184 Chapter 7
4 Conclusions
Glass and ceramics cannot be described with a simple stoichiometric formula,
although both consist mainly of silicon and oxygen. Both are obtained from
very common raw materials, such as sand and clay. Structural changes during
firing turns them into solid and rather durable materials. The complex technol-
ogy behind this simple equation was invented several thousands of years ago
and gave artists the opportunity for creativity and personal expression.
Whereas ceramics are polycrystalline materials, consisting of several
phases (discrete chemical compounds), glass consists of a three-dimensional
network with short-range order. For both, deterioration can occur early due to
daily use or much later during exposure in museums, or due to aggressive soil
environments for archaeological objects or due to weathering of architectural
elements.
Chemical changes on the surface might cause micro-cracks, leading to a
dull appearance of glass. Salt crystallisation can endanger the structure of
ceramics, which may result in crumbling of the ceramic body. For long-term
conservation, a glass might require surface protection, whereas the porous
ceramic body mightneed an in-depth consolidation. Although glass and
ceramics, both derived from silica, are so similar in chemical composition,
the requirements for conservation can be rather different. For glazed ceram-
ics, representing a combination of both materials, a practicable compromise
has to be found for each specific case.
References and Further Reading
D.R. Brothwell and A.M. Pollard, Handbook of Archaeological Sciences,
Wiley, New York, 2001.
S. Buys and V. Oakley, The Conservation and Restoration of Ceramics,
Butterworth-Heinemann, Oxford, 1993.
D.E. Clark and B.K. Zoitos (eds), Corrosion of Glass, Ceramics and Ceramic
Superconductors, Noyes Publication, Park Ridge, NJ, 1992.
S. Davison, Conservation and Restoration of Glass, Butterworth-Heinemann,
Oxford, 2003.
H. Scholze, Glas – Natur, Struktur, Eigenschaften, Springer, Berlin, 1988.
N.H. Tennent, The Conservation of Glass and Ceramics, James & James,
London, 1999.
H. Wedepohl, Glas in Antike und Mittelalter, E. Schweizerbart’sche Verlags-
buchhandlung, Stuttgart, 2003.
A. Wolff, Restaurierung und Konservierung historischer Glasmalereien,
Verlag Philipp von Zabern, Mainz, 2000 (to be translated into English).