1 INTRODUCTION

“IN CONSERVATION WORK, there is a dictum that nothing should be done that cannot, if necessary, be undone easily in the future.” This statement by Plenderleith1 sums up the importance of the reversibility of any treatment applied. That reversibility is one of the most desirable features cannot be denied. Yet the broadness of the term “treatment,” which could include cleaning, gluing, consolidating, etc., makes this issue a very debatable one. For instance, reversibility is rarely mentioned as a consideration in the cleaning of stone, whereas the concept has acted as a severe handicap to the testing of consolidants. Furthermore, it has also allowed for different interpretations of the meaning of “reversibility.” For example, Sanpaolesi interpreted the reversibility of the treatment as a philosophy to be applied to the overall conservation/restoration of a monument; but not to be taken literally when it came down to the actual consolidation of the deteriorating material.2

In the search for a “reversible” consolidation treatment, the more important principle, that any applied treatment should not interfere with future necessary treatments, as mentioned by the 1972 Italian Carta del Restauro3 and given as one of the three conservation principles by Brandi,4 has been generally forgotten. It must also be remembered that “total reversibility” is a theoretical concept which is not found in nature. We propose that total reversibility should be limited to the possibility of complete removal during the application of the treatment, to allow for esthetic adjustments.5

The whole rationale for consolidation is based on the fact that the material is deteriorating so badly that unless it is “treated” it will not survive. The “treatment” will not safeguard the material from further deterioration but will hopefully slow down the deterioration process and give the object a longer life so that in the future a new treatment can be applied if necessary.6

Consolidating and water-repelling treatments based on mixtures of acrylic and silicone resins have been fairly widely used in recent years. In particular, the mixture of Acryloid B72 and DriFilm 104 has found extensive application in Italy.7–9 Because of its wide use it has been subjected to careful laboratory studies.10–12 During these studies it was found that acid rain modified the microstructure of the silicone resin on the surface of the stone, possibly due to a continuation of the polymerization reaction of the resin which still has some alkoxy groups available for further polymerization.11,12 This further polymerization could possibly interfere with the reversibility of the treatment as a whole.

This paper studies the difference in extraction facility of weathered specimens versus unweathered ones, i.e., the reversibility of the treatment after ageing has occurred.