Conservation of Terracotta Temples
Plants taking root, Siva Temple, Kalna
Buildings made from burnt brick (terracotta) and clay binding materials are affected by the environment, pollution, and biological and chemical factors. Dust and dirt from different sources can accumulate on the surfaces of buildings. Various types of "lower" plants such as moss and lichen can grow on the surface, which in the winter can turn black. Lichen and liverworts produce acids that can damage surfaces and and change the smooth surface of bricks and terracotta and make them rough and brittle. Often, on the top of the temple "higher" plants take root, boring into the brickwork and breaking it or making it unstable.
Decorative terracotta sculpture is often hidden or damged by white "salt" forming on the surfaces. The source of this salt is Calcium Oxide in the brick which reacts with moisture to produce Calcium Hydroxide, which in turn reacts with atmospheric Carbon Dioxide to form Calcium Carbonate that is deposited as a solid white crust on and between the terracotta art-work. Surfaces are further deteriorated by Carbonic Acid formed by the reaction of atmospheric Carbon Dioxide with moisture. Many medieval brick monuments have carved wooden doors and windows, or in some cases subsidiary structures such as chandi mandaps entirely build of wood. These are susceptible to damage by insects such as termites and beetles.
White salt and moss, Temple at Jhikira
Damaged or vulnerable buildings can be protected by some simple techniques. Restoring excessively damaged buildings require the services of professional conservation engineers. Temples and mosques near main roads are most easily damaged, so shielding automobile pollution is a simple first step. "Lower" plants such as Algae, Moss and Lichens can be eradicated by soaking the affected area with diluted ammonia solution, then gently brushing the surface to remove the plants. The surface then needs to be washed out thoroughly with neutral liquid detergent and allowed to dry. To prevent re-occurrence, the surface needs to be treated with fungicidal solution once a week.
For the eradication of higher plants such as pipal, the first approach is to try to remove the plant physically. If the plant is too large to remove, it first needs to be killed by spraying a herbicide. In one or two weeks the tree becomes black and falls off. Herbicides can also be injected into the plant body by cutting the plant as far upto the root as possible, making a hole using a drill, and injecting the chemical. After three or four applications, the plant can be cut off and the surface sealed with a sealing agent. Cracks in terracotta bricks or loose joints can cause leakage of water and more damage. Such portions need to be sealed with mortar made by mixing slaked lime and brick dust.
Fungus, Temple at Jhikira
Wood needs to be treated with insecticides and fungicides. Kerosine or linseed oil can be applied to entire wooden object by brushes. Kerosine oil carries insecticide and penetrates deeply into the wood, while linseed oil polymerizes and shields the porous part of the wood, and also provides resistance from insect and water. "White salt" such as calcium carbonate deposited on terracotta surfaces can be removed or cleaned by using Acetic acid solution along with a soft brush, knife and needle. Syltrate and wax can be used to preserve terracotta and stone. Syltrate consolidates flakes in the brick. To make it more water resistant or repellent vaseline or wax can be coated on the surface with a soft brush. The surface may look dull at first but once the wax melts and enters the porous brick it protects the surface and the surface looks clean.