The restoration of the marble base began in September 2012 after the preliminary laboratory work defined the degree of damage. With this knowledge, we were able to establish a restoration timetable. The first survey was initiated in the work site in November 2012 whereby several laboratory analyses were conducted, the first being on the surface which was treated with a consolidant and with a protectant, previously applied during the restoration of 1980. Other lab work entailed the analysis of deposits on eroded surface areas, tests for capillary action of the marble, and checks for biological growth. Over the centuries, the Antoninus Pius column base - made of Carrara marble - has been subjected to alterations, modifications, and various conservation treatments. Research in our historic archives together with the related reports from the 1980 restoration provided startling evidence of its precarious state of preservation. To consolidate the marble surface from evident signs of deterioration, the restorers of the time (1980’s) utilized “potassium aluminate” as a consolidant. This intervention blocked the disintegration of crystals and the erosion of the surface for the time being, but in the long term this “potassium aluminate” created some problems we face today and which will be explained further in the report.

Our intervention began with the removal of white-colored opaque patinas, transparent rose-colored finishes, deposits of cohesive material, insect nests. The presence of numerous fissures and flaking allowed us to map out the fragility of the marble that was detaching in many areas. Some key fragments, at one time, inserted into the base and now conserved in the Magazzino ex Ponteggi deposit, were part of a comparative study by way of the analysis of ancient archival documents (see the art history report by Claudia Valeri). It suffices to say that these fragments did not receive the same restoration treatment as did the original portions of the base and they do not present the same type of deterioration: the marble is coherent and stable, contrary to the antique areas that make up the base whose material is detaching and quite fragile. Detailed visual and photographic records were made of the work, above all to document its state of conservation and the extent of the alterations. The records are presently on paper but will soon be transferred to digital format on 3D tablets using the “Phronesi” program. Thanks to the financing by the Patrons of the Arts it was possible to commission the Digitarca company to create specific software with the collaboration of the Vatican Museum’s Scientific Research lab (Ulderico Santamaria, Fabio Morresi) and the museum’s Stone Restoration Laboratory. As noted, various pieces in marble had been inserted to repair the work during an important restoration done by Giuseppe de Fabris in 1848; these insertions were also documented with detailed drawings. These were also studied and compared with earlier records of previous interventions, above all those executed by Vignoli in 1705 and by G.B. Piranesi in 1750. Thus it was possible to have a truer picture of what the original work looked like when it was discovered in 1704 and what was repaired consequently. The most recent reconstructions date to the restoration of 1980; the work had suffered such damage to the point that the missing heads of several horsemen, praetorians, and horses were reconstructed by making copies of the original heads still intact on the specular side of the work (east face and west face). The reconstructions were made with marble dust and epoxy resin, the same mix used at the time to repair all fissures and stuccoing of various sizes. After obtaining results from the lab results, which identified the substances lying on the work, the methodology for cleaning the marble surface was established. Spot cleaning was tested first on the side we called “pilot” (west face). A fundamental aspect adopted in the method was the “absence of water”, that is, the cleaning operation did not foresee the use of water to not favor a chemical reaction with the potassium aluminate salts already on the work (consolidant of 1980), as such a reaction would have prompted the disintegration of the crystalline structure in the marble.

We had therefore put together a cleaning process made of: Japanese paper, solvent gel (carbopol ultrez 21, ethomeenc25, ethylate), white spirit. The cleaning method gave optimal results after the surface was freed from wedged deposits and other substances; there also emerged areas with fissures and serious “bald” spots that confirmed the extent of the damage, previously mentioned.
During the cleaning phase, we repaired several elements that were at risk of detachment or breakage, being that in its present condition the base material seriously lacked cohesive quality. Worthy of note and to further illustrate the fragility of the ancient piece, during the cleaning process the head of a praetorian suddenly came off entirely, apparently whole and compact, but in reality, the marble on the inside was completely crumbled and had a “sugary” texture; furthermore the corresponding point of detachment showed micro-flaking and oxidized crystals of a brownish color, proving that the fracture had begun quite some time ago. We are now aware that the base of the Antonino Pio column is at risk of damage that can be irreversible and permanent if it continues to be exposed outdoors and therefore subjected to atmospheric agents such as acid rain, humidity, and extreme temperature changes.

We can say that each side of the block is characterized by a conservation curiosity. On the Apotheosis side for example, where Antoninus Pius and his wife Faustina Major are elevated as deities, the figure of the youth below to the left - the personification of the Campo Marzio- and the goddess Roma, seated in full armor, had a layer of oxidation that, while removed with some difficulty, also caused significant chromatic alterations, making minor modifications in some applications necessary. Biological growth was also present on the figure of the youth and on the drapes of the goddess Roma, whereby a biocide treatment on the relevant surface was applied. The east side of the base presented a layer of coherent substances that were extraneous to the stone material, a very thin layer but well attached to the stone. The removal of these substances required diversified interventions but gave very satisfactory results. The side with the inscription in bronze lettering presented drip markings which the restorers lightened or removed after applying packs of a solvent suitable for removal of the oxidation that had penetrated the marble. The cornice on the upper and lower perimeters of the base presented deposits of cohesive substances, which on the lower had biological growth that was successfully treated with biocide after it was cleaned. For the removal of the stucco fillers, made of marble dust and epoxy resin, the pieces were first softened with alcohol and removed mechanically; instead, the stucco insertions constituted specific forms like fingers, noses, etc. were not removed. At present, the surface is undergoing refinishing since the chemical cleaning was not enough on some stubborn areas. Using the QSW Laser the remaining blackish patina and other oxidized substances were removed. After this operation, the deeper fissures will be fixed and a biocide treatment will be applied to the entire surface. The aesthetic interventions for the stucco pieces and the anchorage of the elements removed during the cleaning have been determined but are put on hold for now because the work may be put at risk if moved at this time, a possibility still being considered by the competent authorities. By March 2017 extensive photographic documentation will be completed before covering all the faces of the work to protect the restoration results; this is necessary because even a few months of exposure would gravely compromise the restoration efforts. Experience has shown us how fast the negative effects on newly cleaned marble surfaces can be when not hermetically protected.