Material Marvels: La Specola Observatory

Materials World magazine
1 Jul 2019

From medieval prison tower to observatory and now museum, La Specola has a rich history of redefining itself. Idha Valeur looks into how the building has been adapted for purpose and how it is maintained.

La Specola Observatory sits on the intersection of the Bacchiglione River and the Naviglio Canal in Padua, Italy. Over its many incarnations, it has also been known as the Museum of the Astronomical Observatory of Padua, Museum La Specola or just La Specola.

In the 13th Century, Ezzelino da Romano who ruled Verona, Vicenza and Padua, built a castle with two towers which he used as a prison. The tallest tower of the two eventually became the observatory.

When the Carraresi family, known as the Lords of Padua, ruled the region the 14th Century, they built their castle on the remains of the da Romano building and made the tallest of the towers into a defence post. This medieval structure, then known as the Old Castle, was used as an ammunition depot during the Republic of Venice’s governance in the 18th Century, according to National Institute for Astrophysics (INAF) Head of Museo La Specola and Cultural Heritage, Dr Valeria Zanini.

It was not until 1767 that the main tower of the Old Castle was converted into an observatory, by a Senate of the Republic of Venice decree on 21 May 1761.

In 1806, the building once again reverted to a city prison, run first by the Austrian government, followed by Italian Reign and Republic, and remained this way until 1992. However, during this time the high tower continuously served as the University of Padua’s astronomical observatory.

In 1923, the need for newer and larger astronomical equipment meant it was no longer fit for purpose and a new university observatory was constructed in Asiago. At this point, the castle gained independent institute status and became a museum with an onsite library and archive.

Brick by brick

INAF Architect, Nicola Di Cicco, told Materials World that the ancient tower base of the Old Castle shows evidence of large blocks of Roman trachyte – an igneous volcanic rock with an aphanitic to porphyritic texture.

‘The tower is made of clay bricks with a visible face – some recovery bricks are from the Roman Era. The façades were then plastered with lime-based plaster and painted with white and red panels. Some traces of the original plaster are present in the main façade on the south side [of the tower],’ Di Cicco said.

Historical images courtesy of the Museum La Specola - INAF, Astronomical Observatory of Padova (Italy)

From prison to observatory

When the University of Padua decided to set up an observatory, Professor of Astronomy, Geography and Meteors, Guiseppe Toaldo, proposed the high tower of the Old Castle. According to INAF historical information, the idea was agreed as it was an ideal location on the southern outskirts of the city. This would give an undisrupted view of the southern horizon, as well as saving the cost of constructing a whole new building. Work started in 1767 and lasted for 10 years.

Refurbishment of the tower required several operations and was carried out by Architect Domenico Cerato. It involved, ‘the construction of an upper observatory composed of the Sala delle Figure – the Figures Room – and three small domes above’, De Cicco said, adding that ‘the major changes concern the opening of new windows and the expansion of existing ones, as well as the construction of the internal stairs that connect the fourth floor to the top of the tower’.

Zanini explained that the materials, especially the bricks used to build the new observatory rooms on top of the tower, were all new, and over the roofs of the rooms, terraces were built of Vicenza marble.

While the upper observatory was home to various types of telescopes, the Figures Room was decorated with fresco portraits of famous people in astronomy and meteorology, painted between 1772–1773. Unfortunately, a water leak from the terrace above caused damage that necessitated additional repairs, but nothing was done to protect the frescoes during repainting. A project followed to recover them. ‘The Figures Room was completely restored in 1998 and this work was carried out under the supervision of the Fine Arts Superintendency of Veneto. The figures had completely disappeared under the 19th Century repainting, so we relied on the restorer’s ability and on the competence of the superintendent for their recovery,’ Zanini explained.

Restoration of the frescoes in the 19th Century is outlined in the Restorer Vanni Tiozzi’s 1998 technical report, Relazione sul restauro della Sala delle Figure. ‘The recovery and consolidation were performed with injections of emulsified acrylic resin or nebulised according to the areas with desalinated hydraulic lime, removal of casein repainting with basic packs and scalpel blades, cleaning of sedimentati

ons and spurious repainting, thanks to washes and infills with suitable solutions, biological disinfestation by means of bio-acid solution, packs with deionized water and ammonium carbonate for the removal of anions and cations and elimination of voids,’ it stated. ‘The fixing of the original pigmented layers was done with acrylic resin emulsified with aerial lime and marble dust, while the cracks and the faults were grouted with a mixture similar to the original layering.’

To the museum

In 1994, the formation of the museum was approved by the board of directors, as well as granting the acquisition of the Old Infirmary Room of the Old Castle for the observatory’s library.

Following the founding of the museum and library, Zanini and her colleagues published a paper, The Giovanani Santini library, Padua astronomical observatory: The adapting library in 2015, tracing its history from inception to today.

According to the paper, the library started when the third observatory director, Giovanni Santini, left his private collection to the observatory in 1873. It was stored in three rooms in a building part of the Old Castle for about 100 years.

As the collection grew, it had to be placed on different floors and the donation from Santini was moved into the tower. ‘Even though this solution did not meet specific requirements for the preservation and safekeeping of ancient materials, it did prevent the collection from being split up,’ the paper read.

In the late half of the 1980s, monographs and journals were kept on the second floor of the tower. Adapting to this change ‘a metal intermediate floor was built to support bookshelves, thus optimising the use of the tower’s vertical space, while giving it a distinctive character,’ the paper read. ‘The original materials remained on the tower’s fourth floor. For the first time, the library had a purposely designed space. The new library re-established the symbiotic link between the Observatory and the ancient castle.’ Procurement of the infirmary, which started in the 2000s, freed up space and allowed for the entire tower to act as the museum. ‘A new, large library was designed to finally bring the entire bibliographic heritage in one place. In 2004, the new library included a room for monographs and one for journals, both with an intermediate floor for a total area of about 280m2, which included a large office. There were now spaces created for study and consultation. In 2010, the most ancient volumes were finally moved to an adequately protected and controlled area,’ it stated.

‘With the establishment of the Library and Historical Archives Service of INAF, the collaboration with other institute’s libraries grew stronger. Due to its available space, the Santini library, was chosen as the location to preserve printed copies of the most important journals.’

Today, the observatory tower is one of INAF’s main structures that is devoted to scientific research in various fields of astrophysics after it merged with the observatory in the 2000s. It houses a depot for the Observatory on the first floor, offices for researchers on the second and third floor, and the museum and historical archive from the fourth, all the way to the Figures Room at the top. The rest of the Old Castle is owned by the Italian State and by the municipality of Padua, which is awaiting restoration, Zanini told Materials World.Historical images courtesy of the Museum La Specola - INAF, Astronomical Observatory of Padova (Italy)

Restoring the tower

In 2011, Museum La Specola underwent a round of significant restoration works, mainly on the area of the barbicans at the top of the 14th Century tower. Di Cicco said this project revealed that the barbicans were made of bricks with the insertion of some blocks of nanto sandstone.

Restoration was needed after pieces of brick had fallen down from above, Di Cicco explained. ‘This phenomenon was very dangerous for the safety of personnel passing through the observatory. Furthermore, it was essential to intervene to safeguard the area of the tower barbicans. The project of these works required the favourable opinion of the superintendency because the tower, like the whole castle, is a bound property,’ he said.

Di Ciccio added that this included removing non-historical cement mortars in the phase of detachment, and general cleaning of the masonry facing with spray application of benzalkonium chloride in a water solution to spray on plants, mosses, vegetative patinas and dark patinas. ‘For these applications, a manual pray pump is used, then the surface is rubbed with a sorghum brush. Historical plasters will be protected and consolidated,’ he said. The yellow Vicenza nanto sandstone blocks will also be treated with the water and anti-algae product and brush. Lime mortar – sand and water – was used to fill in the joints between the bricks, in the same colour as the original with a special trowel. ‘The grouting of the joints was carried out by keeping the surface of the grouting set back by about 1cm from the surface of the brick. This is to allow a correct reading of the wall face,’ Di Cicco explained.

The final part of the restoration focused around strengthening the cracks of the nanto stone by applying a silica acid syringe in a water solution with 30% of the solid body. ‘The consolidation will be done by filling the cracks of the stone in such a way that the meteoric water can slide on the surfaces without infiltrating. Subsequent consolidation of the surface of Nanto stone will happen by spraying it with ethyl silicate, which blocks the chalking process,’ Di Cicco said.

For now, all restoration projects have come to an end in a rare period of calm, due to improved conditions and a lack of funding. But this may not last, as Di Cicco said meteoric water can cause damage to the inside of the tower, so perhaps it is only a matter of time.