Fresco Depicting St. Paul

In the niche of the short corridor that unites the Baptistery of the Basilica of St. Paul Outside the Wallswith the room dedicated to Gregory XVI, there is a beautifully resorted fresco depicting St. Paul. The work is attributed to Antonio di Benedetto degli Aquili, better known as Anonianzzo Romano.

The elegantly coffered vault across from the aforementioned fresco is also decorated with brightly colored frescoes. At the base of the vault and along the perimeter of the niche, there is a grotesque frieze featuring fantastical animals interspersed with small palm trees. This roman ornamentation is decorative and demonstrates a typical the Italian Renaissance (XV-XVI century) pictorial practice.

The vault was most likely painted after the fresco of the saint because of its style and the quality of the frieze connected to it, which is more consistent in painted layers and uses more vibrant colors. The vault also appears to be of a different craftsmanship.

Coffered Vault Frieze

Niche Frieze with St. Paul






State of Conservation

The frescoes were seriously damaged by the separation of painted plaster from the wall structure, and the entire surface was at risk of an imminent fall. The separation also caused grave fractures, concentrated for the most part in the area on the top of the vault and in the center of the niche with the saint.

It was discovered that the frescoes had been restored already, and some parts were previously heavily reconstructed with substantial stucco work and pictorial remakes. In the niche fresco, the layers of colors were in some cases not cohesive.

The green background and the Saint’s yellow vestments showed signs of a significant loss of pigment exacerbated by the separation phenomenon. In the past, the painting had been treated with reviving and consolidating substances, which over time chromatically altered the substances, making them opaque and aesthetically spoiling the representations.

Abrasions and scratches were particularly evident and widely diffused, appearing most evidently on the niche’s green background. Dust and surface deposits covered the decorations extensively.

Stuccoing and Reconstruction

Abrasion on green background

Abrasion on St. Paul’s yellow vestments









Techniques of Execution

The direct incisions and compass marks for the design at the base of the vault.

The paintings, as already said, were done in fresco. The niche with the figure of St. Paul was executed with two coats of plaster, one for the saint for whom the Basilica is named and another for the rest of the green background.

Using a technique of indirect engraving i.e. tracing the contours of the figures and internal details, a cardboard inversion of the wall was created. The saint’s halo and the circular knob of the sword’s hilt were drawn with a compass, and a straight edge was used to draw the edges of the blade. There are no traces of incisions or linear transcription on the face and hands, which means the contours were likely delineated with a carbon dust technique and then covered with color. There are very thin but clearly defined direct etchings present on frieze that decorates the lower register of the niche.

Traces of sixteenth-century painting underneath layers of paint

The vault was painted on three segments of plaster, applied along the corridor. The profiles of the coffers were traced with direct incisions while the central rosettes were made with a carbon dusting technique. Traces of the lines used to determine the general design were also detected impressed in the plaster. The small studs, painted on the white segments of the coffers, were formed with a compass. There are no signs of graphic construction i.e. incisions or traces of dust present on the lower frieze, but this is believed to be due to the thickness of the paint layers obscuring this area.

Stratigraphic tests on the vertical walls revealed the presence of painted decorations similar to those of the vault covered by more modern coloring. During a recent meeting of Museum Direction, it was decided to remove the modern additions and bring the original paintings to light.

Scientific Studies

The Vatican Museum’s Diagnostic Laboratory for Conservation and Restoration completed the following scientific studies prior to the restoration:

  • UV fluorescent imaging
  • Infrared false-color imaging
  • IR reflectography taken with a digital camera
  • Geo/Radar structural detection

The UV fluorescent and Infrared false-color images made it possible to precisely determine the presence of retouches and other substance applied during previous restorations (e.g. fixatives) as well as original finishes applied as lacquers on a dry surface. The IR Reflectography gave clear indications of the foundational designs for the figure of St. Paul, and Geo/Radar Detection determined that there are no dangerous static disruptions, even near the plaster fractures.

Digital Photo

IR Reflectography

Infrared false color Image

UV image







Photo Documentation

The Vatican Museum’s Photographic Archive completed a photographic documentation of the restoration for each of the phases  (before, during, and after). The photos were taken with a digital camera.

Graphic Documentation

The work was graphically documented by hand, recording on paper the relative state of the painting’s conservation and techniques used in previous and current restorations. This information will then be digitized using AUTOCAD 2014.

The Restoration Process

The most urgent problem to confront was the painted plaster detaching from the wall structure. First, the parts in danger were “bandaged” using cotton gauze sheets painted onto the surface with lycraine-diluted Cyclododecane (1:1 ratio). The surfaces not covered by the bandages were protected with a layer of Cyclododecane, diluted in 20-40% Ligroin and applied by brush before the restoration work continued.

The restorers then moved on to filling in the gaps proceeding from the bottom to the top. In the thinner cavities, an acrylic resin diluted in water at various percentages was injected (ACRILEM IC 33) while the larger cavities were filled with a pre-mixed hydraulic mortar fluid (LEDAN SM02). To avoid unsecured plasters from falling during the consolidation, the surface was supported with precautionary props. The work yielded very satisfactory results as the plaster is now restored and firmly anchored to the wall structure.


Cyclododecane Usage: surface protection and sealing of plaster fractures; shoring

After the re-adhesion of the detached plaster, the fresco surface was consolidated and the color degradation was addressed. The latter involved soaking especially deteriorated areas with algae. In some cases, restorers also used Paraloid B72 diluted to 3% in acetone.

Restorers applied a paper pulp compress soaked in an ammonium carbonate saturated solution to clean the frescoed surfaces. A sheet of Japanese papers was placed between the fresco and the layers of solution soaked paper pulp. Each compress was applied for 10 minutes on average so as not to damage the image. The more stubborn dirt was then removed using Ammonia suspended in a gel (Carbopol).


Cleaning of the fresco surface


Before & After cleaning

The gaps and fractures in the stuccowork were filled with a mortar made with lime putty, pozzolan, quartzite and marble powders. The very thin fractures were addressed with a ready-made filler (Modostuc).

The entire image was reintegrated using watercolor. In a few cases, however, a titanium white powder was added to the watercolor to lighten some of the stains on the green background.











The fractures on the disfigured face of St. Paul were filled and reintegrated with watercolor restoring the image to its original integrity.









The assistance of Angela Cerreta (cleaning, grouting and retouching) and Federica Cecchetti (retouching) was integral during the final phases of the restoration. The apprentice Giorgia Donadio also participated in all of the stages of work (consolidation, cleaning, grouting and retouching), while the apprentice Ilaria Liguori helped in the final stages of the retouching.