Text of a talk given in the session "When conservator and collections meet" at the Annual Meeting of the Associaton of Art Historians, London, April 7-8, 1995. Not published .
I want to talk about ways of looking at change in museum objects over time, ways of deciding when this change should be called damage, and whether damage can ever be acceptable. It is not a simple subject and the following treatment will be somewhat superficial. In an effort to be as general as possible I am not going to show images of objects or micrographs of deterioration. So if you want to leave...
Whether accidental or deliberate, damage to an object is an important part of its history. Curators, conservation scientists and conservators all have different ways of looking at objects and may therefore have different definitions of what constitutes damage. I hope to show that we can't arrive at a consistent understanding of damage without combining the views of at least these three groups.
Because I have been both a scientist and a conservator I shall concentrate on the contributions that these two groups make and their limitations. I have never been a curator or an art historian and would not presume to discuss their limitations, in public.
There are good reasons to suppose there will be differences of opinion. It is unusual for curators, conservators and scientists to have taken the same educational route to museum work. The objects that conservators spend most time with have been damaged or are about to be. Conservators also spend a great deal of their time in that wonderful other world that you get to through the eyepieces of a binocular microscope. In that world very small signs have great significance. Scientists, especially chemists, will also look for explanations of macroscopic change at the microscopic or submicroscopic level. They will attempt to attach numerical values to small changes.
Here are some examples of museum dialogues in which the subject of damage may arise:
[Overhead 1 accidents authenticity priorities for treatment nature and extent of treatment methods and conditions of display suitability for loan]
Most of these are dealt with to some extent in later papers in this session.
Apart from the obvious " Oh my God I've dropped it!" there is the subject of
Authenticity - where the different perceptions and wisdom of curator, conservator and scientist complement one another. And the presence of the damage caused by old age or by restoration often provides valuable clues.
Priorities - Discussions about which objects to treat when, involve a comparison of different views of urgency. There is the urgency dictated by the timetable for presentation and interpretation. There is the urgency that is based on predictions of future damage.
The nature and extent of treatment.- Discussions about the nature of treatment will be about the inherent risk of the treatment. The probability of damage through loss of material or loss of information. Often these discussions are about the relative importance of future stability compared to present appearance or ease of access. The use of adhesives in textile conservation provides an example of this. The benefits of keeping the fragments of degrading silk together in the future must be weighed against the immediate loss of textile feel and appearance.
Questions about the extent of treatment usually centre on the proposed degree of reintegration of a damaged object. Restoration may lead to loss of information or introduction of misleading information. Both could be considered as damage.
Involvement in display - The necessity of support to minimise handling and to prevent future deterioration is balanced against the immediate desire for unrestricted and aesthetically pleasing interpretation. The mounting of dress is an example.
Conditions for display - Allowable levels of illumination provide the most familiar example of cost-benefit analysis in museums. The benefits to the user of being able to see the exhibit are compared with the costs, measured as damage to the object. We are all familiar with rules or guide-lines about light levels. 50 lux for textiles and works of art on paper. Stipulating the level of lighting without considering the length of exposure is fairly meaningless as far as control of fading is concerned. intensity of exposure and duration can be combined to give a total dose of light. The attempt to prescribe a maximum annual dose for each object makes us face up to the realities of the display / damage relationship. Every exposure will cause some change. What criteria can we use to define an acceptable rate?
Another arena in which conservators and curators may express differences of opinion is in the selection of objects for loan to other institutions. The differences are, of course, more often about the right to decide than the nature of the decision.
The legitimate causes for concern are that travelling, and display in a different environment, will increase the slow cumulative deterioration of the object. And that the act of travelling carries with it the increased risk of catastrophic change including total loss. So again we are faced with looking for criteria for rates of change that are acceptable. In addition we are looking for a definition of an acceptable probability of unacceptable change.
If you ask a simple question such as "what is damage?" it is easy to demonstrate that there cannot be one simple answer. For instance, a conservator cleans and consolidates an object, having with great professional skill solved problems of both longevity and legibility. The art historian takes one look at it and says "My God, you've ruined it!". Two people, one sees the change as acceptable the other finds it totally unacceptable and declares the act of change to be wanton damage.
Diversity of opinion is intellectually stimulating. Museums are interesting (or is it stressful?) places to work because the studies of art and history breed diversity. Yet, economic pressures demand corporate compliance.
For a variety of reasons, ranging from settling insurance claims, to setting environmental parameters for exhibitions, to developing the strategic plan, it is desirable that we control diversity sufficiently to arrive at a succession of consistent decisions.
Even if we know we will never find one simple answer, we may be able to order our thinking and group our various opinions closer together.
In order to bring order to my own thinking, I have been developing an intellectual model of the activities of a museum. Not surprisingly, it centres on the effects that museums have on the physical objects within them.
[Overhead 2 Resources Benefits]
In this mode someone provides the resources to run the museum and someone derives a benefit from the existence of the museum and its collections. It is representatives of Society, principally the government, but also ladies with blue hair and philanthropic arms dealers, that provide resources. And it is Society, or at least certain classes and colours within society, that gain benefit from the efficient allocation and application of these resources within the museum.
[Overhead 3 Resources Environment Treatment Benefits Use]
The resources can be allocated to three areas that affect what happens to the collections:
he first area is the environment, ideally one that is free of floods, earthquakes, thieves and arsonists. Where the roof doesn't leak, where the bugs don't bite and there is control over quantities of heat, light and dirt and air.
Access to the objects is obtained through display, reference collections, handling collections, exhibitions, loans, replicas, research, publications, books CD-ROMs. I have lumped all these together under the general heading-Use.
In the middle we have Treatment. Conservation treatment does not command a large proportion of resources. But I don't know any major collection that doesn't spend some money on interventive treatment each year. But there are two reasons for including it as a major entity I the model. Treatment can have a dramatic effect on individual objects. It affects how long they will last and how easy they are to use. It is also the justification for my salary and so rightly sits at the very centre.
Overhead 4 Resources Environment State Treatment Benefits Use Value]
These three factors; environment, treatment and use have effects on the collections and their individual constituents. I have separated these effects into two. Effects on the state of the object or collection, and effects on the value of the object or collection.
Although both are apparently short and simple, the two words state and value have complex connotations.
Briefly, State is what physically defines an object at any moment in time. All those physical attributes such as material, dimensions, decoration and evidence of manufacture that might appear in a curatorial catalogue entry are combined with what the conservator would recognise as descriptions of condition.
Value is not only what the Museum was or would be willing to pay for the object. It also reflects the return on that investment ,in the number of visitors that choose to see it, the number of students that wish to refer to it, the number of images that are sold or licensed throughout the world. It is a measure of demand for that particular work. It also should contain an element of what economists call Net Present Value. This is the value for us today, of net benefits that are predicted to accrue in the future. Thinking about the long-term benefits does something to eliminate the temporary fluctuations in value due to fashion. It also reminds us that there is current value in preserving some objects for extended periods.
Although the two terms state and value are strongly connected, it is easy to show that they are distinct. A change in relative humidity will alter the weight, dimensions and flexibility of a panel painting but will have no effect on its value. The reattribution of a painting can have a dramatic effect on its monetary and interest value without any change in its state.
[Overhead 5 inputs/outcomes Control Effect Resources Environment State Treatment Benefits Use Value]
To summarise, we have three areas. The area of inputs and outcomes which exists largely outside the museum. The area of control, where through policy, resource allocation and daily practice we decide how we use and abuse the collections. And finally the area where we observe the effects of our decisions on the objects.
To make this a working model we have to examine all the possible relationships between these seven elements. If we alter one of these elements, what effect does this have on any of the others? There are some thirty-two possible interactions in this model. Without discussion I am going to present this highly simplified version in which only ten important interactions are shown.
[Overhead 6] The above with lots of arrows]
In a minute I will use the model to move towards a definition of damage. But before that, just note that If you attempt any cost-benefit analysis of any museum activity that relates to the collections, you have go right around this route. You have to consider the combined effect of all of the possible interactions.
Environment, use and treatment can produce changes in objects. They produce changes in state, which may in turn cause changes in value. These changes in state are called: patina, restoration, or deterioration, depending on whether the change is desirable, deliberate or accidental. By a convention proposed by Canadian conservators ( Michalski, Waller, 1994), and in line with insurance nomenclature, the term "damage" is reserved for a change that invokes some sense of loss-of-property or loss-of-opportunity. In this model we would define damage as: -a change of state that results in a loss in value. Or you could go one step further round the chain and say that damage is something that decreases use or potential use. Or one step further, something that decreases the benefit that society can derive.
[Overhead 7 Rate of benefit X Life-span=total potential benefit]
If we can increase the rate at which society is allowed to benefit from the collections or we can do something to increase the life-span of the individual objects then we will have increased the total potential benefit, the maximum amount of benefit that can ever be derived from that object. This is my interpretation of The V&A's mission statement which is "to increase understanding and enjoyment". This is a mathematical rephrasing of our original problem of balance or compromise. If by increasing rate of enjoyment we decrease life-span we may end up with a lower total benefit. The same will happen if in our attempt to increase life-span we decrease rate of enjoyment.
So a further definition of damage is:
something that by an effect on our level of understanding and enjoyment or on the object's life-span causes a decrease in total benefit.
[Overhead 6 again]
However for the moment we will stay in the area of value. This is the point where the physical state of the object becomes combined with the effects of information about the object and opinion about the object. Understanding the physical state and predicting the life-span is primarily the realm of the scientist and conservator. Information and opinion are very much the realm of art historian, curator and educator. as indeed are understanding and enjoyment.
Linking damage to a change in value begins to lead us somewhere. A definition of damage as "any change of state" does not. The definition of damage as "any undesirable change of state" begs the question of why one state is to be desired rather than another.
Lets look at the methods that we currently use to assess state and then at the relationship between state and value.
When conservators write condition reports they have a wide vocabulary for signs of change of state. There are all sorts of words for things that, in the conservator's opinion, shouldn't have been allowed to happen. Wrinkle, cockle, tent, dent, fade, stain, accretion, loss. But when it comes to comparing one object with another or looking at the same object at different points of time the vocabulary becomes relational and poorly descriptive. Very scratched, considerably faded, more wrinkled. It is because of this lack of a quantitative vocabulary that increasing use is made of photographs in condition reports.
Surveys of the state of whole collections involve an assessor, usually a conservator, placing the observed condition of individual objects into one of several categories.
The categories most frequently used (Keene) are:-
The choice of an even number of categories forces the assessor to place the condition on one or other side of a central dividing line. Above the line we have stable, no action. Below the line we have unstable, action needed. Above the line there is nothing for the conservator to do, below the line the assessor has justified the continued existence of conservators. The majority of judgements are something to do with state, it is above the line that we see judgements about value--in context, disfigured. In fact the assessments are all about changes of state. Unstable means moving from one state to another. Conservators believe that they can make a holistic appraisal of a dynamic process by making a single observation.
The methods of the scientist are in complete contrast.
The scientist will choose one physical or chemical property of one of the materials the object is made of and measure it. The property chosen is one that could reasonably be expected to change with time. The act of measurement is a comparison with some standard, something that is not expected to change.
After a period of natural or accelerated ageing the scientist will take another measurement and record a new value. This process will be repeated at regular intervals so that a graph can be drawn of the change in that attribute with time.
[Overhead 8 (Typical graph showing data points in a line sloping down to the right)]
Time is shown along this axis, the units of measurement could be days, months, years. The measurement of the chosen property is shown by the height of the data point above the baseline. All the points can be joined together to form a line. In this case the line slopes downward from left to right as the numerical value of the observed property decreases with time. This would be the case if the measured characteristic were the tear strength of a piece of paper.
As a definition of state a measurement made by instrumental analysis has the advantage that it can be compared to other measurements using the same methods of analysis. The numbers can be subjected to mathematical and graphical analysis. For instance we can extrapolate and predict that this property will have a value of zero when time equals about twenty one units.
It has the disadvantage that it can only be applied to properties that are subject to quantitative measurement. That is, the attributes are chosen for their relative ease of measurement rather than by their relevance to the way the object is used or valued.
Moreover the strength of the scientific method is also its weakness. Each set of measurements applies to a separate property in isolation. For instance with a suitable instrument we can take colour measurements of small areas on the surface of a watercolour painting. However the appreciation of a watercolour may not just be a function of the reflected colours of small patches of pigment, but of the uniformity of larger patches of that colour, the contrast of colour or density between adjacent areas, or the distribution of different densities across the whole painting. So even though a number of the colours may change quite noticeably, the holistic appreciation of the object may hardly alter. The measurement of state when applied in the real world of people turns out to be an inappropriate measurement of value.
[Overhead 0 (three simple graphs explained in text)]
Given all these difficulties, let us just assume that we can find some measurable property that is universally agreed to have a direct relevance to the way that the object is used or appreciated. The lower this particular quality is, the less easy it is to use the object and the more difficult it is to appreciate it. Using the experienced eye of the conservator or the blind impartially of instrumental analysis, we find that there is a direct linear relationship between state and time. This might also be a picture of state versus hours of light exposure, or cycles of relative humidity or number of trips in the Museum van. With the appropriate units this is the relationship of state to cumulative dose of damaging event.
By using the various sensitivities and sensibilities of art-historians, curators, teachers and exhibition designers we find we have a direct linear relationship between state and value. By combining the two we arrive at a picture of the relationship between value and time. As time-elapsed increases the value decreases. I have defined the starting point at 100%value or 0% damage.
When the graph line hits this axis the value becomes zero and damage 100%. That is one indisputable definition of the limit of acceptable damage. At the top end there is only one point that represents 100% of value. The value is only 100% when exposure is zero. If we want to say that any value below 100% constitutes unacceptable damage then we can never move or expose or use the object in any way. In that case I would maintain that the object might as well not exist.
So if the object is to be used we have to be prepared to go down this road and we have to choose a totally arbitrary number for the acceptable limit to damage somewhere between 0 and 100%. The number doesn't have to be totally random, it could be arrived at by discussion amongst a group of experts, art historians for instance, who agree that at a certain level the object will no longer demonstrate those qualities for which it was acquired. Suppose this number is 75% of the original value. At our present rate of use, the object will have suffered an unacceptable degree of damage after X years.
This is not inevitable. We can exercise some control. Either by reducing the intensity of each exposure to damaging influence or by reducing the duration of exposure, or both. This will make the slope of the graph less steep.
[Overhead 10 graph explained in text]
This way we can increase the object's useful life two times, three times, as many times as we like. But it will always eventually reach that 75% line. So if we want to say there will only be one allowable rate of damage, then there can only be one acceptable slope for this line. The attempt to define a maximum annual dose of light for sensitive objects is such an attempt to fix the slope of this line. To fix that slope we have to define another arbitrary number--the service life of the object.
If we as guardians of this valuable and vulnerable artifact want to control its current use, then we have to declare in advance how long we think it should be allowed to function in the future. I am not being cynical when I say that people will inevitably choose a minimum service life that is long enough to ensure that they are completely retired if not dead by the time the limit is reached. This would tend to make the minimum value ever proposed for minimum service life somewhere in the order of thirty years. In my view an absolute maximum for the minimum service life of sensitive museum objects is two hundred years. That's about double the life of that whole public museum experiment that is being conducted up on Exhibition road.
[Overhead 11 graph explained in text]
Recognising that it is an arbitrary line we may choose this as guidance rather rigid restriction. How much latitude can we allow ourselves?
The upper limit is set by the cost of control and the fact that if you reduce exposure to damage you will reduce the benefit that is derived from exposure. For example, to minimise light damage we rotate displays of sensitive material. There is a manpower cost in constantly changing the display and also an additional risk of mechanical wear and tear. The benefit is severely reduced if levels of light are so low that aspects such as colour cannot be perceived or if objects are visible for so short a time that only a lucky few get to see them.
What about the lower limit? There are cost constraints on increasing the intensity or duration of exposure to damaging factors. For sensitive objects the cost is obvious damage. For robust objects It may actually cost too much to cause noticeable damage through increasing the intensity of routine museum activities. With some types of increased exposure there will be diminishing returns in benefit. For instance of the millions of people who went to the Tutankhamun exhibitions very few actually had time to appreciate the exhibits.
[Overhead 12 graph explained in text]
So you end up with a graph like this where at high rates of damage, benefits decrease and costs escalate and at low rates of damage costs start to rise and benefits drop dramatically. Any rate of damage for which benefits exceed costs will be acceptable. If you are averse to risk, which by definition conservators and possibly curators are, you will be tempted to operate at this low end but should be aware that you are not maximising net benefit.
What I have shown is an exceedingly simplified picture. for instance I have neglected the involvement of treatment in the relationship. It is my observation that people can come to terms with fading as a cost to be set against the benefit of display, but will not accept the mechanical detachment of small pieces of surface decoration. Yet this mechanical loss is easily reversed by treatment, fading is not considered treatable. Bizarre!
Many rates of deterioration are not linear with time. More important, the relationship of state and value is almost certainly not linear.
[Overhead 13 two graphs explained in text]
If you have a very plain surface such as an undecorated ceramic, or a polished metal object like a sword blade or silver vessel, then the first scratch or chip is the one that does most to lessen our enjoyment. The effect of the hundredth scratch on the value is negligible.
Conversely if you take a highly decorated surface with substantial asymmetric variations of hue, density and texture, the development of craquelure may have only a slight effect on one's appreciation. Even a large number of small random losses does not prevent legibility.
I have been looking at methods of quantifying damage as change in value that have been applied in the fields of health and environmental impact. Doctors do not quantify the health of a human being in terms of loss of physical bits and pieces but as decrease of mobility, self-care and social activity. These relate strongly to the value, use, benefit part of my model. It is interesting that when doctors were asked to give relative numerical gradings to increasing degrees of disability, the graph of quality-of-life against degree of disability looks exactly like this (like the curve for damage to a complex object) So I think there is some mileage in further research along these lines.
[Overhead * damage is observer- and context- dependent * Not all change is damage * most damage is the result of use * use increases benefit * some damage must be accepted * no single viewpoint is sufficient to set an acceptable rate.]