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The Scientist's Role In Histonc Preservation with Particular Reference to Stone Conservation GIORGIO TORRACA APPLICATION OF SCIENCE TO CONSERVATION In 1818 Sir Humphrey Davy was sent by the king of England to Naples with the task of speeding up the unrolling of charred papyrus scrolls that had been discovered more than 60 years before in a villa near Herculaneum. In the previous years a local friar had devised a com- plicated contraption with which he was able to separate the papyrus sheets, but with extreme slowness; only a few scrolls were opened in that period. Because it would have taken centuries at that rate to unroll the whole library, all intellectual Europe became impatient. Everybody wished to know the content of the first classical library ever discovered. Davy tried rapid chemical means on 11 scrolls, all of which were destroyed in the process before any attempt to decipher them could be made. Some people think he was unlucky in the choice of scrolls he submitted to the experiment, others that he was dealt the wrong ones on purpose. Whatever the case, one of the first recorded attempts of scientists to meddle with the conservation of antiquities was a complete failure. From a superficial examination of conservation history it appears that the record did not improve very much in ensuing years. Relevant Giorgio Torraca is Deputy Director, International Center for the Study of the Preser- vation and the Restoration of Cultural Property, Rome. 13

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14 CONSERVATION OF HISTORIC STONE BUILDINGS cases include the application of alkali silicates (Kuhiman cat 1830) and fluosilicates (Kessler in 1883) to stone conservation. Little by little, scientists learned to keep away from the dangerous domains of prac- tical conservation. Instead they wandered into the safer pastures of the analysis of artifacts, from which a flourishing new branch of science {archeometry) now grows. Scientific concepts and modern materials have obviously influenced modem conservation practice, but only in- sofar as they have been absorbed, more or less correctly, by the con- servators who tned to adapt them to their needs. SCIENCE AND TECHNOLOGY Some of the difficulties met in the transformation of scientific ideas into conservation processes are common to any branch of technology. In order to overcome these difficulties and to reduce the number of costly failures, industry relies on a particular class of persons of various (and frequently dubious) extraction who claim to be able to translate laboratory data into efficient processes on the production line. I shall designate them as "technologists" or, not so respectfully but more fondly, as "tinkerers." A constant characteristic of any job involving complex techniques is that decisions must be made before a given deadline. There is never time enough to obtain all the data required to build up a scientific mode] of the situation. On the production line, decisions are invariably made on the basis of insufficient information. Errors are frequent, and experience is gained the hard way, by trial and error. The technologist is accustomed to taking risks, gambling on his innate visionary gift to build models from insufficient data, on the experience obtained from previous failures, and finally on his luck. The technologist on the production line is normally the one who survived, so he is bound to be very good or very lucky. Progress in technology may arise from the introduction of new sci- entific ideas from the research laboratory, but frequently it stems from innovation on the production line attempted by a tinkerer of genius who had an urgent problem to solve. It is up to technologists to apply scientific discoveries at least as often as it is up to scientists to explain why something works. In both ways progress is made. PECULIAR ASPECTS OF CONSERVATION TECHNOLOGY If life is difficult for the technologist on any production line, it is even more so in practical conservation. Many variables are involved in con-

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Scientist* Role-in Historic Preservation 15 servation problems, and some of these lie out of the field of competence of any scientist (e.g., historic and aesthetic values). Even within natural science, the disciplines concemed are so varied that the case in which a single scientist may feel competent over the entire field is rather the exception than the rule. The immediate result of conservation processes is evaluated by a customer "historian, architect, or layman) who has little knowledge of the processes and the risks involved, but has strong views on what the result should not be. Anyway, an objective evaluation is always difficult because there are no standard procedures of quality control and no recognized acceptance tests. The final results of conservation processes can be judged only after a long time; this means that the outcome of a prototype operation is not known when the production line starts applying a new process. Because it is so difficult to judge the result (criteria of evaluation are nonscientific and the time required is Tong), it is not surprising that not only the fittest but also the less fit survive among the tinkerers and that the quality of the work produced is quite variable. As a consequence of the frequent reluctance on the part of scientists to become involved with practical conservation, the conservators sel- dom enjoy the services of technologists and of laboratories applying sound testing procedures. Thus conservators are frequently tempted to take over the entire sequence of operations: experiment, application, evaluation of results. Occasionally conservators mask the lack of sci- entific grounding of their efforts by contact with some friendly scientist who offers some amateur collaboration. The scanty and usually irrel- evant results of such collaboration are proudly displayed in reports and exhibitions to guarantee the scientific level of the work done, on which they had no influence whatsoever. ATTITUDES OF THE SCIENTIST IN CONSERVATION A scientist who decides to enter the field of practical conservation is, therefore, confronted with a production line whose quality is dubious and difficult to evaluate. The relevant technical literature is of difficult access and, when available, it looks shallow to the scientific eye (few data, no statistics, no reaction rates, no computerizable models). On the other hand, the scientist is strongly attracted by the domain of conservation. This is partly because the objects to be preserved are fascinating in themselves and partly because, in the multivariable proc- esses that govern deterioration and conservation, the hints for new ideas are innumerable. Even the dumbest scientist can discover new

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16 CONSERVATION OF HISTORIC STONE BUILDINGS schemes in a short time by application of the most standard concepts of his normal branch of activity. AS soon as the scientist has developed some new ideas, he is emo- tionally involved. He starts seeing himself as a savior for the endan- gered antiquities. This is a dangerous attitude, both for the antiquities involved and the scientist himself; just like the conservator, the sci- entist tends to take over the entire field, getting rid of all the other incompetent people. It is not infrequent to see research, development, production, and (positive) evaluation of the result carried out by the same person. This practice obviously is questionable, even if one must admit that the difficulties of collaborating with people of different backgrounds, who also are emotionally involved, may be indeed in- furiating. "Interdisciplinarity" is frequently used as a word but is seldom put into real practice. Nevertheless, effective interdisciplinary work is an absolute requirement for progress in conservation. THE CONSERVATION TECHNOLOGIST A consequence of what has been said above is that, in conservation practice, we frequently meet two anomalous tendencies. On one hand, the conservator tends to improve his scientific background and to do his own research and development; on the other, the specialized sci- entist expands his activity to cover the whole field down to the pro- duction line. A substantial improvement in conservation practice may be brought about only by more technological experimentation and more testing, under the condition that these be carried out by people and laboratories who are specialized in this kind of activity and are not emotionally involved (that is, people who have not invented a new process nor executed the job they must evaluate). In other words the screen of technological tests should be interposed as much as possible between basic research and the actual execution of conservation work. This is occasionally done in some government laboratories, but widespread action will probably require the support of university engineering de- partments, which have the right experience and equipment. To standardize testing procedures, the cooperation of a wide range of specialists within the scientific community is essential, both at the national and the international level. Professional organizations like ASTM and RILEM have an important role to play here. As the improve- ment of the professional Ievel of technologists and of the standardiza- tion of testing bring substantial progress, conservation will probably

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Scientist* Role in Historic Preservation 17 become far less picturesque than it used to be, but more reliable. Considering the high value of the property involved, reliability re- quirements should become more and more stringent, and much work will be needed to reach an adequate level in everyday practice. Much of the trouble in the present situation lies in the insufficient number fend level of competence) of the technologists available. The ideal conservation technologist should be a man of solid scientific background, but with enough versatility and culture to be able to understand the attitudes of all types of specialists involved in the conservation process. He should have a fee] for accurate measurement, fairness in judgment, and a decision-making capability. Above all, he should never invent a new conservation process. The ideal technologist would also understand that conservation re- quirements cover such a wide field that it is almost impossible to find an absence of conflicting requirements in any real problem (e.g., au- thenticity versus mechanical strength). He knows, therefore, that he is always wrong on some accounts when he performs an actual inter- vention on a piece of cultural property. On the other hand, he also knows that action may be required quickly to avoid some worse evil. In such cases the technologist must be able to select the right dead- line, one that leaves sufficient time to collect the minimum of data required but is brief enough to keep the chance of a catastrophic de- velopment to a minimum. The solutions he will choose for his prob- lems will not pretend to be perfect, but only "least evil" choices; he will be well aware of this and conscious that the case is never closed and that dangers lie ahead. A kind of walker on a tightrope, the conservation technologist has as a guideline the so-called principle of minimum intervention. The principle requires that he disturb as little as possible the "information" stored in the objects he must deal with, while ensuring that it is possible to preserve them and to use them for the function assigned by the present society for that will be assigned by a future one). This attitude is very different from that of conservators f end sci- entists) of the past, who tended to do too much, either because of an egotistical tendency to show their ability or in the naive hope of en- suring preservation for eternity. Minimum intervention, however, is applicable only if care and maintenance are foreseen. The advent of the conservation technologist implies, therefore, a general change of conservation policies, shifting the emphasis from spectacular performances in restoration to periodic maintenance rou- tines (survey, documentation, monitoring, repair, environmental pro- tection). If and when this desirable evolution takes place, conservation

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18 CONSERVATION OF HISTORIC STONE BUILDINGS technology will become as reliable as railroad engineering, probably to-the regret of the lovers of adventure who are so abundant in our trade. Luckily for them, the field is so complex and apparently inex- haustible that such a stage is not likely to be reached in a short time. THE CONSERVATOR Do not underrate the conservator. Scientists are frequently tempted to do so when they see him tinkering with "research" ideas and using very peculiar methods. The testing procedures of the conservator are unorthodox. However, by feeling the properties of materials with very accurate instruments (his eyes and hnnds), he can cut his way through a multivariable problem more efficiently than the scientist, who is accustomed to proceeding by logical steps and may have trouble iden- tifying which variable is the relevant one. Mixtures concocted by conservators for cleaning or protection pur- poses have frequently proved surprisingly successful when submitted to comparative tests with other products available on the market or prepared by scientists. In conservation, also, similar materials and pro- cesses may perform quite differently in the hands of different people. The difference may be not only aesthetic {which is quite important in this field), but might involve durabflity. Good eyes and hands are attributes that are slowly developed in a professional career. They are not improvised. A good scientist is not necessarily a good conservator. A flawless execution with a low-per- fonnance material may produce a better overall result than the inept application of a scientifically tested procedure. The conservator of the future wfl] be a noble artisan educated in scientific and technological principles and humanistic culture. His eyes and hands will be as good as they have ever been, but he wit] have reamed to allow other disciplines to aid his work and to extract from any sort of specialists information that is useful to him. He will be tendentially lazy, basing his actions on the principle of minimum intervention. Perhaps he will lose his natural tendency to overdo be- cause he wiB be well paid to look upon the objects entrusted to his continuous care-and to touch them only occasionally and with the lightest possible touch. He will resemble the family doctor who is paid to keep the patient in good shape, rather than the surgeon who performs spectacular operations in desperate cases.

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Scientist* Role in Historic Preservation SCIENTIFIC SUPPORT FOR STONE CONSERVATION 19 If conservation is a difficult field for scientists, stone conservation is one of the worst parts of it. The number of variables is enormous (particularly for objects exposed directly to the environment), deadlines tare stringent (serious damage may take place in a short time), decisions are risky (mode:is for deterioration must be oversimplified to be of any use), criticism is likely to be heavy (the result is frequently under the eye of the community), and, finally, failure is probable (the decay factors are always at work, while maintenance is costly and normally insufficient). Fundamental and technological research have a lot to contribute to stone conservation, however. Two divergent lines of development have appeared: One moves from details to a general scheme; the other pro- ceeds from theory to analysis of single cases. The literature on stone deterioration is enormous, and it is not easy to handle. The available data should be rearranged in such a way that a general theory of the deterioration of brittle, porous materials can be explicitly formulated. Obviously the first formulation of a general scheme is bound to be tentative and should be continuously updated when laboratory and field research show that it is inadequate to explain the facts. The general theory of stone deterioration must include all the rel- event mechanical, chemical, physicochemical, biological, and clima- tological factors and should elucidate their interplay..A theory explains facts and takes definite positions about what is relevant and what is not; it does not limit itself to a list of all.possible deterioration factors. An example may help to. explain the difference between an interpre- tive scheme (a theory) and a list of factors. Most books.and.papers on stone detenoration list thiobaciBi as a possible cause of decay, through the conversion of sulfides or sulfur dioxide to sulfuric acid. Nobody ventures, however, to state if and when this process is important with respect to other possible mechanisms. Extensive researches conducted in Venice and Prague appear, on the basis of isotopic analysis, to ex- clude a relevant role for ~iobacilli in those cities, while chemical- physical (and mechanical) factors are quite adequate to explain the sulfation process that takes place on the stones. A general theory on stone deterioration should include the notion that a relevant contri- bution by thiobaciRi to stone decay in polluted urban areas is im- probable. The second line of development that I mentioned above, the detailed study of. single cases, may appear to contradict what has been said

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20 CONSERVATION OF HISTORIC STONE BUILDINGS about the first. When actual cases of decay are studied for conservation purposes, each should be examined in the greatest possible detail, and a model of the deterioration processes relative to that case only should be built. Conservation provisions should then be made on the basis of the model. The importance of concentrating on isolated cases when considering treatment of stone may be underlined by an example. It is well known that a water-impervious surface coating may be dangerous on a porous material because stresses may be developed behind it if water gains access to the pore system by other ways (interstitial condensation, capillary rise, or rain penetration). The danger, however, is progres- sively reduced when the porosity of the material is lower and amounts to nil if the material is nonporous (e.g., metals). Stones of very low porosity (e.g., marble) have been protected for centuries in Europe by application of hydrophobic coating materials, generally with success. Any general statement about the usefulness of protective coatings in stone conservation would be meaningless. There is no single stone disease, as there is no single human disease. The great variability in properties of both the stone and the environment ensures the existence of a large number of different processes; the importance of the various controlling factors foreseen by the general theory may vary consider- ably from case to case. Substantial progress in stone conservation will be assured when several diseases are isolated and methods of treatment are tailored to each of them separately. Information from the results of attempts to cure the disease will play an essential part in future progress, as hap- pened in the progress of medical practice and science. There is no real divergence between the general theoretical research line and the practical one tied to the study of isolated cases. The interpretive models elaborated for single diseases must be consistent with the general theory, but, conversely, the theory must account for ah the particular cases. The interplay between the general require- ments of the theory and the facts resulting from analysis and practical experience is the basis of ah scientific progress. STONE CONSERVATION PRACTICE Conservation of stone exposed to the environment requires the estab- lishment of conservation policies rather than new conservation pro- cesses. At the present state of the art, the life of stone can be prolonged for very long periods if maintenance routines are established (as is done for steel structures exposed to the atmosphere). Such a policy involves

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Scientist* Role in Historic Preservation 21 considerable cost and effort. If and when it should be implemented is a political decision more than a technical one. There is room for improvement, however. Costs-may be reduced as materials with longer life and greater ease of application are developed; better aesthetic results may be obtained. But we should forget the notion that some day the perfect, eternal treatment will be discovered. Stone is inherently unstable on the earth's surface, and so are the protective materials we can think of. Any consolidation and protection system is necessarily going to be a temporary one. We should stop thinking of ourselves as the saviors of the ruins of the past. We should tackle a more modest task that of improving at all levels a series of maintenance processes, a production line that is already in operation and would keep going even without us. To do so, we must go outside the bounds of our fields of competence and work in close contact with fellow scientists from different disciplines and with nonscientists of variable backgrounds. That such a collaboration is extremely difficult is the plague, but also the beauty, of professional work in conservation.