n. 485 / May 2002

 

The stone paving in Turin helps create the image of the city, as regards both the historic heritage of squares, streets, courtyards and more recent installations. The historic paving (fig. 1) is especially realised using materials from Piedmont, while contemporary renovation or the installation of new paving have often seen local materials flanked by stone from outside Europe. The various materials used are classified petrographically and their conservation status is discussed.

 

As Quatremère de Quincy wrote about Turin in his "Dictionnaire Historique d'Architecture" published in Paris in 1832, "nulle ville, à vrai dire, n'a un aspect plus grandiose, par la juste proportion qui règne entre la hauteur des édifices et la grande largeur des rues". This grandiosity undoubtedly arises "par la grandeur de ses dispositions, la symétrie et la régularité de ses bâtiments" but also through the quality of urban settings and open areas, where stone pavings play a central role.

 

In reality, the Turin described by Quatremère de Quincy was, as regards paving, quite different from the contemporary city: while paving was already extensively present in those times - and can still be seen today in the courtyards of the major Baroque palaces - the full-scale paving of roads and squares began in the mid-1800s alongside the commissioning of the first stretches of the railways.

 

This does not mean, however, that stone paving was not utilised extensively in the past in the urban settings of Turin.

 

The most common and ancient paving involved flagstones, made up of elements generally having rectangular geometry. The most ancient example of this kind is the section of Roman road still preserved near Porta Palatina, made up of slabs of gneiss from the Dora-Maira Massif outcropping in Val di Susa (fig. 2) and inasmuch readily transported to Turin by canal barges.

 

Slabs of gneiss were also used in past centuries to pave the courtyards of palaces, often in combination with river pebbles. The combination of pebbles and slabs (where the flagstones formed the characteristic "tracks" used by wheeled traffic and the edging of roads) was also employed in some streets and squares of the city prior to the organic slabbing of the open areas begun in the mid-1800s. This tasked generally involved not only the gneiss rocks from the nearby Alpine valleys but also magmatic intrusive rocks from Piedmont (fig. 2), i.e. the syenite from the Biella pluton (Fiora et al., 2000b), Lake granites and diorite from Valle Chiusella (Fiora et al., 2000c). There was also exceptional use of cabonatic mica-schists from the Piedmont Zone of the Calceschists with Ophyolites involving several varieties, including one characterised by high content of granatiferous porphyoblasts. Gneiss rocks easily recognised on a macroscopic scale include the micro-occhiadin quarried in the Bagnolo-Luserna area (Luserna stone: Fiora et al., 2000a; Sandrone et al., 2000) and defined by Jervis (1889) as "the best gneiss in Italy for pavement slabs" (fig. 2 & 3) as well as in Valle di Susa, including a variety rich in black prismatic crystals of tormaline of some centimetres in dimensions and another more evidently occhiadin in nature.

 

Paving is also a characteristic feature of all the porticoes that were developed towards the end of the 1800s and by now total more than 20 km in length. The rocks most generally utilised are Dora-Maira gneiss, especially Luserna stone that, as of 1882, could be easily transported from Luserna to Turin on the new railway. Syenite, diorite and granite are used to a lesser extent. Gneiss is always split as found, while the intrusive materials have rough surface processing to avoid slipping on the pavements. Kerbs are also in stone (gneiss, granite, diorite and syenite) and this type of installation is found ni all the pavements of the 1800s.

 

Pebble stone paving is another ancient method used in Turin, typical of courtyards, church sacristies and squares. The elliptical pebbles, with a maximum diameter of 6-8 cm, may all be of the same stone (e.g. ophiolites or gneiss) for a uniform appearance, or involve different varieties of stone for multi-coloured effects. The stone materials utilised (fig. 4) are essentially quartzites and more rarely gneiss for the light-coloured elements, and metaophiolites (serpentinites with subordinate prasinites, meta-gabbroes and and eclogites) for the darker elements; the former essentially come from the flood plains of the Dora Riparia and the latter especially from the flood plains of the Stura di Lanzo (Sacco, 1907), as can be seen in fig. 2.

 

A major example of two-colour pebble paving can be seen in the courtyard of Valentino Castle and in many courtyards of the Baroque palaces. The ancient installation technique involved placing the pebbles close together with a sand binder.

 

Flagstone paving with cuboid as-split stone material elements generally less than 10 cm per side (so-called "pavé") was utilised in sections of squares and streets, often in association with slabs. The most commonly used rock for pavé is Trentino porphyry, dating from the Permian Age from the porhpyry platform in Trentino; Piedmont syenite and diorite were also used to a much lesser extent.

 

"Opus incertum" paving, utilised in the modern period, is limited to pavements in parks and green areas: Luserna stone or Barge quarzite are used, the latter in mosaic elements exploiting the different colour varieties (yellow, grey and olive) of the stone.

 

The paving of the porticoes in the main central street is also highly particular, that is Via Roma, laid 1930-36 with widespread use of various varieties of "marble" and "granite" (Peretti, 1937): these include, for example, Baveno pink granite, Montorfano white granite, Balma syenite, the basic granulite known as Anzola diorite, Carrara marble and Rosso Levanto marble (fig. 5), as well as different types of carbonatic sedimentary rocks from all over Italy. All these rocks were given a polished surface. Some use was made in any case of as-split rocks, includng Barge quarzite and some gneiss from Ossola ("beole").

 

The state of conservation (Normal. 1/88) of the historic stone paving differs depending on location. There are various forms of deterioration, such as gaps and crumbling of the elements in the pebble paving, loose cubes in the "pavé", fractures (fig. 6), chromatic alteration and saline effluorescence in the slabbing. Slabs of occhiadin gneiss may also show signs of the typical differential alteration, with nodules of feldspar quartz in relief (since they are more resistant to wear).

 

The slabbing also presents exfoliation, of the central deterioration type (or dishing or framing deterioration, Calvino, 1967), that typically characterises Luserna stone (Fiora et al., 2000); one can also find tormaliniferous gneiss from Valle Susa: this form of deterioration initially appears as persistent humidity stains in the central part of the slabs and the subsequent formation of increasingly evident "dishing". Exfoliation generally develops in the centre of the slab but in some cases deterioration causes the formation of numerous cavities in portions where water stagnates more readily.

 

Until quite recently, it was unfortunately standard practice to replace such slabs in stone paving with asphalt; this occurred not only in the case of deteriorated slabs but also with material with a good conservation status following road-works (installation and/or maintenance of pipes) - these slabs in any case could have been removed and repositioned.

 

Contemporary paving involves both the renovation of historic installations and new projects associated with major public building work. The former, for example, include the paving in front of Palazzo Madama in Piazza Castello (fig. 7): Luserna stone is prevalently utilised in the form of slabs with flame-finished surfaces but Valle Cervo syenite, a white granite and a gabbro (black granite) obtained on the market international are also used. Street furniture in this area also includes architectural elements in stone, such as benches in Luserna stone with a flame-finished surface and bush-hammered edges (fig. 8), as well as bollards in granite from outside Europe.

 

Numerous renovation projects of pavement and portico slabs have been performed using Luserna stone and, very occasionally, lithotypes from outside Piedmont which are unusual for the city, such as ignimbrite from Latium known as Peperino, used on a small scale in the portico in front of the Teatro Regio in Piazza Castello. Luserna stone is also used in many re-qualification projects in the city's public areas, such as the repaving of the Piazza Madama Cristina market area, where the stone is largely used in the form of slabs with a flame-finished surface and, to a lesser extent, in cubes.

 

New pavings worthy of note include the very recent "Spina Centrale", that is the area restored as an urban boulevard and public area covering the so-called "passante" railway line. The section currently being finalised (Corso Mediterraneo, between Corso Rosselli and Corso Peschiera) involves different stone materials, with emphasis on Piedmont varieties, although the cyclists' path is in a variety of Argentinean porphyry (fig. 9), from the Trelew area in central-southern Argentina. The Piedmont rocks are a light grey variety of diorite (kerbs and slabs), syenite (pavé cubes and slabs) and Montorfano granite, used to produce a number of white bands. Sections of the paving in these avenues are in pebble-stone (fig. 10), that differ from the historic works in terms of dimensions and origin of the pebbles, as well as the type of installation. The maximum dimensions of the elements (diameter 8-12 cm) are larger than in historic paving installations and their lithological composition is not limited to metaophyolites, quartzites and gneiss but also includes basic granulites, granites and occasional acid vulcanites, characteristic of the flood plains of the Ticino (fig. 2). The pebbles are incorporated in a more extensive matrix of sand than in the past and joints are filled with mortar to facilitate cleaning with modern mechanical systems.

 

In the metropolitan area of Turin, over and above the city centre, stone pavings are frequently to be seen in the suburbs, frequently in large pedestrian areas. For example, Orbassano Local Council (fig. 11) has a large market area paved entirely with stone materials, includng Trentino porphyry, Biella granite and Luserna stone.

 

The quality of the stone material used in this recent project was verified prior to installation to eliminate elements characterised by defects (for example, the presence of sulphides which cause rust-coloured stains in "salt and pepper" Montorfano granite and aplitic seams measuring more than ten centimetres in the diorite and syenite). In the cyclists' path, the need to use slabs of higher thickness (14 cm) in road-crossing points saw the choice fall on riolitic ignimbrite, so-called Argentinean porphyry or Porfiris, instead of the Trentino porphyry initially envisaged. Since this material was only recently introduced on to the market international, the appendix includes a brief petrographic description.

 

Contemporary paving in Turin also includes recent "pavé" projects involving Trentino porphyry, syenite, diorite, Luserna stone and, more rarely, white marble.The state of conservation of these recent paving installations is generally good, although some fracturing of slabs can be seen, as well as loose cubes, especially because of occasional transit or parking of heavy vehicles and, at times, acts of vandalism.

 

The stone paving of Turin is an historic heritage of primary importance that, after a period of relative neglect, is currently being re-valorised in view of its undoubted value within the urban setting of the city.

 

This re-assessment is witnessed not only by the closer attention paid to the conservation of such installations but also through the use of historic local stone materials in very recent projects, both those of major impact on the "ground plan" of the future city such as the "Spina Centrale" and those of more modest dimensions, such as the renovation of the market area in Piazza Madama Cristina.

 

The authors wish to thank Ing. Blanchetti (Recchi Co.) and Etco Co. (Venaria Reale, Turin) for information provided about the stone materials used in the "Spina Centrale".

 

Authors: L. FIORA* - A. DE ROSSI** - R. SANDRONE*** - L. ALCIATI****

 

* Dipartimento Scienze Mineralogiche e Petrologiche - Università di Torino

** Dipartimento Progettazione Architettonica - Politecnico di Torino

*** Dipartimento Georisorse e Territorio - Politecnico di Torino

****^Geo B.R. di Torino