Numbers in brackets denote the uncertainties in the final decimal places. Reported values by definition exact when no uncertainties are mentioned.
Section I. Glassmaking
Figure 1 The initial melting step in the making of float glass: the 1‐m deep bath of raw materials melted by the flames of a cross‐fired furnace (Chapter 9.7). Pulls ranging from 500 to 1000 tons/day and mean residence times of at least 24 hours. Electro‐fused refractory materials made up of alumina‐zirconia‐silica in contact with the melt, and of alumina and alumina‐silica elsewhere (cf. Chapter 9.8).
Source: Photo courtesy Simonpietro Di Pierro, Saint‐Gobain Research Paris.
Compared with crude steel (1700 million tons/year worldwide) and especially with cement (4300 Mtons), glass (about 120 Mtons) is produced in relatively small quantities. In terms of product value or volume, however, the imbalance is significantly reduced since the cost of cement is about one sixth of that of window glass and steel about three times as dense. But what differentiates glass most from these other two inorganic pillars of modern civilization is the remarkable diversity of its uses illustrated throughout the Encyclopedia.
In Europe, for which the data are the most readily available, the 35 Mtons produced in 2017 were split into container (21.4), flat (10.1), domestic (1.3), reinforcement (0.7), and other (1.1) glass. For both container and flat glass, the world market is estimated to be in the 60–80 billion $ range and is expected to keep growing in the years to come at yearly rates higher than 5% on average, with large geographical differences (cf. Chapter 9.6). And growth rates should be higher still for new products such as the smart glass used in a variety of electronic devices (cf. Chapter 6.10), whose market should increase by a factor of 3 from 2017 to 2023 from the current few billion $ per year.
Like cement and steel producers, glassmakers sell more than 90% of their production to other industries. Most uses of glass are nonetheless familiar to anyone. These are summarized in the first chapter of this section where R. Conradt points out their strong dependence on chemical composition of the glasses and on their ensuing physical properties, explaining that the reason why the still‐dominant soda‐lime silicates were empirically found so early in the history of glassmaking is simply because they lie close to the eutectic of the Na2O–CaO–SiO2 system.
Even though glass is now made in many different ways for different applications, the traditional procedure of making it by cooling of a batch melted at high temperatures remains by far prevailing. As one readily realizes when looking at the original glazing of late‐nineteenth‐century buildings, the long‐standing problem faced by glassmakers was to achieve chemical homogeneity. The mass production of defect‐free glass is a relatively recent achievement. It has resulted from better furnaces (Figure 1;
