Soapstone (Talc-Chlorite Schist)

Abstract

Talc-chlorite schist in geological, architectural, and local history literature is called “pot stone” or “soapstone”. It is a metamorphic rock consisting of talc, magnesite, and chlorite. Traditionally, this stone was used in everyday life due to its special physical and mechanical properties, such as high heat capacity and low coefficient of thermal expansion. The peasants carved stove pots and other kitchen utensils out of it, for which the stone is called “potted”. Dishes made of this stone retained heat for a long time, due to its high heat capacity. It is also used in the manufacture of stoves and fireplaces. The presence of talc in the rock gives it a greasy shine. For this, the stone is named “soapstone”.

Talc-chlorite schist in geological, architectural, and local history literature is called “pot stone” or “soapstone”. It is a metamorphic rock consisting of talc, magnesite, and chlorite. Traditionally, this stone was used in everyday life due to its special physical and mechanical properties, such as high heat capacity and low coefficient of thermal expansion. The peasants carved stove pots and other kitchen utensils out of it, for which the stone is called “potted”. Dishes made of this stone retained heat for a long time, due to its high heat capacity. It is also used in the manufacture of stoves and fireplaces. The presence of talc in the rock gives it a greasy shine. For this, the stone is named “soapstone”.

The appearance of potted stone in the architecture of St. Petersburg is inextricably linked with the history of the development of the architectural style “modern” in the late nineteenth–early twentieth centuries. In St. Petersburg, the leading variety of Art Nouveau has become the “Northern Art Nouveau” style. This style required a qualitatively new stone, different in properties from granites, marbles, sandstones, quartzites, and other rocks. This place is occupied by a potted stone. It is durable and resistant to urban environments (repels moisture and is relatively slow to pollute). The stone is quite soft and malleable to the sculptor’s chisel. This made it possible to use it as facing slabs with various processing textures and decorate the facades of buildings with bas-reliefs, high reliefs, and sculptures. Having entered the construction practice together with the “Northern Art Nouveau”, potted stone remained in the architecture, cladding, and decoration of buildings built in the style of “neoclassicism” in the second decade of the twentieth century.

Houses built during the period of Northern Art Nouveau and neoclassicism are characterized by a bright and expressive appearance. In St. Petersburg, these periods are inextricably linked with the names of famous architects (F.I. Lidval, S.I. Minash, N.V. Vasiliev, A.F. Bubyr, A. Shulman, V.S. Karpovich, M.H. Dubinsky, I.A. Pretro, V.A. Kosyakov, architects of the Benois family, etc.). To date, there are many buildings and structures decorated with this type of stone in the architecture of St. Petersburg.

Sculpture and bas-reliefs located on the sides of door portals, window frames, and inter-window spaces have become one of the special areas of use of potted stone in architecture. As a rule, these are fabulous and mythical creatures that are combined with the asymmetry of the forms of the building itself. Along with the sculpture in the decoration of the building, slabs of this stone are used with different textures of the processing of the front surface—rocky, smooth polished, hewn, and treated with buchard.

One of the famous examples of Northern Art Nouveau in our city is the building located at the address Kamennoostrovsky Prospekt (house 1–3) (Fig. 1). This apartment building was erected by F.I. Lidval in 1899–1904. The main part of the building consists of three buildings. Various finishing materials are used in the decoration of facades: light brown rough plaster, granite blocks, and slabs of potted stone, made in smooth and rocky textures. The most attention is attracted by the carving of potted stone at the entrance to each building. In the center of the decoration of the central portal is a cartouche with the date of construction of this part of the building—1902. To the right of the date, there is a pine branch with cones, a forest bird resembling a magpie is sitting on it; it tries to peck a hare sitting next to it. Behind him, another hare is seen running out of the thicket. To the left of the date is the head of a lynx with an open mouth. Nearby, on a thick branch, sits an owl with open wings. Above you can see a large relief owl. She tilts her round head down and stares at passers-by with unseeing eyes. On the wall of the left front door, you can see images of fantastic big-headed fish, and above the right front door there are lion masks of various sizes. No less interesting is another house built by F.I. Lidval in St. Petersburg. This is the apartment house of M.N. and N.A. Meltserov. It is located at the intersection of Bolshaya Konyushennaya Street and Volynsky Lane (1904–1905) (Fig. 2). In 1907, at the first facade competition, the building was awarded a medal. The expressiveness of the facade of this building is emphasized by window openings of various shapes, sizes, and solutions: rectangular and oval, narrow and wide, and double and single. In the design of the facade, the architect used a combination of smooth and rough plaster finishes, carved rosettes, ovals, wreaths, cartouches, garlands, and two types of stone surface treatment. In terms of decoration with natural stone, the main role is given to potted stone, the use of which in the decoration is uneven across the floors. To the height of the first two floors, with the exception of the granite basement, the building is lined with potted stone. Already starting from the third floor, the architect gives a big role in the decoration to the plaster technique. Potted stone in the third floor is used for facing semicircular and trapezoidal bay windows. Throughout the third, fourth, and fifth floors, there are inserts into the walls of decorative details from the pot, shaped like bricks. A more massive, solid facing with this stone begins only at the level of the upper part of the windows of the fifth floor and the upper floor of the bay window along Volynsky Lane. Potted stone is used in the cladding of the building in details with different textures of surface treatment from smooth and hewn, to details made in the texture of the rock, or carved elements. The technical side of the cladding was carried out by the “Finnish Joint-Stock Company for the development of potted stone in the city of Vilmanstrand”. Currently, this city is called Lappeenranta (Kirikov 2006).

Fig. 1

Registration of the entrance to the northern volume of building 1–3 on Kamennoostrovsky Avenue from the kurdoner side

Fig. 2

General view of the former apartment building of M.N. and N.A. Meltserov. (Bolshaya Konyushennaya str., 19). Photo 2006

Another landmark and important architectural object from the point of view of the use of materials in the decoration and decoration of facades is House No. 26–28 on Kamennostrovsky Avenue (Fig. 3). This house built in 1911–1913 by order of the first Russian Insurance Company (architects L.N. Benois, A.N. Benois, and Yu.Yu. Benois). The main volumes of the building, forming wings in the plan and facing Kamennostrovsky Avenue, are separated from each other by a large courtyard (kurdoner) oriented in line with Rentegna Street and separated from the avenue by a portal in the form of a transition on granite columns. The building is five-storeyed with a high ground floor. At the first cursory glance, anyone passing by will have the impression that this building is lined with natural stone to its full height. This is not the case. Two stones were used in the cladding and decoration of the walls of the building. Pink granite was for the decoration of a high ground floor and potted stone for wall cladding at the level of the first and second floors and only on the section of the front facades and facades of the passage to the kurdoner to the portal with columns. All finishing above the intermediate cornice (at the level of third–fifth floors) on the front facades and all the finishing from the granite base at the facades in kurdoner is made with decorative plaster. The master plasterers of the beginning of the twentieth century skillfully selected the plaster recipe, which allowed them to visually “deceive” the viewer, giving the front facades of the building the appearance of a palazzo, lined with natural stone to the full height. This effect was achieved both through the use of plaster at high altitude, and through the use of finely ground and sifted potted stone, which was used for lining the walls of the lower floors of the building, as a filler in decorative plaster.

Fig. 3

General view of the left wing of House No. 26–28 on Kamennoostrovsky Avenue

An example of an artful combination of natural stone and plaster finishing is a building located on Vasilievsky Island. This is House No. 8 on the 11th line (Fig. 4). The monumental building was built in 1905–1907 by architect M. H. Dubinsky for the Naval Academy in the neoclassical style. Its distinctive feature is the use of natural stone at the entire height of the facing and decoration of the front facade. It should be noted that for the architecture of St. Petersburg, this is a special and important feature. There are not so many architectural structures in our city, the front facades, which are lined with natural stone to the full height. In most cases, architects tried to skillfully combine natural stone, plaster decoration, and decor (plaster, stucco, ceramic, etc.), which was most likely due to financial reasons and estimates for the construction of an object. In the building under consideration, the low basement is lined with Gangut granite. All other details of the cladding and decor, including rich carved elements above the windows of the second floor, carved capitals of columns, four sculptures in the third floor level, and four sculptures of birds in the attic level, are made of potted stone (Fig. 5).

Fig. 4

General view of the building of the former Naval Academy (11th line V.O., 8)

Fig. 5

Fragments of the carved decoration of the facade of the building of the former Naval Academy (11th line V.O., D. 8)

As part of the restoration work, which became quite active in the early 2000s in connection with the preparation of St. Petersburg for the three-hundredth anniversary, a dispute arose in engineering and design circles about where the potted stone for architectural structures was supplied from. Strangely enough, but at that time there was no unambiguous answer to this question, because various sources of stone receipt were indicated in literary sources. In the 20s of the last century, Vl. Geller, in a review of the stone building materials used in the city, noted that this “wonderful decorative material” was delivered from Sweden. This point of view was subsequently followed by other researchers. In the monograph “Decorative facing stones” published in 1989, M.S. Ziskind pointed to the deposits of talc-chlorite rocks in central Karelia (Listyegubskoye, Kallivo-Murenanvaara, etc.).

Work with literary sources allowed us to identify two main regions in the quarries and deposits of which potstone extraction was potentially possible. Deposits in the east of the central part of the Republic of Finland, located within the so-called Nunnanlakhtinsky field, have been developed since the second half of the nineteenth century. Currently, the deposits are operational. Deposits in the central part of the Republic of Karelia, located on the southern coast of Lake Segozero, were developed by the local population at least since the second half of the nineteenth century.

Finnish deposits of potted stone located in the area of the Nunnanlahtinsky field (modern territory of the Republic of Finland) are indicated as a source of potted stone in the book “The Age of Soapstone 1893–1993” (Kotivuori et al. 1993). It is noted that for the first time the assessment of the potted stone deposits in the area of the city of Nunnanlahti was carried out at the end of the nineteenth century by the Finnish geologist Benjamin Frosterus. It was he who was the first to assess the degree of suitability of the manifestations of talc rocks of the Nunnanlahta region for mining. Already in 1893, an enterprise was created, called in Swedish “Finska Täljstens AB”. The company’s work focused on the Nordic countries and the Russian Empire. The volume of production was more than 2000 cubic meters per year, of which 800 cubic meters are construction and industrial stone and up to 1700 m² meters of facing tiles. By the end of the nineteenth century, potted stone from this region was widely used in the cladding of facades of buildings built in the “northern” Art Nouveau style. At the same time, one of the main markets for products made of this stone was the Russian Empire.

The transportation of soapstone carried out by barges along the waterway that stretched from Lake Pielinen through the Pielisjoki River and the Saimaa Canal to Vyborg. From Vyborg, the stone was delivered by sea to both St. Petersburg and Helsinki. In winter, transportation is carried out on ice using horses. In 1925, after a number of financial and structural changes, the company received the name “Vuolukivi Suomen Oy”. The soapstone of these deposits is a talc-magnesite rock in composition. These rocks lie in layers within the greenstone Archean belt overlain by rocks of the Proterozoic age (Sorjonen-Ward 2002). Currently, in Finland, soapstone is mined at several historical and modern quarries located on the west coast of Lake Pielinen near the settlement and Nunnanlahti.

Karelian deposits of potted stone located on the southern shore of Lake Segozero (modern territory of the Republic of Karelia within the Russian Federation) are indicated as a source of stone for architectural objects of St. Petersburg. The potted stone of the southern coast of Lake Segozero has been known since the second half of the nineteenth century. According to geological descriptions, the potted stone of the Segozersk group of deposits is talc-chlorite schist in composition. Talc-chlorite schists are found in two deposits: Kallievo-Murenanvaara and Turgan–Koyvan–Allusta (Sokolov 1995).

The Kallievo-Murenanvaara deposit was intensively developed from 1925 to 1941 by the explosive method. The upper part of the deposit worked out and flooded. As of 2019, the field is operational (http://atlaspacket.vsegei.ru). The Turgan–Koyvan–Allusta deposit developed in the 1950s. The extraction of the stone was carried out in an explosive way, which led to a decrease in its qualities due to the cracks formed. As of today, there is no information about the extraction of stone at this deposit.

There is a mention that Swedish potted stone was used in the architecture of St. Petersburg. This error is due to the fact that the Swedish company Finska Täljstens AB was engaged in the production of the Finnish Nunnanlahti deposit. The Swedish name of the company gave rise to errors about the Swedish origin of the stone (Shaikh 1972).

Detailed instrumental studies was carried out for samples of natural stone and facing architectural details. The results prove that the soapstone used in the stone decoration of St. Petersburg is most similar in mineral composition and structural and textural features to talc-magnesite stone from quarries near Nunnanlahti (Finland). Unlike Finnish, Karelian soapstone from the southern coast of Lake Segozero has a talc-chlorite composition (Savchenko 2009).

Soapstone from old quarries near Nunnanlahti has an interesting feature: over time, the front surface of the stone changes its color and acquires a yellow–brown hue. On restored buildings, soapstone has a light gray and greenish-gray color.