Archaeological glass alteration products in marine and land-based environments : morphological, chemical and microtextural characterization

Abstract A study was performed on the natural degradation of glass from Italian archaeological sites, both marine and land-based, with the aim of understanding the role that the chemico-physical conditions of the environment had on the morphology and composition of the alteration products. Marine samples shows two different textural morphologies of alteration: multiple layers of iridescent lamellae in colored glass, or an opaque white crust on the surface of colorless glass, characterized by a spongy, distorted, ramified structure extending more and more deeply into the bulk of the glass. Buried glass presents only iridescent lamellae as alteration products. These are mainly composed of a hydrated ‘silica gel’, differing essentially in the extension of alteration lamellae in both submerged and buried glass. The principal events in the process may be summarized as ion exchange reaction, which causes selective leaching of alkalis and protons entering the glass to produce a hydrated, alkali-deficient layer, and congruent dissolution of the glass matrix, with destruction of the silica network and subsequent precipitation of hydrous silica-gel layers as secondary alteration products.

[1]  A. Paccagnella,et al.  Hydrated-layer formation during dissolution of complex silicate glasses and minerals , 1990 .

[2]  R. Conradt.  A proposition for an improved theoretical treatment of the corrosion of multi-component glasses , 2001 .

[3]  J. Thomassin,et al.  Archaeological glasses as modelling of the behavior of buried nuclear waste glass , 1992 .

[4]  R. Newton,et al.  Conservation of glass , 1992 .

[5]  A. Savitzky,et al.  Smoothing and Differentiation of Data by Simplified Least Squares Procedures. , 1964 .

[6]  Charles M. Nelson,et al.  Obsidian Dating and East African Archeology , 1983, Science.

[7]  G. Libourel,et al.  Using stained glass windows to understand the durability of toxic waste matrices , 2001 .

[8]  Robert F. Martin,et al.  Severe leaching of trachytic glass without devitrification, Terceira, Azores , 1994 .

[9]  Herbert Herman,et al.  Treatise on Materials Science and Technology , 1979 .

[10]  Gianmario Molin,et al.  1.8 ka old glass from the Roman ship Julia Felix: glass–water oxygen isotope exchange , 2004 .

[11]  E. C. Subbarao,et al.  Advances in Ceramics , 1981 .

[12]  S. Hart,et al.  Alteration of basaltic glass: Mechanisms and significance for the oceanic crust-seawater budget , 1983 .

[13]  R. Bertoncello,et al.  An archaeometric study of the bulk and surface weathering characteristics of Early Medieval (5th-7th century) glass from the Po valley, northern Italy , 2004 .

[14]  B. C. Bunker,et al.  Molecular mechanisms for corrosion of silica and silicate glasses , 1994 .

[15]  J. Crovisier,et al.  Dissolution of basaltic glass in seawater: Mechanism and rate , 1987 .

[16]  W. B. Stern,et al.  Potassium–Calcium Glass: New Data and Experiments* , 2004 .

[17]  K. Keil,et al.  Alteration of basalt glasses: implications for modelling the long-term stability of nuclear waste glasses , 1985 .

[18]  H. Scholze.  Glass-water interactions , 1988 .

[19]  S. Buol,et al.  EFFECTS OF FLUCTUATIONS IN THE Eh-pH ENVIRONMENT ON IRON AND/OR MANGANESE EQUILIBRIA , 1970 .

[20]  P. Aagaard,et al.  Thermodynamic and kinetic constraints on reaction rates among minerals and aqueous solutions; I, Theoretical considerations , 1982 .

[21]  G. A. Cox,et al.  The long-term corrosion of glass by ground-water , 1993, Journal of Materials Science.

[22]  G. A. Cox,et al.  The corrosion of glass on the sea bed , 1989 .

[23]  Colin Pearson,et al.  Conservation of marine archaeological objects , 1988 .