Source: CCTV news client
At present, Sanxingdui has unearthed a large number of bronzes, including the "top kneeling portrait" and "head-turned kneeling portrait" that became a star cultural relic once discovered. In addition to the star relics, the rust on the surface of a bronze fragment has also surprised archaeologists. Unlike the blue-green main tone of Pit 3, this bronze fragment has a locally tender yellow surface, which is very bright, why is its color so different? Recently, the Palace Museum tested this color.
At a glance, this is like a piece of jade, warm and clear, bright color, blue, green, yellow, white and other colors are layered, giving people a sense of tranquility. In fact, this is the latest excavation of Sanxingdui bronze rust under the microscope imaging. Some of the bronzes in Sanxingdui have rusted, especially in the No. 3 pit, where the yellow is mixed in blue and green, and as soon as the soil layer is exposed, it has aroused the high vigilance of archaeologists.
Liu Jianyu, deputy research librarian of the Institute of Cultural Relics Protection and Standardization of the Palace Museum: During the excavation process, they found that some bronze statues had rust in yellow and white, which needed us to test.
Forbidden City cultural protection experts take the pulse of Sanxingdui bronze "look and smell and cut"
After the first sample test, experts found that the rare yellow rust of sanxingdui bronzes was particularly special in its compound composition. In order to ensure the accuracy of the detection results, in early July this year, the Forbidden City experts rushed to the Sanxingdui archaeological excavation site, in addition to sampling the rust on the bronze cultural relics again, the surrounding soil was also brought back to the Forbidden City, and various means such as Raman spectroscopy and X-ray diffraction spectroscopy were used for detection, and it was finally determined that the yellow rust on the Sanxingdui bronze was the compound lead tin yellow.
Liu Hanwen, librarian of the Institute of Standardization of Cultural Relics Protection of the Palace Museum: The yellow rust of Sanxingdui is a relatively uncommon yellow lead tin yellow, and the composition is mainly lead tintate and lead silicate.
Rust dots the blue and green in the "chemistry class" in the bronze of Sanxingdui
According to experts, China's ancient Shang Zhou period bronze is mainly copper, tin, lead three metal alloys, long-term burial process, with the environment of water, oxygen, carbon dioxide and sulfur and chlorine-containing substances, chemical reactions occur to produce rust, these rust products show a variety of different colors: rust contains copper oxide is red, copper oxide is black, alkaline copper carbonate is green or blue, basic copper chloride is light green, containing extremely harmful copper chloride is grayish white. Common lead corrosion products, lead oxide is orange yellow, also called lead yellow; basic lead carbonate is white, also called lead white. The rust product of tin, cassiterite, is generally gray-brown. However, the yellow rust that appeared on sanxingdui bronzes was rare, surprising archaeologists.
Liu Jianyu, deputy research librarian of the Institute of Cultural Relics Protection and Standardization of the Palace Museum: Lead tin yellow, this is from the perspective of the current literature, and the rust product of this composition has not been found.
Liu Hanwen, librarian of the Institute of Standardization of Cultural Relics Protection of the Palace Museum: Even in the utensils of Sanxingdui, it is not very common, not every one of them, even if there is yellow rust on the utensils, it does not mean that the entire utensils are covered with yellow rust, it may be a small piece or a small piece.
Li Guanghua, librarian of the Institute of Standardization of Cultural Relics Protection of the Palace Museum: This ingredient is relatively similar to the composition of some pigments we use now.
Lead tin yellow: bright and soft color
The color of the rust on this bronze fragment is lead tin yellow. As you can see, lead tin yellow in the dark background, will emit a bright and soft glow. This color can be seen in some early oil paintings and some enamelware in the Forbidden City. However, most of this kind of lead tin yellow is artificially prepared, but on the Sanxingdui bronze ware that was born more than 3,000 years ago, where did these lead tin yellows come from?
Sanxingdui bronze found lead tin yellow source preliminary analysis
Liu Jianyu, deputy research librarian of the Institute of Standardization of Cultural Relics Protection of the Palace Museum: If this lead tin yellow on oil paintings or enamelware is used as pigment, it is prepared manually. This class of compounds found in the rust of Sanxingdui bronzes is more likely to be produced in the process of natural corrosion. The formation of lead tin yellow has a relatively harsh condition on the temperature, and it may produce such corrosion products in the process of burial or in the process of incineration.
Experts at the Forbidden City said that the next step will be to study the formation mechanism of this special yellow rust product and verify it through simulation experiments. After the excavation of Sanxingdui bronze cultural relics and the separation from the original burial environment, will the few lead and tin yellow rust fade? Will it spread further? It is also the focus of research by archaeologists and restoration experts.
Liu Hanwen, librarian of the Institute of Standardization of Cultural Relics Protection of the Palace Museum: Under the condition that the environment is not particularly acidic and alkaline, it will not further deteriorate itself and will not further spread to other parts. Its own chemical composition is very stable.
Liu Hanwen's "stability" means that the lead tin yellow on the Sanxingdui bronze is not a recognized harmful substance. According to reports, in the rust of bronze, harmful substances are mostly basic copper chloride, in the form of powder, it will continue to react to make the bronze corrosion perforation, therefore, the identification of chlorine-containing corrosion products is a very important work, the need for cultural relics experts to completely clean it up.
Liu Jianyu, deputy research librarian of the Institute of Standardization of Cultural Relics Protection of the Palace Museum: But on the artifacts of Sanxingdui, our current test results did not find basic copper chloride. But the absence of discovery does not mean that our protection of it can be taken lightly. What we can do more is to predict how it will develop in the future, and then how to block the trend of its lesions, which is what we have to do in the protection of cultural relics.
(CCTV reporters Zhang Lilei, Tian Yunhua, Wang Shuai, Guo Min)