Scientific research and state of conservation

SCIENTIFIC RESEARCH

This important part of the work will be carried out with the valuable scientific support of the Directorate of the Vatican Museums and in active collaboration with the Governorate of the Vatican City State. The necessary diagnostic investigations will therefore be performed by the Cabinet of Scientific Research applied to Cultural Heritage of the aforementioned Vatican Museums, under the supervision of Dr. Fabio Morresi.

The exciting challenge surrounding all of the operations that make up the restoration project of one of the most iconic works not only in the history of art, but above all, of our Faith, must include the application of a rigorous and target-oriented protocol of scientific research. The work is complex, not only due to its magnitude and architectural characteristics but especially owing to the peculiar nature of the materials it is made of: it is one of the most elaborate and unique multimaterial works of all times. Marble, bronze, wood of various species, gold, and iron alternate and interpenetrate almost following the sinuous movement of the columns. Naturally, each of these materials will require careful scientific study in order to determine accurately its exact conservation status. At the same time, each material requires precise choices to be made, both in the type of analysis to be performed as well as in the differing types of protocols to be implemented for interventions aimed at the work’s preservation. The Cabinet of Scientific Research of the Vatican Museums participates in this adventure with the aim of providing an accurate scientific view, both of the overall state of conservation of the work and of the entire restoration process in all its complexity. The first step will undoubtedly be to define the state of conservation of the artifact accurately. Analyses will be carried out on the substances present on the surface, which have accumulated over centuries of maintenance, and in order to search for any potential states of degradation. Indeed, the maintenance interventions to have been carried out on the work are many and complex. They have all been documented and they range from simple dusting operations to the complete regilding of the baldachin. In the initial phase of research, spectrophotometric measurements will be preferred. These will be performed directly on the surface of the work without any previous material sampling. Analysis using Infrared FT IR and Raman spectrophotometry will be useful to understand the materials which have been applied, especially organic ones, such as waxes and oily compounds. A subsequent set of XRF fluorescence measurements will provide primary qualitative and quantitative information about metal alloys. Endoscopic analyses, radiographic studies, high-resolution 3D surface surveys and colorimetric measurements will be carried out both during the initial cleaning tests and throughout all restoration operations. Simultaneously, a series of additional scientific investigations which are necessary for a systematic study of the execution techniques of the entire complex will be defined. The exact determination of metal alloys, especially that of the bronze of the columns, will be performed using ICP Mass Spectrometry analysis. This extremely sensitive technique will provide accurate data on both the overall composition of the alloy and, above all, will allow information on trace elements. A statistical study of these elements will form the basis for further comparative analyses. A targeted study will then be conducted on gilding techniques. Scanning Electron Microscopy (SEM), EDS analysis and micro 3D recordings will determine both the technique used for gilding and its state of conservation. Throughout this process, drawing on the extensive historical and documentary records held by the Fabric of St. Peter and studying them will be very useful. The reinterpretation of analytical data in light of the data obtained from historical sources adds a strong scientific connotation to the knowledge acquisition process about the materials present in the Baldachin. At the same time, it can be a guide to understand the processes involved in the Baldachin’s construction and how it has been altered.

STATE OF CONSERVATION

All surfaces of the monument are covered by a dark patina, under which the gilding that embellishes the details is visible but partially obscured. As it is located indoors, the Baldachin is not affected by the common phenomenon of green corrosion is always present in bronze monuments placed outdoors and that are thus exposed to the elements: in the basilica, the monument is neither subjected to acid rain, nor to water percolation, nor to bird droppings, etc., which are all typical factors causing deterioration in polluted urban environments. However, the daily presence of thousands of pilgrims and visitors alters the microclimate in which the work is preserved. Strong humidity flows caused by transpiration during the day and significant temperature fluctuations during the nightly closing hours of the basilica inevitably imply an alteration of microclimatic conditions. These have an impact on the baldachin, which, as mentioned earlier, is made up of multiple materials of a very different nature. Thus, while the wooden parts are subjected to continuous expansion and compression owing to the strong fluctuations in air humidity, the metal parts are subject to repeated surface humidification with the consequent triggering of alteration processes and corrosion of the metal. In particular, the iron components of the work, which play the fundamental role of supporting and joining the decorative bronze and copper parts, show signs of alteration and oxidation, making the restoration of the baldachin particularly urgent.

On all surfaces, there are also dark patinas formed by fatty substances which were used in past maintenance interventions. Due to these protective substances, atmospheric powders of various kinds have settled on the surfaces, creating an incoherent material state that uniformly covers all surfaces, especially in the upper part.

Close-up observations during some inspections in the lower part of the column near the statue of St. Helena have revealed that some durals, resulting from restoration interventions, are affected by tiny but numerous formations of swellings due to phenomena which have caused the alteration of the bronze under the precious metal laminate.
More detailed and accurate observations can only be made once the scaffolding has been erected, making access to the higher parts of the baldachin possible, so as to be able to ascertain the extent of degradation of the wooden parts, and even more so of the iron components.
Observations from the photographic documentation taken before the intervention make it possible to anticipate the conservation problems of some parts of the work, such as the external upper covering. The latter is affected by an extensive disconnection of the padding system of wooden planks that lines the perimeter cornice formed of a mixed-line shelf. The lack of many elements, already uprooted, leaves the supporting structure (carpentry and metal constraints) uncovered, exposing the surfaces to the accumulation of particulate matter and semi-coherent residues. Thanks to the analysis of detailed photographic images, the presence of disconnections and detachments in the vast system of planking to which the bas-relief appliqué decorations are anchored has been evidenced also in connection to the ceiling. The polychrome surfaces and gilding show widespread detachment of layers and probably ongoing lifting of the adhesive materials.

The precious documentary evidence preserved in the Archive of the Fabric of St. Peter also makes it possible to affirm that more than one restoration intervention was carried out on the baldachin over the centuries to remedy the inevitable degradation of the constituent materials. The upcoming restoration will also make it possible, through constant recourse to and comparison with archival sources, to study and reconstruct the conservation history of Gianlorenzo Bernini's first masterpiece.