Hairpins form grave 出土髮簪

經過土地的保存,百年後,這些髮簪重見天日

There is some real hair preserved on these hairpins. Please visit this page
Hair Preserved on Hairpins from Graves

【明代金花頭簪】Ming Dynasty flower hairpin

Typical Ming Dynasty form, the outer layer of the flower is gold hammered into thin foil and wrapped around the main body of the copper alloy (or possibly even silver) hairpin. This is an excavated object but it is particularly obvious that the gold foil is un-degraded, even though the copper alloy is heavily covered in corrosion. The shiny gold and patinated "bronze" show a very obvious contrast. It is a practical demonstration of the different chemical stabilites of metals.
​典型的明代形式，
花朵外層為黃金敲成薄片包覆在青銅或銀質簪主體上，此為出土文物，故會特別明顯證明“黃金穩定性佳不會被腐蝕”的化學性質特性。
黃金閃亮依舊，但簪柄早已鏽蝕，兩者呈現非常明顯的對比。

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The corrosion products that form on bronze and other copper alloys is very different from the rust that forms on iron and steel objects. Rust on iron alloys forms very quickly when the metal is exposed to water and oxygen. The reaction is quite energetic and it releases dissolved iron and acid into the local environment. Sometimes gas bubbles can even form. In the soil the dissolved iron surrounds the corroding object and oxidises further, forming an insoluble crust of hard brown rust that contains soil particles and small pores and cracks. The corrosion that forms also contains water in its crystal structure. This crust is very porous and allows oxygen and water to penetrate to the metal below so that the corrosion continues.

​Copper and bronze are much less reactive than iron, although they do still corrode when exposed to water and oxygen. But because the reaction is much slower the corroding object does not flood the surrounding soil with dissolved copper ions. Instead, these copper ions stay close to the surface and react with dissolved alkali and carbon dioxide to form a solid corrosion product. The corrosion that forms (usually green or blue depending upon the soil chemistry) is more compact because it forms slowly, bubbles of hydrogen are not created and the corrosion does not contain water molecules. This compact corrosion helps to prevent water and oxygen penetrating down to the metal below. That is why outdoor bronze sculptures, or copper roofs, may turn green but do not crumble away. Iron on the other hand will quickly begin to suffer bad corrosion and ultimately large pieces of rust will fall off. Iron and steel are always protected by a layer of paint.

In some of the pictures we see a hairpin that is covered in green corrosion but which also has some hair preserved on the surface. Copper salts are natural antibiotics. Dissolved copper ions are toxic to fungi, bacteria and even viruses (https://en.wikipedia.org/wiki/Antimicrobial_properties_of_copper). The bronze hairpin was still being worn by the deceased woman when she was buried. Copper released from the corroding hairpin killed any fungi and bacteria that would have degraded the hair, preserving it long enough for more corrosion to accumulate around it. Ultimately, the pores in the hair are filled with copper corrosion products, essentially creating a corrosion fossil of the hair's structure. This is a phenomenon often seen in metal objects excavated from ancient graves and is not restricted to hairpins. Wood, leather, textiles and hair can be preserved in copper corrosion and even in iron corrosion. Iron corrosion products can form further away from the corroding objects than copper corrosion products so more of the surrounding organic materials are preserved. Organic materials are only preserved if they are lying directly against the corroding bronze.

For a more technical description of copper corrosion the chemical equations below summarise the formation of green patina on copper.