An innovative tool

The computer-based Decision Support System (DSS) MiCorr is a new non-invasive diagnostic tool for metal objects. Three search engines have been developed: the first one uses interlinked keywords, the second a decision chain to identify metal families and the third digital stratigraphies of corrosion forms. The latter, based on Bertholon’s schematic description of metal corrosion[1], is the most innovative tool of this application. Corrosion forms are described as structures of strata (metal, corroded metal, corrosion layers…), each stratum having its specific characteristics (morphology, microstructure, texture and other properties). A modelling program allows to build a corrosion structure from coded building blocks (strata containing up to 30 characteristics).

The same set of analytical techniques with similar operating conditions have been used to characterize the corrosion forms/case studies of the database. Some of them required the destructive sampling of artefacts to determine the precise nature, organization and composition of the corresponding strata. As they are characterized with the same digital construction model which is used for the corrosion forms under investigation a comparison becomes possible.

By comparing the corrosion form of an artefact under observation or a sample from the same artefact observed on cross-section with the database through the DSS, a MiCorr user is able to find case studies/corrosion forms of objects showing similar corrosion phenomena. In case the user is a conservation professional, this should help him.her to implement an appropriate conservation protocol.

The search engines allow the user to question the database but if registered he.she has also the possibility to enrich the database with new corrosion forms and/or case studies, thus becoming an active contributor. The basic format of the corrosion forms can be further improved with any additional analytical data and the operating conditions used.

In short, MiCorr aims to:

  • Promote a transdisciplinary approach to the diagnosis of metal objects. It encourages the compilation of scientific knowledge which is often dispersed within communities (curators, conservators, corrosion scientists, archaeo-metallurgists…) and favours the collaboration between these different actors. Any information on existing or new corrosion forms provided by the group of experts involved will allow MiCorr to become more and more efficient as a diagnostic decision support tool.
  • Facilitate access to existing knowledge and allow comparison with new corrosion forms under investigation.

The didactic, self-learning and freely accessible and participatory MiCorr tool should enable the various scientific communities involved in the analysis and conservation of metals to better understand existing knowledge and contribute to unsolved research problems.

Some background

A thorough understanding of alteration processes developed on metals enables us to slow down, limit and / or stop existing corrosion. In the industrial field, sampling of metals to investigate the amount of alteration observed is not unusual and the information gained provide knowledge on the corrosion developed such as stress corrosion cracking, fatigue corrosion, corrosion due to exposure to high temperature or pressure which are rarely encountered in the heritage domain. If this type of alteration does appear on historic or archaeological artefacts, it will not necessarily be similar due to the long periods of stress or alteration involved. Therefore, the examination of contemporary metals cannot solely be used to predict the long-term preservation of materials (Neff 2006[2]).

When conserving metal artefacts, conservation professionals try to carry out the most precise diagnosis in order to find an appropriate conservation treatment. This diagnosis requires a thorough description of the surface condition of the object under investigation. Based on experience and consultation of corrosion forms published in the literature (Corrosion Science, Studies in Conservation, Journal of Cultural Heritage, etc.), conservation professionals try to find analogies with the observed corrosion forms. On the basis of this knowledge conservation strategies can be proposed.

But the matching between the corrosion forms investigated and those that are used for comparison is difficult to achieve. This is due to the lack of standardization in the description of the object surfaces (according to his/her experience, each conservator perceives the object in a different way) and the heterogeneity of heritage metal surfaces. The use of different analytical tools can bring further bias in the description of corrosion forms.

The professional associations of corrosion experts (NACE - the Professional society for corrosion engineers since 1943 and the European Corrosion Federation since 1955) have published numerous books on metal corrosion. Although the corrosion mechanisms under particular environmental conditions (and the means to prevent it) are known, there are no online diagnostic tools to link observed alterations to the causes of corrosion. Websites such as provide illustrations of corrosion forms. Unlike heritage metals which show extensive and complex corrosion forms, such as active or reactivated corrosion, they only show the result of the reactivity of the clean metal in a corrosive environment. In the conservation domain, only one database ( existed in the past but is no longer available. It offered descriptions of corrosion forms encountered on heritage metals, but did not provide a diagnosis.

Over the years, much research on the diagnosis of corroded heritage metals has been carried out and regularly published: Dillmann and his team (Dillmann 2005[3]) have been investigating the alterations of archaeological and historic iron ; Robbiola (Robbiola 1998[4]) has focused on the study of natural patinas on copper-based alloys and how they undergo changes when buried in a chlorinated soil that favours active corrosion ; Turgoose (Turgoose 1985[5]) has investigated alterations of lead artefacts in organic acid-rich environments, such as those found in museum display cases and storage cabinets. The outcome of all this research is dispersed in the literature due to the different backgrounds of the researchers involved (corrosion scientists, archaeometers, conservation scientists) as well as the audience to which the publications are addressed to (industry, engineering, conservation of cultural heritage).

Most of this research is based on the study of samples taken from the core of the metal under investigation. Until the research of Bertholon on the visual description of corrosion products and their structure (Bertholon 20011 [6]), it was impossible to adequately describe corrosion phenomena in a standardized way and refer then to existing models. Some conservation training programmes such as at HE-Arc CR, are trying to implement this method to diagnose alterations observed on both studied and unstudied heritage metals. MiCorr is the logical continuation of these efforts that will allow a broader community to adopt this methodology and improve their diagnosis on heritage metals.


The research methodology of MiCorr follows the steps of a conservation project. It starts with the visual observation of the altered object, continues with the diagnosis and ends with the proposal of conservation treatments. Figure 1 illustrates these 3 steps:

Figure 1

Fig. 1: Schematic representation of the research methodology.

Development team of the MiCorr expert system

For HE-Arc CR

  • Dr. Christian Degrigny, lecturer-researcher at HE-Arc CR. C. Degrigny has worked on many corrosion forms encountered on heritage artefacts: iron, copper (Degrigny 2012[7]), lead (Degrigny 1999[8]) and silver based (Degrigny 2006[9]) as well as on modern metals such as aluminium alloys (Degrigny 1993[10], [11]) conserved or not in aggressive environments. In each case, the objective of the diagnosis was the definition of adequate conservation treatments (Degrigny 2007[12]). As the coordinator of the MIFAC-Metal research project, he developed with M. Senn (Swiss Federal Laboratories for Materials Science and Technology - EMPA) the methodology to describe corrosion forms on a first group of heritage metals representative of the Swiss collections. Samples that had been taken in the past were re-examined. They constituted the first corrosion forms of the MiCorr database. He contributed as a partner to the MIFAC-Metal online project [13] and was project leader of the ODOP_Corr project during which the robustness of MiCorr was increased. He was research leader of MetalPAT.
  • Valentin Boissonnas, conservator of archaeological and ethnographic artefacts is lecturing at HE-Arc CR. He is responsible of the module on conservation of metal artefacts and has been at the origin of the MIFAC-Metal project. Conservation projects carried out by master students and supervised by V. Boissonnas enrich regularly the database with new corrosion forms.
  • Dr. Régis Bertholon, Head of studies, continuing education and research at HE-Arc CR. As a conservator of archaeological metal artefacts, R. Bertholon has worked extensively on the problem of the location of the limit of the original surface on heavily corroded artefacts (Bertholon 1998[14], Bertholon 2000[15], Bertholon 2001[16], Bertholon 2001[17], Bertholon 2007[18]), on the stabilisation of archaeological copper alloys and conservation treatment of archaeological metal artefacts. As mentioned above he developed a methodology to describe the corrosion forms of heavily corroded metals (Bertholon 2002[19], Bertholon 2003[20]).
  • Romain Jeanneret, conservator of scientific, technical and horology objects. As a research assistant in the Research unit of HE-Arc CR, he contributed to the development of the MiCorr expert system.
  • Naïma Gutknecht, conservator or archaeological objects. As a research assistant in the Research unit of HE-Arc CR during MetalPAT, she also contributed to the development of MiCorr, more particularly the observation of corrosion structures under binocular and the enrichment of the database.

For LMC-Iramat / Nimbe / CNRS / CEA

  • Dr. Philippe Dillmann, Director of research, CNRS –  Laboratoire Métallurgies et Cultures (LMC) IRAMAT – UTBM, Belfort, France specialised in archaeological sciences for the study of the manufacture, use and exchange of metal objects in ancient societies, the long-term alteration of metals and the conservation of metal heritage objects; responsible for the CAI-RN Archaeometry network of the Mission for Transversal and Interdisciplinary Initiatives of the CNRS; research leader of MetalPAT.
  • Dr. Marion Berranger, research engineer, CNRS - LMC-IRAMAT, UTBM, Belfort, archaeologist specialising in protohistoric and ancient siderurgy and in the microscopic and chemical characterisation of ancient materials.
  • Dr. Valentina Valbi, conservation scientist and postdoc at LMC-UTBM, Belfort. Contributed to the development of MiCorr during MetalPAT, more particularly the observation and analysis of corrosion structures in cross-section and the enrichment of the database.

For LAPA / University Paris-Saclay / CEA

  • Dr. Delphine Neff, engineer-researcher, specialised in the long-term corrosion of metals for both the nuclear industry and heritage materials, partner of MetalPAT.

For HEG-Arc

  • Dr. Cédric Gaspoz, Professor in information systems at HEG-Arc. His research activities focus on Decision Support Systems and business intelligence. Project leader of MIFAC-Metal Online during which the MiCorr application was designed. Partner of ODOP_Corr project, which aimed to set up the knowledge sharing required for the further development of MiCorr and to disseminate the application within the professional communities involved in metal conservation. He coordinated the work of bachelor students who contributed to the project and was partner of MetalPAT.
  • Antoine Rosselet, was a research assistant in information systems at HEG-Arc. His main activity in the project was to create the MiCorr application and implement the database which contains representative corrosion forms.
  • Alessio De Santo, got an MSc in information systems. As research assistant at HEG-Arc, he resumed the tasks of Antoine Rosselet and led the application to a first final version.
  • Bernard Letourmy, independant IT consultant and contracted by HEG-Arc during MetalPAT to reshape partly the structure of the MiCorr application and to make it more robust.
  • Nicolas Rosset, research assistant.
  • Stéphane Prestinari.

Administration team

  • Dr. Christian Degrigny, main administrator
  • Bernard Letourmy

Reading committee

  • Dr. Christian Degrigny
  • Dr. Philippe Dillmann
  • Dr. Delphine Neff

[1] Bertholon, R. La limite de la surface d'origine des objets métalliques archéologiques, caractérisation, localisation et approche des mécanismes de conservation. UFR03 Art et Archéologie. Paris, Université Paris 1 Panthéon-Sorbonne, 2000, 419p (

[2] Neff, D., Bellot-Gurlet, L., Dillmann, P., Reguer, S. and Legrand, L. (2006) Raman imaging of ancient rust scales on archaeological iron artefacts for long-term atmospheric corrosion mechanisms study, J. Raman Spectrosc, 37: 1228–1237.

[3] Dillmann, P. (2005) Corrosion des objets archéologiques ferreux, Les Techniques de l’Ingénieur, AF 6920, COR675 : 1-20.

[4] Robbiola, L., Blengino, J-M., Fiaud, C. (1998) Morphology and mechanisms of formation of natural patinas on archaeological Cu-Sn alloys, Corrosion Science, 40, 12, 2083-2111.

[5] Turgoose, S. (1985) The corrosion of lead and tin: before and after excavation, in Lead and tin: Studies in Conservation and Technology, ed. C.E. Miles and S.C. Pollard, UKIC, Occasional Papers, n°3, London, 15-26.

[6] Bertholon, R. (2001) Characterization and location of the original surface of corroded archaeological objects. Surface Engineering, 17 (3), 241-245.

[7] Degrigny, C. (2012) Methodology to study and analyse the microstructures and corrosion forms of ancient and historic metals: application to metallographic samples from Swiss collections, rapport final du projet MIFAC-Métal, rapport interne, HE-Arc CR, 188p. (available from the author).

[8] Degrigny, C. and Le Gall, R. (1999) Conservation of ancient lead artefacts corroded in organic acid environments: electrolytic stabilisation / consolidation, Studies in Conservation, 44, 157-169.

[9] Degrigny, C. and Witschard, D. (2006) La chasse des enfants de Saint Sigismond de l’Abbaye de Saint-Maurice: traitements électrochimiques des reliefs en argent en cours de restauration, in Medieval reliquary shrines and precious metalwork, in Proceedings of a conference at the Musée d’Art et d’Histoire, Geneva, 12-15 September 2001, Anheuser K. and Werner, C. (eds), Archetype, 9-16.

[10] Degrigny, C. (1993) La mise au point d’un traitement cathodique de stabilisation de vestiges aéronautiques immergés en alliages d’aluminium, actes du colloque Sauvegarder le XXème siècle : la conservation des matériaux modernes, Ottawa 1991, Pub. ICC, 373-380.

[11] Degrigny C. and Schröter J. (2019) Aluminium Alloys in Swiss Public Collections: Identification and Development of Diagnostic Tools to Assess Their Condition, in METAL 2019, proceedings of the ICOM-CC Metal WG interim meeting, eds. C. Chemello, L. Brambilla, E. Joseph, Neuchâtel (Switzerland), 408-415.

[12] Degrigny, C. (2007) Examination and conservation of historic and archaeological metal artefacts: a European overview, in Corrosion of metallic heritage artefacts, Dillmann, P. et al. (eds), EFC 48, Woodhead Publishers, 1-17.

[13] Degrigny C., Gaspoz C., Rosselet A., Boissonnas V., Jeanneret R. and Bertholon R. (2016) The MIFAC-Metal Online project: developing a Decision Support System for locally invasive diagnosis of heritage metals, in METAL 2016, proceedings of the ICOM-CC Metal WG interim meeting, eds. R. Menon, C. Chemello and A. Pandya, New Dehli, (India), 220-227.

[14] Bertholon, R., et al. (1998). Corrosion du rouleau de cuivre de Qumrân et localisation de la surface originelle. Metal 98 International Conference on Metals Conservation, Draguignan, James and James

[15] Bertholon, R. (2000). La limite de la surface d'origine des objets métalliques archéologiques. caractérisation, localisation et approche des mécanismes de conservation. UFR03 Art et Archéologie. Paris, Université Paris 1 Panthéon-Sorbonne: 419p.

[16] Bertholon, R. (2001). The location of the original surface, a review of the conservation literature. Metal 2001 Proceedings of the ICOM-CC Metals Working Group, Santiago, Chile 2-6 April 2001, Western Australian Museum.

[17] Bertholon, R. (2001). "Characterisation and Location of the Original Surface of Corroded Archaeological Objects." Surface Engineering 17(3): 241-245.

[18] Bertholon, R. (2007). Archaeological metal artefacts and conservation issues : long-term corrosion studies. Corrosion of metallic heritage artefacts. P. Dillmann, G. Béranger, P. Piccardo and H. Matthiesen. Cambridge, Woodhead Publishing Lmd: 31-40.

[19] Bertholon, R. (2002). "Proposition d'une méthode de description de la corrosion des objets métalliques archéologiques : schéma général." Cahier Technique de Conservation-Restauration des biens culturels 9: 56-65.

[20] Bertholon, R., et al. (2003). Comprehensive approaches of corroded conditions for archaeological iron artefacts : filling the gap between macroscopic observation and microanalysis for conservation diagnosis. International Conference on the Application of Raman Spectroscopy in Art and Archaeology, Ghent.