Today’s world of Building Technology has seen a remarkable growth in terms of material, durability, strength, etc. With the dawn of industrial revolution, there have been various technologies to produce building materials that are improved and sophisticated in terms of durability and productivity. However, mending of natural materials through technological interventions has proved these materials to be efficient and stand the test of time, the materials used in many of our heritage buildings being wonderful examples of the same.
This paper throws light on terracotta, its history, composition, and its use as a building material in historic buildings with Islamic and Hindu Architecture of West Bengal. The main objective is to discuss the construction method practiced through the case study and the various conservation practices taken up for these structures that have incorporated traditional methods of construction and highly intricate craftsmanship.
WHAT IS TERRACOTTA?
Generically, terracotta refers to a high-grade of weathered or aged clay which, when mixed with sand or with pulverized fired clay, can be molded and fired at high temperatures to a hardness and compactness not obtainable with brick. In simple terms, terracotta is an enriched molded clay brick or block. The word terracotta is derived from the Italian word terracotta—literally; “cooked earth.” terracotta clay vary widely in color according to geography and types, ranging from red and brown to white.
TERRACOTTA IN HISTORY:
Clay can be considered as one of the oldest building materials in the history of man after stone. Clay was and is being used for all conceivable purposes due to its abundance and universal supply. The discovery of baking clay provided the permanence to the clay objects. This baked clay is called as Terracotta. Terracotta, a material composed of mud and clay, consolidated, molded and sun-dried or kiln burnt, has been in use ever since the early civilizations of the world. Terracotta or Mud bricks were first used in the Mesopotamian civilization.
“And now I must describe how the soil dug out to make the moat was used, and the method of building the wall. While the digging was going on, the earth that was shoveled out was formed into bricks, which were baked in kilns as soon as sufficient number were made; then using hot bitumen for mortar, the workmen began at riveting the brick each side of the moat, and then went on to erect the actual wall. In both cases they laid rush-mats between every thirty courses of bricks.”
— Herodotus, I. 179 (of Babylon) on the building of the moat and the city wall of Mesopotamia
The use of clay in the form of bricks as a material for construction in India has been practiced ever since the Indus Valley Civilization (3300- 1300 BCE). The Indus Valley cities had a combination of Mud bricks and Baked bricks depending on the quality of spaces. However, terracotta was used through history for sculpture and pottery in addition to bricks and roof shingles. In ancient times, the first clay sculptures were dried (baked) in the sun after being molded. They were later placed on the ashes of open hearths to harden, and finally kilns were used. In India, West Bengal made a specialty of terracotta temples, with the sculpted decoration from the same material as the main brick construction. Terracotta was also used extensively in Islamic architecture of West Bengal, during the late centuries of the Sultanate period.
TERRACOTTA IN WEST BENGAL THROUGH HISTORY:
Due to paucity of stone in Bengal, clay was in use for sculpture & decorations in architecture in Bengal from the ancient times (some evidences are from the Maurya period; around 300 BC). From Gupta period (3rd century AD) this art form flourished and temples & architectural monuments were being decorated with Terracotta art work. This went on up to the Pala and Sena period and stopped briefly after Muslim invasion of Bengal in around 1200 AD. This can be accounted as most of the highly ornamented Hindu temples have suffered high vandalism during this invasion, for a very simple reason that the Muslims were patrons of plain and simple designs.
The reappearance of the practice of using terracotta in the decoration of the architectural monuments was seen from the 14th -15th Century, in the early Muslim/ Sultanate period, as intricate ornamentations and craftsmanship gained patronage. Terracotta panels were extensively used on Muslim buildings like mosques & tombs; However, the terracotta panels adorning the Muslim monuments depict designs of abstract, geometric and floral patterns only. Terracotta art work continued to be used on mosques and other Muslim buildings throughout the Iliyas Shahi and Hussain Shahi periods of Bengal history, as a major work of ornamentation.
Terracotta then flourished not just as a material for ornamentation, but also as a material for the building blocks. The use of terracotta temple architecture of West Bengal started gaining popularity along with the onset of its use in the Muslim architecture.
Pertaining to West Bengal there are two types of terracotta work that was evident to these structures:
- Cut brick (carved brick) terracotta
- Terracotta plaques, consisting of Bas Relief type of work
TERRACOTTA- THE MATERIAL AND ITS COMPOSITION:
Archaeologists and art historians refer to clay objects such as sculptures or tiles, made without a potter’s wheel as terra-cotta. Terra-cotta also refers to the colour of fired earthenware clay that contains a high amount of iron oxide.
Historically there are four types of terracotta, they are: 1. Brown stone terracotta, 2. Fire proof terracotta, 3. Ceramic Veneer and 4. Glazed Architectural terracotta
- Brown stone terracotta is the variety that is dark red or brown in colour, extensively used as a masonry material. It is either glazed or unglazed. It is a hollow cast and can be generally found used in imitation of sandstone, brick or real brownstone. It is often found in the buildings of the Gothic and the Romanesque Revival movements.
- Fire proof terracotta was extensively developed in America as a direct result of the growth of high-rise buildings. Inexpensive, lightweight and fireproof, these rough finished hollow blocks were ideally suited to span the I beam members in the floor, wall and ceiling construction. However this type in no longer employed in the building industry.
- Ceramic Veneer terracotta was developed during the 1930s and is even today used extensively in the building construction industry. Unlike the traditional architectural terracotta, ceramic veneer is not hollow cast, but is a veneer of glazed ceramic tile which is ribbed on the back. It is frequently attached to a grid of metal ties which has been anchored to the building.
- Glazed architectural terra-cotta is one of the most prevalent masonry building materials found in the urban environment today. Popular between the late 19th century and the 1930s, glazed architectural terra-cotta offered a modular, varied and relatively inexpensive approach to wall and floor construction. It was particularly adaptable to vigorous and rich ornamental detailing.
PROCESS OF MAKING TERRACOTTA:
- Finding the right clay: Terra cotta is made from clay. However, different types of terracotta have different names based on where the product is made. This is partly because clay harvested from the ground in any particular region will have a slightly different makeup than clay found elsewhere. However, wherever the terra cotta is made, the first step is finding suitable clay deposits and harvesting the clay from the ground.
- Refining the clay: The raw clay needs to be refined before it is made into tiles, bricks or other products. The process involves drying the clay and then screening and filtering it to remove impurities that affect the consistency, colour and other properties of the clay. Depending on the purity of the clay pit from which the material is drawn, raw clay has foreign materials, rocks and other items that need to be removed during this process.
- Moulding of the refined clay: Once refined, terracotta clay is often pressed into moulds after mixing with water. Roofing tiles, bricks, flooring tiles and architectural embellishments are a few mould types that are used for terracotta in building material applications.
- Firing the moulded clay: Once the terracotta has been pressed into the appropriate shape, it needs to be fired in order to cook and harden. Terracotta falls into the category of low fire clay. Normally terracotta is fired at a temperature between 2048 and 2079 degree Fahrenheit.
CASE STUDY- TERRACOTTA TEMPLES IN BISHNUPUR:
The use of terracotta as a material evolved from making objects of daily needs like vessels, pottery, toys, seals, etc., in ancient times to its use in temples in the 15th– 16th century AD in West Bengal. Until this period stone was the main material used for building temples. The unavailability of stone and the availability of good alluvial soil, led to the use of terracotta to depict stone carvings and sometimes to even resemble the articulation on wooden doors.
Terracotta as a material has taken different influences to reach the urban scale of today’s world. From a material predominantly used for household, it has slowly shifted to being an integral part of the building and construction industry.
- Historic Background of Terracotta in temple architecture in Bengal:
Temples were greatly used as a medium of art expression in West Bengal. Brick temples of Bengal were built between the 16th and 19th centuries. These temples form one of the most distinctive groups of sacred monuments in India. Due to the multiple artistic influences acting upon the region, Bengali temples show a wide range of forms and techniques.
“The Bengali temples nevertheless constitute a coherent series in both their architecture and sculpture, characteristically expressed in brick and terracotta.”
The geographical distribution of the temples is majorly confined to the alluvial delta of Ganges River, which explains the popularity of clay as material for all conceivable purposes.
- Chronology of terracotta temple architecture:
The few temples preserved in Bengal built before 14th century indicates that Bengali architecture was closely associated with contemporary traditions that flourished throughout northern and eastern India. The history of religious architecture in Bengal can be divided into three periods:
1) Early Hindu (up to the end of 12th century)
2) Sultanate period (14th to early 16th century)
3) Hindu revival (16th to 19th century)
In the primitive stage, the Early Hindu period, it the building take the character of the Mauryan and Pre- Mauryan art of India. In this early stage, the terracotta consisted of a stray cut pieces of small sizes.
In the later stages of the 14th– 16th centuries, terracotta plaques appeared with new designs which were different from the primitive illustration of the same Mauryan theme.
In the next stage, terracotta appeared in larger sizes and related to architectural structures, as decorations of facades of temples. Almost all the richly decorated temples of the 16th century still exist and in comparison to the brick structures. The result was not just structural but also decorative.
- Material and Construction technique:
Incorporating a wide range of forms and techniques that are a testimony to the multiple artistic influences acting upon the region, the temples of West Bengal express a faithful picture of the lives of the people through a dynamic natural quality of technique. This was the first time in history that local building forms were translated into permanent materials. Hut shapes were recreated in brick vaulting, together with curved cornices and terracotta façade decoration. An evident blend of Islamic techniques of arches, vaults and domes construction with the Hindu temple planning were used to create this type of architecture.
The Bengali temples constitute a coherent series in both their architecture and sculpture, characteristically expressed in clay bricks and terracotta. The early brick temples of Gupta, Pala and Sena period used stone as door jambs, lintels and pillars. But the brick temples of Bengal have wooden doors which are decorated with terracotta compositions.
It can observed that the brick core of the temples generally consist of well laid horizontal brick courses. Vaults and domes are also created with bricks laid as stretchers. Bricks cut to form tapering voussoirs were extensively used for arches .. Curved layers of brickwork are employed to create vaults as well as swelling contours of temple cornices and roofs. Sometimes bricks are laid diagonally to decorate supporting arches and pendentives. In 18th and 19th century many temple facades were plaster coated in combination with terracotta sculptures.
Fired Bricks were laid in mortar composed of powdered brick and lime. Lime was obtained by processing snail’s shells. Fine but very hard pankha plaster was used to coat roofs, vaults and walls of temples. The surface skin of the terracotta plaques is carefully knitted into the brick core of the building.
Well fired brick is the basic building material for temple making in Bengal. Brick sizes vary, not only from region to region and from century to century but also within the same building. Figure 15 and 16 helps to understand how different sizes of bricks were used to get required effect or to create the pseudo effect of stone construction. Bricks are generally laid as stretchers, with half bricks to fill the gaps and avoid successive vertical joints. Surface brickwork when covered with terracotta sculptures organized into overall façade schemes, displays considerable skill of the craftsman. Different shapes of bricks are used such as long thin bricks laid edgewise as framing bands, triangular bricks as filling pieces and flat plaques coordinated in large-scale sculptural compositions, these all carefully interlock.
DETERIORATION OF TERRACOTTA:
In common as all other building materials, if not maintained properly, terracotta will deteriorate over time. This deterioration can take a number of forms due to a variety of factors. The main indicators of deterioration are as follows: 1. Glaze spalling, 2. Material spalling, and 3. cracking.
Terracotta is often coupled with clay bricks and lime in the traditional method of construction, the case being an explicit example for the same. The main cause for an overall deterioration of the structure is water ingress. This can be caused due to the porous nature of the material itself or by the cracks in the material allowing water to penetrate, excessive wear caused by water run-off. The worst cause of this type of damage is inappropriate cleaning.
- REPOINTING: As with any material which forms masonry in the building, there will be a need to re- point. In the case of the temples of West Bengal lime has been used and it comes in direct contact with the terracotta bricks as well as the terracotta panelling stucco work. This keeps the internal structure of the terracotta system dry and intact. It is also vital to avoid damaging the surrounding terracotta units to ensure that the mortar is not allowed to stain the surface of the material. By using the same lime mortar, moisture which has penetrated into the structure of the building will be allowed to evaporate through the joints. In certain cases, waterproof caulking of joints should be avoided. A lime mortar prepared as per the traditional method of preparation is more durable because it is in itself imparted with antiseptics like Jaggery, egg white, turmeric, etc.
- REPLACEMENT: Sometimes the terracotta has failed to such extent that replacement is the only option. In all cases where replacement is necessary the preferred option should be replication of the original material. Whilst alternative options such as Glass Reinforced Plastic or Glass Reinforced Concrete are sometimes proposed, these can have significant drawbacks. There is a danger in using materials which are heavier than the original terracotta. Sourcing the same clay and the craftsmen in West Bengal is more feasible and economical than using foreign material.
- CLEANING: Terracotta inherently has been designed to be cleaned fairly easily. Most elements can be usually cleaned simply with water and little soap. A soft bristle brush may be used on dirt which is harder to remove. In a few cases of severe soiling, steam cleaning may be appropriate. The use of abrasive cleaning methods, strong acids or metal bristle brushes should be avoided as these may lead to the glaze or the fire skin being abraded. This damage is irreversible and will lead to the long-term deterioration and ultimately need for replacement of the elements affected.
A need of the time, terracotta served as an amazing material in the construction world during the 15th– 19th century AD. Bishnupur is just one example for use of terracotta in the most technological and artistic manner with various methods of construction practiced. However, other than West Bengal and many other Indian cities, terracotta has been extensively used in the field of building and construction in many parts of United Kingdom, Scotland and America. It was a part of the technological innovations of the Chicago school.
Terracotta has been the most befitting material, that it was modified and explored to its fullest in the Hindu and Islamic Architecture of West Bengal. This material has been, with the help of technology, explored as being used as a structural material. There have been remarkable technological innovations of terracotta in its use as a load bearing structural material and interior architecture, which is however a limitation to this paper.
Terracotta as a material has an advantage of being cheap and light. It is adaptable to be mass-produced, the limitation being the incapability for re-use of plaster moulds. Another advantage of this material was it was craftsman friendly, and easy to make custom shaped ornamentations. What took immense effort to be produced out of stone was produced with much less embodied energy. Terracotta as a building block and as a material for ornamentation has been the product of the easy availability and its abundance in the fertile lands around the deltas of the Ganges and the Brahmaputra.
The disadvantage to today’s context is that the material is highly prone to deterioration due to pollution. There is a visible blackening. There are various other effects on these temples, owing to the high rainfalls that West Bengal experiences all through the monsoons. However, architecturally these temples have been built with the traditional Bengali roofs to withstand climatically.
- Chitrolekha International Magazine on Art and Design, (ISSN 2231—4822), Vol. 1, No. 2, August, 2011
- Major reference and citation:
- History of terracotta in Islamic architecture of West Bengal, Article- Terracotta in Islamic structures of West Bengal dated 19th June, 2013
- History of terracotta, extracted from the Introduction notes of the article Terracotta Temples of Bishnupur: Transformation through Time and Technology by Priyanka Mangaonkar
- Types of terracotta, extracted from http://www.nps.gov/tps/how-to-preserve/briefs/7-terra-cotta.htm
- History of terracotta, extracted from the Introduction notes of the article Terracotta Temples of Bishnupur: Transformation through Time and Technology by Priyanka Mangaonkar
- Terracotta Hollow blocks from the article Terracotta Temples of Bishnupur: Transformation through Time and Technology by Priyanka Mangaonkar