conservation

general conservation

• Conservation involves the stabilization and long-term preservation of cultural materials such as:

  • Artworks

  • Textiles

  • Archaeological objects

knowledge required

• Chemistry

• Corrosion

• Material science

• Understanding how different materials react with chemicals is crucial for stabilization.

artefact preservation

• Artifact preservation is vital when recovering materials from marine archaeological sites.

• Artifacts from saltwater environments are often well-preserved but fragile.

• Generally, artifacts from anaerobic marine environments (buried in sediment) are in better condition than those from aerobic environments (water column and surface sediment).

in situ preservation

• The term ‘In Situ’ means on site.

• Some artifacts can remain in their original location for conservation.

• It should be the first option; removal from the site should be a last resort.

• In Situ techniques include:

  • Reburial of remains (sediment blocks oxygen, preventing corrosion).

  • Using a sacrificial anode (more reactive metal) to protect less reactive metals.

siliceous material storage

• Store artifacts in the solution they were found in (e.g., seawater).

• Steps to conserve:

  1. Wet the pottery.

  2. Remove concretion and insoluble salts with dilute acid.

  3. Rinse pottery to remove acid.

  4. Remove iron oxide (rust) stains with $10%$ oxalic acid or $5%$ EDTA and rinse off.

  5. Remove iron sulfide and organic stains by immersing in $10-25%$ hydrogen peroxide.

  6. Consolidate with dilute PVA or Acryloid B-72, then reconstruct if necessary.

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wood conservation

• Storage: Must be in an airtight container of liquid (usually seawater) away from oxygen.

• Transport: Should be done quickly to prevent drying, which can cause cracking and disintegration.

• Conservation Process:

  • Incorporate a material into the wood for strength while removing water (e.g., Polyethylene Glycol - PEG).

  • Remove excess water to prevent shrinkage or distortion (freeze drying).

pPEG polyethylene glycol method

• PEG is a synthetic wax that dissolves in water and alcohol.

• Steps:

  1. Clean the wood surface.

  2. Place the object in a ventilated vat with PEG solution.

  3. Gradually increase the vat temperature to $60,^{\circ}\text{C}$ over days or weeks.

  4. Add more PEG as water evaporates.

  5. Remove the wood, wipe off excess PEG, and cool.

  6. Use a hot air gun or hot water to remove any leftover wax.

sucrose method

• A cheaper alternative to PEG.

• Procedure is similar to the PEG method but uses sucrose instead.

acetone rosin method

• Replaces water in wood with rosin.

• Developed for well-developed hardwood that cannot be treated with PEG.

alcohol ether method

• Initially replaces water with alcohol, then uses ether for drying.

camphor alcohol method

• Displaces water with a water-miscible alcohol, then replaces it with camphor.

• Camphor fills cavities and sublimates without exerting surface tension, preventing collapse or distortion.

freeze drying

• Freezes wood to remove water.

• Steps:

  1. Place wood in PEG solution to kill bacteria.

  2. Freeze and place in a freeze-drying chamber.

  3. Ice crystals sublimate, and water vapor is collected.

  4. Quick freezing in acetone and dry ice is recommended for best results.

metal conservation

• Artifacts from shipwrecks are often in poor condition due to corrosion and encrustation with calcium carbonate.

• Salt buildup can damage artifacts by pushing them out of shape and causing cracks.

• As artifacts are removed from water, evaporation leaves salt behind, which can form at $50%$ humidity.

• Most artifacts are transported in liquid (sodium hydroxide and sodium carbonate) to prevent further corrosion. 

metal concretion removal

• Upon delivery at the laboratory, an X-Ray is taken of the object to determine the condition inside.

• For removing concretion, mechanical cleaning is the most useful technique.

  • Hammers, chisels, etc., are used to chip or scrape away concretion from the metal.

  • Some of the calcium carbonate can be rinsed in a dilute hydrochloric acid to dissolve the encrustation.

  • Disadvantage: This method can take a while.

The artefact is then rinsed in deionised water, dried, and a sealant applied. Recovered artifacts need to be covered with a protective coating to insulate the metal from the effects of moisture, chemically active vapors, and gases.

artefacts must be

• Impervious to water

• Natural looking

• Transparent (clear)

• Reversible

Artefacts are stored below 60% humidity to prevent further corrosion.

Metal Electrochemical Cleaning

Electrochemical and electrolytic reduction cleaning processes are the most common techniques utilized to halt, stabilize, and even reverse the oxidation of the metal.

• Electrochemical reduction cleaning:

  • Involves two metals, one more reactive than the other, in an electrolyte solution.

  • The more reactive metal loses its ions to the least reactive and therefore corrodes, protecting the lesser reactive metal (sacrificial anode).

metal electrolytic cleaning / electrolysis

The essence of the technique involves setting up an electrolytic cell with the artifact to be cleaned as the cathode.

• An electrolytic cell consists of:

  • A compartment or vat with two electrodes: the anode and the cathode.

  • Contains a suitable electricity-conducting solution called the electrolyte.

  • An electric current from an external direct current (DC) power supply is applied to cause oxidation and reduction.

anode and cathode functions

• The anode is the positive terminal of the electrolytic cell:

  • Electrons, negatively charged ions, or colloidal particles travel here when an electric current is passed through the cell.

  • Oxidation occurs at the anode, and oxygen is evolved.

• The cathode is the negative terminal of an electrolytic cell:

  • Positively charged metallic ions travel here.

  • At the cathode, reduction takes place, and hydrogen is evolved.

  • In the reduction process, some of the positively charged metal ions in the compounds on the surface of the artifact are reduced to a metallic state in situ.