Metals conservation, or more precisely conservation-restoration of metals is the activity devoted to the protection and preservation of historical (religious, artistic, technical and ethnographic) and archaeological objects made partly or entirely of metal. In it are included all activities aimed at preventing or slowing deterioration of items, as well as improving accessibility and readability of them as objects of cultural heritage. Despite the fact that metals are generally considered as the relatively permanent and stable materials, in contact with the environment they deteriorate gradually, some faster and some much slower. This applies especially to archaeological finds.
It is very important that a conservator of metals has knowledge of basic metalworking techniques,history of metalwork, history of art, archaeology, corrosion of metals, scientific research methods, theory and ethics of conservation-restoration.
An essential cause of deterioration is corrosion of metal objects or object deterioration by interaction with the environment. As the most influential factors of deterioration of historical objects should be pointed out as the relative humidity and air pollution while in archaeological objects a crucial role has composition, depth, humidity and amount of gasses in the soil. In cases of marine or fresh water finds the most important factors of decay are the amount and composition of soluble salts, water depth, amount of dissolved gases, the direction of water currents and the role of both microscopic and macroscopic living organisms.
Asals deteriorate depending on the origin whether they are organic or inorganic materials. Organic materials usually fail in a relatively short period of time, primarily due to biodegradation.With inorganic materials are these processes considerably longer and more complex.Amount of gases,humidity,depth and composition of soil are very important . In case of salty and sweet water finds essential are amount of gases dissolved in water,depth of water,direction of currents ,and microscopic and macroscopic living organisms.
As with the conservation and restoration works on any other material, here are the basic tenets of conservation-restoration based on the quality of execution and the best possible preservation of cultural , historical and technological identity and integrity of objects. Minimal intervention , reversibility and repeatability of preferred treatment are essential, as well as the possibility of easy identification of restored parts. Recently non-toxic nature of used materials and procedures becomes important too, both in relation to objects and conservator-restorer as a performer,but also in relation to the environment.
Nowadays scientific research is an integral part of the metals conservation treatment ,at least in highly developed countries.
In preparing the strategy of the metals conservation project interdisciplinary approach to the same is essential.It implies the participation of as many experts as is possible , as a minimum, we can take curator (archaeologist, historian, art historian), scientists specialized for corrosion of metallic objects of cultural heritage and the conservator - restorer.
Systematic and well-managed documentation is today an essential prerequisite for quality executed conservation and restoration treatments , including documentation of the state of objects before, during and after treatment. Identification of materials and procedures used to produce object and the results of any scientific research must be part of documentation too.Last but not least- an integral part of the documentation must be a recommendation for further care of object.
The ethical concept of conservation of metal objects in principle is the same as those in other fields of conservation-restoration of cultural heritage.
But there are several specific problems that can only be found in the conservation of metals - problem of heat treatment of archaeological objects, and the problem of radical restoration of historic, mostly technical, but also architectonic objects too.
While in the first case problem is primarily in the destruction of valuable scientific data, in case of the technical, the architectural, and somewhat less often, historical objects problem is that a radically restored items just simulate the original appearance of the object, and so in some ways that objects can be considered even as ,more or less successful fakes, which only superficialy simulate long-lost or never existing state of object.
According to the above-mentioned ,whenever it is possible real historical substance must be preserved.Thoroughly documented and technically professionally executed restoration of objects,must be avoided because such objects must be seen only as freshly painted surrogates of authentic historic substance.
Ethical problems connected with conservation of sacred metallic heritage objects objects can be included too[1]
Metallic heritage objects are sensitive to environmental conditions such as temperature, humidity ,air pollution and exposure to light and ultraviolet light. They must be protected in a controlled environment where such variables are maintained within a range of damage-limiting levels.
Preventive conservation is an important element of museum policy and collections care. It is an essential responsibility of members of the museum profession to create and maintain a protective environment for the collections in their care, whether in store, on display, or in transit. A museum should carefully monitor the condition of collections to determine when an artifact requires conservation work and the services of a qualified conservator.
The simplest and most common procedure(but it can be very complex too) . We distinguish between mechanical, chemical, electrochemical, ultrasonic and laser cleaning. In principle, aimed at removing of dirt and corrosion products.
Aimed at strengthening of the physical structure of the object, and correcting the shape of the object.
In certain cases, metals conservator must re-create the lost parts of objects or restore original surface decoration . This approach is accurate only if we have an exact documentation or photographs of items in a complete, currently non-existent state that we want to return.
New parts must be clearly and visibly marked and at least they must be minimally different from the original historic material.
If needed, those parts must be easily and completely removable from the object, and with methods which will not harm it.
Focused on slowing of deterioration of objects - in case of archaeology objects the thorough removal or blocking of chloride salts.In case of the historical objects it is focused on the use of corrosion inhibitors ,conversion coatings ,rust converters or eventually oxygen free storage.
Still mainly focused on use of clearcoats and waxes,in case of technology objects oil coatings can be used too. In general it supports the stabilization process.
Paraloid B 72
durable and non yellowing acrylic resin,chemically an ethyl methacrylate copolimer.It can be used for conservation of metals.Soluble in acetone,toluene ,xylene,Shell Cyclo Sol® 100/Shell Cyclo Sol® 53,Arcosolv® PM/1-Methoxy-2-propanol[2].
Paraloid B 67
is acrylic resin, chemically it is an isobutyl methacrylate polymer.Soluble in toluene, xylene,acetone,Shell Cyclo Sol® 100/Shell Cyclo Sol® 53,Arcosolv® PM/1-Methoxy-2-propanol[3].
Paraloid B 44
is acrylic resin,chemically it is composed of methyl methacrylate and ethyl acrylate copolimer.Soluble in toluene, xylene, acetone.It is used for paints and clear coating for metals. It is ingredient in Incralac metal coating[4].
Paraloid B 48 N
is acrylic resin,chemically it is copolymer of methyl methacrylate and butyl acrylate.It is used as a clear coating for metals - copper, brass, bronze, and zinc.Soluble in toluene, xylene, methyl ethyl ketone, and acetone[5]
Incralac
is special proprietary clearcoat for copper and its alloys.It is based on Paraloid B 44 acryilic resin dissolved in toluene.It contains benzotriazole as copper corrosion inhibitor too[6].
Nitrocellulose lacquer
is solvent based lacquer that contain nitrocellulose, a resin obtained from the nitration of cotton and other cellulostic materials[7].Can be used on silver objects.Frigilene ,Agateen No.27 and Perlitol RE 1260 are good brands.
ORMOCER
Organically modified ceramic, also known as ORMOCER (ORganically MOdified CERamic) is a type of coating used in the conservation of metals. ORMOCER was originally developed by the Fraunhofer Society for the Advancement of Applied Research in Munich. While it is still in research phase, ORMOCER is essentially a heteropolysiloxane based clear-coat[8].
Renaissance Wax
is a brand of microcrystalline wax polish that is widely encountered in antique restoration and museum curation. Although not appropriate for all materials, it is known to and used by almost every collection. It is also used as a primary finish for cabinetry and furniture. Renaissance wax is also used by reenactors of historic swordsmanship to protect armour and weapons. It is widely recognised that this substance is more protective and longer lasting than oil, especially for swords and helmets that are frequently touched by human hands.
To quote a typical commercial supplier of conservation materials, it is used, to revive and protect valuable furniture, leather, paintings, metals, marble, onyx, ivory etc. Freshens colours and imparts a soft sheen[9]
Cosmolloid 80 H
is refined white microcrystalline wax.It can be used on historical and archaeological metals.Melting point 60-94 C.Soluble in benzol, ether, chloroform, carbon disulfide, carbon tetrachloride, turpentine, petroleum distillates, and fixed oils; partially soluble in acetone, diacetone alcohol. Main ingredient in Renaissance Wax.
Dinitrol 4010
is a long term engine protection proprietary product with heat resistance up to 200 C. It leaves a firm transparent film with short drying time and good adhesion and flexibility on all metal surfaces, rubber and plastic parts. Dinitrol 4010 is resistant to alkali and acidic solutions. According to some research articles it can be used on metallic heritage objects too[10]
The items should be stored in rooms that are protected from polluted air, dust, ultraviolet radiation, and excessive relative humidity - ideal values are temperature of 16-20 °C and up to 40%(35-55% according to recent Canadian Conservation Institute recommendations) relative humidity, noting that if metal is combined with organic materials, relative humidity should not be below 45%. Archaeological objects must be stored in rooms (or plastic boxes)with very low relative humidity, or in the case of particularly valuable items in the chambers with nitrogen or argon. Objects with active corrosion of copper or copper alloys up to 35% RH. Iron objects with active corrosion 12-15% RH. Shelves in the storerooms must be of stainless steel or chlorine and acetate free plastic or powder coated steel. Wood and wood based products(Particle board, plywood) must be avoided. Also do not use rubber, felt or wool .When you are handling metal objects,always wear clean cotton gloves . Lighting levels must be kept below 300 lux (up to 150 lux in case of lacquered or painted objects,up to 50 lux in case of objects with light sensitive materials)[11]
Centro Nacional de Conservacion y Restauracion,Santiago de Chile,objetos arqueológicos, etnográficos e históricos
The University of Melbourne,Centre for Cultural Materials Conservation
Universitaet fuer Angewandte Kunst,Wien,Konservierung/Restaurierung von Objekten
Koninklijke Academie voor schone kunsten,Antwerpen,metalen conservatie
Sveučilište u Dubrovniku,konzervacija restauracija metala(BA+MA)
Hungarian Academy of Fine Arts,Budapest,conservation of metalwork and goldsmiths works
Instituto Centrale per il Restauro,Roma
Instituut Collectie Nederland,Amsterdam,metallrestauratie
Nicolaus Copernicus University in Torun, Institute of Fine Art, Department of Conservation and Restoration of Historic and Artistic Works, graduate program , metal conservation
La Chaux de Fonds,Haute Ecole de Conservation-restauration Arc,objects conservation
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11.METAL 01,Proceedings of International Conference on Metal Conservation,Perth 2002.
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13.METAL 07,Proceedings of International Conference on Metal Conservation,Amsterdam 2007.
14.METAL 2010.,Proceedings of International Conference on Metal Conservation,Charleston 2011.
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19.Selwyn,L. Metals and Corrosion-A Handbook for Conservation Professional,Ottawa 2004.
20.Draymann-Weiser,T. Gilded Metals-History,Technology,Conservation,London 2000.
21.Draymann-Weiser,T. Dialogue/89 - The conservation of bronze sculpture in the outdoor environment : a dialogue among conservators, curators, environmental scientists, and corrosion engineers ,Houston 1992.
22.Dillman,P.;Beranger,G.;Piccardo,P.;Matthiesen,H. Corrosion of metallic heritage artefacts-Investigation,Conservation and Prediction of long term behaviour,Cambridge 2007.
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24. Rodgers,B. The Archaeologist Manual for Conservation-A Guide to Non- toxic,Minimal Intervention Artifact Stabilization,New York 2004.
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28.La Niece,S.;Craddock,P. Metal Plating and Patination: Cultural,Technical and Historical Develpoments,Boston 1993.
29.Horie,C.V. Materials for Conservation,Oxford 2010.
30.Smith,R.D. Make all sure : the conservation and restoration of arms and armour,Leeds 2006.
31.Appelbaum,B. Conservation Treatment Methodology,New York 2007.
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1.The Use of Expert Systems in Conservation
2.The Modular Cleaning Program
3.Download free conservators documentation software
2.BROMEC - Bulletin of Research On Metal Conservation
6.UCLA metals course-archived presentations
7.Society for Historical Archaeology-Conservation FAQ and facts
8.Building Conservation-articles on metals conservation
10.R.W.Hoge:Conservation Rules for Coins and Medals
11.A Framework for Conservation of metals
12.Recognizing Metals and their Corrosion Products
13.*Schotte,B.Adriaens,A. Treatments of Corroded Lead Artefacts - An Overview
14.A Simple Guide for Archaeological Materials Characterization
17.Metallography and Microstructure of Ancient and Historic Metals-download free book
18.Ancient and Historic Metals-Conservation and Scientific Research-download free book
19.METAL 2004-proceedings of conference
20.Big Stuff 2004.- conference papers
21.Big Stuff 2007.-conference papers - DEAD LINK
23.Hamilton,D. Methods of Conserving Archaeological Material from Underwater Sites
25.Native American Jewelry Conservation Project: Part 2
27.Siano,S. Laser Ablation in Conservation of Artworks
28.CCI Notes 9/2 Storage of Metals
29.CCI Notes 9/1 Recognizing Active Corrosion
30.CCI Notes 9/4 Basic Care of Coins and Medals
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35.Bailey,G.T. Stabilization of wrecked and corroded aluminium aircraft
36.CCI Notes 9/3 The Cleaning,Polishing and Protective Waxing of Brass and Copper
37.CCI Silver Care and Tarnish removal
38.CCI Notes 9/8 Mechanical Removal of Rust fom Machined Ferrous Surfaces
39.CCI Notes 9/5 Tannic Acid Treatment
40.Care and Conservation of Pewter
41.Conservation of lead sculpture
42.Conservation of lead and lead alloys
44.Watkinson,D. Conserving cultural material : Ethical challenges for the conservator
46.Minimum Common Standards Definition – Model Curricula Metals -EQF Level 7 - ECPL
47.Laboratorie d archeologie des metaux,Nancy
48.The TIGHAR Guide to Aviation Historic Preservation Terminology
49.Hayha,H.THE HISTORY OF IRON PROTECTION. DESCRIPTION OF MATERIALS AND EVALUATION OF THEIR PROPERTIES
50.La técnica radiográafica en los metales históricos(english translation included),Madrid 2011.
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55.Care and Handling of Bronze Objects
56.Wanhill,R.J.H. Brittle archaeological silver- identification,restoration and conservation
58.Conservation of iron and steelwork in historic structures and machinery/Maintenance handbook
59.Finishing Techniques in Metalwork
1.Conserving Bronze: The Lamp with Erotes from Vani
2.Caring for Metals - Housekeeping for Historic Sites
3.USS Monitor Engine Removed from Water
4.Laser Cleaning of Bronze Eagle in Oak Park
5.Re-Constructing Silver Objects from the Staffordshire Hoard
6.Erik Risser Describes the Conservation of the Apollo Saettante at the Getty Villa
7.CoinScubber - Cleaning Ancient Coins
8.Cleaning an Outdoor Sculpture Part I
9.Parlament Wien, Quadriga, Restaurierung, Bronze
11.Repatination of a Bronze WWII Memorial Plaque
12.how to care for bronze sculptures
13.Restoring an Artifact at the SCCRRMM
14.Clemson Conservation Center: H.L. Hunley submarine - Part 1/3
15.NCPTT Iron Fence Repair - Cemetery Monument Conservation
16.Restoration of the USS Monitor