Preventive protection of bronzes in the collection
The number of bronzes in China's collection is very large, and the measures for the repair and rescue of diseased bronzes are urgent, but the long-term task is preventive protection, creating a good preservation environment, and as far as possible, the bronzes themselves and the various information they carry are no longer lost due to continuous corrosion. Only pay attention to restoration and ignore preventive protection is a one-sided approach, in order to get rid of the passive situation of cultural relics protection work, we must try our best to protect the work before the damage of cultural relics, and combine long-term preventive protection with scientific restoration in order to better play the value of bronzes.
Unlike the passive approach to rescue protection, preventive protection is active protection. Chris Caple, a world-renowned expert in the protection of cultural relics, defines preventive protection as follows: all measures taken to reduce the harm to cultural relics or prevent damage to cultural relics, including a series of measures taken in museums: registration, storage, handling, packaging, transportation, protection, environmental management and other work. Now let's start with improving the preservation environment of museum collections to understand how to avoid and mitigate the damage to collections through preventive conservation measures. The preservation environment of the museum's collection mainly includes the monitoring and control of temperature and humidity, air pollutants and light intensity, and the establishment of facilities to respond to sudden natural disasters.
Environmental monitoring system
Environmental monitoring data
(1) Temperature and humidity
The most basic factors in the preservation environment of bronzes in the collection are the temperature and relative humidity of the air. After the long-term research and practice of domestic and foreign museum collection protection scientists, the standard values of the environmental climate in museum buildings that have been recognized are: temperature is 15 ~ 25 ° C, and relative humidity is 45 ~ 65%. For bronzes, the temperature range does not reach the temperature at which the metal softens or melts, and its original form can be maintained. However, an increase in temperature can accelerate chemical reactions caused by other factors, such as changing the solubility of certain corrosion products, resulting in different corrosion reaction products, resulting in changes in the surface state of the artifact. Humidity is an important factor in the production and development of harmful rust in bronze, and many chemical reactions of bronze corrosive lesions require the participation of water. Research data show that if other conditions are good, bronzes can maintain their relative stability in the case of relative humidity below 35%, so the best preservation environment for bronzes is 15 to 25 °C, and the relative humidity is less than 35%.
Portable temperature and humidity recorder
The temperature and humidity in the museum are affected by monsoons, precipitation, sunshine, audience flow and other factors, and the preservation environment should be controlled within the best range, relying only on natural regulation, which is obviously very difficult and must be supplemented by technical measures. By installing an air conditioning system, using temperature and humidity control equipment such as cabinet-type constant temperature and humidity machine, cold and hot fan, and adding and dehumidifiers to regulate the temperature and humidity of the large environment, you can also use humidification materials such as color-changing silicone to control the small environment of cultural relics cabinets and display cabinets. The museum can choose the appropriate temperature and humidity adjustment materials and equipment according to the actual situation to ensure that the cultural relics are in the best preservation environment.
Warehouse dehumidifier
Dehumidifiers control the microenvironment of the cultural relics in the warehouse
(2) Air pollutants
In addition to the normal air such as nitrogen, oxygen, inert gas and carbon dioxide, which accounts for 99.999% of the total amount of dry air, people are more concerned about the other 0.001% of air pollutants, and the pollutants in the air generally include organic volatiles, nitrogen oxides, sulfides, ozone, formic acid, formaldehyde and other gas pollutants and PM2.5, PM10 and other particulate matter. Nitrogen oxides, ozone, sulfides and other polluting gases mainly come from outdoors, and organic volatiles, formic acid, formaldehyde and other volatiles mainly come from various indoor materials. For bronzes, SO2 forms an acidic medium environment under humid conditions, which will cause the Cu2O film on the copper product to be broken, the place where the surface oxide film is destroyed becomes the anode of the corrosive battery, and the copper body is corroded and dissolved, further forming a less soluble Cu4SO4 (OH)6. Laboratory simulation studies have shown that under the NO2 atmosphere, the surface Layer Cu2O has a tendency to be replaced by basic copper nitrate, and the color is deepened. Ozone is extremely corrosive to copper, it reacts with copper to form copper oxide, and when the concentration increases, it will also catalyze and accelerate the corrosion reaction of the bronze. At the same time, when building materials, decoration materials, collection storage equipment materials and display auxiliary materials and other harmful gases contain volatile properties, it will also cause harm to the collection, such as organic acids and formaldehyde will cause corrosion to bronzes.
Monitoring the collection environment at different monitoring points can create a good preservation environment by installing air filtration equipment, sealing cultural relics cabinets, display cabinets, sealing nitrogen and other methods.
Wireless sensing environmental monitoring equipment in the exhibition hall of the museum
Wireless sensing environmental monitoring data
(3) Illumination
Lighting is a basic requirement for displaying and studying museum collections. The light emitted by the sun is infrared, visible and ultraviolet according to the wavelength from long to short, and the shorter the wavelength, the greater the energy contained, and the greater the damage to the cultural relics on the surface of the cultural relics. Studies have shown that infrared radiation to the surface of cultural relics will increase the surface temperature of cultural relics, which will produce thermal effects; visible light accelerates the atmospheric corrosion of copper and changes the morphology of copper surface corrosion products; ultraviolet rays will accelerate the aging of cultural relics.
For the cultural relics warehouse and exhibition hall with good sealing, the light source on the surface of the cultural relics mainly comes from the artificial light source, and in the selection of the artificial light source, the LED cold light source with low ultraviolet content and adjustable light intensity should be selected as the lighting source. Different materials of cultural relics have different sensitivities to light, such as paper and textile cultural relics with high sensitivity to light, it is recommended that the light intensity is not higher than 50 lux, and the light intensity of bamboo carvings, wood carvings, ivory cultural relics with general light sensitivity should not be higher than 150 lux, and the light intensity should not be higher than 300 lux for metal, ceramic, and stone carving cultural relics that are not sensitive to light intensity. The damage of light to cultural relics is a cumulative process, and exhibits can be rotated regularly in order to minimize the exposure intensity and exposure time of cultural relics without affecting the effect of visiting. At the same time, the exhibition hall should strengthen management and prohibit the use of flash to take pictures. The display cabinet glass can be optionally ultra-white anti-ultraviolet laminated glass to filter out the hazards of ultraviolet rays.
(4) Sudden natural disasters
Sudden natural disasters such as earthquakes, typhoons, floods, and lightning strikes may cause irreparable losses to cultural relics, so cultural relics warehouses and cultural relics cabinets must have lightning protection, earthquake resistance and other properties. The cultural relics in the warehouse are stored in an acid-free capsule box, which can not only isolate the interference of external air on the cultural relics, maintain the stability of the environment in which the cultural relics are located, but also play a role in buffer protection when vibration occurs. Anti-dumping devices should also be installed on the shelves and display cases of cultural relics to avoid accidental collisions or earthquakes when the shelves are overturned and damage cultural relics.
Shock-proof display cases
Every cultural relics protection worker should have the concept of preventive protection, long-term preventive protection combined with the necessary scientific restoration, in order to extend the preservation life of bronzes for the greatest period of time. Although the trend of cultural relics disappearing over time cannot be avoided, we do our best to make this precious wealth pass on for a longer period of time, so that the fruits of human civilization can be inherited and developed.
Note: This article mainly refers to the author's article "Preventive Protection and Restoration of Bronzes in The Collection", cultural relics identification and appreciation; some of the content has been revised and adjusted.
Edit: Bai Dan
Editor-in-charge: Cui Ruihua
Yang Qian
Review: Li Qi