Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
changes caused by water stratification breaking periodically, for now the environmental conditions are
relatively favorable for long term preservation of the wood of the wreck.
Nevertheless, although the deterioration pattern seen in the actual sample and the analogous samples
seem to correlate and there is a good understanding of the environmental conditions, we do not have a
complete picture of present state of preservation of the hull, nor of the deterioration patterns. The
overall interpretation of all the existing data has not been done properly yet and more samples are
needed particularly from the hull. These have to be analyzed together with the analogous samples.
Significantly, the overall situation of accumulated iron and sulfur in the wood has to be clarified. And
it has to be remembered that there is not only wood down there. The condition evaluation of the iron
parts is so far based mostly on hands-on experiences rather than on research of scientific standards.
For all we know the iron fastenings might have been rusted largely away leaving the whole structure
fragile and unable to withstand stresses such as the possible raising would cause. There is not enough
information about the condition of the artifacts either. The hold is largely intact and it is intended to
remain so to keep all the artifacts there undisturbed until clear decision are made for excavations or
other actions.
Now research and monitoring of the wreck should be continued. There are several ways to proceed.
One would be to leave the wreck as it is and monitor it properly and take protective actions should
there be reasons for those. Another option would be to carry out proper excavations, raising and
conserving the artifacts from the hold. The third option would be to raise the whole wreck and make it
a museum exhibit. Although in-situ preservation would be in accordance with the current international
conventions and statutes, valid arguments for the other options have been raised too. Therefore I now
conclude the article by discussing the possible interventive actions.
If the wreck is to be raised, the fundamental problem is the fact that it is a large composite object made
of several contrasting materials. Conservation methods needed for organic materials are basically
damaging to metals and vice versa. Conserving and storing wood and metals separately is
straightforward enough but together they form a tricky combination. For instance, iron has readily
corroded and fused tightly on and in the wood, spreading corrosion products everywhere in the wood
matrix. Furthermore, plenty of other substances, such as the mentioned sulfur compounds, have
accumulated in the materials. It goes without saying that very dramatic deterioration reactions would
take place rapidly if the whole entity is brought up.
How to preserve it then? Mimicking and maintaining the underwater environment already familiar to
the wreck would be one option, and stabilizing the wreck to withstand new kind of conditions another.
The first option refers to storing and displaying the wreck in some kind of an aquarium – which was
actually suggested to us – and the latter option to more conventional interventive conservation actions
that would stabilize the wreck and display it dry.
In theory not actively conserving the wreck but keeping it in an aquarium replicating the underwater
environment could avoid the sulfur-problem and other difficulties of conserved wrecks, but there are
some serious questions marks, at least considering biological problems threatening the materials and
ruining the visibility in the aquarium. It is hard to keep the water clear and artifacts stable even in a
small tank in conservation laboratory. Many methods have been tried to prevent these biological
problems, but none seems to be satisfactory in such a large scale and in a situation where divers should
be able to go into the aquarium.
One interesting approach was investigated in a recent article by Charlotte Björdal et al, which
discusses the possibility of storing and displaying marine archaeological wood in a sealed aquarium in
anoxic conditions. According to this study, the method works and water should remain clear as far as
the material inside is solely wood, but the presence of iron brings up preservation and visibility
problems. The article concludes that so far wrecks containing iron can not be stored this way. [17]
Another approach after raising the wreck would be to conserve it as has been done with the Vasa for
instance. This would certainly be a very difficult task, mainly because of the presence of contrasting
materials and the mentioned accumulation problems. The sulfur-iron issue is still to be solved,
although good progress is being made in the Vasa project and elsewhere. It seems established now,
that iron has to be extracted from the wood-matrix prior or within conservation, which is a difficult
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