Conservation and restoration of shipwreck artifacts

From Wikipedia, the free encyclopedia
Bronze mirror with a cosmological decoration and inscription recovered from the Belitung shipwreck

The conservation and restoration of shipwreck artifacts is the process of caring for cultural heritage that has been part of a shipwreck. Oftentimes these cultural artifacts have been underwater for a great length of time. Without conservation, most artifacts would perish and important historical data would be lost.[1] In archaeological terms, it is usually the responsibility of an archaeologist and conservator to ensure that material recovered from a shipwreck is properly cared for. The conservation phase is often time-consuming and expensive (sometimes costing more than the original excavation), which is one of the most important considerations when planning and implementing any action involving the recovery of artifacts from a shipwreck.

Background[]

Artifacts recovered from a saltwater environment are saturated with salt that must be removed when the artifacts are recovered.[2] Although they are often naturally preserved, they are also fragile and friable. Once these artifacts are exposed to air and light they will degrade rapidly,[3] a concern which highlights the importance of timely conservation efforts. Organic material, such as wood, leather, and textiles, can deteriorate and crumble in a matter of hours if allowed to dry without appropriate treatment. Other materials, such as bone, glass, and pottery, if not conserved, will slowly devitrify and in extreme cases will degenerate into a pile of slivers.[1]

Basic conservation of shipwreck artifacts by material type[]

Bone and ivory[]

Approximately 70% of bone and ivory is made up of an inorganic lattice composed of calcium phosphate and various carbonates and fluorides, and at least 30% is ossein, which is organic. It's difficult to distinguish them unless examined microscopically.[4] Both bone and ivory are easily warped by heat and moisture, and deteriorate by prolonged exposure to water.

Cleaning[]
Removal of soluble salts[]

Bone and ivory being at a saltwater environment will absorb soluble salts and crystallizes when removed from water as the object drys. The salt crystallization will make the surface flake and can destroy the object. In some cases when bone and ivory suffer ossein loss due to hydrolysis, it leaves the calcareous substance; the calcareous substance can cause the materials to fossilise and once organic content is lost resulting in crystallisation, quartz can be formed.[5] The soluble salt must be removed to preserve and stabilize the object when removed from the marine environment. Artifacts of these type of material is recommended to remove all the soluble salts with the use of water.[4]

Removal of stains[]

It is recommended to use mechanical methods over chemical treatments, if chemical treatment is inevitable always make sure that the material is thoroughly wetted with water before any chemical is applied.[4] If the object has iron stains, oxalic acid is used to remove it. Is the object has sulfide stains, oxalic acid is used.

Impregnation and drying[]

To dry bone and ivory it requires a series of alcohol baths. Bone is a material prone to cracks and splits during the dehydration process. If the bone has been established as weak and unstable, and that dehydration can cause cracks and splits to the bone structure, the bone is impregnated prior drying with the use of 50% solution of polyvinyl acetate (PVA(C4H6O2)n) in distilled water.[6] For ivory it is sometimes necessary to go through longer dehydration baths to insure that the surface of the treated material does not delaminate or crack.[4]

Glass[]

Glass is made from silica and a variety of other components that gives the glass color. Glass, usually, is also referred to the most stable of archaeological materials, but glass artifacts, and glass from the 17th century can go through complex disintegration. Normally glass consists of 70% to 74% silica, 16% to 22% alkali and 5% to 10% of flux. The other components and mineral compounds from glass can leach out over time, causing iridescent rainbow patterns and flaking of the outer surface of glass[7]

Conservation[]

Determining the selection of materials and treatment for the glass depends on the level of preservation of the glass. To remove surface corrosion must be made case-by-case bases. The removal of corrosion over the glass surface may significantly reduce the thickness of the walls and weaken it significantly. The removal of surface corrosion can also make the surface blur and/or alter surface details. The corrosion layers on the glass may be part of the object's history and should not be removed without good reasons.[8]

Cleaning[]

When determined to be cleaned, highly damaged glass, the priority is to consolidate the material, and then undertake cleaning. Deposits can be removed with a soft brush, scalpel, and/or cotton swabs soaked in solvents while the glass object is wet. Painted colors and decorations on the glass surface must be protected with a coating of consolidant.[6] Deposits of metal oxides can also be removed by mechanical or controlled use of chemicals; however, metal oxides are often firmly bonded on the glass surface and sometimes its better not to be removed. Calcareous deposits on the glass surface can represent a significant problem; for cleaning it is recommended to use a scalpel while the object is still wet.[6]

Removal of soluble salts[]

When glass is removed from a marine environment it must past through a process called desalination. Desalination is the process to remove soluble salts. The glass can be submerged on tap water baths and distilled water, exchanging the water regularly. Once the process is completed with the removal of soluble salt, the object can be air-dried or undergo consolidation.[6]

Bonding[]

When glass is fragmented it should be bonded the secure the object's stability and aesthetic integrity. The adhesives used to glue glass fragments must be transparent, reversible and with good adhesion, and must not damage the glass. Paraloid B72 acrylic resin and the Araldite 2020 epoxy resin are preferred for its greater duration. The glass fragments must be cleaned and initially joined with adhesive tape or metal omega clips before the use of the adhesive.[6]

Leather[]

Leather is a porous material made from the skin of an animal. Being in a marine environment leather can deteriorate over time. The water-soluble material such as tannins, fats and oils, components part of leather, can dissolve in a marine environment as a result of the collagen's fiber that is susceptible to hydrolysis.

Cleaning[]

Leather must be washed to remove any ingrained dirt; Its ideal to wash leather with water alone. Depending on the condition of the leather, there are variety of mechanical cleaning techniques that may be used and required. Materials such as soft brushes, water jets, ultrasonic cleaners, and ultrasonic dental tools are effective cleaning tools for leather.[9] When leather is mechanically cleaned with a soft steam of water, soft brushed and sponges can also be used. In the case of consistent impurities, leather can be cleaned by chemical means, with the use of small amounts of non-ionic detergents. The chemical cleaning must be followed with a rinse under a stream of water.[6]

Removal of soluble salts[]

It is necessary to remove soluble salts in leather when removed from a marine environment. The removal of soluble salts, desalination, on leather is done with tap water over an extended period of time.

Metal[]

Astrolabes, coins, and other objects recovered from the Padre Island shipwrecks
Gold Ducat (1724) from the Dutch East India Company (VOC) shipwreck de Akerendam

Metal is a solid material that is hard, opaque, and shiny, with a good electrical and thermal conductivity. Metals are also malleable, this allows for metals to be hammered and formed out of shape without being breaking or cracking.

Conservation[]

The conservation of metal artifacts greatly depends on the damage and corrosion they have, the overall state of the object. Before conservation techniques are applied to a metal artifact, it is essential to be aware of the corrosion products that result from the exposure to different environments. The nature of the corrosion determines, including the understanding of the characteristics of the metal of which an object is made, will also determine the techniques and selection of materials that can be effectively used.[6][10] The corrosion of metals is a spontaneous process of unintentional destruction caused by physical, chemical and/or biological agents. Most metals that are in an underwater environment will corrode to a certain extent until they reach an equilibrium with their surrounding environment. Once the metal objects become stable they can survive for some time underwater unless their environment changes[7]

Pure gold will usually survive underwater for a long period of time without corroding. With silver objects, it will corrode quite easily, become very fragile, and form layers of concretion. Copper, brass and bronze can develop a shiny pitted surface and can become covered with a layer of concretion as well as green or black corrosion. Ferrous metals such as cast and wrought iron and steel usually corrode to form thick concretions that can entirely cover the metal object.[7] Marine organisms such as limpets and molluscs can grasp on the metal surfaces and cause fouling corrosion—corrosion.[6]

Cleaning[]

The cleaning process of metals depends on the level of corrosion, oxides, and/or marine organism (limpets, molluscs, calcareous, etc.) accumulation on the metal's surface. There are several methods such as sandblasting and electrolytic reduction, including other methods done mechanically and chemically.[6]

Ceramic and stone[]

Stoneware recovered from the Belitung shipwreck

Ceramics are made from clay and hardened by heat. Ceramics can also be coated with a protective coating to ensure impermeability. Clay is formed by the alteration of feldspathic rocks under the influence of atmospheric agents, such as rain, rivers, winds and gas releases from the Earth's crust.[6]

There are three types of rock differentiated by physical characteristics resulting from their respective formative processes. These three categories are: igneous or volcanic rocks (basalt, granite, etc.), sedimentary or deposit rocks (limestone, sandstone, arenite, etc.), and metamorphic rocks (marble, slate, gypsum, etc.). Igneous rocks are formed by the cooling and/or solidification of magma and the formation of a dense network of crystals—below the Earth's surface as intrusive rock or on the surface as effusive rock. Sedimentary rocks are formed by the deposition of the remains of other rock caused by the action of atmospheric influences. Metamorphic rocks are formed by the transformation of existing rock through the action of temperature and pressure, which cause profound physical and/or chemical changes.[6]

Conservation[]

The conservation of ceramics and stones depends on the object's preservation, the environment where the objects were recovered and the type and quantity of depositions. Any type of conservation intervention and treatment must be minimal to ensure no damage to the objects or leave any trace, causing it stress.

Cleaning[]

The cleaning of ceramics and stones is done mechanically or chemically. This also depends on the types of accumulation from the marine environment, the state of conservation and the materials of which the object is made. When ceramics and stones are extracted from the sea they may have calcareous and siliceous deposits of marine organisms, deposits and/or infiltration of iron and copper oxides, and organic deposits (algae, bacteria, sponges, etc.).[6]

Removal of soluble salts[]

The removal of soluble salts, desalination, of ceramics and stones is carried out by submerging the objects in clean water that is periodically changed. Tap water is used first as part of the desalination process, followed by distilled water in subsequent baths. It is crucial to proceed gradually in order to avoid the overly rapid release of salts that could cause additional damage to the object.[6]

Removal of calcareous and siliceous deposits[]

The calcareous and siliceous deposits, though difficult to remove as they are fused on the object's surface, can be mechanically removed using surgical scalpels, ultrasonic chisels and pins, pneumatic chisels, pressurized water jets and by other means, since siliceous bonds are very resistant to chemicals and do not react to mild acids and bases.[6] If calcareous deposits cannot be removed mechanically, chemicals are used. Cleaning with chemical compounds must be controlled, and mild substances must be used that cannot damage the physical and chemical structure of the object.[6]

Removal of iron and copper oxides[]

Iron and copper oxide stains occur when oxidized metals are located near or in contact with a ceramic or stone object and metal oxide particles pass to the structure of the stone or ceramic. Iron and copper oxides can penetrate deep into the pores of ceramics and stones and create reddish-brown to black stains (iron oxide) and blue-green stains (copper oxides). The use of EDTA salt solution can be used to remove the oxides. A mild solution consists of 3% to 5% of EDTA; 15% to 20% solution in water on ceramics to remove the stains. Iron oxides can be removed from the objects by the use of water in a 10% to 25% solution of hydrogen peroxide. The time required to remove the stains can vary from a few seconds to several hours.[6]

Bonding[]

When objects are found in a fragmented state, the fragments are bonded with adhesives to achieve stability and the integrity of the object. Before bonding the fragments are held with paper adhesive tape in the exact position to join them prior to final gluing. Objects with sensitive surfaces such as glazing and painted decorations on stones and ceramics should be specially protected to avoid breaking off and/or tearing of the surface with paper adhesive tape. Once the fragments are precisely located they are bonded together with adhesives. The use of strong adhesives should be used to glue large ceramics and most stones.[6]

Ceramic and stone deterioration[]

Degradation and alteration are natural processes in the lifetime of every material. The process is constant and unstoppable, though conservators and restorers can undertake a series of treatments on objects to attempt to slow the process of degradation. The degradation of materials usually happens when objects are removed from the environment in which they were located and had achieved a state of equilibrium, even if the environment is imperfect, and the objects are moved to another environment. Alteration refers to the aging of objects accompanied by changes that do not directly affect their preservation and that do not impair their readability. This category of change includes alterations of color, the formation of a superficial patina on objects and so forth.[6]

Textile[]

Textiles are fabrics and woven objects that are products of other kinds of interlacing of yarns, braiding, looping, knitting, lace making, and netting. The textile category also includes materials such as felts and non-woven materials in which the fibers gain coherence by a process other than spinning.[11] The most encountered textile materials in archeological sites are linen, cotton, wool and silk.

Conservation[]

Textile conservation is limited to the following types of textiles: the natural fibers of animal and plants. Textile can be made of wool, hair, silk, cotton, flax, jute, hemp, nettle, among others. Textiles that are made with the fibers of animals are primarily composed of protein, making it more resistant to decompose, compared to plant fibers that are primarily composed with cellulose. Light, insects, micro-organisms and pollution can cause textiles to deteriorate; making it lose strength and pliability. The normal exposure of the atmospheric conditions can cause textiles to weaken and disintegrate[11]

The conservation of textiles should always be left to a specialist conservator. Before any conservation treatment the composition of the textile must be identified. Testing textiles such as burning a sample can quickly identify the presence of animal fiber, animal fiber will not burn readily and shrivel into a carbon residue. Plant fibers burn easily to a fine ash. Overall simple testings can enable the conservator to identify the type of textile fiber. The proper treatment of textiles requires the use of flat, shallow pans, hot plates, and racks, or other devices that can support fragile textiles during rinsing, treatment, and drying.

Cleaning (removes soil, discoloration and stains)[]

Textiles can be cleaned with water, numerable substances can be removed by using water (de-ionized water preferred). For better results add mixture of .4% to 1% ammonium hydroxide to the water. If necessary, of neutral non-ionic detergent to remove stubborn soil. During the cleaning process bleach can be added in a 4% hydrogen peroxide solution. For stubborn stains such as mold, mildew, black sulfide stains, and organic stains, the fabric is soaked in a solution of 1 liter of de- liter de-ionized water, 60 ml 30% hydrogen peroxide and a 2.5 g sodium silicate dissolved in 100 ml hot de-ionized water. Be aware that the latter solutions are damaging to the fibres, they may reduce the visible staining, but this is through a bleaching action that also deteriorate fibres and will make them more brittle over time.[11]

For textiles that cannot be cleaned with water (such as textiles with water-soluble dyes), dry cleaning using organic solvents, such as perchlorethylene or trichlorethylene, or petroleum solvents, such as white spirits, is recommended.

Sterilization[]

For textiles infested with mold (including insects), the infested textiles must be closed in a container with thymol crystals. After treatment with thymol crystals, a solution of .5% to 1% of Lysol is used. Other disinfection solution composed of .1% of (ortho-phenylphenol), 68% of ethanol, and 30% of de-ionized water; the solution will be lethal to most bacteria, fungal spores, and surface mildews.[11]

Wood[]

Wood, an organic material produced by plants, are chemically composed of: carbohydrates (cellulose and hemicellulose), lignin and other components (aliphatic acids, alcohols, proteins and inorganic substances) in a smaller amount. The most important composition of the plant is the cellulose. The cellulose accounts the majority of the cell from 40% to 50% of the wood's total mass. Hemicellulose represents the second most important carbohydrate with accounts 20% to 30% of the wood's cell.[6]

Conservation[]

Wood recovered from a marine environment is referred to archaeological waterlogged wood. Waterlogged wood is defined as wood that does not contain or contains a small amount of air within its cells (capillaries and micro-capillaries). Archaeological Waterlogged normally looks well preserved; however, it is very weak and deteriorates because of the soluble water substance making it dissolve in marine environments.[6] The cellulose of the wood goes through the process of hydrolysis and attacked by anaerobic bacteria that decompose the wood, leaving it only with the lignin network. Over an extended period of time the lignin network will also decompose. The result of the decomposition of cellulose and lignin will increase in the space between cells and the molecules within cells, this will render the wood to a more porous and permeable to water. All of the wood's cavities will be filled with water, and the absorbed water and the remnants of the lignin will maintain the original form of the woods, meaning that the wood will only retain its original form while its underwater. When wood is found in a marine environment, it is recommended to have secured the required conditions for its conservation (water-filled pool or vessel) to extract the wood from water, to prevent the wood from dehydration.[6] If the waterlogged wood is removed from the marine environment and exposed to air, the water will evaporate and the resulting surface tension forces of the evaporating water cause the weakened cell walls to collapse, creating considerable shrinkage and distortion[12]

Cleaning[]

Waterlogged woods extracted from a marine environment may be covered by impurities and sediments. These accumulations can be removed with water, with the use of soft brushed and increased temperature to 30 °C to remove tougher incrustations. The calcareous shells from the marine environment can be a frequent component of accumulations on the surface of waterlogged wood. The calcareous can be removed mechanically using scalpels of various profiles and sizes. Iron can also be present on the waterlogged wood. The accumulation of iron can be removed by treating the wood with a 5% solution of disodium salt of ethylenediaminetetraacetic acid in water.[6]

Removal of soluble salts[]

The removal of soluble salts, desalination, of wood extracted from a marine environment is crucial. Desalination is done with clean water, with disinfectant added to prevent the development of harmful organisms. The disinfectant fungicide, algaecide, orthophenyl phenol; however, the most commonly used and recommended because of its lesser toxicity is a mixture of boric acid and borax. The desalination process takes a long period of time and is necessary that the water is changed until the concentration of excreted of soluble salts reach its maximum.[6]

Impregnation[]

The conservation of waterlogged wood is a complex process that involves impregnating. The impregnation process involves replacing the water with a material that will strengthen the structure of the wood without causing the wood to contract or come apart.[6] There are different methods used to impregnate wood:[12]

  1. Polyethylene glycol (PEG) method
  2. Sucrose method
  3. Acetone-rosin method
  4. Alcohol-ether method
  5. Camphor-alcohol method

Shipwreck[]

The Thistlegorm, a transport ship, was sunk by a German bomber, during the Second World War
View of the bow of the Titanic
Main article: Shipwreck

A shipwreck is the remains of a ship that has been wrecked, found either on land, beached, or sunken at the bottom of the sea. The United Nations Educational, Scientific and Cultural Organization estimated that over 3 million shipwrecks are spread across the ocean floors.[13] Many artifacts can be found through shipwrecks including gold, jewelry, spears, swords, ceremonial axes and hundreds of other objects.[14]

Causes of shipwreck[]

Main article: Shipwrecking

Many factors will contribute to the causes of a shipwreck: poor design and construction, instability, navigation error, warfare, or overloading, among other factors. Other causes of shipwrecks are related to nature, such as atmospheric (tropical storm, hurricane, rain, etc.), climatic (iceberg), oceanic (current, tide, reef, etc.), or tectonic (earthquake, volcano, tsunami, etc.).

Maritime archaeology[]

Main article: Maritime archaeology

The study of shipwrecks and other underwater artifacts is a discipline known as maritime archeology. Maritime Archaeology is a sub-discipline of the field of archaeology. This discipline studies the history and cultural material related to human interaction on, under, near or associated with the sea.[15] From the study of ships and shipwrecks, maritime infrastructure, maritime exploitation, maritime identities and landscapes, seascapes, and other types of heritage, both tangible and intangible. There are other sub-disciplines like nautical and underwater archaeology but these are more concerned with smaller, more specific areas of the discipline. For example, Nautical Archaeology is primarily focused on the “ship”, including its technical and social aspects, whether the ship is on land, underwater or in a museum. Underwater Archeology focus on the archaeological sites located underwater, regardless of their connection to the sea; it includes shipwreck sites, aircraft wrecks, sunken cities, submerged Indigenous habitation sites, among others.[16]

See also[]

References[]

  1. ^ a b Hamilton, D. (1996). Introduction and Overview of Conservation in Archeology. In Basic methods of conserving underwater archaeological material culture (pp. 1–7). Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program.
  2. ^ Hamilton, D. (1996). Basic Conservation Procedure. In Basic Methods of Conserving Underwater Archaeological Material Culture (pp. 8–11). Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program.
  3. ^ Martin, C. (n.d.). An Introduction to Marine Archaeology. Retrieved from: http://www.bbc.co.uk/history/ancient/archaeology/marine_01.shtml#four
  4. ^ a b c d Hamilton, D. (1996). Bone, Ivory, Teeth and Antler. In Basic Methods of Conserving Underwater Archaeological Material Culture (pp. 16–18). Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program.
  5. ^ Conservation of Underwater Cultural Heritage. (n.d.). Retrieved from: http://www.mecd.gob.es/cultura-mecd/en/dms/mecd/cultura-mecd/areas-cultura/patrimonio/mc/libroverde/capitulos/capitulo6EN.pdf
  6. ^ a b c d e f g h i j k l m n o p q r s t u v w x Luka, B., Martina, Ć, Anita, J., Antonija, J., Mladen, M., Tanja, P., & Mladen, P. (2011). Conservation of Underwater Archaeological Finds. Retrieved from: http://icua.hr/images/stories/publikacije/Conservation_of_underwater_archaeological_finds_Manual.pdf
  7. ^ a b c Information Sheet: Caring for Shipwreck Artifacts in Museums. (n.d.). Retrieved from: http://www.mavic.asn.au/assets/Information_Sheet_Caring_for_Shipwreck_Artefacts.pdf
  8. ^ Hamilton, D. (1996). Glass Conservation. In Basic Methods of Conserving Underwater Archaeological Material Culture (pp. 22–24) Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program
  9. ^ Hamilton, D. (1996). Leather Conservation. In Basic Methods of Conserving Underwater Archaeological Material Culture (pp. 33–36). Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program.
  10. ^ Hamilton, D. (1996). Metal Conservation. In Basic Methods of Conserving Underwater Archaeological Material Culture (pp. 42–48). Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program.
  11. ^ a b c d Hamilton, D. (1996). Textile Conservation. In Basic Methods of Conserving Underwater Archaeological Material Culture (pp. 37–41). Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program.
  12. ^ a b Hamilton, D. (1996). Wood Conservation. In Basic Methods of Conserving Underwater Archaeological Material Culture (pp. 25–32). Washington, D.C.: U.S. Dept. of Defense, Legacy Resource Management Program.
  13. ^ Wrecks. (n.d.). Retrieved from: http://www.unesco.org/new/en/culture/themes/underwater-cultural-heritage/the-underwater-heritage/wrecks/
  14. ^ Anissimov, M., & Harris, B. (n.d.). What Is a Shipwreck? Retrieved from: http://www.wisegeek.com/what-is-a-shipwreck.htm
  15. ^ Maritime Archaeology. (n.d.). Retrieved from: http://www.maritimearchaeologytrust.org/whatismaritimearchaeology
  16. ^ What is Maritime Archaeology? (n.d.). Retrieved from: http://www.aima-underwater.org.au/what-is-maritime-archaeology/
Retrieved from ""