However, the interaction between cultural relics and chemical substances is an important factor for the corrosion and damage of cultural relics.
One of the most familiar examples about the chemistry of cultural relics corrosion process may be iron corrosion, which involves at least one well-known battery reaction:
Positive electrode: O2+H2O+2e? 2OH-
Negative electrode: Fe-2e? Fe2+ ion
Another easy-to-understand example is that some tomb murals are often covered with a white film. It is found that this kind of damage is caused by the fact that water dissolved with carbon dioxide can slowly dissolve calcium carbonate into calcium bicarbonate, which is evaporated and dried, and then precipitated and condensed on the surface of murals.
For paper cultural relics, acidic environment is obviously harmful, because when paper is neutral or alkaline, its mechanical properties such as durability, folding resistance, mildew resistance and chemical stability are good, but nitrogen oxides and sulfur dioxide in the air are acidic gases, which easily increase the acidity of paper cultural relics and cause damage to cultural relics.
Chemistry and Cultural Relics Protection
Scientific and technological achievements in chemistry, chemical engineering and material protection can be used for reference and application in cultural relics protection. For example, benzotriazole (BTA) is an excellent corrosion inhibitor for copper and copper alloys, which can also be used for reference in the protection of bronzes and has achieved good results. Generally, lacquered wooden relics are full of water, which is easy to shrink, deform, bend, peel and crack, and must be dehydrated and set. Alum [kal (SO4) 2. 12h2o] method is one of the commonly used methods to dehydrate and shape lacquer wood cultural relics. This method mainly takes advantage of the huge difference in water solubility of alum at different temperatures. First, the lacquer wood relics filled with water are boiled in concentrated alum solution for several hours. This process allows alum to penetrate into the cultural relics and then take it out while it is hot. When it cools, the solubility of alum decreases and condenses in the wood, discharging excess water. This not only eliminates the excess water in the lacquer wood cultural relics, but also strengthens the cultural relics.
The lead white [Pb2(OH)2CO3] in mural pigments turns into black lead sulfide under the action of hydrogen sulfide gas in the air, which affects the color of the picture. When treated with hydrogen peroxide, black lead sulfide can be oxidized to white lead sulfate.
Chemistry has a wide range of applications in cultural relics and archaeology. The above is only a brief introduction to some aspects. But from it, we should realize that chemistry and other natural sciences developed together with archaeology, just as chemistry and other natural sciences developed together with other social sciences.
Archaeological excavation is inseparable from chemistry.
Modern chemical technology is applied to the analysis and identification of antiquities.
(1) to identify the authenticity of cultural relics. Cultural relics can no longer be produced. Many historical heritage cultural relics have high artistic, scientific or economic value, and cases of forging cultural relics often occur in the world. In the past, judging the authenticity of cultural relics mainly depended on observation. The application of modern analysis technology provides a reliable basis for identifying the authenticity of cultural relics. For example, in the 1940s, a number of "pottery figurines" from the Warring States period appeared in the European antique market, which were very expensive and difficult to distinguish between true and false. Later, it was identified by thermoluminescence in Oxford laboratory in England, and the result was a pure fake.
(2) Study the manufacturing technology of cultural relics. Many of China's crafts are among the best in the world, but they have been lost. In order to inherit and develop these processes, modern chemical analysis technology is needed to study the manufacturing process. The mystery of stainless steel in Qin bamboo slips is an excellent example. Qin bamboo slips unearthed from the pit of Qin figurines have been buried underground for more than 2000 years and are still as sharp as new. After analysis and research, its surface is coated with an oxide film containing 2% chromium, so it can prevent rust and protect the front. It was not until the 1930s that this technology was first patented in the West. The gold frame of Famen Temple in Shaanxi has the thinnest gold thread, 0.0 16mm.
③ Explore the source and origin of cultural relics. By measuring the composition and content of cultural relics, we can find out their sources and places of origin. Are the glass products collected in Famen Temple in Shaanxi Province made by China himself in ancient times, or were they introduced to China by cultural exchanges between China and the West? According to the research, the lead content in the glass before Tang and Song Dynasties in China was relatively high, mainly lead glass, while the ancient western glass was mainly soda-lime glass, which basically contained no lead. Through the analysis, we can know that these glass products are the tribute of western countries to the Tang Dynasty, which witnessed the cultural exchange between China and the West. Through the Silk Road, China's exquisite silk products were introduced to the west, and at the same time, a large number of glass products were introduced to China from the west. It can be seen that the open policy in the Tang Dynasty promoted the prosperity of the Tang Dynasty.
preservation of cultural relics
All kinds of cultural relics are put into storage by the museum after mud removal, cleaning, rust removal and protection. Its principle is aimed at the corrosion mechanism of cultural relics of various materials, and on the premise of not affecting the original appearance of cultural relics, the corrosion process is minimized. Its disadvantage is that it cannot fundamentally prevent cultural relics from continuing to corrode, and the protective layer needs to be painted regularly. This paper discusses the chemical problems in the protection of general cultural relics.
1. Metal cultural relics
Gold, silver and copper containers are protected by different methods, and the corrosion degree is different. Generally, only 2%NaOH or 1%HNO3 is used to clean the calcium and deposits on the surface of gold wares, while potassium tartrate solution is used to dissolve the floating rust on the inner layer of gold wares. Serious floating rust must be removed manually under a microscope. Silver rust spots include AgCl, Ag2O and Ag2S. Those with severe black film should be scrubbed with soft cloth dipped in CaCO3—-water slurry or NH3 H2O-C2H5OH and dilute Na2S2O3. Then, the silk soaked in 10%Pb(OAc)2 was isolated from the air and stored in an environment free of H2S and O3 at room temperature. The composition of bronze rust is complex, which often includes Cu2O, CuCl, CuCO3, Cu(OH)2, CuCl2 3cu (OH) 2) 2, Cu2(OH)2CO3 and so on. EDTA consists of NH3·H2O, alkaline glycerin (composed of 12g NaOH, 4mL glycerin and 100mL water), alkaline potassium sodium tartrate (composed of 5g NaOH, 15g potassium sodium tartrate and 100mL water), H2SO4—K2Cr2O7, and hexametaphosphate. You can also use 10%NaOH and proper amount of Zn and Al powder to make a paste and apply it to rusty parts, and then clean it after reduction. Brush benzotriazole on the surface and form it on the copper surface.
"He Zun" bronzes are still intact after this treatment, and the process is as follows:
The corrosion of iron is particularly complicated, and the components of rust are oxide sulfide, sulfate and phosphate. Remove large rust by hand when unearthed, and then use 10%HOAc (adding 0. 1 ~ 1% CrO42-, Cr2O72-, PO43-, pyridine and urotropine as corrosion inhibitors) for further rust removal. For example, a rust remover consisting of 435 parts of H3PO, 5 parts of butanol, 20 parts of ethanol, 1 part of hydroquinone and 39 parts of water also has the function of surface phosphating and rust prevention. Organic complexing agents such as sodium oxalate, sodium EDTA and sodium gluconate can also be used for rust removal. If the ironware is very fragile when unearthed, it should be soaked with 30 ~ 40% polyacrylic resin emulsion at 10 ~ 20mmhg, solidified and reinforced, and surface treated. There are four methods: (1) anticorrosion method: dicyclohexylamine nitrite 10, cyclohexylamine carbonate 10, water. (2) Phosphate protection method: soak with 10%H3PO4. (3) Tannate protection method: 200 copies of tannic acid, ethanol 150mL, water 100mL, repeated brushing for 6 times. (4) Surface sealing: after being treated by any one of the above methods, it is immersed in molten microcrystalline paraffin until it does not bubble. Take it out and wipe off the wax on the surface with a brush dipped in graphite powder.
Tin and lead containers are slightly rusted. Generally, the surface of tin ware is dark gray-white, that is, SnO and SnO2 rust. Zn and Pb were used as anodes and 10%NaOH was used as electrolyte for reduction, which was the same as the previous wax sealing treatment. The oxide film on the surface of lead is fine and also a protective layer. Special treatment: first soak it in 1.2 mol L- 1 HCl until it does not foam, then soak it in distilled water (boiling) for several times, and then soak it in 25 times of 1.2 mol L- 1nh4oac solution lhr. Soak it in distilled water several times after taking it out, then dry it with ethanol and acetone and seal it with wax.
2. Inorganic nonmetallic cultural relics
The protection of non-metallic cultural relics such as stone carvings, stone carvings and murals is mainly to repair damaged lines, characters and paintings in time and restore the original appearance of cultural relics. Then, apply a protective film against ultraviolet rays and use unsaturated polyester resin. Damaged and cracked cultural relics should be bonded and reinforced with resin. Such as polymethacrylic acid resin, polyvinyl acetate emulsion, polyvinyl butyral emulsion, etc. 1986, the Cultural Relics Management Committee of Jiaojiang City, Zhejiang Province dug up the fragments of the broken "Wang Jingwei couple kneeling statue monument" of the Japanese army. Repaired with adhesive, this patriotic textbook was preserved. Ceramic utensils are generally not corroded, and broken fragments can be bonded with epoxy resin.
3. Organic cultural relics
(1) green plant specimen: soak in 10% Cu (OAC) 2-HOAC solution and heat to 85 ~ 90℃. After the specimen turns green, take it out, rinse it, save it with 5% formaldehyde or 70% ethanol, or dry it. For the tender leaves and stems, they were soaked in the mixed solution consisting of ethanol 100 ml, water 100 ml, 36-38% methanol10/ml, glycerol 5.5 ml, acetic acid 5.5 ml and copper chloride 222 g for 3-5 days. The principle is as follows:
The treated green samples were protected by CMC-Na+ membrane.
(2) Paper cultural relics: When unearthed, they must be deacidified, disinfected and coated before they can be collected and preserved. There are many methods of deacidification, which can be divided into wet deacidification and dry deacidification. Wet deacidification is to soak paper products in alkaline solution or spray alkaline solution on paper products. Commonly used alkali liquor includes saturated solutions such as Ba(HCO3)2, Ca(HCO3)2, Sr(HCO3)2 and Mg(HCO3)2. Dry deacidification is fumigation with alkaline substances. Such as NH3, cyclohexylamine carbonate, moline, diethyl zinc, etc. The usual dosage is: NH3: H2O (1: 10), sealed for 24-36 hours, the pH value of the paper is reduced to 6.8-7.2, cyclohexylamine carbonate is immersed in the medicinal paper, inserted into the book every 50 pages and sealed for two weeks. Maureen is fumigated in vacuum 10 minute; Diethylzinc is also widely used in vacuum, but we must pay attention to safety. Deacidification often plays the role of sterilization at the same time. The mechanical properties and light resistance can be improved only by spraying CMC-Na+ liquid film on the surface of paper products.
(3) Bamboo, wood and lacquerware: When unearthed, they will crack and shrink when naturally dried, and must be dehydrated and set by chemical methods. Commonly used methods include alcohol ether method, polyethylene glycol method and silicone polymer method. The alcohol ether method is the simplest. First, cultural relics are constantly soaked in ethanol, and fresh ethanol is constantly replaced, so that the concentration of ethanol increases and the proportion of H2O decreases. Then soaked in ethanol instead of ethanol, ether is volatile and will not cause cell wall collapse. Finally, organic monomers (such as vinyl acetate) infiltrated into the reactor wall, and polymerization was strengthened under the irradiation of 60Co radioactive source. Then fumigate with ethylene oxide, carbon disulfide, etc. Insecticide and sterilization.
(4) Textile cultural relics: protection includes cleaning, rinsing, pest control, deterioration and reinforcement. Clean with boric acid (1%) first, and the process is as follows:
nabo 2·3H2O·H2O 2→nabo 2+3H2O+H2O 2
The released H2O2 does not exceed 0.7%, which will not damage the fabric. Secondly, reducing Na2S2O4, NaHSO2 CH2O 2H2O (sodium formaldehyde thiosulfate) and 5%HOAc were used for bleaching.
Fumigation with ethylene oxide can kill insects and act on the active groups such as —SH, OH, —NH2 and —COOH in bacteria and pest protein, thus achieving the effects of killing insects and sterilizing. The optimum operating conditions are: relative humidity 25 ~ 50%, 54℃. Finally, 5% nylon ethanol solution, 2% polymethylmethacrylate toluene solution and 5% polyvinyl acetal ethanol solution were selected to coat the protective layer for reinforcement. The "clay gold and silver flame printed yarn" unearthed in Mawangdui is reinforced and protected with raw rubber protein, and the effect is very good. The protection methods and steps of leather and bone fragments are similar. 1 ~ 3% trimethyl resin acetone solution was used to fill and bond the ivory fragments unearthed from Fu Hao's tomb 1976.
The protection of ancient buildings and cultural relics mostly adopts the method of repair and reinforcement rather than reconstruction. Generally, unsaturated polyesters are used as reinforcing agents. For example, the reinforcement of Ling 'en Temple in the Ming Tombs is to mix 307# resin and 18 1# resin in a ratio of 3: 1, and then add 2% o.p. (benzoyl peroxide) and 0.2% cobalt naphthalate, which can be used in the whole building component. After curing, it can be used with floor yellow and soil. The treatment also has the functions of moisture prevention, termite prevention and fire prevention.
In a word, the protection of unearthed cultural relics is an arduous task, and many new materials and technologies will be introduced into cultural relics protection soon. For example, silicone resin with good performance, 14C dating, X-ray diffraction phase analysis, scanning electron microscope and electron probe have been gradually applied to the analysis and protection of cultural relics. Better protect and develop the civilization left by our ancestors.