ASSESSMENT OF RECENT SURFACE CONSOLIDATION AND PROTECTION TREATMENTS ON SELECTED ARCHAEOLOGICAL MONUMENTS IN ROME

The original intention of this research was to assess the condition of ancient marble monument surfaces treated with three different consolidant and protective materials employed during the 1980s in Rome. These were: an acrylic resin (Paraloid B-72) in solution, an inorganic consolidant (Wacker OH) containing silicic acid ester plus a catalyst, and a traditional material, lime water (from slaked or hydraulic lime). For protection, monuments were treated after conservation with either Paraloid B-72, or a siloxane water-repellent (Wacker 290L or 280), or a semi-transparent lime wash. At the time there was considerable debate among the conservation authorities and conservators involved regarding the choice of materials, and in some cases changes in method occurred during the period of treatment of the same monument. Ten to fifteen years later the monuments of Rome provide an excellent opportunity to learn from past experiences and observe how the different conservation materials have performed longterm in situ in a polluted environment. The methodology of the planned evaluation consisted of a review of published treatment reports, consultation of more detailed archival documentation, especially in cases where no publication exists, an examination of the monument surfaces, and in situ testing. However, obtaining access to archival material proved difficult and sometimes impossible. Therefore, most of the information regarding past treatments was obtained from publications (for example, [1]). These sources revealed that conservation treatments of monuments in Rome during the 1980s witnessed the increasing use of Wacker OH for the surface consolidation of marble; it replaced Paraloid B-72, and in some cases was used in conjunction with lime. Although Wacker OH has been recommended by the manufacturer and conservation scientists in the past for use on sandstone in particular, it has been chosen for use on marble for a variety of reasons, including its lack of observed color alteration over time in situ, ease of cleaning after use for pre-consolidation and, by now, its proven track record on marble surfaces, except those severely lacking in cohesion. However, several conser-, vators during this period used only lime as a consolidant, and reported its effectiveness. The use of water-repellent protectants has become increasingly common in Rome since the mid-1980s, with a clear preference for siloxanes. The majority of these treatments have utilized Wacker 280 (formerly 290L), although Paraloid B-72 was used frequently until the mid-1980s, and lime washes have also been chosen by a few conservators. Several significant monuments were not treated with any protectant. The preliminary research and visual inspection of treated surfaces was done in connection with a national survey of treated monuments undertaken by the Italian National Research Council (CNR) and the Federation of European Chemical Societies (FECS). The information on treatments obtained from publications (and from archives when available) was compiled on data sheets (CNR Firenze, Centro di Studio sulle Cause di Deperimento e Metodi di Conservazione delle Opere d' Arte) for the different monuments. Subsequent visual examinations were carried out, using binoculars when' necessary, and FECS condition survey forms were filled in as much as possible for each monument. The documentation was then provided to the survey coordinator for Rome, Dr Laurenzi Tabasso. Photographs of treated surfaces were taken at the same time. Whenever possible, these were compared with photographs taken before and after treatment. Obtaining authorization for in situ testing also proved to be problematic. Conversations with partiCIpants during the 1995 ICC ROM Colloquium 'Methods of Evaluating Products for the Conservation of Porous Building Materials in Monuments' confirmed that obstacles were encountered around the world by those attempting to evaluate past treatments, unless they or their institutions were responsible for them originally (two examples of such 'self-evaluation', one in Italy and one in England, are given in [2] and [3]). The conference also revealed that there are a limited number of in situ tests available, particularly given the increasing opposition to destructive methods. Furthermore, any test will only be of value if the same test was carried out before treatment, or if untreated areas of the monument are still available in order to make a comparison. This is often not the case with past treatments, but on Roman monuments in the 1980s test panels of different materials were sometimes carried out on surfaces during treatment. Despite the difficulties of in situ treatment assessment, especially if performed by external researchers, thanks to the generous cooperation of the Soprintendenza Archeologica di Roma it will be possible for the author to conduct tests of water absorption and color on two marble monuments in the Forum Romanum treated in the mid-1980s with Paraloid B-72 as a consolidant and protectant. Although this material is generally no longer used on outdoor monuments in Rome, the tests of the two monuments could verify and quantify the darkening of surfaces that its use has been observed to cause in certain cases, while confirming its continued effectiveness as a water-repellent. The results of tests on the Column of Foca and the Temple of Vespasian will also be presented. The information obtained from the tests will provide important reference data for future testing of the long-term performance of the treatment and give indications for the future maintenance of the monuments, including the option of removal of the protectant and possible re-treatment with a different material. And finally, the tests of certain aspects of the performance of a frequently used organic resin on outdoor marble monuments may also provide a useful comparison with in situ assessments of other conservation materials on other Roman monuments being carried out by the Istituto Centrale per il Restauro and the Soprintendenza Archeologica di Roma. Thomas C. Roby is a private conservator based in Rome, c/o American Academy in Rome, Via Angelo Masina 5, 00153 Roma, Italy.