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9.6 Shipwrecks, Corrosion and Conservation: 7. Conservation and Restoration

Syllabus reference (October 2002 version)
7. Salvage, conservation and restoration of objects from wrecks requires careful planning and understanding of the behaviour of chemicals
Students learn to: Students:
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 objects.

perform investigations and gather information from secondary sources to compare conservation and restoration techniques applied in two Australian maritime archaeological projects

Definitions:

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.

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explain that artefacts from long submerged wrecks will be saturated with dissolved chlorides and sulfates.

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describe the processes that occur when a saturated solution evaporates and relate this to the potential damage to drying artefacts.

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identify the use of electrolysis as a means of removing salt

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identify the use of electrolysis as a means of cleaning and stabilising iron, copper and lead artefacts

More detail

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 the artefact.

An inert electrode such as stainless steel is used as the anode.

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 immersed.

Depending on the size of the object and the extent of corrosion, electrolytic reduction may take days or weeks to complete

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discuss 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 procedure

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