Conservation of Ancient Timbers from the Sea 305
being sprayed with an aqueous solution of PEG 200). The starting concentra-
tion was 10% and over a 10-year period was raised to a final concentration of
40%. In 2006, the hull timbers will be sprayed with a 40% solution of PEG
2000 to consolidate the very decayed outer timber surfaces. This will take
approximately 5 years to achieve optimum levels for surface stabilisation. In
2011, the PEG treated timbers of the Mary Rosehull will be air dried.
5.4 In-situPolymerisation with Radiation Curing Monomers
and Resins
As an alternative to PEG treatment of waterlogged wood, attempts have been
made to use a radiation curing method involving a range of monomers and
resins. The aim of such treatments is to reduce treatment times and achieve a
more stable artefact. Styrene, vinyl acetate, acrylonitrile, acrylates and metha-
crylates are the most studied monomers in the treatment of waterlogged archae-
ological wood. The most widely used of these monomers is the water-soluble
vinylpyrrolidone and methacrylamide and the non-water soluble chemicals
such as n-butyl methacrylate monomer or unsaturated polyester resin.
For water-soluble chemicals, there is direct water monomer exchange, while
the non-water soluble chemical is dehydrated by means of a solvent such as
acetone and then immersed in a solution of the monomer. After a suitable
impregnation period, polymerisation is induced by exposure to gamma rays
emitted by a cobalt 60 source. To date the results achieved for either water-
soluble or solvent-soluble monomers have not given satisfactory results.
Methods using monomers and gamma irradiation require highly-specialised
applications and the process is very costly. In general, such methods should
only be adopted if PEG treatment cannot be used or if waterlogged wooden
objects are heavily contaminated with iron and/or sulfur compounds.
5.5 Drying Following Conservation Treatment
The removal of water from saturated wooden objects without destroying the
object is a significant challenge for conservators.
Air Drying. This is the simplest drying technique in which water undergoes
a phase change to the vapour state, and is removed as such. This technique
can result in unacceptable amounts of damage to a waterlogged wooden arte-
fact because of excessive cell wall shrinkage and collapse. Some type of
treatment is usually applied beforehand to prevent the dimensional response
of an object to drying. Both bulking and lumen-filling treatments are used
before air drying an object. An object having a highly deteriorated surface
with a well-preserved core is usually pre-treated with a combination of a