SCULPTUREs AND STATUARY

THE RESTORATION AND CONSERVATION OF THREE STATUES BY ANTONIO RIZZO (1400s) IN THE DOGE'S PALACE, VENICE

Introduction

When wandering through the museum of the Doge's Palace in Venice, before entering into the Sala of the Maggior Consiglio, one encounters three freestanding, larger than life-size statues, made from Carrara marble. They represent Adam, Eve and a Warrior/Mars and were sculpted by the Veronese artist Antonio Rizzo during the last quarter of the 1400s. The statues have been housed within the palace for over 60 years but originally these figures occupied niches along the exterior of the Foscari Arch in the palace's courtyard; niches now occupied by bronze copies of these originals. Covered with layers of dirt, crusts, and materials from past treatments the statues had acquired a black and shiny appearance that had caused more than one observer to describe them as bronzes. Signs of heavy weathering of the marble indicate how important it was for their conservation to have been brought indoors, protected from the aggressive outdoor elements. Yet once inside, the figures seem to have been left relatively untouched, as remnants of pigeon guano still found on the stone surface could attest. Only a few precisely aimed interventions had been undertaken since they had been brought inside (the replacement of Eve's right arm in marble and the retouching of certain white and eroded areas with an acrylic patina). As such, these works were long over due for a conservation treatment.

When considering the type of conservation intervention to be conducted, the most evident and disturbing alteration to the statues was the black patina that covered most of the surfaces. This patina was most likely applied at the beginning of the XX century to imitate bronze, eliminating the need to homogenize the statues' surfaces through cleaning by making them homogeneously black. It was a layer that covered dirt deposits, gypsum crusts and the various replacement pieces from the sixteenth and seventeenth centuries which had substituted damaged or loss areas of the statues. Unfortunately, over time this patina had become very blotchy and uneven. Other evident problems to the statues were the grey/white efflorescence of the fills around the replacement pieces caused by the use of an inappropriate mortar, as well as small areas of stone de-cohesion that were still slightly sugaring, heavy layers of a calcite incrustations, found particularly on Eve, and areas of erosion from rain found on Adam and the Warrior. Yet, the most pressing problem was the removal of the black layers in order to eliminate any potentially damaging crusts, to better understand the conservation problems of the marble underneath and to better read the works.

Cleaning

Before undertaking any sort of conservation treatment one needs to identify the various materials that are present on the sculptures and the only definite way of doing so is through the sampling and analysis of different areas of the statues. This analysis was conducted by the conservation science laboratory of the CNR (Consiglio Nazionale delle Ricerche) of Milan and was able to answer many questions as to the nature of the materials found on the surfaces, while leaving a few unresolved. The results confirmed that the marble is from Carrara, that there were heavy deposits of gypsum on the surface as well as calcium oxalates . Traces of paraffin and of an acrylic resin were found on the surface but the organic component of the patina was not identifiable. Remains of a lead and zinc yellow were found on the tree trunks of both Adam and Eve, while sodium chloride was found on the statues, a presence linked to the marine environment of Venice.

With such a plethora of materials to respect and to remove, a series of cleaning tests commenced, using various solvents and poultices, but with the result that no one chemical method could clean the statues in a homogeneous way. Since the patinas and surfaces of the statues were very delicate, the possibility of mechanical cleaning was not considered, leading to the subsequent testing of laser cleaning. Since a laser works on optical principals (we tested a type of laser that is absorbed and reacts with dark areas while being reflected by lighter areas) it is able to remove the various black layers irregardless of their composition. The result was a sort of unveiling of the statues from the pollutant and human-applied layers, laying bare the marble surface underneath.

Of course the marble surfaces no longer resemble that of when the statues were originally sculpted. Not just pollutants but also oils and waxes applied to the statues over the centuries have been absorbed by the stone and mineralized within its pores, leaving a brownish staining that can no longer be removed. Constant exposure to rain and the path of run-off water has eroded this coloration in certain areas leaving them lighter in color. Overall, however, the cleaning has allowed to better read the forms and shadows of the sculptures as well as giving a clearer understanding of the condition of the marble hidden below.

As a small aside to the laser cleaning, Eve had some very thick calcite incrustations on her right arm, reaching up to a centimeter in thickness. Since the laser did not react with these incrustations, they were removed mechanically, first with a dremel tool and then with ultrasound vibrations. Since the stone underneath had been protected from direct contact with pollutants and organic materials by these incrustations, the area resulted lighter in color than the surrounding areas.

Consolidation

With the cleaning terminated, the next step was the treatment of any weak areas of the marble. While a pre-consolidation of several very fragile areas had been performed with Paraloid B-72, an acrylic resin, before the cleaning had begun, these and many other areas of heavy weathering needed further consolidation in order to be stabilized. Where the stone matrix was decayed and showed sugaring or meso-fissures, this acrylic resin was applied repeatedly in doses of 5-10% in butyl acetate. Interesting to note was that much of the fissuring was not visible until after the cleaning. This fissuring was mostly caused by thermal dilatation of the marble crystals as they were heated by the sun during the day and then quickly cooled once the sun set. In fact, the presence of fissuring is found only on south/southwest-facing elements of the statues and was most likely augmented by the heat absorbing black layers that had dirtied the figures.

On a whole, the statues appeared to be in structurally good condition, but a fracture in the Warrior's left ankle and a small lesion on the wrist of Adam's right hand were in delicate points and required a verification of their condition. Along with this were the various replacement pieces that had been attached in an unknown fashion. As a result a series of analyses using first ultrasound and then radiography were conducted to better understand the solidity of these areas. The ultrasonic analysis revealed that the two fractured areas had discontinuity up to a depth of almost 3 centimeters. As a result these areas were consolidated first with Paraloid B-72 and then with the injection of a liquid epoxy resin to solidify the fractures. The radiography, instead, found that almost all of the replacement pieces, no matter how small, had been fixed using pins. While most of these pins are hidden under the marble surface and radiography cannot reveal their composition, from the analysis of the few pins that were accessible, it can be quite certainly implied that they are all of either bronze or copper.

Final Details:

With the cleaning and consolidation completed, the last operations needed to conclude the intervention were the filling of the joins and of a few cracks and the subsequent chromatic retouching of these joins to match the color of marble. Of course the goal of the repointing is to make a mortar close in color to that of the stone so as to minimize the amount of in-painting. In order to create a mortar that gave a texture similar to the marble it was decided to use the acrylic resin Acril AC33 as the binder, allow to create a smoother surface than traditional lime-based mortars. A series of sifted stone powder mixes were compiled to give a range of colors to adopt depending on where the fill was on a given figure. The mortar was also used to fill in any large fissures and cracks. Once the repointing was completed, the fills that did not chromatically match their surrounds perfectly were retouched with a completely reversible patina made of slake lime, Acril AC33 and natural earth pigments. A few other areas, which were chromatically disturbing, were also retouched very slightly, such as the damaged surfaces of Adam's upper lip and of the curls of his hair, as well as replacement pieces such as Eve's right hand and fore-arm. As a final protective layer, the statues were treated with a thin layer of microcrystalline wax which also gives a slight shine to the surfaces.