Briefly describe the development of bronze wares and their aesthetic differences in the times.

There were bronze containers and weapons in the Xia Dynasty. In the middle of Shang Dynasty, the varieties of bronzes were very rich, with inscriptions and exquisite patterns. From the late Shang Dynasty to the early Western Zhou Dynasty, it was the heyday of bronze ware development, with diverse shapes, rich inscriptions and rich patterns. Subsequently, the bronze matrix began to thin, and the decorative pattern gradually simplified.

Artistic value:

Ancient Chinese bronzes not only have high artistic appreciation value, but also have high scientific research value. The so-called artistic appreciation value refers to the superb plastic arts of bronzes, such as painting one word at a time, which gives people pleasing artistic enjoyment.

The artistic charm of bronzes is manifested in several aspects: ingenious shape, rich and exquisite ornamentation and various inscriptions.

During this period, the shape and appearance of bronzes were very rich. In addition, with the combined casting method, generally only one vessel is cast in one model, and there are few bronzes with identical faces, so the faces of each piece are different, which broadens the horizons of artistic appreciation. Especially among them, excellent products are one after another, which is amazing. Especially in the late Shang dynasty, bronzes have always been cherished by the world.

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Aesthetic ways and means of Chinese bronzes

Protection of bronze ware in raw pit

1. Factors affecting the corrosion damage of archaeological bronze relics

The surface corrosion of archaeological bronzes is very complicated. XPS analysis shows that there are some oxides and chlorides, and these corrosion surfaces are formed in the environment of being buried underground for thousands of years. Its structure is loose, its pores are widely distributed, and it can adsorb water and gas. Once the cultural relics are unearthed, the rust layer is exposed to the atmospheric environment, and oxygen, carbon monoxide, carbon dioxide, water, sulfur dioxide and nitrogen oxides in the air have strong adhesion on the surface, so the surface not only has electrochemistry, but also chemical corrosion and light corrosion. From the above analysis, the corrosion of bronze cultural relics depends on two factors: the characteristics of cultural relics materials and the environment in which cultural relics are located. The preservation of archaeological bronze cultural relics depends on its corrosion resistance and environment to some extent. There are some factors in the environment that can affect the corrosion of archaeological bronze relics, such as temperature, humidity, gas acid, alkali, salt, biology, light and so on. When various environmental factors coexist, corrosion is often a synergistic effect.

(1) Temperature and humidity. Cultural relics will react chemically in the natural environment, which means that cultural relics have been destroyed. The speed of chemical reaction is related to temperature. Arrhenius empirical formula is expressed by activation energy-related temperature and reaction speed as follows: log10r 1/R2 = 52e (1/T2/1/t1), where r1and R2 are t655, respectively. E is the activation energy: the reaction rate increases exponentially with the increase of KJ/mol temperature 10℃. Humidity and "Bronze Disease": The critical state of bronze latent "powder rust" is that the relative humidity is 42% RH-46% RH and the relative humidity exceeds 55%RH. Cuprous chloride reacts rapidly with water in air: CuCl+H2O←→Cu2O+HCl. With the increase of humidity, the reaction speed is accelerated. The experimental results of different relative humidity show that cuprous chloride reacts in 97%, 78% and 58%RH environment for 2, 4 and 24 hours to produce basic copper chloride. At this relative humidity of 35%, chloride is infinitely stable. The experiment also proves that cuprous chloride will react quickly when the relative humidity RH is 55%. However, the moisture content of humid air is as high as 80%-90%, and water is often called "universal catalyst", which can not only promote many chemical reactions, but also breed organisms.

(2) Gas: oxygen accounts for 265,438+0% of the atmospheric content. As a gas, oxygen mainly exists in the environment where archaeological bronzes are stored. When the balance of unearthed archaeological bronzes is destroyed, unstable cuprous chloride will immediately react with water and oxygen in humid air to generate white powdery rust [cucl2 3cu (oh) 2]. The reaction formula: 4cucl (s)+4h2o+O2 (g) → cucl2 3cu (oh) 2 (s)+2hcl (AQ). White-green powdery rust cucl23cu (oh) 2 is commonly known as "bronze disease" and "powdery rust". In the early stage of powdery rust formation, its particle size is extremely small, and the particle size of slightly spherical rust is about 0.8- 1.2 nm, which is relatively uniform. This tiny particle has two outstanding characteristics: it can basically get rid of the influence of gravity field and migrate with the airflow. Under proper conditions, it can be deposited on other bronzes and react as follows: 2cu2 (OH) 3cl+Cu+6h +→ 2cuCl+3cu+6H2O (acidic environment), 4cuCl+O2+4h2o → 2cu2 (OH) 3cl+2.

Using carbon dioxide, oxygen, H2O and some available trace elements, microbial cells proliferate. In this process, its metabolites are gradually released and accumulated on the surface of bronzes. Metabolites are slightly acidic, which can corrode bronzes and form rust after a long time. In a dry environment, microbial cells generally exist as spores. Once the conditions are suitable, especially when the environmental humidity increases, microorganisms can easily float with the air and multiply on bronze wares. This may be another reason for the infection and spread of "bronze disease".

Nitrogen oxides: Nitrogen oxides mainly come from automobile exhaust gas. When the engine runs at high speed, the NOX content is high. NO2 gas forms nitric acid, nitrite and nitrate in the air or on the surface of objects. Accelerate bronze corrosion.

Sulfur dioxide: Sulfur dioxide gas will corrode bronzes under appropriate temperature and humidity conditions. The experiment shows that when Rh is 75%-96%, the corrosion rate of bronze increases significantly, which is because SO2 participates in cathodic depolarization and accelerates the moisture absorption of loose corrosion products.

(3) Light: Cuprous oxide exists on the surface of archaeological bronzes near the basement, which generates photogenerated holes and photogenerated electrons under the irradiation of light. Photogenerated holes with high energy can obtain electrons from metal atoms and corrode them. At the same time, under the irradiation of light, cuprous oxide can adsorb oxygen, and the highly active adsorbed oxygen will approach the copper alloy matrix along the loose pores, corrode the alloy components, and make the surface rust layer thicken continuously.

Second, the rust color identification of archaeological bronzes

The age of archaeological bronzes is different, the casting process is different, and the environment is different, so the rust layer formed is very complicated. Common ones are: black copper oxide: CuO (black copper ore); Red cuprous oxide: Cu2O (chalcopyrite); Indigo copper sulfide: CuS (Indigo copper ore, azurite); Black cuprous sulfide: CU2S (chalcocite); Basic copper carbonate (there are three kinds): dark green CuCO3 Cu(OH)2 (malachite, stone green); Blue 2CuCO3 Cu(OH)2 (kyanite, azurite); Blue 2cuco33cu (OH) 2; Basic copper chloride (there are two isomers): green to dark green Cu2(OH)3Cl (chalcopyrite); Light green Cu2(OH)3Cl (trichlorophenol); Blue copper sulfate CuSO4 5H2O (gallstone); Green basic copper sulfate: CuSO4 3Cu(OH)2 (copper sulfate hydrate); White cuprous chloride: CuCl (cuprous chloride); White tin oxide: SnO2 (cassiterite), etc. These bronze rusts with different compositions can be divided into harmful rust and harmless rust. Harmless rust is also called elemental rust or inert rust, mainly copper oxide and basic copper carbonate. These rusts are harmless and antique, which is a symbol of the age. Harmful rust, also called "powdery rust", is a mixture of basic copper chloride, cuprous chloride, lead oxide and tin dioxide.

Third, the protection of archaeological bronzes.

1. On-site protection of archaeological bronzes

More and more attention has been paid to the protection of cultural relics in field archaeological sites. Archaeological bronzes have been buried underground for thousands of years in a relatively stable environment, and their corrosion process has tended to be balanced. After the bronze ware was unearthed, this balance was broken, and then all kinds of corrosion appeared. The job of the archaeological site is to try to prevent all kinds of corrosion. Therefore, the unearthed complete bronzes are carefully cleaned and dehydrated at the scene, then stored in closed packaging bags and transported indoors. For broken bronzes, especially some thin-walled bronzes, we often find them in tatters when unearthed, and some of them have become fragments and mixed with soil, so we should treat them differently according to the situation in the protection of cultural relics in the site.

(1) For some bronze fragments mixed with soil, the basic shape of the container is still preserved in most cases. When cleaning, first use a bamboo knife or angle knife to remove the soil outside (keep the soil in the container). When the shape of the container comes out completely, coat a layer of wet cotton paper (cotton paper should be just soaked with water) on the surface of the bronze fragments and then stick a layer of dry cotton paper; Brush a thin layer of peach gum outside the cotton paper for reinforcement; When the tissue paper is dry, take away the bronze fragments (together with the soil fragments) with a tray and transport them indoors for cleaning.

Both indoor cleaning and outdoor cleaning should be carried out as soon as possible. Before cleaning, measure and record external dimensions (abdominal diameter, caliber, height, etc.). ) and the position of the copper, in order to sort out and repair in the future.

(2) Bronzes of weapons and tools. Such as swords and knives. When unearthed, it often breaks into several pieces or decays into powder. Especially when the carcass of the utensil is thin, carefully remove the soil on the surface of the utensil with a bamboo knife or a horn knife, and then paste 1-2 layers of wet cotton paper on the surface of the bronze fragments, and make a layer of gypsum with a thickness of about 0.5 cm on the cotton paper. After the gypsum is basically hardened, the soil around the vessel and the gypsum layer should be clamped and bound together, and then packed and transported back to the room for cleaning.

(3) Bronzes with gold patterns. When bronzes with gold patterns are unearthed, most of the gold patterns fall off, but there are traces on the bronzes. These gold-plated patterns are carved in pieces with gold foil, and then pasted on the bronze surface to form a complete pattern. The principle of on-site protection of such cultural relics is to minimize contact, lift them from the bottom of the cultural relics when they are taken out of the tomb pit, and use trays for larger cultural relics. The gold foil falling off around the bronze should be picked up in different directions, corresponding to the direction of the bronze, and all kinds of records should be made at the same time. The removed gold foil is lightly washed with distilled water with a fine brush, and then the gold foil is sandwiched between two layers of cotton paper and stored with a three-splint, which is convenient for indoor sorting and recycling. On the surface of this kind of bronzes, only local soil is cleaned on site, and patterns and even traces are usually left untreated to prevent traces from being erased. The specific method is to make a frame with wooden strips, fix the bottom and mouth of the vessel, put it into plastic bags and transport it indoors.

(4) Ancient bronzes with black paint and green paint protective layers. Blue lacquer antiques and black lacquer antiques are the names given by antique dealers to a special black or green lacquer-like corrosion layer on the surface of unearthed bronzes. This corrosion layer is dense, smooth and waxy, which has a good protective effect on bronzes. This kind of surface layer mostly appears on the bronze mirrors of the Warring States and the Han and Tang Dynasties, and occasionally similar phenomena appear on the weapons of the Spring and Autumn Warring States, the pre-Qin artifacts such as halogen, pots and statues, and the bronze seals of the Warring States, Qin and Han Dynasties. This kind of rust layer is beautiful and simple, which is a symbol of ancient times and is deeply loved by people. Scholars at home and abroad have conducted extensive and in-depth research on the causes of the formation of black lacquer ancient and blue lacquer ancient, and it is recognized that the research results are related to the burial environment. For thousands of years, the long-term effect of underground humic acid is the main reason for the formation of green lacquer antiquity and black lacquer antiquity on the surface of bronzes. The main components of blue lacquer ancient and black lacquer ancient are tin oxide and a certain amount of copper oxide Tin oxide forms a dense rust layer on the surface of bronze in crystalline state.

Due to the low hardness of oxides on the surfaces of ancient bronzes with black paint and ancient bronzes with green paint, scratches can be left on them with bamboo knives. Therefore, when cleaning on site, soak the soft brush in distilled water and slowly wash away dirt and other pollutants. Dehydrate with 95% ethanol, and then wrap with soft materials such as cotton or cotton paper to avoid contact and collision with sharp objects.

2. Indoor protection of archaeological bronzes

The forms of bronze ware protection can be summarized into three categories: mechanical derusting protection, chemical derusting protection, chemical control and surface structure improvement protection. The objects, advantages and disadvantages of various protection methods are analyzed and compared as follows.

(1) mechanical derusting

Mechanical derusting: Mechanical derusting is generally aimed at bronzes that are partially rusted. The method is to observe with a magnifying glass or a stereomicroscope, and use a scalpel, a steel needle, a chisel, etc. To clean the parts that need to rust. Be careful not to leave scratches on the surface of bronze ware. Ultrasonic vibration method to remove harmful rust: the biggest feature of ultrasonic rust removal is that it can completely remove powdery rust without damaging other copper rust. Laser derusting bronze powder rust: Laser derusting mainly uses the huge light energy excited by laser to instantly act on the surface rust layer, which makes the surface temperature rise rapidly. Due to the loose structure of the rust layer and strong energy absorption ability, rust is quickly melted and vaporized and separated from the body. In the process of laser action, the bronze surface also undergoes phase transformation hardening, forming a dense hardened protective layer, which has a certain protective effect on the external conditions that lead to the continued corrosion of bronze. Although mechanical derusting can remove the derusting layer simply and quickly, it is inevitable that the metal parts are directly exposed to the atmosphere.

(2) Chemical derusting protection

For archaeological bronzes corroded in a large area, the method adopted is to mix chemically pure sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) in the same molar number, and then dissolve them in distilled water to prepare a series of solutions of 10%-20%, and the common solution is 5%. Copper carbonate generally contains crystal water, which should be taken into account when preparing the solution. When bronzes are immersed in this solution, harmful rust (cuprous chloride) is gradually transformed into copper carbonate, and its action process is that Na2CO3 in the solution is hydrolyzed into alkalinity: CO-3+H2O→HCO3 1-+HO- In the sodium sesquicarbonate immersion solution, there is the following balance: CuCL (solid) → Cu+Cl-KSP =/Kloc-.

Because of Ksp(CuCO3) Ksp(CuCl), this replacement process is easy to happen. With the consumption of CO2-3 and HCO-3 in the solution, harmful rust (CuCl) is gradually transformed into stable CuCO3. At this time, Cl- is replaced into the solution, and the vessel is soaked with fresh solution until no chloride ion can be detected in the solution. Then soak the vessel in distilled water to wash away the residual sodium carbonate and sodium bicarbonate. Sometimes, in order to accelerate the washing speed, the soaking solution can be controlled at about 50 degrees, and the ion diffusion and reaction are accelerated due to the increase of temperature. Although this method is stable, it takes a long time, sometimes one to two years to clean an object. In addition, the insoluble copper carbonate adheres to the surface of the utensil, which makes the treated appearance deeper and greener than before, and changes the appearance of the utensil.

For small-area objects with harmful rust, that is, objects with small spots of harmful rust in archaeological bronzes, steel needles or small scalpels can be used to remove rust spots, and the removal range is slightly larger than powdery rust. In particular, the harmful rust that produces "bronze disease" should be cleaned until fresh bronze is seen, and then the holes should be scrubbed with acetone solution. After drying, silver oxide (analytically pure) powder is mixed with ethanol or isopropanol to form a paste and carefully rubbed into the hole. Then the vessel is stored in saturated steam or humid environment for a day and night, so that silver oxide and cuprous oxide can fully act to form a protective film, which can also be used to test the tightness. If new green spots are found, the operation can be repeated until no new green spots are produced after being placed in saturated steam for one day and night. Its chemical reaction formula: Ag20+2 CuCl→2 AgCl+Cu2O. The appearance of spots treated with silver oxide is brown, which can be coordinated with other copper rust on bronzes.

(3) Using chemical reagents to control and improve the protection of surface structure.

The principle of controlling and improving surface structure protection with chemical reagents is corrosion inhibition. This technology is an important research object in archaeological bronze protection research, and it is also the development trend of metal cultural relics protection technology. The method can be as follows: 1. Determine the type of corrosion inhibitor, the type of interaction between corrosion inhibitor and metal, functional group or molecular orientation; 2. Investigate the corrosion inhibition process and performance of corrosion inhibitors, the synergistic effect and competitive adsorption among different corrosion inhibitors; 3. Study the behavior characteristics of aggressive ions on metal surface and its influence on corrosion inhibition.

In recent years, in order not to change the color of bronze corrosion, more and more metal corrosion inhibitors have been used in bronze cultural relics. Benzotriazole is a very effective bronze corrosion inhibitor, abbreviated as BTA. It is milky white powder crystal, soluble in organic solutions such as ethanol. Benzotriazole can form a transparent covering film insoluble in water and some organic solvents with copper and copper alloys, and the obtained film is relatively firm. Copper and benzotriazole in bronze alternately combine to form Cu-BTA metal coordination polymer complex. Moreover, this green insoluble polymer complex can cover the details of bronze patterns. It is not suitable for protecting small decorative items, such as coins and statues. Organic heterocyclic compound 5- amino -2- mercapto-1, 3,4-thiadiazole (AMT) is a yellowish crystalline solid, which is used to protect articles with fine patterns, serious corrosion and few copper cores. Melted and ignited at 238℃, soluble in hot water and alcohol. The method is to immerse the cleaned object in 0.0 1M AMT aqueous solution. To speed up the reaction, a few drops of nitric acid (1: 1) were added. Then the solution was heated to 60℃. At this time, yellow-green curd-like precipitation can be observed in the corrosion area of the vessel. After 65438 0 hours, take out the vessel, wash it with distilled water, and repeat the process until no precipitate is generated. Experiments show that AMT compounds form complexes with ionized copper in bronze disease. This complex appears in bronze area in the form of yellow-green precipitate. So bronzes can be removed from bronzes. This process continues until the bronze disease is completely eliminated from the corrosion products and the micropores of the underlying metal. After removing bronze, AMT forms a uniform and thin multi-component complex protective film on the metal surface.

The soil buried in archaeological bronzes is composed of corrosion products of various minerals and organic acids, which is a multiphase porous capillary colloid system with ionic conductivity. According to the theory of soft and hard acids and bases: "Any molecule, ion or radical that can give electron pairs is called alkali, and any molecule, ion or radical that can accept electron pairs is called acid." Rust on archaeological bronzes can be divided into hard acid Cu++ and soft acid Cu+. Roche salt complexing agent is a hard base, which can form a stable complex with hard acid cations. Thiourea is a weak base complexing agent, which is easy to combine with weak acid cation Cu+ and is stable. EDTA is an organic complex based on aminodiacetic acid, which has two nucleophilic coordination atoms, nitrogen and hydroxyl, and has strong complexing ability, and can form stable complexes with various metal ions. In the study of corrosion inhibitors, according to this principle, it is much better to use composite corrosion inhibitors, and its corrosion inhibition rate is much higher than that of simple addition. This effect of exerting the functions of each component is called "synergistic" effect of corrosion inhibitor.

The use of 10% thiourea+10%EDTA+ 10% Roche salt can effectively remove patina, cupric oxide and rust layer mixed into soil. In addition, the composite formula of 0.5% BTA+0.5 mol/NNA 2M0D4+5% nahco 3 has good corrosion inhibition effect. Sodium molybdate solution can improve the chloride ion resistance of metal passivation film and reduce the chloride ion enrichment in some metal pitting pores, and the effect will be more obvious with the increase of sodium molybdate.

It is a good bronze corrosion inhibitor to add potassium iodide or p-aminophenylarsonic acid to benzotriazole by quantitative method. Its molecular formula is BTA0.2mol/L, APA0.005mol/l and PH=4. Or BTA 0.2 mol/L, KI 0.0 1 mol/L, pH = 6.3 1, solution temperature 60℃, and solvent composition: ethanol (95%)/ water =2/3 (. The surface sealing agent is a mixture of silica glass resin and benzotriazole, in which the concentration of BTA is 0.1mol/L. A small amount of potassium iodide is added to benzotriazole, because iodine ions preferentially adsorb on the bronze surface, which leads to the decrease of initial potential and the increase of adsorption capacity of benzotriazole, and the excess KI can also be removed by air oxidation. After adding a small amount of p-aminobenzoic acid to benzotriazole, benzotriazole preferentially adsorbs copper spots, while p-aminobenzoic acid preferentially adsorbs tin spots and lead spots, which complement each other and form a dense protective layer on the bronze surface, thus leading to an increase in corrosion inhibition rate.

In short, we must make a protection plan for each archaeological bronze ware according to local conditions to avoid one cure for all diseases.