292 Chapter 11
light are often used for the storage of smaller items. The advantage of this
type of container is that it can be placed in a cold storage room. For larger
wooden artefacts (gun carriages, etc.) recovered from marine wreck sites,
purposely built tanks are required and are constructed from a variety of mate-
rial, such as polyethylene, GRP and stainless-steel tanks. These tanks are
lidded to prevent light penetration. All water storage tanks are usually kept
inside a building to prevent exposure to temperature extremes.
Although this method is successful in preventing moisture loss from stored
waterlogged archaeological wood, growth of slime and wood degrading organ-
isms is often observed. From time to time it is necessary to control the growth
of microorganisms within storage tanks. Cool temperatures alone are not
able to prevent slime formation, but can help in retarding its development.
Bio-control using snails (Physasp.) or fish (perch) has proved effective in con-
trolling bacterial slimes, while ultraviolet light performs relatively poorly. The
poor penetrative powers of ultraviolet radiation limit its application to surface
sterilisation of water-stored timbers, but ultraviolet radiation has been used
as a means for reducing algal growth in freshwater storage tanks containing
heavily degraded archaeological wood.
Biocides have also been employed in attempts to control microbial growth
within water storage tanks. However, the hazardous nature of biocides to
the conservator and environment and their limited efficacy over time makes
re-treatment necessary at regular intervals. When considering the use of bio-
cides, several factors need to be considered: (i) effectiveness, (ii) resistance to
biocide,(iii) toxicity and (iv) compatibility with the stored artefactal material.
Often biocides tend to be more effective on certain groups of organisms. Before
choosing a biocide, the agents of decay should be identified and a suitable
concentration to control the problem determined. Some organisms such as
bacteria have the ability to become resistant to a biocide (usually a genetic
ability). This problem of resistant strains of bacteria emerging often necessi-
tates a change in the type of biocide. A biocide should not pose a health haz-
ard to operatives applying it and should be compatible with future conservation
treatment methods. A list of biocides used in the control of microbes and insects
include phenols, chlorophenols, orthophenyl phenol, thymol, amphoteric sur-
factants (Tego), salicylanilides, quaternary ammonium compounds, hypochlo-
rites and boric acid/borax.
More recently, metal ions and ion complexes (copper:silver ion disinfection
technique) have been used to disinfect conservation water storage tanks con-
taining waterlogged archaeological wood. The special properties of copper as
a bacteriocide, fungicide and an algicide, and silver as a bacteriocide are well
documented. Copper and silver are introduced into the tank by the ionisation
of Cu:Ag alloy electrodes and it is recommended that the treatment solution
does not exceed 7.4 pH or there is the likelihood of the copper coming out of