This is a brief report of chemical conservation of monuments in Nepal. The chapters of this article are as follows.
Table of Contents
Man-made historical, cultural, religious and architectural important sites, which are more than hundred years old are termed as Historical Monuments. There are certain rules and regulations for the declaration of monument and monumental zone as mentioned in “Ancient Monument Preservation Act 2013 (including amendments) published by His Majesty’s Government, Department of Archaeology, Nepal. Dhungedhara, Temples, Monasteries (Viharas, Bahal, Bahi), wayside rest house (Patis, Pauwahs and Sattals), Stupas (chaityas), tank or Pokharis, Palaces, common man’s house and forts etc. come under this heading. Such monuments give the historical information of the country and great person. Information about these things is either engraving or handwritten on Golden plates, Copper plates, Stone slabs, Wooden objects, Birch barks, palm leaves, Parchments, and papers etc. So far His Majesty’s Government of Nepal and UNESCO World Heritage Committee convened in Cairo in 1979, accepted and declared following sites to be enlisted in world Heritage and monument sites list.
Likewise Lumbini also declared as World Heritage site in 1997 AD.
Different types of monuments used different organic as well as inorganic raw materials such as stones, bricks (terracotta), copper plate, brass plates, mud, tiles, and wood. So these are being deteriorated by different factors like environment, Pollution, Biological, Mechanical, and chemicals. Such monuments attract thousands and thousands of national and international tourist, which generate a lot of money. Not only this but also give information regarding the history of the country and great person. Hence it is essential and important to preserve and conserve them. Here the author is interested to explain some preservation and chemical conservation work of Bhaktapur Durbar Square monuments because this site is not only enlisted in world heritage site but also important in tourism aspect too.
There is a different way of classification of monuments. As mentioned in the Ancient monument Act 2013 and 2048 (including amendments). monuments are categorized into three different groups from a touristic point of view.
Some classified monument into two groups from use point of view,
From the traditional architecture view, temples are divided into following groups.
On considering the temples of Bhaktapur Durbar Square area there are:
Beside these are other very interesting monuments such as 55 (fifty-five) windows Durbar, which was built in 1697 AD during Bhupatendra Malla period.
Swornadhokaorgolden gate, which was gilded in 1754 AD during Ranjit Malla period (1722-69AD).
There are a lot of beautiful wood carving, tudals, toran, windows, doors, cornices etc., besides these many other materials are associated with the monuments such as stone, clay, terracotta, copper, bronze, silver and gold etc.
Deteriorating factors of monuments are basically based upon its surrounding environment, pollution, biological condition, chemical and so on. The condition of the monuments depend on the use of them, also plays a vital role, which deteriorates the monuments. On considering few examples of Bhaktapur Durbar Square temples and other monuments give a basic idea about problems of the monuments.
i. Vatsala Durga (Annapurna) and Shiddhi-Laxmi: Both of these are shikhara style, temples made of stone, usually sandstones type found around Kathmandu Valley, are used in these temples. The sandstones could easily be deteriorated, due to the unfavorable condition of environment & pollution. Dust from different sources like automobile, dismantling houses and other could be accumulated on its surface; wind and birds also carry different seeds of the plant. During the monsoon season and thunderstorms, the acid rain can drop on stone surface & water percolates from the stone joint and cracks portion. Some of the water-soluble salt is deposited on the surface. It looks white in color, maybe some salt (of) chloride/Sulphate/Carbonate. Due to deposition of such salt flaking of stone chips are also noted.
Under the favorable condition, some of the cryptogamic groups of plants: Algae, Moss, Lichens, and others are grown up on a broken joint portion of the stone. They die in dry weather and proliferate again forming humus. Taller plant or higher group of plants: Peepal, Bhimsenpati and other grown up, when some birds excreta with seed drops on this surface. under the favorable condition it grown up, after years and years it makes ugly look the temple, finally, they damage the stone temples, such examples are seen over there.
ii. Rameshwar Temple (Shiva): This is Shikhara style terracotta temple. In this temple burnt brick (terracotta), wooden materials and clay binding materials (mortar+slaked lime) are used. This temple deteriorated by the environment, pollution, biological and chemical factors. Dust and dirt from different sources accumulated on the surface of this temple, also some of the plant seeds, plenty of lower plants were seen on the surface. On winter season surface of such plant changed into black color. Some of the lower plants like Lichen produce Lichenic acid, Liverworts plant produce humic acid, such acids damage and change the smooth surface of bricks and terracotta into rough and brittle. On the top of the temple (i.e. GAJUR), higher plant were also observed, turning the temple into the ugly structure.
Around the middle portion of the temple at four sides East, West, North, and South. there are beautiful decorative terracotta objects of different varieties i.e. arts of god and goddess, such decorative terracotta objects were highly deteriorated by white color salt formation. Such salt formation is caused due to the environment, pollution and chemical effect. There are different views of the formation of a white color solid salt, was identified as Calcium Carbonate or chalk because of effervescent with Hydrochloric acid possible reaction as below:
CaCo3+ 2HCl → CaCl2 + Co2↑ + H2O
Formation of calcium carbonate in terracotta object:-
Ca(OH)2 + CO2 → CaCO3↓ + H2O
Ca CO3 + CO2 + H2O → Ca(HCO3)2
Ca(HCO3)2 sunny day → CaCO3↓ + H2O
In newly made terracotta objects remain some Calcium Oxide, which on reacts with moisture changed into Calcium Hydroxide, when it reacts with atmospheric Carbon dioxide form white solid materials i.e. Calcium Carbonate or chalk. On continuous reaction with atmospheric Carbon dioxide on moist condition white solid materials disappeared, i.e. Calcium bicarbonate on a sunny day again form which solid materials i.e. Calcium Carbonate as indicated above chemical reaction.
Mechanism of chemical reaction for the formation of calcium carbonate.
C02+H2O → H2CO3 (carbonic acid)
H2CO3 + CaCO3 → Ca (HCO3)2
Ca (OH)2 + Ca(HCO3)2 → CaCo3↓ + 2H2O
Here also atmospheric Carbon dioxide reacts with atmospheric moisture under suitable condition form Carbonic acid; on reaction with Calcium Carbonate which forms Calciumbicarbonate. Some time Calcium bicarbonate reacts with Calcium Hydroxide and from Calcium Carbonate and water. Such Calcium Carbonate appeared as a white solid material on the surface of the terracotta objects, it looks ugly and finally, they are filled in the carving portion of the terracotta object.
There are some wood carvings (door, window and plain plank) fitted in different parts of the temple. Such wooden objects are deteriorated by insects like termites, beetles. Effect of such biodeterioration manly depends upon the quality of the wood and environmental condition of its surrounding. Softwood is affected quickly by the insect but same is difficult in hardwood. After the great earthquake of 1934 in Nepal, the majority of woods were replaced by soft wood, so biodeterioration rate is higher in such
case. Observation of anatomy of soft and hardwood is clearly indicated that softwood is quickly affected by insect rather than hardwood, because of many insect food materials like carbohydrate, starch and, some insect edible plant cells present in it. The durability of some wooden species are Illustrated below:
For the preservation of monument from the environment and pollution, His Majesty’sGovernment of Nepal and Bhaktapur Municipality have jointly conducted the programme on control of automobile movement inside the Durbar square area”. It helps to control the automobile pollution i.e. the effect of various inorganic as well as organic gases (Nitric acid Sulphuric acid & Carbon monoxide)etc. Beside these vibration movements on monuments is automatically controlled. His Majesty’s government of Nepal and the government of Federal Republic did a great job by preserving the whole city of Bhaktapur from dust, dirt and drainage pollution by laying burnt bricks on roads, courtyard and other empty spaces, not only this but also made proper water and sewerage system in different areas. It controlled the dust, dirt, biogasses and other gas pollutions, which creates adverse effects on the monument, it also gives a good impression to the tourist.
The treatment for the eradication of cryptogamic plants: Algae, Moss, and Lichens are also very important and essential. Firstly soak such affected area with 2-3% dil. ammonia solution in both stone and terracotta, then gently brush with jute or hairbrush depending upon the condition of the objects, wash out thoroughly with neutral liquid detergent, then cleaned surface kept dried at usual temperature, applied with 1-2% aqueous fungicidal solution. This treatment repeated after an interval of about a week. For the eradication of higher plants. Pipal, Bhimsenpati and other, is controlled in different ways: i. Physical ii. Chemical
In physical method removed the plant completely from the monument. If the plants are not possible to remove completely use the chemical methods. In the chemicals method, two different chemicals methods used:
In the first case spray herbicide like Glyphosate 40% S.L. (1: 1) in the water on the whole plant, after one or two weeks all the photosynthesis process is arrested and the tree becomes black and green leaves change into black color. Similarly, the same chemical can be injected into plant body also. Beside this chemical, there are other herbicides also available in the market such as Paraquat, Diaquate, Dinoseb acetate, 2-40 (Disodium salt), Atrazine, Picloram, Dalapon, Dicamba. In second case plant body cut off down to root portion as far as possible, make hole using drilling machine, injected 1-3% aqueous Sodium Arsenate solution, preventive care should be taken while using these chemicals, because of toxicity to human beings and other animals. After three or four applications of these chemicals, plant cut off surface sealed by some sealing agent Wax/Epoxy Resin.
The treatment of the wood, in the Rameshwar temple (Terracotta Shikhara), fitted wood carved doors, Dhalin (Beam), Nina (Lintel) Tham (wooden post), Sa (Along peg) and other. After the earthquake in 1934 AD (1990 BS), some of the wooden materials were replaced by softwood i.e. Pinewood. Chemically it contains Resin, & Turpentine oil. It is durable also but not extremely and even very durable. Beside this wood Sal and Sakhu also used, it also contains chemicals like Formic acid but this wood is very durable. Both of these woods are made of the organic compound, maybe the food of insect as well as fungi. Due to this post insecticidal and fungicidal treatment is necessary. Following types of insecticides are available in the market and also the chemical laboratory of DOA.
Among these chemicals, Xylophene in kerosine, linseed oil (0.5:9:1) was applied to the entire wooden object by brushing technique. Herekerosineoil carries insecticide and penetrates deeply into the wood, whereas linseed oil polymerizes and shields the porous part of the wood, not only this but also it gives good resistance to insect and water.
The treatment of the metallic object (copper and brass) in Gajur and bell in the temples, due to formation different color salt i.e.
Red and Brown → Cu2O cupreous oxide.
Green → CuCo3 Cu (OH)2 Malachite
Blue → CuCo3 Cu (OH)2 Azurite
Blue → Cu2O (Ch3COO)2 Basic copper acetate
Bluish Green → CuCl cuprous chloride
Pale Green → CuCl(OH) Basic cupric chloride
Green Colour → CuSo4 3Cu (OH2) Basic copper sulphate
…deteriorate the metallic object, these are cleaned one of the following chemical treatment:
Here used number 4 and 6 chemicals after complete chemical treatment residue of these chemicals thoroughly washed out with a neutral detergent. Further control of Copper salt formation used 3% Benzol triazole in Methanol and 3% Polyvinyl Acetate in Sulphur free Toluene.
The treatment of terracotta objects and stone objects in the temples, crack portion or joint portion caused the leakage of water during rainy season, such portions are sealed by mortar mixing slaked lime and brick dust. Besides these, there are other joining materials e.g.
– a mixture of Rosine/jute/sawdust
– sand + chalk dust
– Cement + sand + brick dust
– Slaked lime + Stone powder + black urad dal + biocide + PVA
1.0:3.0 (6-10%) (1-2%) (10%)
White calcareous materials or calcium carbonate deposited on terracotta object removed or cleaned by using 510% aqueous Acetic acid solution using a soft brush, knife, and needle, the chemical reaction of this treatment as follows:
Ca Co3 + 2CH3 COOH → (CH3COO)2 Ca + CO2↑ + H20
Here calcium carbonate reacts with Acetic acid and form soluble salt of Calcium Acetate, Carbon dioxide gas, and water. Some of the Calcium Carbonate and Calcium Acetate may still be present in the terracotta object, removed by mechanical method. After removing all the white solid materials, thoroughly wash out with neutral detergent to remove all the acid from the terracotta object, leave them to dry at room temperature.
Different types of terracotta and stone preservatives are available in the market i.e. Siliconate, syltrate, Monsonary, PVA, chemisol, and wax etc. Water resistance tested result of these chemical result shown below, indicated that:
|Samples||Bank (drying time)||10% Sample(drying time)|
|Siliconate||0.08 hrs||2.19 hrs|
|Syltrate||0.08 hrs||2.54 hrs|
|Monsonary||0.08 hrs||1.35 hrs|
|P.V.A||0.08 hrs||2.14 hrs|
|Chemisol||0.08 hrs||1.15 hrs|
with and without chemicals at 250°C Ssyltrate is better than PVA, siliconate, monsonary and chemisol. Sosyltratecompound is used in terracotta objects and 2-3% PVA is used in stone temples. It acts as consolidation for flake stone object. To make more water resistance or repellent Vaseline form of wax is coated on it with hairbrush up to 1mm thickness. Firstly object looks dull, after 48 hours some of the wax melts and penetrates into porous part of the stone, due to the effect of heat from the sun, wax acts as good consolidant as well as waterproofing agent finally looks object very nice.
For the preservations of Nepalese Ancient monument, His Majesty’s Government had given full responsibility to the Department of Archaeology (DOA), in 1952. Not only this but also passed the Act i.e.TheprachinSmarakSamrakshan Ain2013 (1956- 1957). Beside this UNESCO and World Heritage committee listed some Nepalese monuments on considering the Kathmandu, Patan and Bhaktapur Durbar square, there are full of different categories of monuments: shikhara temples, traditional Nepalese style, Dome style, Big bell, a statue of late kings and rest houses. The temples and monuments generally deteriorated by Environment, Pollution, Biological, Chemical and mechanical factors, are now in controlled condition. Within Kathmandu Durbar Square roads and open space are laid with squares flagstones, whereas Patan and Bhaktapur Durbar squares are covered or laid with burnt bricks. Vehicular movement is strictly controlled which made the area free from the dust, dirt and gas pollution. Besides these, Government has managed properly water and sewerage system to control the effect of inorganic and biogas pollution in the monument. It also gives an excellent impression to tourist. For technology development on the chemical conservation of monument His Majesty’s Government of Nepal has established chemical conservation laboratory in 1972 and provided all the necessary requirements like chemicals, tools and technical assistance from UNESCO. The staffs are also trained inside the country as well as in abroad. For the eradication of plant, pre and post herbicide treatment are recommended, the author further suggested that to use suitable soil i.e. Dark yellow soil (Mahshucha), mixing with some herbicide (Karmex in alcohol), while using tile in multi-roof temples and brickwork. White salt formation on the terracotta object should be clean with organic acid rather than inorganic acid, preservative coatings either on stone or terracotta should be done after testing. Water-soluble syltrate and wax Vaseline in terracotta and stone objects have shown the excellent result. To control the insect deterioration the author suggested to use hardwood rather than softwood, because of various biodeterioration problems. Some of the insecticides and its application technology are recommended which are available in market and chemical laboratory. Herbicidal, Insecticidal and other chemical treatment should be done under the well-protected condition and in presence of trained chemist, because of strong toxicity to the human being. Finally to prolong the life of the monuments “Preservation is better than cure” principle should be followed up.