Metals conservation



Metals conservation, or more precisely conservation-restoration of metals is the activity dedicated 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 arts, archaeology, corrosion of metals, scientific research methods, theory and  ethics of  conservation-restoration

Metals and alloys commonly used for cultural heritage objects
• 3

Metals and Alloys Less Comonly used for cultural heritage objects
• 3

Basic techniques

 * Casting
 * Forging
 * Folding
 * Sawing
 * Cutting
 * Bending
 * Drilling
 * Filing
 * Piercing
 * Sanding
 * Polishing

Joining techniques
soft
 * Soldering

hard electric arc
 * Welding

tack

oxyacetilene

laser


 * Mechanical joining
 * Gluing/cementing

Some suplementary techniques

 * Repousse and chasing
 * Raising
 * Spinning
 * Annealing

Surface decoration techniques

 * Enameling
 * Niello
 * Engraving
 * Etching
 * Granulation
 * Filigree
 * Inlay
 * Mokume gane
 * Pattern Welding
 * Plating
 * Chemical coloring of metals
 * Heat coloring
 * Combining metals and  other materials

Some Contemporary Techniques

 * Electroforming
 * Reticulation
 * Anodizing
 * Photoetching

Deterioration of metals
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.

Deterioration of materials associated with metals
Associated materials 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.

Organic materials

 * Leather
 * Wood
 * Paper
 * Fur
 * Feathers
 * Textile
 * Bone
 * Horn
 * Tortoiseshell
 * Amber
 * Plant fiber
 * Shell
 * Pearls
 * Ivory
 * Coral
 * Jet

Inorganic materials

 * Precious and semiprecious stones
 * Glass
 * Enamel
 * Niello
 * Ceramics
 * Porcelain
 * Plastics

Ethics and ethical problems in metals  conservation
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 ,successfull 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( is it acceptable that believer of one religion works  on sacred objects that belong to another religious group?).

Identification of metals and alloys
visual examination,spot tests,specific gravity
 * Simple methods

xrf,xrd,pixe,libs,SEM,electrochemical techniques,metallography
 * Scientific methods

Identification of corrosion processes and products
visual examination,spot tests
 * Simple method

xrd,SEM,metallography
 * Scientific methods

Identification of materials  associated with  metals
visual examination,spot tests,specific gravity
 * Simple methods

xrf,chromatography
 * Scientific methods

Identification of technology used to produce objects
visual examination
 * Simple methods

metallography,x-ray radiography,x-ray computed tomography
 * Scientific mehods

Documentation
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.

Basics
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, retreat-ability 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

Preventive Conservation
Metallic heritage objects are sensitive to environmental conditions such as temperature, humidity ,polluted air 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(specially archaeological metallic objects).

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.

Cleaning
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.Archaeology objects must be cleaned only mechanically.


 * Mechanical
 * Chemical
 * Electrochemical
 * Ultrasonic
 * Laser

Structural Consolidation
Aimed at strengthening of the physical structure of the object, and correcting the shape of the object.


 * Mechanical joining
 * Soldering
 * Welding
 * Gluing/Cementing

Reconstruction of missing parts or decorative  surfaces
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.

Stabilization
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 ,or eventually oxygen free storage.


 * Chloride removal(chemical processes,electrochemical processes)
 * Corrosion inhibitors (benzotriazole,tannin)
 * Rust converters˙
 * Conversion coatings(phosphate conversion coatings,phosphate/tannin, etc.)
 * Oxygen free storage

Protective Coatings
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
 * Clearcoats

Paraloid B 67

Paraloid B 44

Paraloid B 48 N

Incralac

Nitrocellulose lacquer

ORMOCER Renaissance Wax
 * Waxes

Cosmolloid 80 H

Dinitrol 4010 WD 40
 * Oils

Ballistol

20 parts fish oil + 80 parts white spirit basecoat Paraloid B 72 + topcoat Renaissance Wax etc.
 * Combinations

Storage of metallic heritage objects
The items should be stored in areas 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 reccomendations) relative humidity, noting that if  metal is combined with organic materials, relative humidity should not be below 45%. Archaeological objects must be kept in rooms ( or 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 must be avoided. Also do not use rubber ,felt or wool .When you are handling metal objects,always wear clean cotton gloves.Ligting levels must be kept bellow 300 lux (up to 150 lux in case of lacquered or painted objects,up to 50 lux in case of objects with ligtht sensitive materials)

History of metals conservation
1.V.Boissonnas:An introduction to the history of metals conservation-presentation

2.Caldararo,N.L. An Outline - History of Conservation in Archaeology and Anthropology Presented through Its Publications

3.A PERSPECTIVE ON THE HISTORY OF THE CONSERVATION OF ARCHAEOLOGICAL COPPER ALLOYS IN THE UNITED STATES,by TERRY DRAYMAN-WEISSER

Specializations within the profession

 * Conservation of Historical Metal Objects
 * Conservation of Archaeological Metal Objects
 * Conservation of Technological Metal Objects
 * Conservation of Etnographic Metal Objects
 * Conservation of Architectural Metal Objects
 * Conservation of Metal Sculpture
 * Conservation of Gold and Silversmiths Works
 * Conservation of Arms and Armour

USA

 * Bufallo State College,Art Conservation Department,objects specialization
 * UCLA/Getty Masters Program - Conservation of Archaeological and Etnographic Materials

Canada

 * Queens University,Art Conservation,objects specialization
 * Fleming College, Collections Conservation and Management

South America

 * Chile
 * Centro Nacional de Conservacion y Restauracion,Santiago de Chile,objetos arqueológicos, etnográficos e históricos

Australia
The University of Melbourne,Centre for Cultural Materials Conservation

University of Canberra, Cultural Heritage Conservation

Europe

 * Austria
 * Universitaet fuer Angewandte Kunst,Wien,Konservierung/Restaurierung von Objekten


 * Belgium
 * Koninklijke Academie voor schone kunsten,Antwerpen,metalen conservatie


 * Croatia
 * Sveučilište u Dubrovniku,konzervacija restauracija metala(BA+MA)


 * France


 * Germany
 * Roemisch Germanisches Zentralmuseum,Mainz,Ausbildung zum Restaurator des Fachbereischs Archeologie
 * Hochschule fuer Technik und Wirtschaft,Berlin, schwerpunkt Archaeologisch-Historisches Kulturgut
 * Staatlische Akademie der Bildende Kuenste,Stuttgart,Objekt Restaurierung
 * Fachhochschule Potsdam,Metallkonservierung


 * Hungary
 * Hungarian Academy of  Fine Arts,Budapest


 * Italy
 * Instituto Centrale per il Restauro,Roma


 * Netherlands
 * Instituut Collectie Nederland,Amsterdam,metallrestauratie


 * Poland
 * Nicolaus Copernicus University in Torun, Institute of Fine Art, Department of Conservation and Restoration of Historic and Artistic Works, graduate program, metal conservation


 * United Kingdom
 * West Dean College,metalwork conservation
 * University of Sussex,metalwork conservation


 * Switzerland
 * La Chaux de Fonds,Haute Ecole de Conservation-restauration Arc,objects  conservation

Russian Federation

 * Akademiya Imeni S.G.Stroganova,Moscow-katedra"Restavraciya hudozhestvennogo metalla"(Conservation of artistic metalwork)

Important older books
1.Rathgen,F. Die Konservierung von Altertumsfunden,Berlin 1898.(chapter on metals  conservation).(online)

2.Flinders Petrie,W.M. Method and Aims in Archaeology,London 1904. (chapter on conservation)(online)

3.Rosenberg,G. Antiquités en fer et en bronze : leur transformation dans la terre contenant de l'acide carbonique et des chlorures et leur conservation ,Copenhagen 1917.

4.Fink,C.G.;Eldridge,C.H. The restoration of ancient bronzes and  other alloys,New York 1925.

5.Galnbek,I.A. Ochistka i sohranenie metalicheskih predmetov drevnosti,Leningrad 1925.

6.Scott, A. The cleaning and restoration of museum exhibits (report upon investigation conducted at the British Museum, Department of Scientific and Industrial Research). London 1921.

7.Scott, A. The cleaning and restoration of museum exhibits, 2d report. British Museum, Department of Scientific and Industrial Research. London 1923.

8.Scott, A. The cleaning and restoration of museum exhibits, 3d report. British Museum, Department of Scientific and Industrial Research. London 1926.

9.Lucas, A. Antiques: Their restoration and preservation. London 1924.(chapter on metals conservation)(online)

10.Nichols, H. W. Restoration of ancient bronzes and cure of malignant patina. Chicago 1930..(online)

11.Plenderleith,H.J. The Preservation of Antiquities ,London 1934.

12.Ocherki po metodike tehnologicheskog issledovaniya restavracii i konservacii drevnih metalicheskih izdeliy ,Moscow 1935.(online)

13.Farmakovskiy,M.V. Konservaciya i restavraciya muzeinih kollekciy ,Moscow 1946.(chapter on metals  conservation)(online)

14.Plenderleith,H.J. The Conservation of Antiquities and Works of Art,London 1956.(chapter on metals  conservation)

15.France-Lanord,A. La conservation des antiquites metalliques,Paris 1962.

Important books in languages other than english
1.Heinrich,P.(Hrsg.) Metallrestaurierung,Muenchen 1994.

2.Stambolov,T.;Bleck,R.D.;Eichelmann,N. Korrosion und Konservierung von Kunst und Kulturgut aus Metall,Weimar I/1987.(online),II/1988.(online)

3.Mourey, W. La conservation des antiquités métalliques, du chantier de fouilles au musée, Draguignan 1987.

4.Volfovsky,C.;Philippon,J. La Conservation des metaux,Paris 2001.

5.Marabelli,M. Conservazione e restauro dei metalli d`arte,Rome 1995.

6.Schemahanskaya,M.S. Restavraciya metalla,Moscow 1989.(online)

7.Minzhulin,O.I. Restavraciya tvoriv z metalu,Kiev 1998.

8.Catello,D Il restauro delle opere in argento.Restoration of silver artifacts,Naples 2008.

9.Meissner,B.;Doktor,A.;Mach,M. Bronze ud Galvanoplastik-Geschichte-Materialanalyse-Restaurierung,Dresden 2000.(online)

10.Mach,M. Metallrestaurierung/Metal Restoration,Muenchen 1997.

11.Krist,G. Metallrestaurierung-Metallkonservierung:Geschichte,Methode und Praxis,Wien 2009.

12.Schmidt-Ott,K. Das Plasma in der Metallkonservierung-Moeglichkeiten und Grenzen,Zurich 2010.

13.Anheuser,K. Im Feuer Vergoldet,AdR-Schriftenreihe zur Restaurierung und Grabungstechnik, Band 4 / 1998.

14.Diaz Martinez,S.;Garcia Alonso,E. Tecnicas metodologicas aplicadas a conservacion-restauracion del patrimonio metalico,Madrid 2011. (online)

15.La técnica radiográafica en los metales históricos(including english translation),Madrid 2011. (online)

16.Barrio Martin,J.;Chamon Frenandez,J. Proyecto Dorados:tecnología, conservación y restauración de los metales dorados medievales,Madrid 2011.

17.Salvi,A. Meteo e metalli.Conservazione e restauro delle sculture al aperto.Dal Perseo all arte contemporanea,Florence 2007.

18.Bruecke,D.Die Konservierung pigmentierter Altbeschichtungen auf Stahlbauten,Saarbrucken 2011.

19.Fischer,A. Reste von organischen Materialien an Bodenfunden aus Metall – Identifizierung und Erhaltung für die archäologische Forschung,Muenchen 1997.

20.Schlaepfer,B.R. Metais:Restauracao e conservacao,Rio de Janeiro 2009.

21.Gaomez Moral,F. Conservacion De Metales De Interes Cultural ,Quito 2004.

22.Krause,J. Sarkofagi cynowe : problematyka technologiczna warsztatowa i konserwatorska ,Torun 1995.

23.Mach,M.;Moetnner,P.Zinkguß, die Konservierung von Denkmälern aus Zink ,Muenchen 1999.

24.Barrandon,J.N.;Meyer-Roudet,H. A la recherche du métal perdu : nouvelles technologies dans la restauration des métaux archéologiques,Paris 1999.

25.Ronald Gobiet (Ed.),Die Salzburger Mariensäule - Zur Konservierung monumentaler Bleiplastiken / Sulla conservazione dei monumenti in piombo,Salzburg 2006.

26.Letardi,P.;Trentin,I.;Cutugno,G. Monumenti in bronzo all'aperto. Esperienze di conservazione e confronto.,Genova 2004.

27.Melucca Vaccaro,A.;De Palma,G. I Bronzi di Riace : restauro come conoscenza : 1: archeologia, restauro, conservazione/vol.1 ,Roma 2003.

28.Born,H. Restaurierung Antike Bronzewaffen,Mainz 1993.

29.Brueggerhoff,S.;Koenigfeld,P. Farbige Eisengitter der Barockzeit: Beiträge zu Geschichte und Funktion, Korrosion und Konservierung ,Bochum 2002.

30.Barrio,J.;Cano,E. (Editores). MetalEspaña ’08. Congreso de Conservación y Restauración del Patrimonio Metálico. UAM-CSIC, Madrid 2009.

Free software
The following is a list of free software packages that can be used for metals conservation:
 * The Use of Expert Systems in Conservation
 * The Modular Cleaning Program
 * Download free conservators documentation software

Metals conservation video files
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

10.Dorure au mercure

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.Metallrestaurator.avi

17.Apoxyomenos de Croacia 5

18.Bronze Age Fibula

19.Masterclass -silverplating