The Role of Heritage Science in Conservation Philosophy and Practice

Craig J. Kennedy

School of Energy, Geoscience, Infrastructure and Society,

Heriot Watt University,

Edinburgh,

UK,

EH14 4AS

Email: craig.kennedy@hw.ac.uk

Phone: +44 131 451 4629

1

Abstract

For many years the relationship between science and conservation has been

growing. Scientific research to understand historic materials and inform evidence-led

conservation practices is increasingly seen as an important step towards ensuring

positive long-term outcomes for cultural property. ‘Heritage Science’ is emerging as

a discipline within its own right. The development of heritage science with specific

reference to its application to building conservation is considered. The role of

science within building conservation philosophy and practice is discussed, and

barriers to effective evidence-led conservation identified. A set of seven

recommendations for heritage science applied to building conservation are

proposed. It is expected that these recommendations, if implemented, will help to

balance the needs of heritage practitioners whose work aligns with conservation

philosophy, and scientists who require the ability to gather meaningful data from

historic buildings and sites. This is intended to encourage and enhance collaboration

between scientists and practitioners.

Keywords

Conservation, Heritage, Philosophy, Practice, Principles, Research, Science

Biography

Craig Kennedy is an Associate Professor at Heriot Watt University. Prior to this he

was Head of Science at Historic Scotland. His key research interest is historic

building materials decay and conservation.

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Introduction

Conservation, restoration and preservation of buildings and other historical artefacts

has gone on for centuries. In the 20th century, scientists took an increasing interest in

analysing materials of historic value, leading to discrete scientific disciplines such as

archaeometry, conservation science and artefact studies.

In recent years a new discipline has emerged which aims to encompass all of these

domains and bring them together to aid in conservation practice: heritage science.

The phrase ‘heritage science’ was coined in the UK in 2006 by the House of Lords

Science and Technology sub-committee report in to Science and Heritage1 as a

replacement for a collection of other terms such as ‘conservation science’ and

‘archaeological science’, though the previous terms still live on.

Following the House of Lords Report, a UK national heritage science steering

committee was formed, composed of members representing heritage agencies,

institutions and academia. This committee produced a number of publications: three

2,3,4 (outlining the role of science in the management of heritage assets; the use of

science to understand the past; and the capacity in the heritage sector at that time.

The committee’s final publication was the UK national heritage science strategy5

which set out aims and objectives for the heritage science sector, and recommended

the formation of a National Heritage Science Forum, which now exists.

This paper considers the practical application of heritage science to the building

conservation sector, and how best to marry conservation philosophy with scientific

investigations.

3

Heritage Science as a Discipline

Many cultural institutions have a scientific research department which undertakes

research for the benefit of conservation. Over the last century many institutions have

incorporated a laboratory as part of the curatorial process when dealing with, for

example, museum collections. Early examples of laboratory installations include The

Staatliche Museum of Berlin, which opened a laboratory in 1888 and the British

Museum in London in 1919. Laboratories within museums increased in number after

World War I and again after World War II6. Built heritage organisations such as

Historic Scotland and English Heritage have employed scientific staff and equipped

laboratories in recent years with the aim of understanding the decay of building

materials, testing new conservation materials and providing evidence to aid in the

decision making process during conservation works. As well as undertaking direct

scientific work, these organisations work with a vibrant, international academic

community which retains a strong interest in understanding historic materials, their

decay and conservation in order to increase understanding of material properties at

a fundamental level7,8.

‘Conservation science’ existed for decades in this form before the emergence of the

term ‘heritage science’. Giovanni Urbani9 considered that conservation research

should evolve in to an independent scientific discipline, as scientists who were

primarily focused in non-heritage areas such as physics or chemistry would consider

only the constituent parts of a piece of cultural property, and not other aspects such

as aesthetic appreciation or heritage value. Considerable advancement has taken

place in the three decades since Urbani’s argument; Matija Strlic10 has set out a

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theoretical basis for heritage science based on a series of ten premises which

strongly consider the nature of the relationship between research and heritage value.

In the UK, matters coalesced in the mid-2000s with the House of Lords Science and

Technology sub-committee report into Science and Heritage1. This process involved

the gathering of evidence from across the scientific community working on the four

main areas of heritage: built heritage; collections; libraries and archives; and

archaeology. One outcome of this report was the formation of the UK national

heritage science strategy5 which sought to bring together a fragmented community

and encourage collaboration between scientists, conservation professionals,

heritage managers and stakeholders.

The national heritage science strategy gives two strategic aims:

‘1. Demonstrate the public benefit of heritage science and increase public

engagement and support for it.

2. Improve partnership within the sector and with others by increasing collaboration

to help practice make better use of research, knowledge and innovation and to

enhance resources, funding and skills.’

Each aim is underpinned by a number of objectives that will, if fully carried out,

improve the standing of heritage science. In terms of considering the application of

heritage science to building conservation philosophy and practice, the objective of

most relevance is:

‘Improving preservation.

The sector has made great strides in understanding materials and the mechanisms

of decay as well as developing ways to assess, monitor and record condition.

5

Through the application of heritage science we will continue to improve conservation

practice ... ’5

This objective links heritage science to conservation practice, but as yet the linkage

between the two is informal and the practical application of heritage science to

building conservation has not fully been considered.

Building Conservation Philosophy and Practice

Historic building conservation, replication or restoration has existed in various forms

for centuries. Jukka Jokilehto11 details the development of international building

conservation philosophies from the Italian Renaissance through to the 20 th century.

Today, repairs to historic buildings and monuments should be carried out with an

understanding and basis within building conservation philosophy. International

charters by the International Council on Monuments and Sites (ICOMOS), the

manifesto of Society for the Protection of Ancient Buildings (SPAB) and other

publications have evolved and been updated over time to meet the developing ideas

behind sensitive conservation. Forster12,13 discusses the ethics and principles behind

building conservation philosophy for masonry repair. Briefly, these are listed as:

Ethics: authenticity; integrity; avoidance of conjecture; respect for age and historic

patina; respect for the contribution of all periods; inseparable bond with setting; rights

of the indigenous community.

Principles: minimal intervention; legibility (honesty and distinguishability); materials

and techniques (use of ‘like for like’ materials); reversibility; documentation;

sustainability.

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The British Standard which relates to conservation of historic buildings – BS 7913 –

was updated in 201314. This document brings the fundamentals of conservation

philosophy into practice, with a strong emphasis on heritage management,

conservation plans, values, significance, and how these relate to the flow of work

during conservation projects.

Further translating conservation philosophy to practice is the accreditation process

for professionals. Accredited conservators undergo rigorous evaluation to ensure

that their work portfolio is aligned with these philosophical points. The Institute for

Conservation (ICON) manages the professional accreditation for conservator-

restorers (PACR) process in the UK. This process encompasses conservators

working in all areas of heritage, and as such their guidance is not built heritage-

specific. The PACR guidance15 lists five key standards for members undergoing the

accreditation process: assessment of cultural heritage; conservation options and

strategies; conservation measures; organisation and management; and professional

development. Alongside these five standards are thirteen professional judgement

and ethics (J&E) principles, including ‘understanding principles and practice’ and

‘conversance with guidelines’.

The Institute for Historic Building Conservation (IHBC) has an accreditation process

for practitioners working specifically in the historic buildings sector. The IHBC

structures its accreditation process around the main elements of the ‘areas of

competence’. These areas of competence are divided into two sections: professional

and practical. Within the ‘professional’ competence, the membership standards,

criteria and guidelines16 states that professionals working in conservation require an

understanding of conservation philosophy and its application to practice.

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Heritage Science as a part of Conservation Philosophy

Ethical considerations of conservation philosophy do not occur in isolation. Scientific

research may have a part to play in ensuring the effective application of ethical

values to conservation.

When considering authenticity, the ability to distinguish between original material and

later repairs is important. In many cases scientific equipment may not be needed –

for example, plastic repairs from the latter half of the 20th century on a building that is

centuries old will be distinguishable to a competent practitioner. However, for other

forms where effort has been made to ensure that the repair is indistinguishable from

the original material, scientific methods may be needed to provide an additional

dimension to the available information. An example of the use of science to establish

authenticity is the identification of original window glass in historic buildings using

portable X-ray fluorescence17.

Integrity of a structure is discussed by Forster, who makes the distinction between

‘living’ and ‘dead’ buildings and how integrity may conflict with authenticity in these

cases. For a ‘living’ building which is still in use and functioning (as opposed to, say,

a ruin), the replacement of a failed section would require some scientific intervention

to ensure that the appropriate material is selected18.

The avoidance of conjecture (the need for incontestable evidence) and restoration

are wholly reliant on having as complete an evidence base as possible. Restoration

is taking a building back to a specific point in time and to do so effectively requires

interpretation of all the available evidence from that time. Forster notes that evidence

of this nature is rarely available without good historical documentation. Taking a

recent example, the restoration of the palace at Stirling Castle which was completed

8

in 2011 relied on an extensive research programme analysing historic plans,

furnishings and excavation reports19. Scientific information has the potential to

complement such historical research, through the analysis of the building fabric to

determine origin, provenance or conservation history.

Respect for age and patina are considerations for conservation, as patina is

regarded as having aesthetic and historic qualities20 . Research has a role in this

regard, by ensuring that cleaning techniques are not overly aggressive. Disruptive

techniques have the potential to destroy the patina in order to make a material look

like new. Stone cleaning carried out using inappropriate methods in the 20 th century

has allowed buildings to lose their historic patina and, in some cases, discolour the

stone21. This realisation led to research into different methods that has allowed for

gentler methods of stone cleaning which retain the historic patina to be highlighted.

Similarly, research carried out on historic wrought iron has sought to develop a

cleaning method that will not disrupt the oxide layer that forms on the iron surface

over time, demonstrating that scientific testing can lead to positive outcomes from

cleaning that will not significantly harm the heritage value of an object or building22.

As well as ethical considerations, the principles of building conservation philosophy

can be enhanced through scientific input.

Perhaps the most obvious example is use of ‘like for like’ materials for repair, as it

may be necessary to scientifically determine which replacement material bears the

closest resemblance in terms of material properties to the original. A clear illustration

of this is petrographic analysis of building stones, a technique that considers which

stones available from currently operating quarries most closely match historic stones

in terms of properties such as porosity and sorting23. Over time, this will ensure that

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the replacement stone does not accelerate the decay of the historic stones

surrounding it, as can happen if a dense stone is placed in the midst of porous

stones, hastening the decline of the historic elements of the building fabric. Other

innovations in this field include the potential use of near-infrared spectroscopy (NIR)

and soil micromorphology to identify appropriate repair materials for earth

buildings24,25.

Scientific input has the potential to allow for a greater understanding of the condition

of existing historic sections of a building and may aid in keeping in place materials

that could otherwise be removed unnecessarily. This will aid in honouring the

principle of least or minimal intervention. Timber is a good example of this—timber

members within a building are visually assessed as part of a condition survey and a

decision is made to remove the member or keep it in place. The member may still be

load bearing but if the surface of the timber is eroded by, for example, rot or

woodworm the decision may be taken to remove it. Recent experiments have taken

place to attempt to develop a non-destructive acoustic method of assessing timber

strength in situ. This type of testing has the potential to protect many timbers within

historic buildings from being removed and replaced26.

Reversibility of a conservation application is an important philosophical principle. Any

action taken to conserve an object or building should have the ability to be removed

should it prove harmful to the substrate. Included in this are short-term remedies,

such as the application of facing materials to structural paintings for transportation

and storage. Theur27 conducted a series of experiments to understand the effects of

commonly used facing materials on long-term storage of paintings and painted

ceilings, and their ability to be removed after prolonged periods.

10

The ability of science to influence and improve conservation has long been

recognised, and as such is included in international charters and professional

guidance. Article 2 of the ICOMOS Venice charter28 states:

‘The conservation and restoration of monuments must have recourse to all the

sciences and techniques which can contribute to the study and safeguarding of the

architectural heritage’

The ICOMOS charter ‘Principles for the analysis, conservation and structural

restoration of architectural heritage29’ considers the role of research more fully, and

has a key guiding principle listed as ‘Research and diagnosis’. This principle relates

to the approach that should be taken when undertaking research into historic

buildings, including two which specifically relate to scientific analysis of a building

(2.3 and 2.5). These can be summarised as the requirement for a full understanding

of the structural and material characteristics required in conservation practice; and

the approaches that should be made when diagnosing defects. Specifically, in terms

of science:

‘the quantitative approach mainly [based] on material and structural tests, monitoring

and structural analysis.’

An example of using science to diagnose defects in historic buildings is the analysis

of hair used in lime plasters30 which found that repair materials that have been pre-

treated with bleach or acid will lose performance significantly, leading to failures.

British Standard BS 791314 makes several explicit references to research in support

of evidence-led conservation, including a statement that good conservation depends

11

on ‘a sound research evidence base and the use of competent advisors and

contractors.’

Two statements in the Standard clearly define the role of science as an essential

part of conservation work:

‘Work proposals should be based on an appropriate level of research into the historic

building in order to understand its significance, structure, fabric, design, layout,

services and other parameters.’

And:

‘The correct choice of materials for conservation works is important for historic

buildings. Where possible, existing materials should be investigated and tested so

that good performance and aesthetic matches can be achieved.’

The role of science has also made its way in to the professional accreditation

process for heritage practitioners. Standard 3 of the ICON guidance15 – conservation

measures – makes several references to taking in to account current research as

part of the decision-making process when considering conservation measures and

techniques. In 2006/7 the Institute of Conservation Science (ICS) joined ICON to

become the ICON Science Group. This merger was designed to improve the scope

for closer interaction between conservation and science.

The Institute for Historic Building Conservation (IHBC) recognises the value of

incorporating research to conservation, and has produced guidance to work towards

evidence-based conservation standards31. This stems from a belief that ‘effective

conservation standards should be developed out of research-based evidence

supported by practice-based guidance’. This statement clearly places research in a

12

key role in the conservation process. The IHBC lists ‘Research, Recording &

Analysis’ as an area of competence in their membership standards, criteria and

guidelines, further aligning research and practical conservation for professional

members.

From these examples, it may be considered that science not only has a role to play

in informing conservation practice, but that scientific research is essential in ensuring

that conservation carried out is evidence-based, increasing the likelihood of a

positive outcome. Scientific research has been a central theme of conservation

philosophy for over half a century, though its utilisation in practice has perhaps not

been fully realised.

Barriers to Effective Heritage Science

Whilst the role of heritage science in conservation philosophy is explicitly stated in

conservation charters, it is often not possible to utilise heritage science fully for the

purposes of conservation.

One key issue faced by heritage scientists is sampling. In order to fully understand a

material, it may be necessary to extract sections to be taken for laboratory

investigations. Heritage managers are often reluctant to allow sampling, and if

allowed it is often at a level inadequate for statistically significant findings to be

gleaned.

This is perhaps related to heritage managers considering loss of historic fabric for

testing as inadvisable, or inappropriate. Under the heading ‘Heritage Management

Principles’ in BS 791314 it is stated that the principle of minimal intervention is

13

important; that is, as much fabric as possible should be retained when a repair or

other intervention is required.

This leaves the heritage manager with the task of balancing the need for sampling in

order to gain an understanding of the building materials with the pressure to allow as

little material to be taken from the site as possible. Torraca32 describes balancing

minimum intervention and the requirement for testing as a ‘tightrope’ in the context of

stone conservation, whereby as little of the ‘information’ stored in objects is disturbed

as possible, whilst ensuring that the object can be preserved for the present and

future.

In many cases the level of sampling allowed is in proportion to the status of the

building being examined; a traditional building with no statutory protection such as

listed status may be sampled extensively with the owner’s permission, but a building

of national importance such as a scheduled ancient monument is unlikely to be

sampled at all. Ironically, conservation is allowed on many high-status buildings but

the lack of scientific input, brought about by a desire to protect the building, may lead

to a less than ideal long-term outcome from the conservation works.

A second issue facing heritage scientists is a lack of knowledge of the provenance of

a sample. It may be the case that the building under study is centuries old and has

undergone a series of changes over time, such as extensions, renovations,

restorations and conservation works. It may not always be apparent if a sample is

original to the building, or as the result of a later intervention. As such, one emerging

branch of heritage science is that of understanding provenance, as observed in

recent papers by Dungworth33, Avino & Rosada34 and Ortega et al35.

14

Linked to the issue of provenance is the history of a sample. If a sample is original it

may have undergone conservation works in the past, and this may not be known to

the scientist if appropriate recording has not been taken. Here, it is important that a

scientist working on a building has access to conservation records so that it may

inform the results and recommendations arising from scientific investigation.

Strlic10 notes an issue regarding scientific values with regards to heritage science: it

can be neither experimental nor fundamental. When analysing historic items,

experiments are not repeatable and so taking a typical scientific approach to an

experimental programme is not possible in these instances. Equally, the objective of

heritage science is always known, and so it cannot be considered fundamental

research.

Developing a Set of Recommendations for Practicing Heritage Science

It is clear from the conservation charters and the national heritage science strategy

that science has a central role to play in informing conservation practice. Here, a set

of recommendations are proposed which are designed to meet the requirements of

scientists, conservators and heritage managers which share the same vision of

favourable outcomes for historic buildings following conservation interventions.

1. A team-based approach to developing evidence-based conservation.

This is a reflection of principle 2.1 of the ICOMOS charter ‘Principles for the analysis,

conservation and structural restoration of architectural heritage’. When undertaking

building conservation, the scientist should be part of the multidisciplinary team with a

specific remit to investigate the building and help inform the physical conservation of

the building. Ideally as part of a planning process scientific investigations should take

15

place ahead of the conservation work. This form of interaction will help to highlight

the positive role that a scientist can take in the conservation process, and also help

the scientist take direction and understand underlying issues facing the building.

2. Preference for non-destructive or micro-destructive testing.

A major barrier to effective scientific input is the constraints placed on scientists

regarding sampling. Here, two approaches are proposed which will allow heritage

managers to be satisfied that excessive sampling is not taking place and allow the

scientist to glean meaningful, statistically significant data.

The recent development of portable laboratory equipment with capabilities

analogous to larger laboratory-based systems has allowed for an effective revolution

in heritage science. Recent advances in portable technology have included Near-

Infrared spectroscopy (NIR), X-ray fluorescence (XRF), hyperspectral imaging,

thermal imaging, laser scanning, Raman spectroscopy and many others.17,24,36,37,38,39

Such systems have allowed scientists to take the laboratory to the site, gathering a

large quantity of highly relevant data without the need for physical sampling. Where

appropriate and possible, non-destructive testing should be the preferred method of

scientific investigation of historic buildings and sites.

The type of equipment used should be appropriate for the type of information being

sought, and often more than one technique will need to be employed at any one

time.

It may also be the case that sampling is required, should such portable devices

either be unavailable or not suited for the type of scientific investigation needed. X-

ray diffraction is an example of a technique that is highly useful for the analysis of

16

stone and mortar materials, but is not available as a portable instrument. Should

sampling be required, it is recommended that a high number of very small samples

from various places across the area of interest (i.e. façade) are taken. Such micro-

testing is already in place in other sectors of heritage, for example micro-drilling of

parchment for document conservation40.

3. Gathering Large Data Sets

The nature of historic monuments and sites means that they often consist of a

collection of various materials combined to form the whole. The building may also be

subject to microclimates and discrete variations in fabric that mean different sections

of the building becoming weathered at different rates. As such, data should be taken

from across the whole site where possible. This would allow for a more complete

understanding of the behaviour of the whole area of interest and reduce the chances

that a sample taken from an unusual area – for instance, an area subjected to a

microclimate different from the rest of the site – could skew results and produce less

than ideal scientific conclusions. It is not advisable to take only a few samples, or

sample from a limited area, so as to extrapolate information on the whole building

from such small data sets may not be beneficial to conservation works.

4. Use of modern analogue materials

For robust scientific investigations on how a material may respond to specific

circumstances, the development of modern equivalents that can be tested

extensively is encouraged, though with caution. For example, Historic Scotland

commissioned the construction of experimental earth walls in locations across

Scotland to determine their responses to climate41. The same organisation also

constructed a sandstone wall in order to examine the effects of extreme salt

17

damage, exposing the analogue to conditions that would not be allowable on a

heritage asset (figure 1).

Strlic10 considers the benefits of using ‘mock or surrogate objects for research’. As

stated previously, scientific investigations taking place on historic materials are not

repeatable, and as such heritage science cannot be considered experimental.

However, when using analogous materials experiments can be reproduced allowing

for typical scientific principles to remain intact.

Care must be taken when comparing modern analogues to historical materials.

Historic building elements may have been constructed in a subtly different manner

from the modern analogues and will have been subjected to weathering over a long

period of time. Additionally, historic materials may be naturally different from modern

equivalents – one example is timber, which historically was slow grown for a longer

period of time compared to modern timber which may be faster grow for a shorter

period of time. Altering the growth regime for timbers in such a way will significantly

alter the physical properties42.

As such, although useful information may be gained from modern analogues, it may

be the case that historic building materials behave in a different manner.

5. Stress Testing (Artificial or Accelerated Ageing)

Accelerated or artificial ageing is a concept used in heritage science since the

nineteen fifties43. Much of the research carried out on accelerated ageing relates to

shelf life of perishable materials, and in the heritage sector the key output has been

for studies on historic paper. This form of testing requires a material to be placed in

an environmental chamber and exposed to extreme conditions; in theory, such

18

conditions speed up the natural ageing of the material (figure 2). Such tests are done

in order to determine the effects of a conservation treatment or to evaluate the future

condition of a historic material44,45,46.

The basis for this type of test is the Arrhenius equation (figure 3), a formula for the

temperature dependence of chemical reaction rates. A generalisation of this

equation is that for common chemical reactions at room temperature, the reaction

rate doubles for each 10 degrees Celsius rise in temperature47. Extrapolating the

Arrhenius equation to a log-plot of reaction rates (k) or degradation times (1/k)

versus inverse temperature (1/T) should result in a straight line, allowing

extrapolations to be made at lower temperatures. Hence, for data gathered on a

material at high temperature over a period of weeks, the rate of degradation can be

calculated at low temperature for a period of years.

However, there is some scepticism as to the validity of these ageing methods as a

means of predicting behaviour of historic materials43,48. One argument against

Arrhenius ageing is that the equation was designed to consider elementary chemical

reactions, whilst historic materials are complicated aggregates of differing systems.

Another is that Arrhenius behaviour does not match experimentally derived data49.

To improve accelerated ageing results, more complicated systems of ageing have

been proposed which include elevated temperature, controlled humidity, irradiation,

and the inclusion of pollutants47,50. However, no standard method of accelerated

ageing has yet been devised that can accurately predict the behaviour of a building

material after many years of natural ageing.

For the purposes of understanding reactions of historic building materials to

environmental conditions, it may be wise to stop references to ageing and instead

19

replace these forms of experiments with a title such as ‘stress tests’. Such tests are

valuable in determining a material’s durability following conservation works.

Renaming these tests will remove the inference that the results of such experiments

are representative of the future condition of samples.

6. Openness of Access to Experimental Data

Recording and documentation is a principle of building conservation. This is

essential in tracking the changes undergone over the lifetime of a building. Regular

condition surveys chart the emergence of any potential problems that threaten the

building. More recently laser scanning has become an integrated part of the

condition survey36. When building conservation works are carried out extensive

reports are written, photographs taken and the final work is archived for future

conservators. Results of scientific investigations should be included as part of the

building conservation records with a similar view in mind: in future years, when

conservators and scientists revisit a site they should have access to as much

detailed information as possible about the building they are about to embark working

on.

As well as summary reports of scientific investigations, raw data should be included

where possible so that comparisons may be made in future which may highlight any

changes that have taken place to the material over time.

Additionally, publication of scientific material relating to conservation should be

encouraged. For evidence-led conservation to become the norm, the overall

knowledge base regarding traditional building materials must be increased. This

would allow scientists worldwide to have access to a wealth of data which may

inform their own conservation programmes.

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7. Integrating heritage science as part of the overall heritage experience

Heritage science is an increasingly significant aspect of conservation work. Where

possible, the investigative aspects of conservation should also be highlighted. This

will boost both the profile of heritage science, and also enhance the public

understanding of how key decisions are reached with regards to conservation.

Heritage institution websites, magazines and technical publications often hold

articles on how an object or building was investigated and conserved51,52. This level

of openly available information has the potential to expand the visitor experience,

and consideration should be taken as to how this could be achieved.

This principle links directly to the strategic aim of the national heritage science

strategy to demonstrate the public benefit of, and increase support for, heritage

science.

Conclusion

Here, seven recommendations are suggested which relate to how heritage science

can be of practical help to building conservation works, enhancing the quality and

outcomes of conservation work. These principles align with the established

philosophical basis for conservation of buildings. On a practical level, these also aim

to balance the needs of the scientist with heritage management principles.

21

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