COMPATIBILITY OF CONSERVATION INTERVENTIONS IN

ARCHAEOLOGICAL SITES - THEORETICAL BACKGROUND AND PRACTICAL PERSPECTIVES

J. Delgado Rodrigues

Geologist, Principal Research Officer (ret.), National Laboratory of Civil Engineering,

Lisbon, Portugal, delgado@lnec.pt

SUMMARY

Conservation interventions in archaeological sites, whatever the object and the

intervention are, cannot be taken as a common technical matter. They bear a

unique character for being operated in objects of relevant cultural significance and

impossible to be repeated. Authenticity and integrity are the key-contents of the

object to be respected and compatibility can be the operative concept for guiding

the operators in crossing the intricate frontier between technology and cultural

values. In this framework, compatibility should not be restricted to the material

aspects of the problem, but it rather has to encompass other components such as

socio-cultural and operational issues. In spite of the different nature of these

components, they can be integrated in a conceptual model to constitute an

operative tool for achieving the best conservation practices. The model sustains

that compatibility reasoning is important and can be taken into account in all

phases of a conservation intervention, from the initial pre-diagnostic to the design

and implementation phases.

The paper addresses the theoretical background of the concept and of its relation

with other related concepts of use in conservation intervention, such as effective-

ness, harmfulness and reversibility. It also addresses the methodology developed in

the framework of the European research project PRODOMEA for turning this con-

cept into an operative tool in the conservation practice. Finally, it will go through

the sequential steps that may constitute the ideal process to be followed in conser-

vation interventions highlighting the topics where compatibility issues are present

and where the compatibility approach can help to reaching better results.

1. INTRODUCTION

Ancient sites are witnesses of the Human History that are important for the amount

of information they may carry with them and for the emotions and pleasure they

may convey to us when contemplating them. Some may consist of ingenious engi-

neering structures, others are humble testimonies of a past civilization, here we

may find an outstanding work of art, and there it may consist of a rudely cut piece

of stone. Variety and diversity are the rule and the size and appearance may not

disclose immediately all the interest the object may have for History and Human-

kind. They all share a common identity: all of them are objects of cultural interest.

Historic, aesthetic and any other cultural values are perceptions that may vary from

place to place, from time to time and from individual to individual. They are rooted

to the particular civilization that produced them, but they cannot live without the

particular cultural and civilization context of the individual or society that handle or

contemplate them. In many circumstances, these are relative and not absolute

values. The relativistic character of the cultural values brings about particular

responsibilities to the society, at local, regional, national and global levels. First of

all, it is imprudent (not to use a more drastic term) to minimize or downgrade the

cultural significance of an object and when this downsizing is carried out with

preconceptions it turns into a cultural crime. Unfortunately, downsizing is frequently

made for reaching economic advantages and then it constitutes also a civil crime.

Any society is expected to care for their cultural values and this incumbency in-

cludes typically the study and the preservation of the objects that materialise those

values. As said, such objects may vary in type and significance, but they also vary

in the material and in the state of conservation. And, consequently, they have

different conservation needs and require different conservation approaches.

Diversity and specificity are key-words of enormous significance in the realm of

preservation of cultural property, and constitute good pillars to support preserva-

tion strategies. And as an obvious consequence of this statement, multidisciplinary

means and interdisciplinary approaches should integrate the central core of the

research and implementation plans.

The multidisciplinary character of cultural property preservation means that many

disciplines may be called to contribute and implies that an endless number of

equipments and methodologies may find a place in this field of activity. Engineering

sciences are obvious components in such interdisciplinary approaches. However,

quite frequently, engineering interventions carried out to preserve the objects of

cultural interest are too drastic, even inappropriate, not to mention the cases when

the interventions ignore, abuse, or purposely destroy those cultural objects. This

means that intervening in such objects is more than a technical question, and re-

quires more than technical and scientific skills. It demands that a cultural approach

is embedded in the engineering solution, after balancing all the technical and

cultural values at stake.

The need to have professionals with good scientific background, high technical skills

and well supported in cultural values lead ICCROM to work on the definition of a

new professional profile, the “Conservation Scientist”, and to point out a definition

for this new category of professionals:

“Conservation scientist today can be defined as a scientist with a degree in one of the natural, physical and/or applied scientific disciplines and with further knowledge in conser-

vation (ethics, cultural values…) which enables him/her to contribute to the study and

conservation of cultural heritage within an interdisciplinary team”1.

This definition assumes that this should be the background required for those that

may bring about any technical impact on the cultural object. Of course, in many

circumstances (frequently the case with engineering sciences) it is difficult to find

conservation scientists with the capabilities required to solve specific problems or

situations that require highly specialised skills. Then, the most competent persons

should be called to contribute, yet their participation and the proposed solutions

must be integrated in intervention approaches lead or supervised by conservation

scientists.

The present paper aims at spreading some concepts and ideas that may contribute

to raise the quality of interventions in archaeological sites, particularly when engi-

neering needs are considered.

2. TECHNICAL VERSUS CULTURAL APPROACHES

As said by one of the great theoreticians of modern Restoration, Cesare Brandi,

only the material component of the work of art is susceptible to be restored2. This

axiom implies that in a conservation action all technical and scientific means are

acceptable to get the necessary knowledge about the material component, and the

unrepeatable character of a work of art implies that all the efforts to get informa-

tion and new knowledge are not only legitimate but also imperative. However, it

should be realised that any intervention in the material component may compromi-

se the historic significance and interfere with the aesthetic component, situations

that may jeopardise the work of art and all or part of its cultural values. The above

statements are necessary to underline that conservation and restoration have evi-

dent technical components, but they cannot be carried out under a technocratic

approach. Interventions in Ancient Sites of historic and aesthetic significance are

included and therefore they should be performed under strict and validated cultural

ambiances (Fig. 1).

Figure 1 - Multifaceted questions in the preservation of ancient sites. Shall an excavated structure be kept visible and accessible or should it be buried again? Does the society have the means to take care of it? How to maintain an archaeological site? How to protect a wall from environment factors? Shall a ruined structure be rebuilt or just stabilised? Shall a revetment mortar be replaced, consolidated or just let to fall down? How to deal with visitors?

The built patrimony may include settings of relevant cultural significance, both

when they are composed of grandiose structures and when they are current and

humble man-made constructions. The apparent similarity of those settings with

current unclassified structures may hidden the presence of relevant differences,

namely in the “invisible” historic and other cultural aspects. The temptation to use

the same methods and approaches for both situations is high and, unfortunately,

cases where this use has been made with profound misconceptions are not rare.

The “rehabilitation” actions carried out in ancient urban settlements with the aim of

preserving them introduce relevant changes and may strongly interfere with the

cultural significance of the sites. We must admit that it is virtually impossible to

preserve the sites integrally without lessening the cultural values; in some cases,

however, the changes are predictable and unavoidable consequences of a careful

action, in others, unfortunately, they may occur as a product of biased and

culturally unsupported decisions. The historic centres of ancient cities require

continuous maintenance and care and even the most judicious and well prepared

interventions may lead to variable interference in the cultural values. However,

when for economic and political reasons or for simple ignorance, the entire

buildings are emptied, transformed and refurbished although keeping their façades

as they were, it configures a cultural abuse, to say the least, and implies

irremediable losses of historical significance.

The intervention in high seismic-prone areas may require a totally different atti-

tude. In general, traditional structures are insufficiently resistant to high seismic

loads and to save ancient sites in these areas may require very intrusive actions.

When the alternative is the risk of total loss of the object or the partial compromise

of its cultural values, it is obvious that this compromise has to be reached and

some losses are to be accepted. However, even in such situations different levels of

interference can be used and to be able to graduate the intervention is also a

distinguishing feature of any culturally friendly intervention.

Solving the instability problems of a cathedral, repairing an old bridge or stabilising

a leaning tower are demanding engineering undertakings that may require that

highly specialised experts are called to tackle them. With the contribution of the

experts a solution is obtained in terms of the necessary effectiveness, yet this

solution may bring about negative side effects or may be excessively intrusive and

alternative solutions might be necessary. That is to say, for the interventions in

ancient sites, namely in archaeological items, an effective solution for a problem

may be insufficient, and other concepts need to be integrated in the assessment of

a potential solution before accepting it to be implemented. Some of these concepts

will be further detailed in the next chapter.

3. SOME LEADING CONCEPTS

It is a trivial statement to say that any conservation presupposes that there is a

problem to be solved; otherwise it would configure an abusive intervention and a

waste of means and money. A problem requires a solution and to be a solution

implies that the proposed action or actions are able and sufficient to solve the prob-

lem. We could then extract the corollary that effectiveness is the first criterion to be

matched when a solution is delineated. Apparently this is obvious, since no reason-

able person would apply a solution knowing that it is not effective. It is obvious, yet

exceptions are not that rare!

In principle, we can assume that effectiveness is the first criterion to be matched,

and we should admit that it is worthless to proceed in the scrutiny of any alterna-

tive that fails to demonstrate to fulfil this criterion.

Adequate and timely decided actions save objects and sites; when inappropriate or

ill-defined they may bring about additional problems and may jeopardise the object

or the site. All and every single action should be confronted with the possibility of

being detrimental to the object and it is of utmost importance to identify the nega-

tive side effects that may be induced and to assess their absolute or relative impor-

tance.

Several concepts have been used to name the negative side effects. Harmfulness is

a current term used when treatments are concerned and it may encompass all the

negative side effects that may be brought about by the concerned action.

Reversibility is another term applied in the conservation field. The concept is simple

and its justification seems straightforward. For very specific cases this statement

may apply; if something is added to a cultural object and it can be removed after-

wards without any interference in the object, it may be called a reversible action. A

shelter added to a site may fit in this concept, but there are not many other situa-

tions where reversibility can be fully guaranteed. Furthermore, a shelter or any

other adding may constitute reversible solutions, yet they also have to guarantee

that they are not harmful to the object.

At a certain epoch, the concept of reversibility was pushed too far in the field of

conservation even to situations where it is clearly inapplicable. It was sparsely used

in the field of consolidation of porous materials as a requirement for the selection of

consolidating products; some known products, such as Paraloid B72, were used in

stone consolidation supported in the “reversibility” characteristics of the acrylate

product on which it is based. However, being able to dissolve an acrylate product is

not the same as to be able to extract an acrylate from the interior of a consolidated

decayed stone and, in spite of the potential reversibility of the product, the consoli-

dation action is, in itself, a totally irreversible operation. The concept of reversibi-

lity, nowadays, is considered of little use in conservation and it is operative in very

peculiar situations only.

Compatibility is another concept of common use in conservation. In its current

significance, “in harmony with …”, the term has been applied to the most diversified

situations, in restrictive and broad senses. It has been applied to qualify products

or processes as well as for supporting or qualifying policies and strategies outside

and inside the conservation field. The term may well be used to select a stone

consolidant or a repair mortar, or to characterise a process of implementing a

conservation intervention as a whole.

Figure 2 - Multiple perspectives of compatibility. The use of a too resistant revetment

mortar (top left) illustrates a typical material incompatibility. An intrusive reinforcement (top right) shows evident aesthetic incompatibility, yet it is essential to keep the stretch of wall able to resist to seismic loads. Interventions in historic city centres (bottom) are often made without supporting conservation concepts and some of them show absolute disrespect for pre-existing constructions, leading to dramatic losses in cultural values

In real situations, things are not “black and white” - fully compatible/fully incom-

patible – and expressions of the type “…more compatible than…” are trivial ones. In

the domain of conservation of archaeological sites, this concept is particularly rele-

vant and very likely nobody questions its importance in this particular field. How-

ever, most archaeological sites suffer from incorrect intervention actions, poor

selection of materials, wrong intervention practices and wrong policy decisions, or

all of them together, and many items of cultural significance and historical docu-

ments have been definitively lost due to incompatible interventions. As a matter of

fact, compatibility has not been widely and properly used in the field of conserva-

tion of ancient sites.

4. COMPATIBILITY ISSUES

There is an increasing awareness on the need to follow high quality standards in

conservation actions and on the importance of the analytical management activities

and of their contribution to more effective planning. It is generally considered that

conservation interventions, namely in ancient or archaeological sites, carry a cer-

tain level of risk and that it is not technically and economically feasible to sustain

that only interventions without risk should be acceptable. Therefore, the ultimate

achievable aim is certainly not to find "perfectly compatible" actions, but to find

those that minimise the degree of incompatibility. However, it is not easy to identify

all the possible causes of errors and to assess on what degree a certain action may

or may not be detrimental to the object under consideration.

When a given action is under scrutiny, it is necessary to demonstrate that it is

effective and at the same time identify in what extent it may carry any risk to the

object. In general it is necessary to go through a process of balancing the benefits

and the shortcomings and to build up a decision where all the parameters available

are included. In most valuable objects, a “No-risk” option may be desirable, but

even in such situations this is more a wishful thinking than an absolute achievable

aim.

Justification of options taken in the conservation practice can be found in the litera-

ture, yet in general the references constitute qualitative evaluations and fuzzy des-

criptions of the decision-making process, leaving little or no possibility to recom-

pose and validate the decision process that effectively supported that option. One

simple reason stays in the fact that the decision process has to cope with multiple

influencing factors that turn the process into a very complex intellectual challenge.

The potential factors that may constitute causes of failure are multiple, their roles

are not linear and they are differently influencing. To work in such a multivariate

field is not simple.

Management of the conservation process has not precise methodologies for defining

the strategies to follow and the actions to be implemented and has difficulties to

identify the specific motivations that influence the decision making processes. The

broad concept of compatibility may help in this endeavour, namely by contributing

to find a suitable methodology to tackle complex cases such as the interventions in

ancient or archaeological sites. It supports a management instrument where the

compatibility model is the central operative tool. The guiding concepts of this

instrument are supported on criteria of technical, operational, environmental, social

and cultural types.

This methodology was developed under the research carried out in the framework

of the EU research project PRODOMEA and can be consulted in Delgado Rodrigues

and Grossi, 20073 and will be just superficially approached in this paper.

In a very simplistic way, the methodology sustains that sources of incompatibility

may derive from poor technical choices (e.g. the use of a very hard cement mortar

to repair an old traditional lime mortar), from the improper consideration of the

environmental conditions (e.g. disregarding the high loads that very large tempera-

ture variations may induce), but also from operational reasons and social and cul-

tural mismatches. To proceed with a conservation intervention without a clear defi-

nition of the conservation concept or the selection of a contractor based on the

costs alone are also potential causes of malfunction and they are clearly situated in

the domain of management and cultural assessment. Disregarding the local and

regional social environments may not be a direct cause of immediate failure but

forgetting them may result in important obstacles for the acceptance of the con-

cerned intervention by the local population and for promoting the future protection

of the site next to the social and scientific communities.

The above mentioned paper presents several tables for illustrating how compatibili-

ty issues can be integrated in the assessment process. The table that follows illus-

trates the methodology and exemplifies how different indicators can be identified

and their role evaluated in terms of the risks that they may bring for the overall

assessment of the intervention. Going through the table one may extract, for

instance, that “critical missings in the scientific and ethical principles” may consti-

tute a very High risk of incompatibility.

Table 1 – Operational conditionings that potentially affect performance

Criteria Compatibility indicators Incompatibility risks *

(L= Low; M= Moderate; H= High)

Definition of objectives and targets

Elaboration of a conservation concept

Diagnostic phase and incorporation of existing information

Filling gaps in information

Intervention phasing and conceptualisation

Definition of actions/Project

Good → L

Fair → M

None → H

Sequence and hierarchy of actions

Intervention planning

Interaction among actions

Logical and justified → L

Some gaps and doubts → M

No planning → H

Identification of needed skills

Available skills

Team composition

Definition of responsibilities

Properly done → L

Relevant missings → M

Critical missings → H

Minimum intervention

Compatibility concern Scientific and ethical

principles

Effectiveness and harmfulness

Properly considered and assumed → L

Relevant missings → M

Critical missings → H

Alternatives Costs

Cost control plan

Considered → L

Not considered → M

Durability assessment

Maintenance plan Inspection and monitoring

Considered and well done → L

Relevant omissions → M

Absent or critical omissions → H

Of the start-up situation Documentation of the intervention

Of the works carried out

Considered and well done → L

Poorly done → M

Absent or with critical errors → H

* The risks can be attributed as numeric values and this will allow to integrate them in an overall assessment of compatibility through the appropriate rating and weighing of the different indicators, as suggested in the quoted paper (Delgado Rodrigues and Grossi, 2007).

Similar tables were prepared for helping in the assessment of the incompatibility

risks concerning the material components, for instance, for selecting a mortar to be

used in a traditional masonry, a consolidant or a water repellent to be applied in

stone surfaces, etc.

5. A SUGGESTED METHODOLOGY

In general, conservation interventions are complex sets of actions, distributed in

space and developed in time, that integrate different actors and encompass several

successive steps. Analysing unsuccessful cases one may easily detect that causes of

failure may occur in different phases of the process and the actors responsible for

the critical failures may belong to any of the major groups involved: authorities,

technical and scientific participants and executors (contractors).

For minimizing the risks of malfunction and maximize the benefits, it is important to

have clear ideas about the different phases that may integrate a conservation inter-

vention, about the role of the different actors and of their position on the decision-

making process, as well as about the tasks that may integrate each phase of the

process. Compatibility issues are relevant items in several phases and they may

constitute work instruments to improve the quality of the process and to reach

more effective and compatible solutions.

In a schematic form, a conservation intervention may be subdivided into the typical

phases illustrated in Table 2:

Table 2 - Typical phases of a conservation intervention (simplified)

Typical phases Key-actors Check-list of the relevant actions and deliverables

Compatibility

issues

A. Pre-diagnostic

Art historian, Archaeologist, Architect, Conservator, Conservation scientist

� production of photographs � architectural investigation � archive investigation � mapping of degradation forms � mapping of distinctive materials � Preparation of report of Pre-diagnostic phase

Minor

B. Diagnostic Phase … … Minor

C. Conservation concept … … Relevant

D. Intervention actions

(from the scientific and technological points of view)

Conservation scientist, Other professionals

� Take into account the environmental impacts,

� Identification, execution and interpretation of field tests,

� Selection of materials to be used,

� Definition of procedures to implement the actions,

� Establish a hierarchical sequence of actions,

� Anticipate the potential interaction between procedures,

� Elaboration of reports

Relevant

E. Intervention plan … … Relevant

F. Selection of operators … … Relevant

G. Execution plan … … Relevant

H. Intervention execution … … Relevant

Typically, a conservation intervention involves several actors that play distinct roles

according to the phase under consideration and each phase integrates a set of

tasks that are required to be duly fulfilled in order to get the best possible results.

Table 2 exemplifies this concept for Phases A: Pre-diagnostic and D: Intervention

actions; a similar reasoning can be used to expand the table to all the other

phases. To identify the key-actors in each phase and to identify and describe as

precisely as possible the actions required in each phase is an exercise that will have

highly positive repercussion in the overall standard of any intervention.

The last column indicates the phases where compatibility issues are relevant and

this indicates that this concept cannot be disregarded when preparing, selecting

and implementing any conservation intervention. The proper use of this multi-para-

metric situation may raise difficulties, depending on the complexity of the inter-

vention and the experience of the relevant actors. The above quoted project oper-

ates a web site where an IT Tool and some hints on how to use it are available

(www.prodomea.com).

Based on the briefly exposed concepts, a methodology for dealing with conservation

interventions could be delineated as follows:

1. prepare a flow chart with the phases that integrate the intervention, iden-tify the main key-actors and the actions to integrate in each phase,

2. consider the compatibility issues to a given phase as a whole or to each individual action. For instance, the “operational conditionings” can be

applied to phases E & F (see table 1 for better understanding), while the

“Physical and chemical branch of compatibility” can be applied to the

individual actions under scrutiny. To opt between two different repair

mortars or between two stone consolidants will benefit from the application

of the incompatibility ratings.

The analysis of past interventions in ancient sites may be very informative and

provide important clues for future interventions. Both when they have performed

correctly and incorrectly relevant information is there, yet it may be not easy to

disclose why they have performed in such way and what were the parameters that

may better explain the observed performance. The use of compatibility indicators

(such as the ones shown in table 1) may help explaining the poor performances

observed and therefore they may provide hints on good/bad conservation practices.

In this aspect, the methodology can be considered a learning tool and an instru-

ment for reaching better conservation interventions.

ACKNOWLEDGEMENTS

This work was partially based on the results obtained in the framework of the EU

project PODOMEA, under the contract ICA3-CT-2002-10021. The contributions of all

partners and especially Arch. A. Grossi are acknowledged.

REFERENCES

1 ICCROM - The Bologna document. CURRIC Int. Seminar on University Post-graduate

Curricula for Conservation Scientists, ICCROM, Rome, 1999.

2 Brandi, C. – “Teoria del Restauro”. Piccola Biblioteca Einaudi, Turim, 1977 (2nd edition).

3 Delgado Rodrigues, J. and Grossi, A. - “Indicators and ratings for the compatibility

assessment of conservation actions”. Journal of Cultural Heritage, 8 (2007), pp. 32-43.