Ancient glass studies

TABLE 31 Analytical Techniques Frequently Used to Study Ancient Glass  

Auger emission spectroscopy Surface Ciliberto and Spoto (2003) 

The main source of silica in antiquity, as today, was sand and, very occasionally, cmshed rock or pebbles. The most common modifier was soda, which was obtained from natron lakes, as in ancient Egypt, for example, or from vegetable ash. Most lime was derived from limestone, although some lime could also enter the mixture of glass raw materials together with soda 

FIGURE 22 Obsidian in the eastern Mediterranean Sea area. Studying the relative concentration of trace elements in obsidian makes it possible to identify the obsidian and to determine its provenance. Determining the relative amounts of barium and zirconium in ancient obsidian tools and in samples from different sources of the natural glass, for example, made it possible to identify the provenance of obsidian used in eastern Mediterranean Sea area sites (Renfrew and Dixon 1976). 

The natural composition of obsidian includes very little water, generally less than 0.1%. When new obsidian surfaces are created, either by the natural breakdown of obsidian bulks or by human activity, the exposure of a new surface to humidity in the air or to water brings about a process known as hydration the surface adsorbs (takes up) water and becomes 

Once initiated, and provided the surface continues to be exposed to the environment, the process of hydration continues at a slow, but measurable rate. The adsorption of the water is accompanied by changes in the physical properties of the obsidian. The refractive index of the obsidian, for example, is altered as it becomes hydrated. If the obsidian was subjected to alternative wet and dry periods, successive hydrated layers are formed on the surface. The differences in refractive index between the bulk and the hydrated layer (or layers) creates an interface between the bulk and the hydrated layer, and between the layers, that stands out sharply when observing a cross-cut section of obsidian under a microscope (see Fig. 23). Thus the thickness of the hydrated layer, or layers, can be measured. 

The rate at which the hydration process proceeds, that is, the amount by which the layer grows in thickness per unit time (e.g., per year), is deter- 

FIGURE 23 Hydration layer in obsidian. When obsidian is broken into two or more pieces, new surfaces are created. As a new surface is exposed to the environment, water (from atmospheric humidity, rain, or the ground) penetrates the surface gradually, the water diffuses into the bulk and forms hydrated obsidian, that is, obsidian containing water. With time, the thickness of the hydration layer, as such a layer is known, gradually increases the rate of increase is affected by such factors as the vapor pressure of the water in the atmosphere, the environmental temperature, and the composition of the surrounding environment as well as of the obsidian. If the hydration layer reaches a thickness of 0.5 microns or more, it becomes discernible under a microscope, the thickness can be measured, and the age of the surface calculated. The microphotograph shows an hydration layer on obsidian. 

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Gan, F., H. Cheng, and Q. Li (2006), Origin of Chinese ancient glasses - Study on the earliest Chinese ancient glasses, Science in China, Ser. E Tech. Sci. 49, 701-713. 

Brill, R. H. et al. (1990), Scientific Investigations of Ancient Glasses and Lead-Isotope Studies, Collected Papers, Lexis Nexis, New York. 

Turner, W. E. S. (1959), Studies in ancient glasses and glass-making processes (VI) The composition and physical characteristics of the glass of the Portland vase, /. Soc. Glass Technol. 43, T262-T284. 

Turner, W. E. S. and H. P. Rooksby (1959), A study of opalizing agents of ancient glass throughout 3400 years, Glasstechnische Berichte 32(K), 17-28. 

Werner, A. E., M. Bimson, and N. D. Meeks (1975), The use of replica techniques and the scanning electron microscope in the study of ancient glass, /. Glass Stud. 17, 158-160. 

Secondary ion mass spectrometry (SIMS) is a widespread analytical technique for the study of surfaces in materials science. Mostly used for elemental analyses and depth profiling, it is particularly relevant for many different fields of research including cultural heritage studies. Reviews of its use for the study of ancient glasses or metal artefacts already exist in the literature [Spoto 2000, Darque-Ceretti and Aucouturier 2004, Dowsett and Adriaens 2004, Adriens and Dowsett 2006, Anderle et al. 2006, McPhail 2006], but as only elemental information is obtained, these studies are limited to inorganic materials. 

An extensive study of ancient glass (first millennium, from Britain) was carried out by Sanderson, Hunter, and Warren (9) using XRF. Because these specimens were only lightly tinted, the interests of the authors were focused on the chemistry of the glass composition and the applicability of XRF to its determination rather than to the identification of the coloring agents. 

Sayre EV, Smith RW (1974) Analytical Studies of Ancient Egyptian Glass, in Recent Advances in Science and Technology of Materials, (ed. Bishay A) Vol. 3 p. 47, New York, Plenum Press Sayre EV (1963) The Intentional Use of Antimony and Manganese in Ancient Glasses, in ... 

SIMS has been frequently used in the study of the deterioration of glass objects. Glass is commonly susceptible to a variety of reactions that affect its durability. Ancient glasses most clearly show the consequences of the relatively limited resistance of this material to attack by water, acid, and alkaline aqueous solutions steam or... 

Study of the trading of ancient glass beads over the Indian Ocean... 

Turner Rooksby (1959) Turner, W.E.S. Rooksby, H.C. A Study of the Opalizing Agents in Ancient Glasses throughout Three Thousand Four Hundred Years Glastechnische Berichte 32K 8(1959) 17-28... 

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