Why the bronze sword unearthed in the Qin mausoleum prevented rust for a thousand years

Why bronze swords unearthed in the Qin Mausoleum prevented rust for a thousand years

Shaanxi Archaeological Society, edited by the book "Shaanxi Archaeological Significant Discoveries (1949-1984), published in 1986, wrote: "For a long time, the Chinese intellectual community has circulated the saying that as early as more than 2,000 years ago, Chinese craftsmen in the Qin Dynasty have mastered the advanced chromate conversion coating technology to prevent metal corrosion. to prevent metals from being corroded. The reason is that many of the bronze weapons unearthed from the Qin Tombs are well preserved and chromium has been detected on the surface of some of them, as demonstrated by a number of illustrative arguments in previous research results.

Qin terracotta pits unearthed bronze weapons, swords, gorges, spears, beryllium, halberd, battle-axe, Shu, machete, arrowheads, etc., the manufacturing process is extremely delicate, sharp edge, especially the surface of bronze swords through the oxidation of chromium salts, with the role of anti-rust and anti-corrosion. This process, Europe and the United States capitalist countries until modern times to master, and our country in more than two thousand years ago has created this advanced process, indicating that the progress of China's ancient gold treatment technology, reflecting the ingenuity of the ancient Chinese working people."

In 1996, compiled and published by the Museum of the Terracotta Warriors and Horses of the First Emperor of Qin, the book "Research on Terracotta Warriors and Horses of Qin", there is a similar content: "In foreign countries, it was only in 1937 that Germany invented the chrome-plating process. The widespread use of chrome-plating to prevent rust is a matter of recent decades, and the time of rust prevention can generally be maintained for sixty years. The discovery of bronze swords in the Qin Dynasty proves that the chromium salt oxidation method was used in China as far back as two thousand one hundred years ago, and it has not lost its protective effect yet."

Is this the key to determining whether the bronze swords of the Qin Mausoleum will remain rust-free for a thousand years or not? A study on how the bronze weapons of the Terracotta Army at Qinling have been preserved to this day unravels the layers of this mystery. This latest study on the bronze weapons of the Terracotta Warriors at the Qinling Mausoleum, published online in Scientific Reportsvolume and involving both Chinese and foreign scholars***, disproves these claims.

Questions -

The Chinese and foreign scholars focused their attention on the following questions:

(1) What is the probability of the presence of chromium on the surface of the weapons?

(2) Is there a correlation between the presence of chromium on the surface and the longevity of bronze weapons?

(3) Where is the source of the chromium?

(4) Was the chromium on the surface of the weapons intentional?

The study analyzed a large number of samples of unearthed weapons, soil and related materials, and also conducted experiments on chromium coating treatment and accelerated aging of bronze.

Answers-

(1) Chromium was detected in only 37 of the 464 weapon parts at concentrations ≥0.1%, which proves that its presence is not widespread.

(2) Chromium has nothing to do with the long-lasting preservation of bronze weapons; what really makes a difference is the high tin content of the bronze and its stable composition, as well as the pH of the loess at the burial site, where the soil particles are very small and can impede the aeration and humidity necessary for metal corrosion.

(3) The main source of chromium is lacquer. Lacquer was used to coat the terracotta warriors and non-metallic parts of the weapons (such as wooden sword hilts and scabbards) during the construction of the Qin Tombs. Therefore, chromium is often found on metal surfaces similar to these parts, and vice versa, rarely. As for the source of chromium in lacquer, further research is needed.

(4) Qin Dynasty craftsmen did not master the technology of using chromium for metal preservation, the chromium on the surface of the metal is the result of contamination after burial.

In fact, a similar questioning does not begin today, in 1996, the scholar He Tangkun in the "Archaeology" magazine article, published his own six pieces of surface chromium-containing bronzes test results. According to these test results, He believes:

"Today's analysis of the six specimens of the original Department of tin-plated artifacts, did not carry out artificial chromium treatment, chromium on the surface is in use, buried in the process of accidental penetration, the specimen surface of the color of all kinds of state, is the natural corrosion caused by. Qin terracotta pit copper arrowheads, Manchu Han Tomb copper surface chromium distribution state and this 6 pieces of specimens very similar to, only the color there are large differences, the same is difficult to exclude the possibility of natural pollution."

There are five specific reasons:

(1) There are very few examples. Including the six bronzes tested by He himself, "the total number of bronze specimens known today (referring to 1996) to contain chromium on their surfaces in China's antiquity*** is less than 10, and there has been no increase in the number for more than a decade."

(2) The chromium content on the surface of these bronzes is low. "The average composition of the 10 analyzed points of six specimens was 1.065%, and the highest chromium content was only 2.170%."

(3) It is difficult to understand the motivation for describing this chromium as deliberately artificial. The surface of the bronzes was treated either for decoration or for anticorrosion. But the study of the six chromium-containing samples of different colors, creamy gray, off-white, green-gray, gray-green, gray-black, not with chromium to decorate the coloring of the phenomenon should be; samples of arrowheads, arrowheads are a large number of consumables, and there is no anticorrosion necessary, and really want to anticorrosive plating of tin on it, "chromium-containing surface of the corrosion-resistant may not outperform the tin-plating of surface layer".

(4) bronze surface containing chromium is not uniform. This phenomenon is quite unreasonable if it is needed for decoration or corrosion resistance.

(5) The chromium plating technique lacks written records. Other tin-plating, gold-plating and silver-plating techniques can be found in ancient texts.

Compared with the previous questioning, this study by Chinese and foreign scholars gives more detailed data and more accurate analysis, and the conclusion is more credible.