 3.13 and 6.2). Chemical inertness is another major traditional asset of glass, which is in contrast purposely avoided in water glass (Chapter 7.5) and bioactive glasses (Chapter 8.4) whose usefulness rests on their intrinsically high chemical reactivity. And whereas extremely low impurity levels are required in optical fibers and other optoelectronic devices (Chapters 6.3–6.6), storage of municipal and nuclear waste relies on the capacity of glass matrices to incorporate large amounts of a great many elements (Chapters 9.10 and 9.11).
Additional examples are not needed here to illustrate further the point as they will be found in numbers in the Encyclopedia. It is more appropriate to stress that most of these engineering developments have relied on the improved understanding of the glassy state brought by a better knowledge of its physical, chemical, and structural properties. What a long way has therefore been traveled since man made acquaintance with a strange, dark rock differing from all others by its luster and especially, when split into pieces, by its extremely sharp edges that even flint could not match!
1.2 An Economic Forerunner
Obsidian (Figure 1), a natural glass found in volcanic provinces in various parts of the Earth, has been known from time immemorial. From arrowheads (Figure 2) to blades of any kinds and purposes (Figure 3), its unique properties made it so valuable to hunter‐gatherers that it was the very first item to be extensively exchanged over long distances [5]. Well before any man‐made object was produced, obsidian thus embodied at an early stage of human evolution the economic notion of competitive advantage, which eventually resulted in its real trade (Chapter 10.1). At the heart of a dynamic corridor between Eurasia and Africa, present‐day Armenia played a significant role in this history as a material source for a wide area in the Near East, initially through moving communities that were carrying their tools with them [6]. Armenia is also important because of the new light it has recently shed on the far‐reaching issue of the expansion of archaic Homo sapiens out of Africa.
Figure 2 The delicate stone knapping of an arrowhead made possible by obsidian in Pre‐Colombian present‐day Arizona.
Source: Photo courtesy Alexandra Navrotsky.
Figure 3 The striking stone‐knapping difference between a biface (left) and Levallois point and blade, all made from obsidian (right); length: 20 cm: (a) Acheulean hand axe produced by serial removal of small flakes with a soft hammer (Kuchak‐3 open‐air site, Aparan Depression, Central Armenia); (b) Levallois Mousterian point, with its plano‐convex profile, produced before the repreparation of core convexities, and the recurrent method, in which multiple Levallois flakes are detached before repreparation (Barozh‐12 open‐air site, Ararat Depression, Eastern Armenia); (c) Regular flake of the Chalcolithic period produced by pressure flaking from a prismatic core with the aid of a lever (Mastara‐1 settlement, Ararat Depression).
Source: Photos courtesy Boris Gasparyan.
According to a claim often made, this expansion followed the important technical change from bifacial to Levallois technique of stone knapping (Figure 3, cf. [7] for their differences). At the Nor Geghi‐I site, near Yerevan, both types of tools actually coexist within alluvial sediments sandwiched in between lava flows dated to 441 000 ± 6 000 and 197 000 ± 7 000 years [8]. From a fundamental standpoint, the synchronic use of both techniques by a single human group at this site thus indicates instead that, after human dispersion, the transition occurred independently within geographically distinct areas. From a practical standpoint, the change allowed better tools to be obtained so much faster from a large core (Figure 1) and with little waste. One could in fact conclude from the incredibly high abundance of artifacts buried in a Middle‐Paleolithic site such as Barozh 12 [9], next to the Arteni Complex Volcano (Eastern Armenia), that the concept of disposable object was born with obsidian in the Paleolithic!
Man‐made glass appeared considerably later, only three and a half millennia ago in the Late Bronze Age in a wide area ranging from the Near East to Egypt and Greece (Chapter 10.2). The vividly colored but expensive material newly produced was originally the preserve of elites who had recognized its aesthetic and practical interest. After 15 centuries of technical improvements and decreases of production costs, it became a basic commodity in the Roman Empire as acknowledged by Petronius (first century CE) in the Satyricon where one of his characters uttered: “You will forgive me if I say that personally I prefer glass; glass does not smell. If it were not so breakable I should prefer it to gold; as it is, it is so cheap” [10]. This chemical inertness achieved at reduced cost was of course one of the early assets of glass. As we now know, others were resulting from its lack
