From Excavation to Preservation: Preventive Conservation Approaches in Archaeological Bronze...

LES DOSSIERSDE L’IPW15

Institut du Patrimoine wallon

La conservation-restaurationdes métaux archéologiques :des premiers soins à la conservation durable

Sébastien Clerbois (dir.),

Cristel CappuCCi, Joëlle Moulin, Letizia nonne, Sylvia pierMarini, Marie-Hélène sChuMaCher (éd.)

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bleLe traitement de conservation-restauration et la mise en valeur patrimoniale des métaux

archéologiques sont des questions complexes. Le développement de l’archéologie, notamment préventive, oblige les administrateurs en charge des fouilles à gérer une quantité de plus en plus grande de matériel. Avec le développement des métiers du patrimoine, le nombre d’intervenants, de la fouille au musée, est de plus en plus grand, et ces acteurs sont de plus en plus spécialisés. En ce qui concerne la conservation-restauration, les méthodes évoluent vite. Du travail mécanique au plasma, les moyens d’interventions ne manquent pas, mais la pertinence est encore débattue au niveau international. Autre problème : le long de la chaîne opératoire, les acteurs n’ont pas souvent l’occasion de faire converger leurs approches pour optimiser l’étude et la conservation. Mise en état de l’objet pour étude, stabilisation, consolidation, conservation passive et/ou restauration, comment aborder ces questions collectivement pour définir au mieux les gestes techniques, et en particulier dans les contextes d’urgence et de budgets réduits de l’archéologie préventive ? L’ambition de cet ouvrage vise à enrichir les pratiques de chaque discipline sur base d’un dialogue interdisciplinaire et à stimuler la pratique de l’intervention concertée de manière à rassembler les gestes techniques dans ce qui serait un protocole de traitement global, bien défini, du sol à la vitrine de musée.

Prix de vente : 25 €ISBN : 978-2-87522-152-0

La conservation-restauration des métaux archéologiques :

des premiers soins à la conservation durable

La conservation-restauration des métaux archéologiques :

des premiers soins à la conservation durable

Actes du colloque organisé par la Direction de l’Archéologie du Service public de Wallonie et la DGO4, la FAW (Fédération des Archéologues

de Wallonie et de Bruxelles) et le CReA-Patrimoine (ULB), à l’Université libre de Bruxelles, salle Dupréel, les 8 et 9 mai 2014.

Sébastien Clerbois (dir.)Cristel CappuCCi, Joëlle Moulin, Letizia nonne, Sylvia pierMarini,

Marie-Hélène sChuMaCher (éd.)

LES DOSSIERSDE L’IPW, 15

5

TABLE DES MATIÈRESREMERCIEMENTS ___________________________________________________________________________________________________________________________ 11

AVEC LE SOUTIEN DE _____________________________________________________________________________________________________________________ 11

PRÉFACE J. Plumier _________________________________________________________________________________________________________________________ 13

LES MÉTAUX, ÉPISTÉMOLOGIE D’UN DOSSIER SENSIBLE DE LA CONSERVATION-RESTAURATION DU PATRIMOINE ARCHÉOLOGIQUE C. CaPPuCCi et al. ________________________________________________________________________ 15

THE MONITORING OF ARCHAEOLOGICAL METALS, FROM EXCAVATIONS TO MUSEUM: SOME ISSUES AND PERSPECTIVES R. Bertholon _____________________________________________________________________________ 19

TransmiTTing informaTion _____________________________________________________________________________________________________________ 20Developing communicaTion Tools beTween professionals __________________________________________________________________ 20increasing number of arTefacTs ____________________________________________________________________________________________________ 21from prevenTive To preDicTive conservaTion ___________________________________________________________________________________ 22DocumenTing inTangible conDiTion as well as maTerial conDiTion _______________________________________________________ 22locaTing The limiT of The original surface _____________________________________________________________________________________ 23imaging Techniques ______________________________________________________________________________________________________________________ 24fuTure works _____________________________________________________________________________________________________________________________ 24acknowleDgmenTs ________________________________________________________________________________________________________________________ 25

01. La préservation des métaux archéologiques dès la fouille : protocoles de prélèvement et techniques de conservation sur les chantiers archéologiques Archaeological Metals Taking and Preservation from the Excavations:

Sample Techniques and Preservation Methods on the Excavation Fields

FROM EXCAVATION TO PRESERVATION: PREVENTIVE CONSERVATION APPROACHES IN ARCHAEOLOGICAL BRONZE COLLECTIONS O. oudBashi ____________________________________________________________________ 29

inTroDucTion _______________________________________________________________________________________________________________________________ 29

corrosion of archaeological bronzes: a shorT DescripTion __________________________________________________________ 29

main risk facTors ______________________________________________________________________________________________________________________ 30

prevenTive conservaTion in archaeological bronze collecTions _____________________________________________________ 31

pre-excavaTion consiDeraTions ____________________________________________________________________________________________________ 31

During-excavaTion acTiviTies _______________________________________________________________________________________________________ 32

long-Term preservaTion ______________________________________________________________________________________________________________ 32

inTegraTing prevenTive conservaTion: The global approach ____________________________________________________________ 33

conclusion _________________________________________________________________________________________________________________________________ 35

acknowleDgemenTs ______________________________________________________________________________________________________________________ 35

LA CONSERVATION PRÉVENTIVE DES MÉTAUX IN SITU, DIALOGUE ENTRE L’ARCHÉOLOGUE DE TERRAIN ET LE SPÉCIALISTE EN CONSERVATION-RESTAURATION ? C. Proust _____________________________ 37

La conservation-restauration des métaux archéologiques :des premiers soins à la conservation durable

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02. L’apport des études métallographiques pour la conservation-restauration des métaux anciens The Contribution of Archaeometallurgic Studies for Preservation and Restauration of Ancien Metals

PATINES NATURELLES DES BRONZES – QUELQUES DÉVELOPPEMENTS MAJEURS L. roBBiola ___________ 45inTroDucTion _______________________________________________________________________________________________________________________________ 45

a. paTine proTecTrice Des bronzes en milieu naTurel _______________________________________________________________________ 47A. 1. Cas général et décuprification _____________________________________________________________________________________ 47A. 2. Altération des patines protectrices : variations morphologiques ___________________________________ 48

b. paTine « vile » eT corrosion imporTanTe ___________________________________________________________________________________ 49

conclusion _________________________________________________________________________________________________________________________________ 50

OBJETS FERREUX : APPROCHES ARCHÉOMÉTRIQUES P. dillmann ____________________________________________________ 51inTroDucTion _______________________________________________________________________________________________________________________________ 51

pourquoi analyser : comprenDre la place Du fer Dans les sociéTés anciennes ____________________________________ 51

commenT analyser : aDapTer les méThoDes aux quesTionnemenTs hisToriques _______________________________________ 55

conclusion _________________________________________________________________________________________________________________________________ 57

COMPOSITION AND CORROSION FORMS ON ARCHAEOLOGICAL AND NON-ARCHAEOLOGICAL HISTORIC PRINTING LETTERS FROM THE MORAVIAN MUSEUM, MEMORIAL OF KRALICE BIBLE, THE CZECH REPUBLIC AND THE MUSEUM PLANTIN-MORETUS ANTWERP, BELGIUM P. storme et al. ____________________ 59

inTroDucTion _______________________________________________________________________________________________________________________________ 59

The museum planTin-moreTus ______________________________________________________________________________________________________ 59

The memorial of kralice _____________________________________________________________________________________________________________ 60

1. research objecTives ________________________________________________________________________________________________________________ 61

2. experimenTal __________________________________________________________________________________________________________________________ 612. 1. Analysis of the printing letter stored in the Museum Plantin-Moretus (Antwerp) ___________ 612. 2. Analysis of the printing letters in the Kralice Memorial of Brno _____________________________________ 62

3. resulTs __________________________________________________________________________________________________________________________________ 623. 1. Museum Plantin-Moretus types ____________________________________________________________________________________ 62

3. 1. 1. Composition __________________________________________________________________________________________________________ 623. 1. 2. Corrosion ______________________________________________________________________________________________________________ 633. 1. 3. Relation composition-corrosion ________________________________________________________________________________ 63

3. 2. Kralice Memorial types _________________________________________________________________________________________________ 633. 2. 1. Composition __________________________________________________________________________________________________________ 633. 2. 2. Experiment description ___________________________________________________________________________________________ 643. 2. 3. Corrosion ______________________________________________________________________________________________________________ 643. 2. 4. Relation composition-corrosion ________________________________________________________________________________ 64

4. conclusion ____________________________________________________________________________________________________________________________ 65

Table des matières


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LA PRISE EN COMPTE DES SURFACES ET PATINES ANTIQUES DANS LA RESTAURATION DES MÉTAUX ARCHÉOLOGIQUES : ÉTUDE DE LA PLAQUE À L’AURIGE D. roBCis et al. ________________________ 67

inTroDucTion _______________________________________________________________________________________________________________________________ 67

la plaque à l’aurige, présenTaTion eT examen général _____________________________________________________________________ 68

raDiographie eT émissiographie De rayons x ___________________________________________________________________________________ 70

analyses élémenTaires __________________________________________________________________________________________________________________ 70

DiffracTion De rayons x ______________________________________________________________________________________________________________ 72

Discussion _________________________________________________________________________________________________________________________________ 73

conclusion _________________________________________________________________________________________________________________________________ 74

03. Les techniques de restauration : une mise en perspective critique The Restauration Techniques: a Critical Approach

CONSERVE ALL, RESTORE NOTHING? CHANGING ATTITUDES IN METAL CONSERVATION B. sChmutzler ____ 79inTroDucTion _______________________________________________________________________________________________________________________________ 79

Terms anD DefiniTions __________________________________________________________________________________________________________________ 80

eThics of conservaTion anD resToraTion ________________________________________________________________________________________ 80

The role of conservaTion science ________________________________________________________________________________________________ 82

research projecT saving from rusT (sfr) ___________________________________________________________________________________ 82

DigiTal conservaTion ___________________________________________________________________________________________________________________ 84

conclusion _________________________________________________________________________________________________________________________________ 85

acknowleDgmenTs ________________________________________________________________________________________________________________________ 85

COMPARISON OF CONSERVATION METHODS APPLIED TO IRON ARTEFACTS K. sChmidt-ott ______________ 87inTroDucTion _______________________________________________________________________________________________________________________________ 87

iron corrosion ___________________________________________________________________________________________________________________________ 87

early conservaTion TreaTmenTs ______________________________________________________________________________________________________ 88

conservaTion aT The swiss naTional museum __________________________________________________________________________________ 89

DesalinaTion in alkaline sulphiTe ___________________________________________________________________________________________________ 89

prevenTive conservaTion ______________________________________________________________________________________________________________ 91

special challenges ______________________________________________________________________________________________________________________ 91

Table des matières


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CONSERVATION OF ARCHAEOLOGICAL IRON: CONSERVATION, PLANNING AND THE RETRIEVAL OF ARCHAEOLOGICAL INFORMATION – A DIFFERENTIATED APPROACH N. Cleeren _______________________________ 93

inTroDucTion _______________________________________________________________________________________________________________________________ 93

The conservaTion process ___________________________________________________________________________________________________________ 941. Conservation as a means of gathering of information ______________________________________________________ 94

1. 1. Four levels of information ___________________________________________________________________________________________ 941. 2. Common Practice – diagnostic and investigative cleaning ______________________________________________ 951. 3. Optimal retrieval of information? _________________________________________________________________________________ 951. 4. Other non-invasive techniques in search for more detailed information ____________________________ 961. 5. Cost-effectiveness of different approaches ___________________________________________________________________ 98

2. Conserving this information in its physical form ______________________________________________________________ 983. Presentation ____________________________________________________________________________________________________________________ 99

conclusion _________________________________________________________________________________________________________________________________ 99

acknowleDgmenTs ________________________________________________________________________________________________________________________ 99

04. Musée et conservation préventive Museums and Sustainable Preservation

ENVIRONNEMENT MUSÉOGRAPHIQUE : QUEL IMPACT SUR LES OBJETS MÉTALLIQUES ? P. de ViViés ______ 103première éTuDe De cas : les maTériaux en alliage cuivreux... ou apparenTés _____________________________________ 103

seconDe éTuDe De cas : les maTériaux en plomb _____________________________________________________________________________ 105

Troisième éTuDe De cas : les objeTs en argenT _______________________________________________________________________________ 106

quaTrième éTuDe De cas : les objeTs en fer ___________________________________________________________________________________ 106

LES POLLUANTS DANS LES COLLECTIONS ET LES MATÉRIAUX POUR LA CONSERVATION. DÉTECTION ET QUANTIFICATION PAR VOLTAMMÉTRIE, EXEMPLES D’APPLICATION F. urBan __________ 109

quels carTons uTiliser pour conserver les DaguerréoTypes ? ________________________________________________________ 110

Du sable en fonD De viTrine ? _____________________________________________________________________________________________________ 111

le rôle De la poussière ______________________________________________________________________________________________________________ 111

conclusion _______________________________________________________________________________________________________________________________ 112

LONG-TERM METALS PRESERVATION IN ARCHAEOLOGICAL STORAGES AND MUSEUMS M. duBus et al. ____ 1131. inTroDucTion ________________________________________________________________________________________________________________________ 113

2. experimenTal ________________________________________________________________________________________________________________________ 114

3. resulTs ________________________________________________________________________________________________________________________________ 114

4. conclusions _________________________________________________________________________________________________________________________ 115

5. acknowleDgmenTs __________________________________________________________________________________________________________________ 116

Table des matières


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05. Vers une plateforme des bonnes pratiques. Gestion des réserves et conservation durable Towards a Platform of Good Practices. Managing the Museum Reserves for Long-term Preservation

LE CENTRE DES COLLECTIONS DU MUSÉE NATIONAL SUISSE ET L’ENTREPOSAGE DES OBJETS DE COLLECTION B. sChüle _________________________________________________________________________________________ 121

affolTern am albis ___________________________________________________________________________________________________________________ 121

l’enTreposage Des objeTs De collecTion ________________________________________________________________________________________ 122

conclusion _______________________________________________________________________________________________________________________________ 125

LE MOBILIER ARCHÉOLOGIQUE MÉTALLIQUE DANS UN CHANTIER DES COLLECTIONS S. Païn ________ 127inTroDucTion _____________________________________________________________________________________________________________________________ 127

1. concevoir un chanTier Des collecTions ___________________________________________________________________________________ 127

2. la prise en compTe De la conservaTion _____________________________________________________________________________________ 1282. 1. Conservation préventive _____________________________________________________________________________________________ 1282. 2. Conservation curative et restauration ________________________________________________________________________ 128

3. la Dimension DocumenTaire eT l’accessibiliTé ____________________________________________________________________________ 129

conclusion. le chanTier pour aujourD’hui eT pour Demain _____________________________________________________________ 130

LA PRÉSERVATION DES OBJETS MÉTALLIQUES AU PAIR : LES PROCÉDURES ET LEUR ADAPTATION S. milBled et al. ______________________________________________________________ 133

1. le parcours De l’objeT méTallique : les DifférenTes éTapes eT les procéDures _____________________________ 1331.1. Prélèvement ________________________________________________________________________________________________________________ 1331.2. Première phase d’inventaire _______________________________________________________________________________________ 1341.3. Premières interventions d’urgence et / ou séchage contrôlé ________________________________________ 1351.4. Deuxième phase d’inventaire ______________________________________________________________________________________ 1351.5. Sélection des objets pour traitement pour étude et / ou radiographie X _______________________ 1351.6. Étude et précision des choix de traitement __________________________________________________________________ 1361.7. Contrôle et rangement ________________________________________________________________________________________________ 1371.8. Sélection pour conservation ________________________________________________________________________________________ 1371.9. Sélection pour valorisation __________________________________________________________________________________________ 1381.10. Veille sanitaire __________________________________________________________________________________________________________ 138

2. facTeurs influanT sur les choix De prise en charge __________________________________________________________________ 1382.1. La considération de l’objet __________________________________________________________________________________________ 1382.2. Les difficultés de conservation et les adaptations _______________________________________________________ 1392.3. Le statut juridique de l’objet et responsabilités ___________________________________________________________ 141

conclusion _______________________________________________________________________________________________________________________________ 142

remerciemenTs __________________________________________________________________________________________________________________________ 142

Table des matières


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LA MISE EN PLACE D’UN OUTIL POUR LA CONSERVATION À LONG TERME DES COLLECTIONS ARCHÉOLOGIQUES DU SERVICE PUBLIC DE WALLONIE M.-H. sChumaCher ______________________________________ 143

genèse Du projeT _______________________________________________________________________________________________________________________ 143

le projeT prenD forme _______________________________________________________________________________________________________________ 144

zoom sur la prise en charge parTiculière Des objeTs méTalliques ___________________________________________________ 145

conclusion eT perspecTives ________________________________________________________________________________________________________ 146

LISTE DES AUTEURS _____________________________________________________________________________________________________________________ 149

BIBLIOGRAPHIE ___________________________________________________________________________________________________________________________ 153


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Nettoyage mécanique, à l’aide de meulettes diamantées montées sur micro-tour, d’un fragment de hache en fer du cimetière mérovingien de Grez-Doiceau (Brabant wallon) (Service public de Wallonie).© Guy Focant, Département du Patrimoine du Service public

de Wallonie


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FROM EXCAVATION TO PRESERVATION: PREVENTIVE CONSERVATION APPROACHES IN ARCHAEOLOGICAL BRONZE COLLECTIONS

Omid oudbashi

inTroDucTion

Ancient copper and bronze artefacts are one of the most discovered burial finds in archaeological excavations during the last decades. These are valuable documents from technology of metallurgy and artistic, religion or living activities in the an-cient world (bertholon 2007). They may find as collections with considerable numbers of objects (figure 2). The corrosion events of bronze alloys occurred in burial environments make problems for archaeologists and conservators to prevent fur-ther deterioration after excavation (selWyn 2006 ; Watkinson 2010). Bronze artefacts may reach to equilibrium conditions with soil environment dur-ing long-term burial and corrosion rate may be reduced or controlled (sCott 2002). On the other hand, the excavation and the removal of objects from the ground may change the environment and the equilibrated conditions and lead to restart the corrosion or increase its rate by which serious problems will occur in excavated bronzes (bernard and Joiret 2009 ; bertholon 2007).

In this paper an integrated preventive conserva-tion approach for archaeological bronzes before, during and after excavation, have been reviewed. The aim of this paper is not to present a detailed guideline to preventive conservation operations for archaeological bronze collections, but to try to de-velop and explain a global approach that covers all aspects of preventive conservation from exca-vation to preservation of ancient bronze artefacts.

corrosion of archaeological bronzes: a shorT DescripTion

The corrosion in archaeological bronze collections could be classified as three parts:

– Long-term corrosion in burial environment;– During/post-excavation corrosion influenced by

nature of corrosion products and changing en-vironment after excavation;

– Corrosion of bronze due to conditions of stor-age/display environment and facilities.

The buried bronzes deteriorate in soil during long-term burial. Long-term corrosion of bronzes in bur-ial environment (i.e. soil) may lead to various cor-rosion morphologies and phenomena from noble patina with passive and stable corrosion products, vile patina with thick multiple layers of various corrosion products forms, or completely corroded object without any sound metal remnants (sCott

Figure 2.

Some bronze artefacts found during excavation from Sangtarashan (Iron Age), Western Iran.© Archaeological Campaign of

Sangtarashan


30La préservation des métaux archéologiques dès la fouille Archaeological Metals Taking and Preservation from the Excavations

2002 ; selWyn 2006 ; robbiola, blengino and fiaud 1998 ; piCCardo, Mille and robbiola 2007 ; oudbashi and eMaMi 2010). These phenomena could be referring to characteristics of burial environment and factors that may influence corrosion mecha-nism of metals as well as metallurgical features of bronzes (selWyn 2006 ; angelini, rosalbino, grass-ini e.a. 2007 ; robbiola, blengino and fiaud 1998 ; Chase 1994 ; sCott 2002 ; tyleCote 1979 ; nord, Mattsson and tronner 2005).

There is no problem in excavation of bronzes with noble patina. After unearthing the bronzes from Cl-containing soils, the post-excavation corrosion process may happen (figure 3). The post-ex-cavation corrosion in copper alloys is named as «bronze disease» or «active corrosio» and occurs

due to reaction of copper chloride with oxygen and water in the shape of relative humidity (RH) (sCott 2000, 1990, 2002 ; selWyn 2006 ; Casaletto, de Caro, ingo e.a. 2006). Usually, the critical RH for bronze disease is about 55-60%. Nevertheless, there is no evidence of continuing active corrosion in RH lower than 42-46% (selWyn 2007 ; sCott 1990 ; papapelekanos 2010).

Corrosion of archaeological bronze collections in museum environment and display/storage condi-tions would be more referred to RH and various pollutants in the museum. The RH can affect cor-rosion on archaeological bronzes suffering from bronze disease as noted above. Also, new corro-sion events may start in presence of pollutants re-sulting from air and materials constructing storage and display cases and other fabricated products in the museum (such as organic acids and alde-hydes) as well as gaseous pollutants (such as NOX, SO2 and CH3COOH). These situations can cause various corrosion processes in bronze objects, especially in presence of a high level of relative humidity (sCott 2002 ; tétreault, Cano, van boM-Mel e.a. 2003 ; hatChfield and Carpenter 1986 ; thiCkett and lee 2004). Of course, these corrosion phenomena are not related to long-term corrosion of bronze in the burial environment and condi-tions, and should be referred to new environment and materials used for display/storage of bronze collections.

Figure 3.

Powdery pale-green bronze disease corrosion products

on a bronze artefact from Haft Tappeh (Elamite),

Southwest Iran.© Omid oudbashi

main risk facTors

The impact of the various environments in which archaeological bronze objects are exposed has to be assessed by evaluating the risks posed by the overall environmental conditions during burial and after excavation.

Based on corrosion events noted above, the main environmental risk factors in the burial time, un-earthing processes and maintenance environment of museums and storages are:

– Chloride contamination in soil;– Water content of soil;– Relative humidity (%) during the excavation

and also in museum environment;

– Materials used for storage/display.

These factors influence corrosion events on ar-chaeological bronzes and may cause problems for the conservation of bronze collections. In fact, the main aim of preventive conservation must be controlling effects of these factors on bronze artefacts. The chloride and pollutions from museum materials affect archaeological bronzes by occurring corrosion events and transforming the metal to corrosion products while RH and water are the environmental fac-tors which influence the corrosion mechanisms explained previously.



prevenTive conservaTion in archaeological bronze collecTions

The corrosion of excavated bronzes is extremely influenced by the condition of burial and the main-tenance environment. With regard to deterioration processes of bronzes, chloride contamination and bronze disease, relative humidity and indoor corro-sive agents in the museum are the most important factors that must be considered in the planning of preventive conservation in bronze collections.

The conservation process in cultural heritage ma-terials could be categorized in two main types: pre-ventive conservation (passive) and interventive conservation (active) (Caple 2004 ; Mathias 1993). The preventive conservation is all activities to con-trol all kinds of deterioration or to reduce its rate in cultural materials without any direct intervention

on the objects themselves such as physical/chem-ical treatments. In fact, the preventive conserva-tion consists of monitoring and controlling storage and display environment, risk assessment and other indirect activities in collections (Caple 2004 ; Charola and koestler 2006, 29 ; keene 2005).

For this purpose, it may be considered to reduce the effect of factors influencing further corrosion in archaeological bronzes during/after excavation by preventing the relationship between metal and environment. Thus, a preventive conservation ap-proach for archaeological bronze collections can be divided in three main stages: pre-excavation activities, during excavation first aids and long-term preservation in museum (figure 4).

Pre-Excavation Considerations During-Excavation Activities Long-Term Preservation

Site Identification / Soil Assesment

Avoiding AcceleratedChanges

Controlling MuseumEnvironment

Preventive Conservation Approaches

Figure 4.

The preventive conservation approach for archaeological bronze collections.

pre-excavaTion consiDeraTionsThe first step is to identify the nature of the burial environment and the probable corrosion phenom-ena occurred in buried bronzes before excavation. This can be achieved by the examination of the soil parameters influencing the corrosion process and the climate in the site location. In many ar-chaeological excavation teams, there are no lab-oratory facilities to examine the soil conditions. It

must be noted that the soil of the archaeological site should be examined enough before excava-tion as to get required data and a site evaluation to prepare a preventive conservation approach for metals. The experimentation can be from a sim-ple qualitative determination methods of corrosive parameters (especially presence of soluble chlo-ride) to a subtle study of the soil with in situ and



laboratory methods for quantitative identifications. Based on the results of pre–excavation studies, ar-chaeological conservators can predict conditions of burial bronzes and establish an excavation plan as well as all facilities, tools and equipments re-quired for operate preventive conservation during excavation. Thus, the pre-excavation considera-tion could be classified as followed:

– Identification of local climate to know about RH, temperature, rainfall… ;

– Examination of the soil based on factors influ-encing on corrosion in soil (preliminary or sub-tle laboratory examination) ;

– Assessment of the situation of buried bronzes before starting the excavation to plan the exca-vation program.

During-excavaTion acTiviTies

Excavation may lead to change bronze object con-ditions and start or accelerate further corrosion (selWyn 2006 ; sease 1994, 1995). The aims of preventive approaches during excavation are:

– Reduce the influence of immediate environ-mental changes ;

– Preserve historic/artistic documents in archae-ological finds ;

– Apply storage tools and materials to reach long term controlling deterioration before any inter-vention in laboratory ;

– To enhance the bronzes life time before the es-tablishment of a long-term preventive conser-vation approach in the museum/storage.

To avoid activating corrosion or bronze disease in archaeological bronzes, the main activity during excavation is to prevent immediately nantokite to transform itself into copper trihy-droxichlorides for a short time (Cronyn 1990 ; sease 1994). On the other hand, some oper-ations are performed during the excavation to avoid physical decays such as breaking, re-moval probable decorations… (sease 1994). For this purpose, first-aid preventive conserva-tion approaches in the field include the remov-al of the bronzes from the soil (unearthing), to clean the contaminants, to dry in the site and to pack in the field.

long-Term preservaTion

The main factors that must be considered in long-term preservation of archaeological bronze collections are relative humidity and storage/display materials. Occurrence of bronze disease must be considered to provide with appropriate conditions the long-term preservation of bronz-es. The evidences such as pitting and pale-green powdery corrosion products are serious. Also,

results of in site and laboratory experiments are very useful to plan the preservation in museum environment. As noted above, relative humidity is the main factor influencing bronze disease occur-rence in copper alloys. Based on literature, range of RH in relation with active corrosion of bronzes may be explained as follow (sCott 1990 ; papape-lekanos 2010) (figure 5):

Safe Range

30% 40% 50% 60% 70%

Critical Range Dangerous Range

Increasing Probability of Bronze Disease with increasing RH

Figure 5.

Relationship between RH and bronze disease in

archaeological bronzes.



– RH lower than 40% is appropriate to preserve archaeological bronzes suffering from bronze disease ;

– RH between 40-55% has been reported as criti-cal RH for bronze disease in various literatures ;

– RH higher than 55% affects bronzes and ac-celerates active corrosion. In 70% and more, the reaction will be accelerated heavily and the bronze disease may occur in one day.

On the other hand, using inappropriate materials to make storage/display facilities and spaces could

affect further long-term corrosion in bronze arte-facts. In fact, the source of the pollutants-affect-ing corrosion is attributed to the materials used to create storage facilities (cases, cabinets, drawers, shelving…).

The main approaches in long term preventive con-servation are (figure 6):

– Controlling relative humidity in storage/display environment ;

– Application of suitable materials for storage/dis-play bronze collections in the museum.

Long Term Preservationof Bronze Collections

Controling RH under Critical Value Selecting Inert Materials for Storage

Figure 6.

Items influencing long-term preservation of bronze collections.

inTegraTing prevenTive conservaTion: The global approachPreventive conservation today is very important for archaeological finds and must be considered as a main approach for preserving the metal objects before any intervention and treatment. A good preventive conservation gives the possibility of identifying all values in metallic objects and makes time to study, characterize and display different aspects that are present in archaeological finds. Before any excavation, the recognition of the site and of the bronzes conditions and before any in-terventive conservation, the preservation and the making of long-term storage environment are the most important.

Based on the stages noted above, a global ap-proach for preventive conservation of archaeolog-ical bronze collections can be suggested in three specified stages of pre/during/post-excavation approaches. Figure 9 presents the detailed chart of the global approach. It includes all items that are explained as preventive conservation of bronze collections. The main subject is that this approach

must be considered as an integrated way to con-trol the influencing environmental conditions and to avoid inappropriate changes on the excavated bronzes. It means that all parts and items must be used during the excavation, first aids and long term preservation to reach suitable and great pre-ventive conservation. In fact, the conservation of

Figure 7.

Bronzes with active corrosion in a display case without controlling RH, Haft Tappeh Museum, southwest Iran.© Omid oudbashi



archaeological metal artefacts needs to consider all aspects that may influence stability, durability and all values present in cultural artefacts. Thus, the global and integrated approach considers all aspects, including the environmental conditions in which the bronzes were, are and will be located, materials applied for preventive conservation and therefore, providing suitable conditions in all stag-es of archaeological and conservation activities from excavation to preservation.

Preventive Conservation Approach for Archaeological Bronze Collections

Pre-

Exca

vatio

n Ap

proa

ches

Durin

g-Ex

cava

tion

Appr

oach

esPo

st-E

xcav

atio

n Ap

proa

ches

Site Studies

Archaeological Excavation

Long-Term Preservation

Active/Passive Corrosion Climate Identification

In Field Preventive Conservation Approach based on Site Study

Selection Inert Materials for Storage/Display Controlling Relative Humidity

Planning for Excavation and Conservation

Transmitting to Museum

Continuous Monitoring of Collection and Storage Environment

Unearthing Preliminary Cleaning Packing Drying

Figure 8.

Storage in paper and carton boxes in a close cabinet without controlling RH, Haft Tappeh Museum,

southwest Iran.© Omid oudbashi

Figure 9.

Integrated and global preventive conservation

approach for archaeological bronze collections.



conclusionThe integrated preventive conservation approach for archaeological bronze collections was re-viewed to explain various aspects of conservation activities in this field. The integrated approach was categorized as three individual steps: pre-ex-cavation considerations, during excavation activ-ities and long-term preservation. This approach intends to consider all features of bronze deterio-ration in archaeological collections with regard to the factors influencing bronze corrosion in three

noted steps. In this approach, all factors and their effects on bronze artefacts must be considered and preventive activities must be done as an in-tegrated conservation planning from the archaeo-logical site to the museum. In fact, this approach tries to make relations between archaeological conservation and preventive conservation by the study the risk factors, their effects and the required conservation activities in archaeological metal artefacts.

acknowleDgmenTs

The author is very thankful from Dr. Sébastien Clerbois, Letizia Nonne and their colleagues from CReA-Patrimoine, the Université libre de Brux-elles as well as the Fédération des Archéologues de Wallonie et de Bruxelles (FAW) and the Direc-

tion de l’Archéologie du Service public de Wallonie (Département du Patrimoine-DGO4) for inviting him to Brussels to present this paper and the best organization of the conference.

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