Band 22, Heft 2-3 -

The forthcoming restoration campaign of the former house of the Flemish Baroque painter Pieter Paul Rubens (1577–1640) in Antwerp includes the design and construction of a new glass canopy. It is to replace the actual non-transparent roof structure, which was erected in the 1990s to protect the portico, separating the inner court yard of the house from the gardens, and especially its sculptural artworks from further material loss. The design parameters of the new glass canopy were evaluated based on the distribution probability of the rain on the portico as a function of rain intensity and wind velocity, while the rain distribution was determined based on the raindrop trajectories combining the vertical raindrop velocity and the horizontal drag from the wind. A minimum wind velocity of 40 km/h is required before rain can reach the feet of the sculptured artworks during intense rain showers. Statistical analysis of the hourly wind velocity and rain shower duration and intensity reveals a return period of approximately 4.2 years when the portico is protected by a glass canopy with identical dimensions of the actual provisory roof structure. Although the influence of intermittent wind gusts and squalls, which will more frequently drag along rainwater to the critical areas, and increase the amount of rainwater attaining the artworks during storms, could so far not be studied more in detail. The above risks are however considered acceptable to prevent future damage accumulation.

The roof of the Ensor-gallery at Ostend is a cylindrical vault, constructed as a coarse grillage of reinforced concrete, with embedded reinforced concrete roof panels with prismatic glass tiles. The concrete ribs of the roof shell were heavily damaged by long term exposure to the chloride containing sea air, causing severe reinforcement corrosion. The paper presents the experimental data on the degradation, as well as the alternative approach used in the restoration project to avoid the loss of a major part of the authentic material. The approach is based on a combination of galvanic cathodic protection with embedded and bored in sacrificing anodes, the application of a chloride-inhibiting impregnation followed by a re-alkalizing treatment on the preserved parts, concrete repair and reconstruction with a self-compacting, shrinkage-compensating, polymer-modified repair mortar. Completely denuded steel reinforcement bars were replaced by glass fiber reinforced polyester rods.

The equestrian statue of D. José I, in Lisbon, Portugal, stands on an elegant and decorated plinth fashioned in a very dense limestone. The sculptor, Joaquim Machado de Castro, designed the pedestal with colossal stone pieces and selected one of the best Portuguese stones for this purpose, the Lioz limestone. The same stone was also used for the flanking sculpture groups and the base This stone is a very pure reef limestone, rich in fossils and a low porosity <1 %. It is extremely compact and highly resistant, even in the harsh environment of a busy metropolis and within the impact of marine winds. The generalized deterioration is surface erosion caused by direct runoff water, with some incipient black crusts and soiling incrustations occurring in sheltered places. In some areas copper stains originating from the metal statue were also found. An extensive network of cracks was found, mostly at or near the top of the plinth, which could be ascribed to the presence of iron rods and clamps left inside the structure to hold the stone pieces together. During the intervention, these cracks were sealed with a multi-barrier system, given the impossibility to access the interior to remove or directly passivate the iron inclusions. Inoperative joints were cleaned out and repointed. Black deposits could be eliminated by nebulized water and soft brushing while the copper stains required the application of poultices with ammonium carbonate, in some cases requiring the addition of a complexing agent.

The equestrian statue of D. José I, in Lisbon, is a masterpiece of the sculptor Joaquim Machado de Castro. It weights over thirty eight tons and was made in a single casting by Bartolomeu da Costa in a copper alloy (brass). After over two centuries exposure, the statue presented an unappealing heterogeneous appearance and showed some deterioration features that required attention. Preliminary studies showed that the deterioration phenomena were typical of copper alloys exposed to outdoor urban environments. The proximity of the seacoast also contributed to some specific decay mechanisms. The highly contrasting patterns of the superficial patinas consisted of black dense deposits covering an original cuprite layer side by side with the common green deposits of basic copper sulfates, hydroxides and chlorides. The highly corrosive nantokite was present in sheltered areas, where chlorides are able to accumulate. The conservation intervention included cleaning, mostly carried out with low pressure jets of round glass beads. Onsite tests were made to select the cleaning levels required to match the areas of black and green patinas. A reddish brown cuprite layer was found underneath most of the areas with black dense deposits, while it could only be perceived by transparency on the green covered areas. When a high contrast remained between the two areas, these were mitigated with the application of water colors during the final protection phase. Nantokite active areas were passivated with sodium oxalate after the entire statue was first washed with clean water and treated with lime water to leave an alkaline reserve to slow down the eventual corrosion process, and the sculpture rinsed with ethanol to accelerate its drying. The final protection was made with Paraloid B44 and microcrystalline waxes.