surface. The presence of flight holes or small piles of frass (insect droppings)
was often the only visible indication that the timbers were infested. Damage
caused by the wharf-borer larvae is often extensive. They produce tunnels
throughout the softer decayed regions of the timbers. Study of polyethylene-
wrapped timbers also indicated that the adult beetle could penetrate the poly-
ethylene enclosure. To prevent infestation of insects, stored archaeological
wooden artefacts should be wrapped in a metallised polyester barrier film and
all edges hermetically sealed.
Biocides have been employed in attempts to control insect and microbial
activity in polyethylene-wrapped timbers. However, their limited efficacy over
time makes re-treatment necessary. This is often time consuming and creates
future problems for conservators in the handling of the wood and in the safe
disposal of the biocide solution. It must also be noted that biocides may inter-
fere with radiocarbon dating and future active conservation treatment processes.
Alternatively cold storage of polyethylene-wrapped wood revealed that the
activity of wood-degrading microbes is arrested. However, the viability of the
bacteria and fungi was not affected by cold storage. The threat of renewed
decay under more favourable conditions therefore exists. Cold storage and
biocide treatments are therefore only suitable for the short-term storage (less
than 1 year) of wrapped timbers where the risk of biodeterioration is con-
sidered low. A number of Mary Rosewrapped timbers were stored in a CO 2
atmosphere. This method was ineffective in preventing wood decay activity,
or the viability of the mixed microbial flora supported by wrapped archaeo-
logical timbers. During a study to evaluate the efficacy of this method, the
anaerobic environment created was found to support the growth of anaerobic
human pathogens, presenting a serious health risk to conservators. In addition,
many fungi are able to grow at very low oxygen tensions, thus presenting a
biodeterioration risk to the wood if complete anaerobiosis is not achieved and
maintained in storage.
In many archaeological projects involving marine wrecks of historic import-
ance, the temporary storage of waterlogged wood all too frequently turns into
longer-term storage while conservation issues, such as funding, are debated or
deferred. Extending passive storage indefinitely may lead to further decay of the
wooden artefact over a period of several years until it is in too poor a condition
for active conservation. To prevent this situation from developing, conservators
have used gamma irradiation to control bacteria, fungi and insects living in poly-
ethylene-wrapped waterlogged wood. It is suggested that gamma irradiation of
waterlogged archaeological wood at a dose sufficient to kill biodeteriogens but
not have adverse effects on wood quality could be an effective passive conser-
vation treatment for the long-term storage of waterlogged wood. The application
of irradiation as a means of killing microorganisms and insects has been exten-
sively researched in the field of conservation. A number of workers have
Conservation of Ancient Timbers from the Sea 289