Home > Chemistry > Options > Shipwrecks, Corrosion and Conservation > Shipwrecks, Corrosion and Conservation: 7. Conservation and Restoration
9.6 Shipwrecks, Corrosion and Conservation: 7.
Conservation and Restoration
Extract from Chemistry Stage 6 Syllabus (Amended
October 2002). © Board of Studies, NSW.
[Edit: 26 Jun 08]
Background: Salvage, conservation and
restoration of objects from wrecks require careful planning.
Artefacts brought to the surface and not treated correctly
may continued to corrode, some at an accelerated rate. Others
are lost because of the inappropriate procedures used to
clean and preserve them. Understanding chemistry is
important in the conservation of marine archaeological
investigations and gather
information from secondary sources to compare
conservation and restoration techniques applied in two
Australian maritime archaeological projects
Conservation is saving or preserving to prevent
further deterioration. It involves cleaning, preserving
and stabilizing an artefact.
Full restoration is restoring an artefact as
close as possible to its original condition. This can
be a much more challenging technique than conservation.
- Gather information to select two
Australian maritime archaeological projects and
compare conservation and restoration
techniques applied. The easiest way to find this
information is by going to the Internet.
The Western Australian Maritme Museum in Fremantle has
information on dutch shipwrecks. One shipwreck is the Batavia.
Scroll down and click on this to obtain more
- You now need to find one other archaeological project in Australia to compare
them. A good place to look is the Australasian
Institute for Maritime Archaeology. What you are comparing are the conservation
and restoration techniques of the projects you have chosen.
that artefacts from long submerged wrecks will be saturated
with dissolved chlorides and sulfates.
Artefacts recovered from shipwrecks are generally in poor
- metals are corroded
- objects are encrusted with calcium carbonate
- porous objects are soaked in seawater rich in
chloride and sulfate salts. Care is required to restore
these artefacts to their original condition.
the processes that occur when a saturated solution evaporates
and relate this to the potential damage to drying
- The solution becomes more concentrated as water
- At some time a saturated solution is formed.
- Further evaporation from the saturated solution results
in the production of salt crystals.
- These salt crystals can form throughout the
- The slower the evaporation of the water the larger the
salt crystals formed.
- The formation of salt crystals can damage the artefact
by pushing it out of shape, causing the object to crack.
Concentrated salt solution may form in air humidity as low
as 50% and then react chemically with the artefact.
the use of electrolysis as a means of removing
- Chloride is difficult to remove from iron objects by
- Insoluble hydroxy chlorides such as Fe(OH)Cl can
be trapped in Fe(OH)2 or
Fe2O3.x H2O deposits.
- Electrolysis is used to free the chloride ions from the
insoluble compounds into the solution.
the use of electrolysis as a means of cleaning and
stabilising iron, copper and lead artefacts
- Artefacts made from metals such as iron, copper and
lead (and their alloys) can be cleaned and stabilised by
In this process the artefact is used as the cathode.
The metal ions in the insoluble corrosion products are
reduced to metal atoms.
The metal atoms formed are deposited on the surface of
An inert electrode such as stainless steel is used as
Various oxidation reactions may occur at the anode
depending on the voltage of the applied current and the
concentration of the anions.
Alkaline solutions such as dilute sodium hydroxide or
sodium carbonate solutions are used as the electrolyte as
the high pH discourages further corrosion of the metal.
Because lead oxide and lead hydroxide are soluble in
alkaline solutions the current should be turned on before
immersing a lead artefact. Care should be taken that
current flow continues while the lead artefact is
Depending on the size of the object and the extent of
corrosion, electrolytic reduction may take days or weeks to
the range of chemical procedures which can be used to clean,
preserve and stabilise artefacts from wrecks and, where
possible, provide an example of the use of each
- Artefacts are subjected to a range of procedures so
they may be preserved.
- The surface deposits of calcium carbonate, including
coral, on the artefact are removed by physically chipping
them away or by dissolving them in dilute acid. (Both
methods should be applied carefully as there is the
possibility of damaging the artefact).
- The artefact is restored by electrolytic reduction to
remove chloride ions and sulfate ions and to reduce metal
oxides and sulfides.
- The artefact is preserved by coating it in a layer of
clear polyurethane polymer or microcrystalline wax.
Detailed descriptions of the
methods used to conserve archaeological material from
underwater sites , Nautical Archaeology Program, Texas
A&M University. Texas, USA.