Museum Material Conservation
Museum Material Conservation the process used for preventing the damage/destruction of the museum materials, ie objects of artistic, cultural, historical or scientific importance and interest in the museums.
In Bangladesh, museum materials are those things having more than hundred years of age, have relation with art-culture, history, literature, science and technology, philosophy and social life of human being which include palm leaf, bark and paper materials as ancient manuscripts, sanad, forman, official records, books, journals, maps, drawings, paintings; ivory objects as throne, mat, ornament box, toys; wooden objects as furniture, architectural pieces, images; design terracotta, pottery; metallic objects as house hold utensils, images, coins, swords, daggers, war weapons, copper plates; stone objects as images of Hindus' gods and goddesses, architectural pieces containing calligraphy, etc. All of these are national heritage symbols.
Disease of museum antiquities In different museums in Bangladesh whether it is situated in urban or rural area, the common diseases observed on palm leaf, bark and paper materials, parchment, skin, hide, leather and wooden objects are various species of fungus, dampness, weak fibre strength, acidity, the whole materials becoming yellow or brown or black, stiff, brittle and innumerable tiny holes. Corrosion is a common term for mentioning the disease of metallic objects. Rust and white incrustation on iron object; black layer or patina on copper and its alloys objects, pale greenish powdery spot (bronze disease) on bronze and brass objects; tarnish on silver objects; reddish yellow layer on black basalt object; damp, white powdery surface, crack and flake off surface layer of sand stone objects; algae, lichen on stone objects, all of these represent the deteriorated condition of inorganic antiquities.
Before applying preservation treatment it is essential to know specifically the actual causes of deterioration of the materials. From the conservation point of view, museum materials are divided into two categories- (a) organic antiquities and (b) inorganic antiquities.
Causes of deterioration of organic antiquities In the extreme tropical climate of Bangladesh, organic antiquities specially cellulosic origin are degraded by biological agents as fungi (different species of Penicillium, Aspergilus), bacteria, worms (book worm, book lice, moth), beetles (furniture beetle, death watch beetle, carpet and case-bearing beetles), insects (silverfish, termite, cockroach) and small animals (rat and rodent). As a result the materials get colour spots, weak acid, weak fibre strength and loss area. By the effect of physical agents such as sun light, all artificial light, heat and high humidity, oxidation and photo oxidation reactions occur in the materials resulting discoloration, yellow and brown stains, stiff, weak fibre strength and brittle due to formation of short chain compounds like aldehyde, ketone, carboxylic acid and amino acid hydrochloride from cellulose the chief component of the antiquity.
Causes of deterioration of metal objects In Bangladesh, most of the time of the year high humidity remains in the atmosphere, which has a drastic effect on metallic objects. In wet seasons condition of museum iron, copper, lead and their alloys oxidise to form a layer of corrosion on the objects which gradually advances towards the core of the metal and that continues until destroying the metallic core which disfigures the objects. In urban areas silver objects of museum are readily tarnished by the formation of a thin film of silver sulphide. The archaeological silver objects containing chloride that is transferred to the surface, as silver chloride looks grey earthy appearance.
Causes of deterioration of stone objects Sandstone and limestone objects of museum in the urban atmosphere containing sulphur dioxide which is eventually converted into sulphuric acid, the formation of calcium sulphate weakens the surface to such an extent that the surface tends to flake off. When the archaeological stone objects are brought to the galleries of the museum owing to fluctuation of relative humidity and temperature the soluble salts will tend to work their ways to the surface of the stone, where they will crystallise and sometimes as a hard deposit, but more frequently in the form of filamentous crystal which appears as if extruded from pores. The growth of crystal imposes strain that surface becomes fragile and may eventually break away so that ornamental details are defaced and incised inscriptions become fragile.
Conservation In Bangladesh two types of preservation technique may be taken into account, which are (a) indigenous method, and (b) modern scientific method.
Indigenous method means native technique by which an antiquity can be cured, got life for its existence. In the country it was in practice when the modern concept of conservation was unknown. The ancient people had the idea about damp, fungus (locally called sata) and insect (locally called poka) in books, garments, furniture, bamboo and cane materials. During the wet season, when these materials became damp, fungus and insect affected were exposed to sunlight for eliminating the dampness, fungus and insects. After a while they were taken away, cleaned by brushing with cloth duster and kept them to dry in safe places. When bamboo and cane materials beetles affected, were treated with kerosene oil. These were soaked with the help of a piece of cloth moistened in kerosene, kept under sun light for sometimes and taken, away to safe place.
There was another way to kill the beetles or insects in which the affected materials were kept by special arrangement within a dense fume made from straws or dry leaves for a definite period, taken away and cleaned with kerosene. The beetle or insect affected wooden furniture were submerged under water for one to two months, picked up, dried at room temperature and treated with copper sulphate solution in water and dried. Then they remained safe for a long time. Ancient manuscripts made of traditionally made papers look yellow and brownish colour due to treatment with turmeric solution and a paste prepared from the crushed seeds of Tamarind and Hartaki in view of preventing future attack of fungi and insects. For removing dirt, the textiles were boiled with the burning dust of banana trees and water for sometimes, picked up, washed in the pond or river water, and dried under direct sun light.
Iron objects were corroded in the form of rust and chloride layer. A light layer of rust was cleaned by rubbing with jhhama (over burned black portion of brick) and sand. The superficial dust layer was removed, with a cloth duster. Sometimes heavy rusted objects dipped in kerosene oil for one or two days on occasion of softening the rust, then picked up, and cleaned by brushing and washed with kerosene oil. After drying at room temperature the objects were coated with grease or vaseline or molten wax for protection against moisture. The corroded copper, bronze and brass objects were treated with ripen tamarind solution in water, then brushed, washed with water and kept at room temperature for drying. After then the objects were coated with mustard oil or grease. Gold and silver ornaments were cleaned by dipping them in tartaric solution for one to two days, brushed, washed with water and dried at room temperature.
In the ancient period, to get rid of worms and insects neem (Azadirachta indica) leaves with a small branch and sometimes kalizira (black cumin) in a mini cloth- bags were hung to the area where the paper and textile materials are kept. Early 19th century naphthalene cakes or balls came to be used for this purpose. So, these were in a mini cloth bags which spread to show cases or almiras of books or textiles as insect repellent. Still today this practice is going on.
Modern scientific method means the technique by which the methodical preservation treatment is applied to the antiquities according to conservation science for curing or controlling their diseases. To serve the purpose there are two laboratories in all over Bangladesh which are (1) Conservation and Research Laboratory at bangladesh national museum, Shahbagh, Dhaka and (2) Archaeological Conservation Laboratory under the Directorate of Archaeology, Mohammadpur, Dhaka. The main objective of these laboratories is to preserve our cultural heritage in time applying proper chemical treatment. The museum conservation science is not included as an academic discipline of any educational institution in Bangladesh, so the techniques and procedures employed for the preservation of museum materials are foreign origin. In Bangladesh the conservation treatments, selected for specific classes of museum materials are described below:
Conservation of cellulose based materials The chief ingredient of paper, textile, wood and their objects is cellulose, so the museum objects falling under these groups are cellulose based museum materials. In Bangladesh the following preservation and restoration treatments are employed to these materials for curing the disease.
The fumigation is one of the first aid treatment of organic antiquities by which fungus, worm, beetle and insect on the materials are killed. Another way of killing insects in the museum is to spray insecticides like aerosol in the gallery and storage area which have also given the best result to eradicate silverfish, termites and cockroaches.
Cleaning includes two methods - (a) physical cleaning and (b) chemical cleaning. Chemical cleaning is of two types: (i) aqueous washing and (ii) non-aqueous washing. After washing, if the materials show acidic nature, it would be necessary for deacidification. There are two types of deacidification which are (a) aqueous deacidification and (b) non-aqueous deacidification.
There are so many restoration treatments for cellulose materials like pasting, lamination, mending, patching, lining, trip lining, sizing, consolidation and impregnation. Lamination is one of the popular restoration treatment for paper materials in Bangladesh. Conservation scientists of Bangladesh National Museum prefer solvent lamination but those of Archaeological Conservation Laboratory choose heat lamination. One of the main causes of deterioration of cellulose material is oxidation. To prevent or control such reaction in the materials, antioxidant preservation treatments have been developed in the conservation and Research laboratory of Bangladesh National Museum, Dhaka.
Conservation of metallic objects Thin layer of oxide on iron and lead objects is removed by brushing with dilute solution of sodium hydroxide and that on copper objects is removed by brushing with dilute solution of sulphuric acid. The tarnish on silver objects is cleaned by the treatment with the mixture of dil hydrochloric acid and EDTA (Disodium dihydrogen ethylene diamine tetra acetic acid). Each of the above cases, adequate washing with hot distilled water, drying and coating with Erealine lacquer is necessary. Bronze disease on objects is treated with the paste of silver oxide in methylated spirit.
Thick corrosion layer on metallic objects containing chloride or sulphate is cleaned by electrolytic reduction using 5% sodium hydroxide as electrolyte and steel sheet or bar as anode. After completion of electrolysis, the softened corrosion products are removed by brushing under running tap water and finally washed with hot distilled water. The object is then dried in an oven and coated with Brcaline lacquer.
Conservation of stone and terracotta materials The problem of preserving sedimentary rocks is essentially one of overcoming surface frailty. If the sandstone or limestone is exposed to an urban atmosphere containing sulphur dioxide which is eventually converted into sulphuric acid, the formation of calcium sulphate soon weakens the surface to such an extent that the surface tends off.
Removal of soluble salts The soluble salts remaining within the stone and terracotta material is removed either by immersion method or by extraction method.
Removal of dampness and plants Dampness on the monuments or buildings is generally removed by spraying ripen tamarind solution in water. There is another way of curing damp on building is to cover that area applying Burger's silicon paint. This paint layer obstructs the penetration of moisture. Moss, algae, lichen and other plants on outdoors stone objects or terracotta plaques are destroyed by treating with arsenic oxide or sodium benzoate.
After the salts have been removed from stone, or terracotta, it is often necessary to strengthen the surface. It is done by consolidation with beeswax in turpentine, white shellac in alcohol, cellulose nitrate and polyvinyl acetate in toluene or acetone. For slabs of sandstone and siliceous limestone of fare dimensions, which are kept indoors, a possible strengthening agent is silicon ester that might be a solution of ethyl silicate in ethyl alcohol. [Md Saber Ali]