Ancient coins are loved by players because of their rich and colorful rust colors, and some people even spare no effort to collect rust-colored ancient coins such as red, green and blue, and the rust-colored ancient coins of the Northern Song Dynasty.
Familiarity with different rust colors is one of the basic skills of counterfeiting. How many rust colors are there on ancient coins, why are there red crystals, blue, green, black and other rust colors, and even some coins set red, green and blue together or four colors, five colors in one? After reading this article, you will understand.
Common terms for talking about rust of ancient coins are as follows:
1. Raw pit: Bronze coins excavated in various types of soil, with obvious corrosion and well preserved, are called raw pits. It is one-sided and inaccurate to say only that "the surface oxidation is serious", and it should be changed to "obvious corrosion" of copper coins. Because it not only has rust on the surface, but also has intergranular corrosion inside.
2. Cooked pit: bronze coins that have been unearthed for many years but still retain some rust. Also known as "old life pit".
3, handed down from generation to generation: stored in the atmosphere of rusty bronze coins, and often play, the surface is black and bright.
4, black lacquer ancient: stored in a dry environment of bronze coins, not played, the surface is black.
5, mercury ancient: bronze coins have high tin content and form a visible "mercury light" in neutral soil, that is, there is a silvery-white rust layer on the surface. Some books only say that the surface of the silvery-white oxide layer is one-sided and inaccurate.
6, pulp: bronze coins in water or dry environment after rusting in a variety of colors, that is, red, yellow, green rust "black paint ancient" money.
Bronze coins have long been stored in acidic soils, alkaline soils, neutral soils, water, atmosphere and lime substances, and the rust formed varies.
Ancient coins rust color is formed
1. Peacock color, blue, green rust - rust mechanism analysis of bronze coins buried in acidic soil:
The rust color of the bronze coin buried in the acidic (PH4-7) soil for a long time is generally green (the color gradually changes from apple green - light green - medium green - dark green - olive green), and produces a basic copper carbonate [Cu2 (OH) 2CO3] is light green, and sometimes the basic copper sulfate [Cu2 (OH) 2SO4] is olive green, and a stable protective film is formed on the surface of the money.
Basic copper carbonate crystallization
Due to the different thickness of rust, the chemical composition of rust is different, and the content is also different, so it will form a variety of shades of green. Commonly known as pine green, melon peel green, pure green, green lacquer ancient, indigo green and so on. This type of rust is often a combination of comprehensive and localized corrosion, and also produces electrochemical corrosion.
Therefore, the money surface will be spotted, grooved and pitted, and because of intergranular corrosion and selective corrosion, the perishable parts such as tin and lead inside the copper coin are corroded, and the proportion of the copper coin is reduced to become lighter, and a fine needle eye is produced, making the money sound dumb, and the green rust is produced from the hole, commonly known as "bone rust".
2. Analysis of rust mechanism of cinnabar rust - bronze money buried in alkaline soil:
Bronze coins are generally used in the folk circulation for decades or even hundreds of years, it will rust to produce alkaline copper sulfate, and then buried in alkaline soil (PH7-10), and reducing substances such as organic sugars have a chemical reaction to produce copper oxide [Cu2O] dark red, but also lead dan [Pb3O4] is a big red.
Therefore, it is called cinnabar rust, chicken blood spots, jujube skin red, macula and so on. At the same time, it also retains part of the basic copper sulfate, part of the green rust, so the bronze coin is red and green rust.
Cuprous oxide
Buried in the soil will also produce local corrosion and electrochemical corrosion, the formation of tiny needles in the eye also has red and green rust, so it is called bone rust.
From the above, it can be seen that the bronze coin must first produce green rust before it is reduced and generate red rust, which is red rust and green rust. In the sand, "dry sand rust" is formed, that is, there is sand in the green and there are yellow and red spots.
3. Mercury light - rust mechanism analysis of bronze coins stored in neutral soil for a long time:
Bronze coins buried in neutral soil (PH7) for a long time generally do not rust. However, the tin content of some bronze coins is high, and if the tin is 15-32%, it is analyzed from the "copper-tin state diagram" to form a solid solution crystal and a eutecsole. Among them, the phases (Cu3Sn) and SN, due to tin precipitation to the surface of the money to form the so-called "mercury light", also known as "mercury immersion".
At the same time, tin bronze will also have a "reverse segregation" trend, that is, tin is precipitated from inside and outside, so that the surface of the copper coin is "white spots" and is also called "tin sweat". When the tin content is 10-30%, it also produces tin dioxide [SnO2] silver gray.
Mineral cassiterite
These phenomena will also occur at the same time, or separately, which will cause the surface of the copper coin to form a "mercury light". Because the neutral soil is extremely unstable, it is easy to change into acidic or alkaline soil, so some bronze coins first form a small amount of red and green rust before producing "mercury light".
4. Puddle - Analysis of the rust mechanism of long-term immersion in water of bronze coins:
Bronze copper coins are buried in cleaner rivers and rivers for a long time, and the corrosion is extremely weak, generally less than 0.0025 mm / year, and the brass coins are slightly faster.
If the bronze coin is buried in a polluted paddy field or in the mineral water containing iron sulfate [Fe2(SO)], the copper coin will be seriously corroded, forming copper oxide and copper sulfide [Cu2S] one red, one black, and evenly distributed, so that the surface of the money forms a thin shell-like gray rust (the color is gradient from sea ash - silver gray - light gray - medium gray - dark gray).
Puddle Chongning Tongbao
5. Analysis of the rust mechanism of black lacquer antique - bronze money stored in the atmosphere for a long time:
Copper, bronze, brass coins are very stable in the atmosphere, generally less than 0.00015 mm / year, on the surface of the copper coins will form a very stable protective film, mainly alkaline copper sulfate is olive green, but also will produce copper oxide [CuO] black, copper sulfide black, and stannous oxide [SnO] brownish black.
The older the age, the thicker the rust layer, the darker the color, commonly known as "black lacquer ancient". If you play in your hands for a long time, it will make the surface of the money as bright as a mirror, commonly known as "passed down from generation to generation". However, electrochemical corrosion is also produced in this type of bronze coin, so it is a "dumb sound".
If the bronze coin is in a dry environment (in the atmosphere or in the soil) for a long time, it will also produce copper oxide and sub-Venus oxide that is dark black, commonly known as "black lacquer ancient". Some copper money becomes red and green rust, and then generates copper oxide and sub-Venus oxide in a dry environment, generally called this "black lacquer ancient" money with red and green rust as "pulp".
Black paint ancient
Heirloom pack pulp
6. Lime rust - analysis of the rust mechanism of bronze coins stored in lime materials for a long time:
The main components of lime are calcium carbonate [CaCO3] and calcium hydroxide [Ca(OH)2]. The main component of limestone is calcium carbonate [CaCO3]. The money is buried in the ground containing lime substance, and the two corrode and attach to each other, resulting in lime rust and cream rust.
Generally, lime rust is mostly found in a large number of coins unearthed in the Ming Dynasty, such as: Chongzhen, Dashun Beihu, Taichang Tongbao, Tianqi Tongbao and so on. The unearthing of bright money from the north and south has such a phenomenon analysis, and the reason is not only related to the land, but also more reasons may be related to the composition of the money body.
In general, the color of the pulp rust that appears in ancient coins is basically the above several. This article is a basic popular science popularization knowledge, aimed at novice exchange and learning, so it uses simple and easy-to-understand theoretical data. The gods are also welcome to point out.