weld
For an incomplete unearthed bronze cultural relic, it is necessary to weld the bronze into a finished product. Welding is an important link in traditional repair technology, and it is the main means to repair damaged bronzes and restore their shapes. It is necessary to adopt different welding methods according to the different properties, damage and corrosion of bronze, that is, "big welding" and "small welding". File the welded joint with a hammer, then melt the tin with an electric soldering iron and inject it into the bronze to be repaired for welding.
supplement
Complementary matching is an important technology to repair the defective parts in traditional bronze restoration technology. Complement means that an incomplete bronze ware is incomplete. According to the types, shapes and incomplete parts of bronzes. Tonics should be developed according to the decorative patterns of bronzes, and then the shape of tonics should be made through the decorative patterns.
Then spell out a finished bronze relic.
Do plastic surgery
Buried bronzes were crushed and deformed due to the collapse of tombs and the change of strata, and cracks appeared. Unearthed bronzes often need shaping. The modeling methods of bronze ware include hammering, modeling, sawing, heating modeling and physical modeling. The selection method is based on the deformation degree of the utensils and the texture of the bronzes.
Corrosion mechanism of cultural relics
In order to repair and protect bronzes, it is necessary to explore the corrosion mechanism of bronzes in order to take correct and effective protection measures. With the development of science, the corrosion mechanism of bronzes is also developing, and various theories and viewpoints are constantly emerging. However, it is more consistent that when an object is buried underground, it comes into contact with chloride, because the radius of chloride ion is small, and it is easy to penetrate the water film and react with copper to generate cuprous chloride: cuccl =→ cucl →1e cuprous chloride reacts with water to generate cuprous oxide and hydrochloric acid: 2CuCl → Cu20 12 2HCl cuprous oxide can generate basic carbonate when it meets oxygen, water and carbon dioxide. Cu20-02X H20X C02→cuc 03 Cu(OH)2 Copper oxide can be converted into basic copper chloride when it meets water, oxygen and hydrochloric acid: 2Cu20 H20X 02X HCl → CuCl2 3Cu (0H) 2. Therefore, under the influence of the external environment, the corrosion products of bronzes are layered structures of CuCl and Cu20 from inside to outside, followed by CuC03.3cu (OH) 2 or CuCl2.3cu (OH) 2, or both. X-ray diffraction analysis confirmed this result. Due to the loose expansion of basic copper chloride, which is usually called powdery rust, oxygen and water can still enter it, so that the cuprous chloride layer is transformed into basic copper chloride: 4cucl10214h2o → cucl23cu (0h) 2hcl, which creates conditions for the internal generation of powdery rust. The generated hydrochloric acid satisfies the * * * structure, and copper is converted into cuprous chloride: the cuprous chloride formed by 4cu14hcl102 → 4hcl2h2o reacts with oxygen and water immersed in it to generate basic cuprous chloride. This cycle makes the corrosion products of bronzes continuously expand and deepen until the objects fester and perforate, which is the so-called "Bronze Disease". Some materials think that the corrosion mechanism of bronze is also related to tin in bronze; Lead is closely related. This sulfide is converted from hydrogen sulfide produced by sulfate reduction of microorganisms under the action of anaerobic bacteria. The theory of the relationship between biology and bronze rust needs further study.
Rust removal and protection
Most bronzes were once buried underground, so they were corroded to varying degrees. As a corrosive medium, the capillaries and pores of soil are filled with air, water and electrolyte. Buried in the ground, bronzes naturally form corrosion coatings with different colors under the action of air, water and electrolyte, including black copper oxide (CuO), red copper oxide (Cu2O), indigo copper sulfate (CuSO4), blue copper sulfate (CuSO4 5H2O) and green basic copper sulfate (CuSO4+3Ca(OH)2). Most of them are corrosive products, which not only did not destroy ancient works of art, but also increased the artistic effect of bronzes. The antique corrosion layer has become a symbol of the solemnity, simplicity and age of bronzes. The rust layer generally does not change the shape of bronze ware, and the nature of copper rust is relatively stable and will not cause damage to bronze ware. Therefore, this corrosion layer should be retained. However, in view of the fact that most unearthed bronzes are basically covered with soil and rust, rust removal is necessary to reveal the background color, patterns, patterns and inscriptions. However, rust removal cannot damage the bronze tire, and good rust color should be preserved. Different from foundation rust removal is the removal of "powder rust". The main mechanism of bronze corrosion is that the existence of chloride ion has the greatest influence on bronze corrosion and is the main reason for bronze damage. To protect bronzes well, the key lies in how to deal with chloride ions, how to remove chloride ions from the inner layer of utensils, or how to seal and stabilize chloride ions in the interior of utensils, so as to isolate them from oxygen and moisture and avoid the influence of external environmental factors. There are many ways to remove excess bronze rust and "powdery rust". What method to adopt depends on the specific situation of each cultural relic, but there is a general principle that the original appearance of cultural relics must be maintained, especially the inscriptions, patterns and ancient spots of cultural relics must not be damaged.
Rust removal method
There are three main treatment methods: mechanical method, chemical method and electrochemical reduction method. These three methods work together.
First, mechanical methods: divided into manual operation and mechanical operation. Manual operation: mostly used for powdery rust that has been exposed on the surface of bronze ware. Various tools can be used, such as stainless steel needle, hammer carving knife, chisel, chisel, stainless steel scalpel, multifunctional carving pen, tooth cleaner and so on. , directly operate on the appliance, and carefully remove the powdery rust. After the powdery rust is removed, a very thin layer of copper is often found, which is not the copper body of bronze ware, but the copper produced during the hydrolysis of copper chloride. It is often covered with a large amount of gray-white cuprous chloride. So after piercing a thin layer of copper with a steel needle, it was found that chloride could be removed until the copper body was seen. Mechanical methods include digging, cutting, scraping, sawing, sweeping, sweeping and polishing. Mechanical operations include: sandblasting machine: it can be used to remove rust and corrosion on metal surfaces. Its derusting principle is to spray metal particles by air pressure, and the derusting will be quick. This method is quick and convenient, and the derusting area can be large or small, which has greater advantages than laser derusting and ultrasonic derusting, and rust in some holes can also be removed. Laser derusting: It is accurate and easy to remove chloride from the deep focus of bronze caves by laser. It mainly uses the exciting huge light energy to act on the surface rust layer instantly, which makes the surface temperature rise rapidly, and uses the optical effects such as photothermal, photochemical and photo-pressure produced by the interaction between laser beam and matter. Because of its loose structure and strong energy absorption, the rust layer quickly melts, vaporizes and leaves the body, which can quickly, efficiently and pollution-free remove the green and harmful powdery rust on the bronze surface, thus achieving the purpose of prolonging the service life of the bronze and effectively protecting cultural relics. This method is not suitable for removing large areas of harmful rust. Ultrasonic derusting method: the ultrasonic cleaning machine adopts ultrasonic micromechanical oscillation wave, which can spread in the form of wave in both solid and gas media. The mechanism is that the liquid impacted and vibrated by cavitation at high frequency is subjected to negative pressure within a certain period of ultrasonic wave, and the liquid is pumped away at the liquid-solid interface to become a vacuum, resulting in cavitation bubbles. On the other hand, the process from the formation to the rupture of cavitation bubbles is repeated with high frequency, which periodically and strongly impacts the dirt on the cleaned object to separate it from the object, further promoting the violent oscillation of cavitation bubbles on the surface of the dirty object. You can also add sodium sesquicarbonate solution to soak, and accelerate the reaction by ultrasonic wave to achieve the effect of long-term soaking treatment in a short time. In addition, you can also use ultrasonic dental scalers, lettering pens, etc.
Second, the chemical method uses chemical reagents to prepare derusting fluid, and there are many formulas for derusting fluid.
1, with 5%- 10% citric acid, 5%- 10% ammonium hydroxide and alkaline potassium sodium tartrate, the bronze ware can be directly soaked in the rust removing liquid, or dipped in the rust removing liquid with absorbent cotton, and then coated on the rusty parts.
2. Sodium sesquicarbonate method: sodium sesquicarbonate is also called alkali bath soaking method. The chemicals used are sodium carbonate and sodium bicarbonate, which are prepared into trisodium bicarbonate solution. Bronzes containing chloride are soaked in 1% or 5% sodium sesquicarbonate (Na2CO3 nahco3 2h2o) solution, and it is best to heat them when soaking, so as to keep the liquid temperature at about 40℃ during the day. Cool yourself at night. Until no chloride ions appear in the immersion liquid. Then soak the vessel in distilled water and clean it. Put the corroded bronzes into the solution and replace them once a week. After a few weeks, they can change for half a month or more. Soak for at least three months until the chloride ion concentration is below 4PPm. This method has been used for a long time, but it is extremely time-consuming. This method makes chloride ions enter the solution to react with sodium sesquicarbonate by soaking corrosion products, which is beneficial to the preservation of green patina. When inscriptions, patterns and ancient spots need to be preserved, this method is more suitable, so it is still widely used. However, the efficiency of removing chloride ions is not particularly good, because the corrosion layer on the bronze surface is affected by many factors and is a dynamic process controlled by diffusion. Only by changing the soaking solution several times can chloride ions continue to diffuse out. In order to improve the derusting effect, it is necessary to extend the soaking time. If the concentration of sodium sesquicarbonate is 5%. It not only releases a lot of chloride ions, but also has a fast speed, but the consumption of copper also increases accordingly, so it is not suitable to use too concentrated sodium sesquicarbonate solution.
3. Benzotriazole (BTA) method: BTA method is a very effective bronze corrosion inhibitor used to protect copper and copper alloys at home and abroad. It was used to protect ancient bronzes and achieved good results. Benzotriazole is a white to milky powder crystal, which can be dissolved in organic solvents such as ethanol and benzene. There are two main mechanisms for BTA to inhibit copper corrosion, namely adsorption theory and film forming theory. According to the adsorption theory, after BTA is adsorbed on copper surface, the interface structure between metal and solution is changed, and the activation energy of anode reaction is significantly increased, thus reducing the reaction ability of copper itself. According to the film-forming theory, the protective effect of BTA on copper is related to the existence of Cu20 film. Cu20 film can form Cu (I)-BTA composite protective film, and it can also form Cu (I)-BTA composite protective film on the surface of Cu0, which has good covering performance. Close to the outside of the metal, the metal surface is separated from the corrosive medium, forming a transparent covering film insoluble in water and some organic solvents, forming a relatively firm film, greatly reducing the degree of dissolution or ionization of the metal and playing a role in protecting the metal. For example, the mixture of BTA and benzylamine not only accelerates the film formation speed, but also improves the corrosion inhibition ability. When BTA is mixed with molybdate, its corrosion inhibition effect doubles.
4. Hydrogen peroxide method: hydrogen peroxide is used as oxidant to remove chloride ions by oxidation. The concentration depends on the corrosion situation, and the remaining hydrogen peroxide can be completely decomposed with a little heating without any influence on the vessel. Compared with sodium sesquicarbonate soaking method, this method has the advantages of short treatment time and thorough chloride ion removal. Compared with local electric erosion method and silver oxide sealing method, hydrogen peroxide method can remove powder rust in different areas and depths, with wide application range and simple treatment.
5. The second method: add 50%, 5% acetonitrile and 5% ethanol to 10O%. Acetonitrile and cuprous ions in this solution form stable basic copper chloride, and this solution has poor effect and can't play its role in a short time. The disadvantage of this method is that long soaking time will lead to the blackening of green patina, and because B-eye steam is moderately toxic, good ventilation environment or sealing measures are needed during soaking.
6. Silver oxide protection method: This method is suitable for local corrosion of spotted "powdery rust". It uses the contact between silver oxide and cuprous chloride to form an angular silver film to seal the exposed surface of cuprous chloride under the action of water vapor in the air, thus achieving the purpose of controlling bronze corrosion. Firstly, cuprous chloride, the root of powdery rust, was removed mechanically until fresh copper was seen. Then, wipe the corroded area clean with acetone. Then silver oxide is mixed with ethanol to fill the removed part, so that the uncleared cuprous chloride reacts with silver oxide to form an angular silver film, which prevents the action of chloride ions and makes the bronze tend to be stable. However, brown spots will be formed on the surface of pits filled by this method, and color matching is needed.
7. Deionized water method: For the cleaning of general bronzes, the corroded bronzes can be washed repeatedly with deionized water or distilled water at 40℃-60℃, which can not only wash away chloride ions, but also will not change the bronze rust.
8. Mixed solution method of citric acid and thiourea: use 5% citric acid and 1% thiourea aqueous solution (PH = O.95) to remove local harmful rust, and then use 1% nah co 3 aqueous solution to neutralize the residual reagent. This method can show good results on large bronze cultural relics, especially when surface inscriptions and patterns need to be revealed.
9. Alkaline sodium hydrosulfite method: soak the vessel in 5% sodium hydrosulfite aqueous solution for 24 hours, and then remove sulfate with alkaline sodium hydrosulfite solution. When using alkaline sodium dithionite solution to remove chloride, we should pay attention to control the PH value of the solution below 13. After treatment, it should be washed in distilled water for 48 hours to remove the residual corrosive solution. Sodium dithionite has a strong pungent smell, so the treatment must be carried out in a closed container.