CRITERIA FOR TREATMENT: REVERSIBILITY
10 DEGREES OF REVERSIBILITY AND EXTERNAL SUPPORTS
Reversibility is not a simple “yes” or “no” proposition. Within the wide range of treatments of which the results can be undone, there are degrees of reversibility, depending on how much time and trouble are involved, and on what risk it poses for the object, since a troublesome or time-consuming job for the conservator almost inevitably involves an ordeal for the object under treatment. How much flexibility for the future is built into the treatment? Is it possible to undo some of the treatment without undoing the rest? Specifically, can external supports, like patches or linings be removed without weakening internal consolidation materials?
The choice of auxiliary support in the restretching of a painting is an example of a treatment procedure which offers alternatives similar in other respects but differing in their degrees of reversibility. If a painting stretched on a stretcher were scratched or dented, ease of access to the reverse would usually permit local treatment. However, if the painting had been stretched around, or adhered to, a solid support, complete removal would probably be necessary to allow access to the reverse. This could entail a major treatment instead of a minor one. The sewing of textiles to a stretched fabric is analogous. With time, particularly if a textile is on exhibition or stored vertically, the textile may stretch slightly and “belly out” from the support. Small fragments may come loose. If the textile has been kept on its mounting strainer, more sewing can be done easily. If, however, the mounting fabric has been cut loose from its strainer and wrapped around a solid support, sewing can only be done with a curved needle, if at all, a procedure extremely tedious and quite stressful on the object. The ease of re-treatment could make reversing the original treatment unnecessary, thus avoiding major stress on both the object and the conservator.
Ease of reversibility is also an issue with textiles because the mounting is both an aesthetic setting (equivalent to the mat of a work on paper or the frame of a painting) and a structural support (equivalent to a lining). As exhibition conditions, ownership, or styles change, the color or texture of the mount could become objectionable, but changing the appearance could necessitate complete removal and redoing of the treatment. Although there are seldom technical problems involved in un-sewing a textile, it can be extremely time-consuming and therefore extremely costly. The removal of sewing threads can cause significant powdering of the original, and the handling required can cause additional loss. The need for re-treatment in this case can cause exactly the kind of damage that the first treatment was designed to avoid. In general the reversibility of sewing as a treatment needs some critical re-examination.12
Proper consideration of the principle of reversibility in a particular treatment will answer the following questions: what is the relationship of the solubility of the added material to its removal? If it cannot be removed by dissolution, are its physical properties different enough from those of the original to make mechanical removal possible? If a treatment is reversible, how difficult, expensive, time-consuming, or risky to the piece would the process be? If removal of an added material is impossible, is the piece re-treatable with the same or different materials? To what extent can aesthetic changes be made without undoing the structural aspects of the treatment? What future events might necessitate re-treatment, and how could they be handled most efficiently? Conservators' attempts to project the behavior of complex systems far into the future is, as seen above, extremely difficult. As well-informed as we try to be, we can only guess at the pitfalls of our treatments. It is for this reason that reversibility is such an important concept. Our obligation is to make treatments as easily reversible as possible.
As important as the concept of reversibility is in the modern fields of conservation, it does not necessarily have a direct connection with the propriety or advisability of a treatment. An easily reversible treatment may damage an object, and an irreversible treatment may be the best under a particular set of circumstances. Many desirable attributes of a conservation material in a particular treatment do not relate directly to reversibility, but to other issues entirely. Some are concerned with the compatibility of added materials with those of the original. Such properties include response to changes in temperature and relative humidity, development of physical stresses from shrinkage, and the production of potentially harmful byproducts of deterioration. Possibly the most important criterion in judging a treatment is whether it provides the help the piece needs; in medical terms, whether it cures the disease. This must be judged on a case-by-case basis.
Even if a treatment is, unavoidably, not reversible, the conservator is not absolved from responsibility for the future of the piece, or to those who must treat it in the future. The fundamental reason we do our work is to insure that the pieces we treat will last forever. Therefore, unless it is destroyed first, every piece we treat will be treated again, and some provision must be made for future treatment. Particularly when novel or complex treatments are proposed, we have an obligation to future custodians to consider in detail the choices they will have to make when they deal with the products of our labors.