Conservation
Now that the Hamilton and Scourge
have been found and investigated, they may need to be conserved, especially if they are
ever raised. Click on a topic below to learn about various issues in conservation
(including information provided by Cliff Cook of the Canadian Conservation Institute).
Conservation
and Protection - An example from the Vasa
Now that more and more underwater sites are
being discovered the question of what to do with the vessels and the artifacts found must
be answered. Each government has its own answers but the debate rages as to who actually
owns the wrecks and what measures must be put in place to conserve and protect the sites
from destruction.
The recovery of the Vasa from Stockholm
harbour in 1961 marked a revolutionary event in underwater archaeology. This 17th century
war ship was raised in successive stages by passing heavy steel cables in tunnels dug
below the hull. The raising of the ship to the surface represented an extraordinary
technical feat.
The work did not end here though. Conservation
of the metal and wooden artifacts associated with the ship was an enormous problem to the
technical teams charged with preserving the remains once exposed to air.
Conservation
of Wood: the Vasa
Wooden artifacts from the Vasa was
preserved by impregnating the water-logged wood cells with a water soluble wax-like
chemical called PEG (polyethylene glycol). When the Vasa was raised in
1961, the 700 cubic metres of wood from the hull and artifacts (mostly oak) in need of
conservation presented an opportune test case. For the artifacts. experimentation
demonstrated that PEG was most effective after being diluted and heated to 65 degrees
Celsius. After 17 months of soaking in a tank each piece of wood was dried for six months.
At the end of this period PEG accounted for 40% of the weight of the wood. Conservation of
all wooden artifacts took almost 20 years. The ship's hull was kept intact and
sprayed with a PEG solution for 206 months and then was slowly air dried for many years
(source: Brigitta Hafors, "The Drying pattern of the Outer Planking of the Wasa
hull" in Waterlogged Wood Study and Conservation, Proceedings of the 2nd ICOM
Waterlogged Wood Working Group Conference, 28-31 August 1980, ed. Regis Ramiere and Michel
Colardelle, pp. 313-326).
In view of the cost and time involved for PEG
treatment, alternatives are now being sought by conservators. A treatment for artifacts
that has been extensively researched in Canada involves freeze-drying wood under reduced
pressure. This technique was derived directly from industrial and medical research. Vacuum
freeze-drying will vaporize the ice in the artifact without melting it, thus limiting the
drying stresses within the structure of the degraded wood. Impregnation of the wood with
PEG is still an essential step in the freeze-drying process.
Preserving
Iron Artifacts
Metals brought up from a salt-water environment
are threatened as soon as they are exposed to air. The main cause of deterioration occurs
when salt (sodium chloride) combines with the metal which then crystallizes upon exposure
to air. Conservation techniques such as electrolysis (see the next paragraph for details)
are aimed at eliminating salt crystallization in a gradual but effective manner.
The metals found on the wrecks of the Hamilton
and Scourge will not require extensive chloride removal when compared to those
recovered from salt water sites. The most common metal will be iron, but there will
also be copper alloys (i.e.: brass) and probably lead. In all cases, the objects
will have to be kept wet after excavation until they can be cleaned and stabilized.
It is much easier to remove sediment or encrustations that have not dried out. To
aid in cleaning, and to remove any soluble salts that might be present, electrolysis might
be used. Electrolysis is especially effective at cleaning and stabilizing cast iron
- the material that most of the cannon on the ships are made from. After cleaning,
metal artifacts are usually washed with distilled water to remove residues of soluble
salts and other chemicals. The metal can then be dried. The final step is
almost always the application of a protective surface coating (source: Katherine Singley, The
Conservation of Archaeological Artifacts from Freshwater Environments, 1988).
In-Situ
Preservation
A new concept in the conservation of underwater
sites has recently emerged. Underwater objects may be kept in situ, which means in place,
to alleviate the problem of conserving large-scale metallic or wooden artifacts. Wrecks
left in place on the ocean floor or lake beds can be stabilized underwater and converted
into a monument which can be visited by the diving public. This approach has been used
with 22 wrecks found in Fathom Five
National Marine Park at the mouth of Georgian Bay. These wrecks are preserved in
the water and are visited by thousands of divers each year.
Similarly, the wreck of the Célèbre, a warship
built in 1755 and sunk during the siege of Louisbourg
in 1758, has been left intact for divers to visit. Divers are presented with a map of the
wreck site to guide their visit. This type of approach represents an original solution to
the problem of conserving or excavating wrecks in their entirety.
Another type of in-situ preservation is the
burial or re-burial of historical material after excavation and study. Between 1980
and 1984 the wreck of the San Juan, a 16th century whaling ship sunk in Red Bay, Labrador,
was excavated and dismantled piece by piece for study by Parks Canada marine
archaeologists. The complications and costs that would be result from extensive
conservation of the remains were avoided by reburial on the bottom of the harbour of most
of the wreck. The individual components were placed in three layers surrounded with
sand and the entire mound was covered with a geotextile to keep the wreck protected
(source: John Stewart and Lorne Murdock, "Reburial of the Red Bay Wreck
as a form of Preservation and Protection of the Historic Resource," in Material
Issues in Archaeology IV: Symposium held May 16-21, 1994, Cancun, Mexico. pp.
791-805).
Conservation Issues for the Hamilton & Scourge
The question of conserving the hulls and
the artifacts from the Hamilton and Scourge is a complicated and
controversial one. It is worth noting that the environment surrounding the vessel is
probably the most amenable one possible for preserving cultural resources in an underwater
archaeological context. The depth of the water and the resulting low temperatures and low
light penetration, combined with the lack of salinity, has most likely reduced the rate of
deterioration of the ships and associated material.
If the hulls or associated artifacts were
excavated, the freshwater nature of the environment would greatly shorten the time
required for cleaning and conservation when compared to cultural material from salt water
environments. However, the massive long-term problem of hull conservation
remains the most important project consideration. If the ships are ever raised, some
of the conservation techniques outlined on this page will likely be employed.
Learn more about work on
Other Ships
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