Restoration of Maritime Artifacts - slider-chemistry-12

Restoration of Maritime
Chloride and Sulfate Saturation
Artifacts are often saturated with Cl- and SO42- ions as
these are commonly found in sea water.
 Crystallisation: once an artifact has been brought to
the surface, it can dry out allowing salts of chloride
and sulfate to crystallise. This can destroy the
cellular structure of wooden items as they dry.
 Soaking: to prevent the damage caused by these
salts, wooden items need to soak for long periods in
fresh water solutions to dissolve minerals.
Removal of charged particles by charged electrodes that
attract the charged particles out of organic materials
such as wood or pottery.
+ ions
- ions
Artifacts can also be coated in deposits of sand and
compounds such as CaCO3. These deposits often
form hard, solid coverings known as concretions
or encrustations.
Concretions are commonly
removed by soaking in 1M HCl or a
weaker acid such as acetic acid.
They may also be chipped away.
The photographs show the concretion of a side
plate from a firearm recovered from the ship
Queen Anne’s Revenge. X-rays are used to identify
the object and prevent damage when removing
Restoration of Iron Artefacts
Desalination: Chloride and sulfate compounds must
again be prevented from crystallising, so the object is
kept moist until they are removed by soaking.
To prevent further corrosion due to potentially acidic
conditions in the ocean iron artefacts are commonly
soaked in slightly alkaline solutions of dithionate (S2O42-),
which is reducing agent that prevents further corrosion.
Dilute NaOH is also sometimes used which converts FeCl2
to Fe(OH)2 and releases chloride ions from the surface
and forms a protective oxide layer.
Electrolysis: iron or steel object is placed in
dilute NaOH or Na2CO3 . The artefact is the
cathode (-) where water is reduced:
2H2O + 2e-  H2 + 2OHThe hydrogen gas helps loosen the calcareous
deposits. The anode (+) is a steel mesh that
attracts the negative chloride ions.
Restoration of other metals
Silver: Black Ag2S is a common compound
found on silver artefacts. Electrolysis can be
used to convert this compound back to silver
metal. Again the artefact is the cathode (-) and
the anode is stainless steel.
Ag2S(s) + 2e-  2Ag(s) + S2-(aq)
Copper, bronze, brass and lead can
also be treated by electrolysis.
CuS(s) + 2e-  Cu(s) + S2-(aq)
Leather Restoration
Water and physical means such as soft
brushes and ultrasonic baths can be
used to clean the object of dirt. A mild
detergent may also be used.
Any calcareous deposits can be removed
with dilute ammonium citrate.
Waterlogged leather is then treated with
a polyethylene glycol (PEG) solution
which softens the leather.
Boric acid may be added to the above
solution as a fungicide.
Freeze-drying is then accomplished over
a few weeks.
This leather shoe was found off
Newfoundland from a whaling ship that
sank in 1565

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