Chinese archaeologists frequently unearth ancient coins at tomb sites. While old Chinese coins do not have actual dates on them, they do have inscriptions which can help date the site being excavated.
Having been buried for hundreds or thousands of years, it is quite common for these old bronze coins to be so severely corroded that the inscriptions cannot be read.
Coin collectors are always warned not to clean coins because the process will lessen the value of the coin or even ruin it.
But what do Chinese archaeologists do when they have a coin that is too corroded to identify but which could potentially provide valuable information as to when the tomb was built?
An article discussing a tomb being excavated in the city of Fuzhou (福州) in Fujian Province provides the answer.
More than ten old Chinese cash coins were discovered during the dig but could not be identified because of heavy corrosion.
If you have seen archaeologists at a site then you know they work very slowly and methodically to avoid any damage to the buried cultural relics.
You might expect they would employ a similar degree of care when it comes to cleaning coins.
In this case, however, the archaeologists were less concerned about preserving the coins than just being able to identify them.
The archaeologists simply put the coins in vinegar, which is a mild acid, to soak for two or three days to remove the surface dirt and corrosion. The coins were then removed and a common toothpick was used to scrap out any corrosion in the Chinese characters. Finally, a rubbing was made of the coins.
While the coins would certainly not be very pretty after such treatment, the rubbing did reveal the inscription as sheng song yuan bao (圣宋元宝).
Sheng song yuan bao coins were cast during the reign of Emperor Huizong (徽宗) of the Northern Song Dynasty beginning in the year 1101.
An “uncleaned” sheng song yuan bao coin, which would be similar to the ones found in the tomb, is shown at the left.
The archaeologists were quick to point out that this discovery does not necessarily mean that the tomb dates from the Northern Song because in ancient China coins continued to circulate for many years after they were produced.
The archaeologists speculate that once the tomb is completely excavated it may be determined to actually be from the slightly later Southern Song Dynasty (1127-1279).
We usually picture archaeologists as using soft brushes to gently remove dirt from cultural artifacts but sometimes more aggressive measures are used on ancient coins when they are the key to dating a site.