The Malta site

Cleaning

 

Situated in the proximity of Italy, North Africa and Greece, Malta has always been a crossroads of peoples. Since ancient times, the great civilizations having played a dominant role in the Mediterranean region have claimed possession of the island. Before its independence in the 1970s, Malta has lied under the influence of the Greeks and the Romans, then was dominated by the Arabs, Byzantines and the Kingdom of Sicily up to modern times, when the island was conquered first by the French and then by the British. (figure 1)

Given its strategic position, Malta has always been a contested territory. Therefore, build imposing defence infrastructure was needed. The first fortifications were raised in the Middle Ages to ward off an invasion by the Arabs who had ruled over the island until the 11th century. Further and massive fortification works were started by the Knights Hospitaller during the 16th century, after successfully resisting the siege by the Ottoman Empire. With the British occupation of the island, the ancient infrastructure was restored, extended and renovated to meet the military needs of the second world war.

Since then, no major restoration interventions have been carried out on Malta’s historic walls. Over the past few years, thanks to European funds, the Maltese archipelago has been subject to a restoration campaign involving the most ancient and prestigious sites of the island, such as the Valletta and Medina fortifications and the Birgu walls.

The funds have contributed to raise in the Country the deepest awareness regarding restoration, thus addressing the lack of a true culture of conservation in the island so far. The Maltese government has immediately identified Italy as the reference model to properly plan the renovation interventions and, thanks to the creation of an Italy-inspired Superintendence-based system, they were able to achieve extraordinary results in little time. The Maltese authorities have joined a project of cultural exchange with our Country in order to learn how to master architectural and stone restoration and conservation techniques.

The EU prerequisites were the guarantee of excellent results and the implementation on the Maltese territory of specific facilities dedicated to the conservation and restoration of artwork, in order to encourage the transfer of technical knowledge and know-how from Italian experts to local technicians. The Polidano Group, the Maltese company which usually deals with the construction of infrastructure, was awarded the tender contract for the conservation works of the walls of Birgu, on condition that they cooperated with an Italian restoration firm. The first stage of works on site consisted in pre-intervention analysis, through preliminary testing and surveys to identify the best operative method and to acquire as much information possible on the surfaces and their state of conservation. (figure 2)

Analysis were implemented using, among other tools, the IBIX MOBILE LAB, a fully-equipped portable laboratory which allows to carry out diagnostic surveys on historical building materials directly on site, and to get a precise classification of the natural and artificial stone materials and relative degradation. It is an essential tool that can provide validated parameters for intervention in a simple and inexpensive way, according to a scientifically-based approach to restoration work thus putting an end to what Dezzi Bardeschi used to define as “The romantic figure of an inspired technician electing himself as sole judge of the monument on which to intervene”.1
The analysis carried out determined the conditions of the surfaces by means of a series of parameters being measured: moisture, quantity of salts present in the materials and their classification. The possibility to carry out multiple on-site surveys with limited costs and skipping the usual lab waiting time, has been a tremendous advantage in the execution of the intervention. (figure 3)

As a matter of fact, the walls presented completely different characteristics based on their location and only correct measuring of the reference parameters could have provided the needed information to decide on the proper conservation approach. For example, the exposure to weather conditions, wind and sea air rich in salt produced a characteristic concentration of chlorides which was found to be significantly lower in inland areas. In this case, having divided the site in different areas for measuring has led to the acquisition of precise knowledge on the degradation phenomena – chemical, physical and biological - thus enabling planning of an accurate intervention project. (figures 4-6)

Another fundamental aspect involved in the determination of the conservation approach was the type of stone on which the intervention was to be carried out. Indeed, the Malta stone features characteristics which are unique in the world. Similar to the Lecce stone, the Malta stone is a Miocene limestone (21 million years ago): its specific components lend it unique compactness, colour and structure. The presence of fossil fragments gives the stone further appeal and geological value. The types classified differ in colour, homogeneity, compactness and age. (figure 7)

Fully aware that cleaning is probably the most delicate phase in the conservation cycle, as it is irreversible, minimally-invasive techniques are to be preferred in order to best preserve the artefact. In fact, the wrong intervention could cause irreparable damage to the artefact, accelerating the degradation process and causing the loss of material essential to the understanding of the history of the artefact. Cultural objects are unique and irreplaceable, made of unique materials for which no standard method is adequate. Each cleaning intervention must be carefully planned, on the basis of deep diagnostic analysis and preliminary cleaning testing to identify the best cleaning techniques for each specific case. Indeed, in compliance with the legislation, "The materials and processes to be used must be chosen based on the results of necessary assessment carried out by qualified and industry-specialised laboratories to determine the effectiveness and/or any side effects".2 All the different analyses carried out on the Malta stone, under the supervision of the local superintendence, have identified only two possible viable cleaning processes: manual cleaning with broomcorn brushes following treatment with chemical agents or selective cleaning with micro-air-abrasion system with helical vortex nozzle by IBIX. Any process involving the use of water during cleaning was categorically excluded.

The outcomes of the preliminary tests and previous knowledge on the Malta stone - its characteristics and damage - have led to the choice of cleaning through IBIX air-abrasion systems, taking into consideration the enormous amount of time saved and, as a consequence, the reduction of labour costs. Furthermore, an higher safety and uniformity of the intervention was guaranteed by the possibility to “customize” the system functioning parameters of working pressure (as low as 0.1 bar), nozzle size (as little as 0.8 mm), grain size of the abrasive material (as small as 38 micron), flow type (vertical or tangential) etc. (figure 8)

HELIX® is a special gun able to give a rotatory motion to the abrasive exiting the micro sandblasters. This exclusive IBIX patent has been developed and produced in Italy. Thanks to this special technology the impact of the abrasive on the surface is not vertical but tangential, so that the abrasion is more gentle and respectful of the treated surface, increasing at the same time the contact area and the machine effectiveness. The HELIX® system offers, for the same nozzle dimensions, an increased tangential contact area, maintaining a uniform and calibrated action of the aggregates on a given surface: this makes it possible to increase the distance of the operator from the treated surface, minimising invasiveness without losing the regularity and evenness of cleaning. (figure 9)

In the Birgu site, the dry HELIX® equipment was used with calcium carbonate based aggregates of extremely fine grain size in order to remove dirt residues, particularly stubborn “black crusts” and salt efflorescences. The material, which is the main component of marble and limestone, is 100% compatible with porous stones allowing for a gentle, yet effective, cleaning also on delicate materials such as the Malta stone. The aero-abrasive machines were set at best based on the data collected with previous analysis: thus, the working pressure and quantity of abrasive exiting the gun were adjusted to the specificities of the area being treated.
The outcomes were excellent and met the expectations for the intervention. The use of the HELIX® system ensured low running costs and labour savings, reduced strain on the operators and cut off the duration of the works, all while respecting the absolute ban on the use of water. Cleaning, in line with the technical tests carried out, was uniform and matched the colour of the original stone. Especially in those areas which are less exposed to weathering, the historical patina was perfectly preserved and even enhanced by the elimination of unwanted deposited material, both of chemical and biological origin. (figure 10)

In conclusion, the restoration intervention was fully successful, entirely meeting the expectation of the Maltese safeguarding authorities. However, the importance of the project has gone beyond restoring the original beauty of the Walls of Malta: further grounds for satisfaction lied in the fruitful cooperation among all the subjects involved in the intervention. With regards to the goals of the European tender, the project has left Malta something more than the beauty of its monuments, transferring precious working know-how and a newly-found awareness for restoration and conservation issues to local operators.

[by Caterina Giovannini]

(Article based on: “Scuola di Restauro – Heritage Conservation in Italy and in Russia”, curated by N. Berlucchi, D. Fiorani, A. Grilletto, S. Kulikov, O. Pyatkina, T. Vyatchanina - Nardini Editore)

 

FOOTNOTE
1. M. Dezzi Bardeschi, Restauro: punto a capo, 1991
2. Uni Beni Culturali 11182:2006

 

REFERENCES
Alessandrini G., Feltrami C., Cordaro M., Torraca G., Patine, pellicole e patinature, in Diagnosi e progetto per la conservazione dei materiali dell’architettura, De Luca Editore, 1998, Roma.
Alessandrini G., Patine su materiali lapidei, in AA.VV., Atti del Workshop: Genesi, significato, conservazione, curated by Tiano P., Pardini C., Nardini Editore, 2005, Firenze.
Campanella C., Capitolato speciale d'appalto, Pirola - Sole 24Ore, 1997, Milano.
Del Vecchio G., Per Malta, Volpe Editore, 1967, Roma.
Dezzi Bardeschi M., Il punto di vista dell’Architetto, in AA.VV., Atti del Workshop: Genesi, significato, conservazione, a cura P. Tiano, C. Pardini, Nardini Editore, 2005, Firenze.
Dezzi Bardeschi M., Restauro: punto a capo, frammenti per una (impossibile) teoria, curated by V. Locatelli, Franco Angeli, settima edizione, 1991, Milano.
Mattini M., Introduzione, Atti del Workshop: Genesi, significato, conservazione, curated by Tiano P., Pardini C., Nardini Editore, 2005, Firenze.
UNI Beni Culturali, Materiali lapidei naturali ed artificiali. Descrizione della forma di alterazione - Termini e definizioni, UNI Standard 11182:2006.