have a high degree of cross-linking that imparts good mechanical strength to
these resins. Typical examples in this group include epoxies and polyester resins.
Thermoplastics in the form of a lacquer have poorer mechanical strength than
the thermosetting resins but are more easily removed, should this prove nec-
essary. Polyvinyl acetate and polyurethane are good examples of this class of
consolidants, particularly on wrought iron artefacts. Many of the copper and
copper-based alloys, such as bronzes and brasses recovered from the Mary Rose,
were consolidated with a solution of acrylic resin dissolved in toluene (Incralac).
Waxes are probably the most extensively employed consolidants because of
their versatility. The artefact could be immersed in molten wax, which solidifies
within the pores of the corrosion layers. Naturally-occurring beeswax is a
common example, while microcrystalline waxes are now formulated to meet the
requirements of the conservator such as hardness, colour, melting point, etc. The
surface of the wax can now be further modified by the application of graphite
powder to give an appearance similar to that of a wrought iron finish.
6 Conclusions
In treatment of metal artefacts, the conservation scientist must have knowl-
edge of metallurgy, corrosion and chemistry. Marine artefacts recovered are
invariably covered in concretions but a radiograph helps to ascertain the
shape of the metal underneath prior to removal of this layer. Identification of
the metal or alloy follows, together with mode of manufacture and any ther-
mal treatments used to improve mechanical properties. This information,
together with knowledge of the burial environment, will allow the conserva-
tion scientist to predict the nature of the corrosion products enveloping the
remaining metal and indicate the most suitable method of conservation.
Finally, once the object is conserved, post-conservation treatments must be
carried out or metal corrosion will soon recommence.
References and Further Reading
C. Pearson, Conservation of Marine Archaeological Objects, Butterworths,
London, 1987.
D.A. Scott, Metallography of Ancient Objects, Summer School Press,
Institute of Archaeology, London, 1987.
D.A. Scott, J. Podany and B.B. Considine, Ancient and Historic Metals:
Conservation and Scientific Research, Getty Conservation Institute,
Singapore, 1994.
D. Watkinson, First Aid for Finds, UKIC Archaeology Section, London,
1987.
G. Wranglen, An Introduction to Corrosion and Protection of Metals,
Chapman & Hall, London, 1985.
Metals 159