The Samuel H. Kress Foundation,
which generously provided financial support,
the Art Conservation Department at the University of Delaware, USA,
which facilitated the grant process,
the Laboratoire d'Archéologie des Métaux (LAM, Nancy, France),
and in particular Michel Folzan and Paul Merluzzo,
who kindly made original samples available for the project,
the Laboratoire de Recherche des Monuments Historiques
(LRMH, Champs-sur-Marne, France), and its Director, Isabelle Pallot-Frossard,
who kindly offered the use of microscope facilities (optical and SEM/EDS),
Conservation scientist and ICCROM fellow 2009,
who proposed the project, carried out all the laboratory work, as well as
the cards update, revision and reformatting process,
Gaël de Guichen,
Advisor to the Director-General of ICCROM and preventive conservation specialist,
who provided the historical background information,
Head of research on Cultural material science, Laboratoire Traces, CNRS-Uni Toulouse
who kindly reviewed the cards content,
Lecturer in conservation studies, UCL Qatar,
who contributed to technical editing
Pixel Age, who developed the web pages and card design,
and the family of Albert France-Lanord who supported this initiative.
On the occasion of my stay as an ICCROM fellow in 2009, I found in the storage room of the laboratory a collection of technical cards about metals conservation. They were prepared in the seventies by Albert France-Lanord, a well known French metallurgist as a support for the international course, Fundamental Principles of Conservation. Speaking then with Gaël de Guichen, he shared with me fascinating details about that particular work and period at ICCROM. I was very impressed with the amount of information about ancient metals and their conservation, kept in just a few boxes of cards, and at the same time, aware of the great need of such information in the conservation field.
During the last 15 years I have visited and collaborated with numerous institutions, regularly giving lectures and workshops about metals conservation in different countries. What I see is that people involved in metals conservation today pay less attention to metallic structures and the important information they can disclose. In all these years, I have seen many conservators applying treatments, and conservation scientists doing analysis, without ever having seen what the structure of a metal looks like, and how much it could change after a treatment. Lack of such knowledge can lead to misguided conservation actions or erroneous analytical results.
This has made me realize the fundamental importance of having good reference images that show the structural characteristics of ancient metals. Until now, the only comprehensive and accessible publication on the subject is that from D. Scott's Metallography and microstructure of ancient and historic metals (1991), and it is what I use in my courses, but the images are small and often difficult to use to illustrate the features I would like to show.
I have often wondered whether other metals conservation professionals experience the same need, and for this reason, I made the suggestion to ICCROM the the France-Lanord Cards be recovered from their boxes and updated, making them active again as a source of learning for the profession.
I am very grateful to the people and institutions who, together with ICCROM, allowed me to carry out this project.
I must also express my objective to strengthen the didactic potential of this material instead of building a visual catalogue for its own sake.
Forty years ago, ICCROM (then called the Rome Centre) noticed that while scientists could play an important role in conservation of cultural property, they were given no preparation to answer the questions brought to them by curators and conservators- restorers. To address this situation, ICCROM decided to launch an international course called Fundamental Principles of Conservation. This course aimed at providing a common language for the main three actors of the conservation process: the curator, the conservator-restorer and the scientist.
The 4-month course, organized in Rome and held in French and English, was attended by groups of 15 young professionals from different parts of the world. In order to ensure that the dialogue would be balanced, the selection of participants was rigorous, making sure that one third of the participants were curators, one third conservators-restorers and one third scientists.
Following a general introduction to environmental issues - at the time, the concept of preventive conservation was in its infancy, and the focus of attention was mostly on climate and light - and basic concepts of applied chemistry, each week was dedicated to one of the main materials to be found in heritage objects: wood, paper, textiles, leather, ceramics, glass, stone and metals.
The shaping of the contents of this innovative course took almost two years of discussions, meetings and written correspondence. This process included Paul Phillipot, the director of ICCROM, his deputy Giorgio Torraca, as well as Garry Thomson, Bruno Muhlethaler, Robert Organ, René Sneyers and Albert France-Lanord. As the scientific and course assistant at ICCROM, I was the secretary of the group.
In order to avoid the risk of confusion emerging from the fact that neither English nor French was spoken perfectly by neither teachers nor participants, and to strengthen the information transfer it was decided to create didactic materials in the form of technical cards.
These technical cards would focus on specific aspects of each section of the course: the structure of the materials, manufacture techniques, deterioration, remedial conservation and restoration.
The A4 size cards contained paper prints of the most important slides used during the course, accompanied by a short explanation. The course participants could consult the cards between course hours in case something was not understood, and then refer back to the teachers.
Albert France-Lanord was in charge of the section of the course on metals. He was an engineer, alumnus of the Ecole Centrale de Lyon in France, and the head of a family firm of public works, but his passion was archaeology. At the age of 18 he was made curator at the Musée historique de Nancy and subsequently founded the Musée de l'histoire du fer, of which he was the Director. At the time, this museum had a conservation laboratory that was exemplary for this period, where the most important archaeological metal objects found in France were treated, for example, the Vix Krater. Albert France-Lanord had extremely good manual skills which he put to use in the treatment of objects (he was even a jeweller!). Last but not least, he was an excellent photographer, documenting all the treatments and developing himself his colour photographs at home, involving his wife and 4 sons.
Drawing upon the photographic archives of 30 years of work, it was very easy for him to put together for the metals course almost 300 technical cards, which he generously donated to ICCROM. The historic importance of these cards is even greater in light of having been translated into English by Harold Plenderleith himself, the first Director of ICCROM.
Today scientists subscribe to non-destructive analytical methods. This was not the case of Albert France-Lanord, who, if he spotted didactic potential, did not hesitate to polish a small part of an object that was hidden from view for metallographic microscopy, or even to take a sample for a metallographic cross-section. This experience led him ultimately to better define the concept of epidermis of a corroded object, to replace the subjective and imprecise one of patina. Thanks to this daring and rational attitude and his generosity, ICCROM today has a great number of reference materials, many of which have made possible the work presented here.
Albert France-Lanord was a pioneer in the area of knowledge about, and treatment of, ancient metals. Today, ICCROM is happy to remember his important role and to allow an even greater number of professionals to benefit from his work.
There is no doubt about the importance of understanding the structure of metallic artifacts for their conservation, from investigative studies to assess the manufacturing process or the degree of corrosion of an object, to the implications of some new conservation treatment on their metallographic structure. The recognition of significant features combined with an appreciation of physical metallurgy provides a powerful basis for rationalization and diagnosis. To teach this art requires carefully selected examples placed within the context of real issues. This work is intended to contribute to such vehicle.
Through the revaluation of a selection of ICCROM's France- Lanord technical cards, this publication aims at making this unique resource available for people wanting to enlarge and enrich their understanding about metal collections. Characterization of metallic alloys is not only a question of their chemical composition, but also of their structure, which may be formed by the combination of many elements to form new phases. Only metallographic examinations, like those presented in the cards, can give an overview of structural and compositional features (grains, phases, distribution of different components and how they affect properties of the metals themselves). Access to such information is of essential importance for young researchers and students of conservation and conservation science, in order to be aware of these points before treating and / or analyzing cultural objects.
Since the original pictures in the cards have yellowed, a re-examination of the samples was necessary to regain their representativity. For this, a set of about 50 samples was selected taking into consideration the information their microstructure could provide about manufacture techniques as well as particular forms of deterioration. The samples were in good state and have been re-polished. Examination has been performed using an optical microscope, and in some cases, a scanning electron microscope (SEM). The examination of samples has been guided by information from the original cards, mostly hand-written key words by France-Lanord.
The final product of this work is a digital version of the cards, presenting a dynamic design inspired by the original layout. The updated pictures can be easily enlarged for detailed observation of particular features described in the corresponding captions. This learning resource is now accessible to individuals as well any educational and professional organization working in metals conservation.
Insofar as the intent was not to produce a handbook about microstructures of ancient metals, readers without background on the subject should refer to classic works, some of them listed in the bibliography. An introduction to the subject is "Ancient metals: structure and characteristics", by Albert France-Lanord (see bibliography). It deals with basic aspects concerning structure and properties of ancient metals and alloys, and contains some practical remarks about preparation of metallographic cross sections for examination.
The digital cards presented here include original and current information. The original written records by France-Lanord are organized under the titles 'Identification' and 'Description'. They are accompanied by the newly-updated pictures and captions, containing a short account of the observed structure including the most remarkable features.
Since many different alloys (with respect to parent metals, provenance and time) are represented in the cards, there is no preferential organization and they are just presented following the original sample numbers. Cards can be consulted in any order, or on the basis of interest in a particular feature. This will be guided by the glossary which refers to examples presenting specific features.
Finally, as a way to test and retain the information learned from the cards, a short quiz is included.
(adapted from ASM handbook (c2004) and Scott (1991), see bibliography)
alloy systema complete series of compositions produced by mixing in all proportions any group of two or more components, at least one of which is a metal.annealing
a generic term denoting a treatment (heating to and holding at a suitable temperature followed by cooling at a suitable rate) used primarily to soften metallic materials, but also to produce desired changes simultaneously in other properties or in microstructure. In nonferrous alloys, annealing cycles are designed to remove part or all the effects of cold working.brass
an alloy of copper and zinc, usually with copper as the major alloying element and a zinc content up to 40% by weight. The colour of brass changes with increasing zinc content from a rich copper-red through pale yellow to white. (examples: A182)bronze
in ancient and historical usage, the term refers to an alloy of copper and tin. Usually with up to 14% tin, but many examples of ancient alloys are known with higher tin contents. In modern usage, the term bronze is associated with a number of copper alloys that may contain no tin at all and the composition of the alloy must be specified. (examples: A35, A38, A41, A43, A46, A47, A79, A135, A163, A167, A183, B03, B04, B07, B10, B12, B14, B41, B42, B82, B93, B95) cast structure
the metallographic structure of a casting evidenced by shape and orientation of grains as well as segregation of impurities. (examples: A47, A58, A79, A167, B82)cold-working
the plastic deformation of a metal at a temperature low enough to cause permanent strain hardening. It usually consists of rolling, hammering or drawing at room temperature. The hardness and tensile strength of the metal increase with the amount of cold-work, but the ductility and impact strength are reduced. (examples: A32, A46, B03, B07, B09, B14, B42, B46, B82)coring
a variation in composition between the centre and surface of a unit of structure, such as a dendrite, a grain or a carbide particle, that results from non-equilibrium growth over a temperature range. It is especially common in ancient cast bronzes and cast silver-copper alloys. (examples: A58, A135, A167, B04, B22)dendrite
a crystal with a treelike branching pattern. It is most evident in cast metals slowly cooled through the solidification range. (examples: A47, A58, A79, A135, A167, A195, B04, B22, B41, B81, B82, B95)elongated grain
a grain with one principal axis significantly longer than either of the other two. (examples: A182, B09, B44)equiaxed grain
a grain that has approximately the same dimensions in all directions.(examples: A32, A39, A183)etching
subjecting the surface of a metal to preferential chemical or electrolytic attack to reveal structural details for metallographic examination.eutectic
in binary alloys the composition with the lowest melting point, and is often a fine intermixture of two phases. (example: A195)eutectoid
structure resulting from decomposition from a solid phase in two finely dispersed solid phases. (examples: A46, A47, A58, A135, A167, B04, B07, B41, B42, B78, B81, B93, B95)ferrite
an interstitial solid solution of carbon in -iron (body-centered cubic iron). (examples: A06, A83, A185, B66)flow lines (banding)
texture showing the direction of metal flow during hot or cold working; inhomogeneous distribution of alloying elements or phases aligned in filaments or plates parallel to the direction of working. (examples: A06, A159, B10, B52)grain
an individual crystal in a polycrystalline metal or alloy, including twinned regions or sub-grains if present.grain boundary
an interface separating two grains at which the orientation of the crystal lattice changes from that of one grain to that of the other. hot-working
deformation of the metal or alloy under conditions that result in crystallization.inclusions
particles of foreign material in a metallic matrix. The particles are usually compounds, such as oxides, sulphides or silicates, but may also be any substance foreign to and essentially insoluble in the matrix. (examples: A35, A38, A41, A43, A46, A47, A79, A83, A135, A142, A148, A163, B04, B07, B22, B37, B41, B42, B44, B46, B53, B63, B66, B78, B80, B81, B93)interdendritic
located within the branches of a dendrite or between the boundaries of two or more dendrites. (examples: A58, A167, A195, B04, B81, B82, B95)intergranular crack / corrosion
a crack or corrosion that occurs between the grains or crystals in a polycrystalline aggregate. (examples: A35, A38, A39, A43, A142, A163, A184, B03, B12, B46, B53, B78, B80, B91, B93)matrix
the continuous or principal phase in which other constituent is dispersed. (examples: A38, B07, B66)microstructure
the structure (size, shape and arrangement of phases) of a prepared surface of a metal revealed by a microscope at a magnification exceeding 25×.pearlite
a fine mixture of alternating lamellae of ferrite and cementite found in steels. (examples: A83, A185)phase
a physically homogenous and distinct portion of a material system.porosity
holes in a solid; not necessarily interconnected, usually produced in a casting or weld by gas bubbles trapped during solidification. (examples: A41, A47, A58, A148, A167, A185, B12, B22, B46, B53, B63, B66, B80, B91, B95)recrystallized grain
a new strain-free grain developed by heating cold-worked metal above its recrystallization temperature. (examples: A35, A90, A182, A183, A184, B14, B22, B37, B42, B44, B50, B80, B91, B93)segregation
a non-uniform distribution of alloying elements, impurities or phases.shrinkage crack
a crack that forms because of the shrinkage stresses accumulated during solidification of a metal casting. (examples: A58, A135, A167)slag
a non-metallic product resulting from mutual dissolution of flux and non-metallic impurities in smelting and refining operations; usually found in ancient or historic wrought iron. (ex.: A06)strain (slip) lines
thin bands or lines produced by cold working in the grains of some metals (particularly those with face-centered cubic structure). (examples: A06, A32, A35, A39, A43, A46, A82, A91, A159, A182, A183, B03, B07, B09, B12, B14, B41, B42, B46, B80, B93)transcrystalline cracking
cracking or fracturing that occurs through or across a crystal. Also termed intracrystalline or transgranular cracking. (examples: A32, A46, B03, B12)twins
band markings in the grains, characteristic of metals with a particular type of atomic arrangement (i.e. the face-centered cubic structure) in the recrystallized condition. They represent regions of changing atomic orientation within the crystal and develop during recrystallization. (examples: A39, A43, A46, A182, A184, B09, B10, B12, B14, B37, B44, B46, B50, B80, B93)wrought iron
iron that has been produced from the bloomery process and has been consolidated by hammering and annealing into a wrought product. Wrought iron usually contains slag stringers that have been elongated and flattened in the process of working from the bloom. (example : A06)
ASM handbook. Volume 9, Metallography and microstructures. Materials Park, OH : ASM International, c2004.
Bailey, A.R. Introductory practical metallography: a basic course of microstructures with 37 specimens. 2nd ed. Betchworth, England : Metallurgical Services, 1966.
Bailey, A.R. The role of microstructure in metals : an introductory volume. 2nd ed. Betchworth, England : Metallurgical Services, 1982.
France-Lanord, A. Ancient metals, structure and characteristics : technical cards = Métaux anciens, structure et caracteristiques : fiches techniques. Rome : ICCROM, 1980.
Norton, J. T. "Metallography and the study of art objects." In: Application of science in examination of works of art: proceedings of the seminar, September 7-16, 1965, conducted by the Research Laboratory, Museum of Fine Arts, Boston, Massachusetts, p. 13-19. Boston : Museum of Fine Arts, 1967.
Organ, R.M. "Analysis and microscopic study of metals." In: Pyddoke, Edward, ed. The scientist and archaeology, p. 27. London : Phoenix House, 1963.
Rostoker, W. and Dvorak, J.R. Interpretation of metallographic structures. 3rd ed. San Diego : Academic Press, 1990.
Scott, D. A. Metallography and microstructure of ancient and historic metals. Los Angeles, CA : The J. Paul Getty Trust, 1991. http://www.getty.edu/conservation/publications_resources/pdf_publications/metallography.pdf
Smith, C. S. The search for structure : selected essays on science, art, and history. Cambridge, Mass : MIT Press, 1981.
Wang, Quanyu. Metalworking technology and deterioration of Jin bronzes from the Tianma-Qucun site, Shanxi, China. BAR International Series 1023. Oxford : Archaeopress, 2002.