A photographic introduction to items from the collection

The raw materials and manufacturing techniques of the Twelve Imperial Coins

In 708, the first year of the Wado era, coins called "Wadokaichin" were issued in what was the first full-scale and continuous minting of a large quantity of coins in Japan. They reason why we describe these coins adjectively as "Wadokaichin" and cannot simply refer to them as the first Japanese coins is that they were not the first coins in Japan. They were preceded by unmarked silver coins, Fuhon coins, and round unmarked copper coins, though none of these coins was circulated as currency on a significant scale. What is more, up until this time rice, cloth and other items had been used as "material money". For a period of approximately 250 years from the time when the Wadokaichin were issued up to 958 when coins called Kengen Taiho were issued, twelve types of copper coins were issued in Japan. These are referred to as the "Twelve Imperial Coins" ("kocho ju-ni sen").

It is possible to separate the Wadokaichin into two main varieties. The first is the "Kowado", literally "old Wado", on account of their somewhat ancient and rustic fabrication and lettering. These Kowado coins were minted in both silver and copper. Surviving copper coins are extremely few in number, as only one in every ten surviving "Kowado" coins is a copper coin. The second variety is the "Shinwado" ("new Wado"), which are only copper. According to the Shoku Nihongi (Continued Chronicles of Japan), silver coins were first issued in the fifth month of 708, but their use was discontinued in the eighth month of the following year. Consequently, silver coins were issued and used for an extremely short period of time.

The main reason for issuing the Wadokaichin was to create a source of revenue to build a capital immediately prior to the relocation of the capital to Heijo in 710. Since a one-mon copper coin was equivalent in value to one day's wages working on the construction of the Heijo capital, it had a relatively high value that was three to five times the value of the raw copper material.

無文銀銭 富本銭 古和同
Unmarked silver coin (Museum collection).
Pieces of silver have been attached to the obverse side. It is believed that this was done to make the coin a prescribed weight.
Fuhon coin (reproduction from the Museum's collection. The original was excavated from the Heijo site in Nara Prefecture and is held by the Nara National research Institute for Cultural Properties).
Excavated from the Asuka-ike site in Nara Prefecture, it has been confirmed that these coins pre-date the Wadokaichin.
Kowado (silver coin, Museum collection)
古和同 新和同
Kowado (copper coin, Museum collection).
On the whole, copper Kowado coins have low concentrations of lead and tin.
Shinwado (Museum collection).
The lettering differs from that on the Kowado.

This naturally led to the emergence of many people who made counterfeit coins. We know that counterfeit coins were widespread from the introduction of penalties as early as 709 for anyone caught minting counterfeit silver coins. This was one reason why the Wado silver coins were abolished. Because there was no let-up in the minting of counterfeit copper coins either, the death penalty was applied for this crime in 711, though this did not see an end to the minting of counterfeit coins. Furthermore, the price of rice rose sharply as a result of a famine, which caused a gradual decline in the coin's value. The authorities responded by issuing a new coin called the Man'nen Tsuho, whose value was ten times that of the Wadokaichin. However, the decline in the value of these coins did not abate, so that over time a succession of different coins, twelve in total, were issued. These are known as the Twelve Imperial Coins (kocho ju-ni sen). Those accused of minting counterfeit coins included lower ranking Buddhist monks in Kyoto and Nara as well as officials working in police and court administrations whose job was to catch criminals. This widespread manufacture of counterfeit coins also attests to the pervasion among the populace of sophisticated casting technology introduced by foreigners which could be used to produce coins.

These coins were normally called "copper coins," though most were not pure copper but were made of bronze, and alloy of copper and tin. In East Asia most bronze items, including the Twelve Imperial Coins, contained lead. Lead was included because it lowered the melting point during casting and enhanced the fluidity of the molten alloy. Another reason was that the bullion price of lead was lower than that of copper.

種銭をはさみ、まず目の細かい土を上からかぶせる さらに目の粗い土をかぶせて押し固める 鋳型は表裏2枚で一組となる
1. Place the master die in the middle and first cover with fine-grained clay. 2. Then cover with coarse-grained clay and press down firmly. 3. The mold consists of two sheets, a front and back.。
受け口をつけ、再び2枚の鋳型を合わせる 受け口をつけ、再び2枚の鋳型を合わせる 鋳型を焼き固め、まだ熱いうちに熔けた青銅を流し込み、鋳造する
4. Cut in channels for pouring the molten bronze into and take out the master die. 5. Make an opening and put the two sheets of the mold back together again. 6. Bake the mold so that it hardens and pour in the molten bronze while it is still hot.
鋳造後の「枝銭」。1枚ずつ切り離し、バリをとって完成 できあがった和同開珎。当時の偽金作りの技術にどれだけ近づけたかは不明
7. A "coin branch" after casting. Take each coin off individually and finish by fettling the burr. 8. A finished Wadokaichin. It is unclear how close this technique is to the technique used to counterfeit coins at that time.

An investigation into the constituents of the Twelve Imperial Coins revealed that only four early types of these coins, and relatively few of coins in total, contained more than several percent of tin. They are the Wadokaichin (Shinwado), Man'nen Tsuho, Jingo Kaiho and the Ryuhei Eiho. Most coins that came after these four types contained less than one percent tin. When classified according to levels of lead concentration, three main stages emerge for the Twelve Imperial Coins. The first stage comprises many coins from the Wadokaichin through the Ryuhei Eiho, which had low levels of lead concentration, mainly ten percent or less. The second stage consists of coins from the Fuju Shinpo through Kanpyo Taiho, which had generally high concentrations of lead ranging from ten to forty percent. In the third stage covering coins from the Engi Tsuho through to the Kengen Taiho, there emerged lead coins, though all coins of these types were not lead. It is believed that these changes occurred because it gradually became more difficult to obtain copper used for minting coins. This was due to the decrease over time in the amount of copper that was mined and the waning power of the Ritsuryo state, which eventually led to its inability to get hold of copper from mining regions.

We are also able to learn of changes to techniques from impurities contained in the coins. Wadokaichin, Man'nen Tsuho and Jingo Kaiho coins from the Nara period, the first three of the Twelve Imperial Coins, contain several percent iron, whereas virtually no iron was found in Ryuhei Eiho coins and other types issued from the Heian period onwards. It is hard to believe that iron would have been deliberately mixed in, as mixing iron with copper lessens copper's metal properties. We may assume that copper pyrite (CuFeS2), which consists largely of ore which contains iron, was used as the raw material and that smelting techniques for removing iron changed around this time.

Because it is written in the Shoku Nihongi that "copper (written as "wado") was produced in Chichibu county in Musashi Province" in the same year that Wadokaichin coins were issued, these two events have been linked, leading to the commonly accepted theory that Wadokaichin coins were made from this copper. In fact, the characters read as "wado" do not refer to "(the first) copper made in Japan", but are read "niki akagane" meaning "smooth copper". That is to say, "wado" refers to "natural copper", which is copper that is already a metal and does not require smelting.

鉛同位体比を測定する装置 抽出した鉛を載せるフィラメント
System for measuring lead isotope ratio (thermal ionization mass spectrometer) Extracted lead is placed on this filament

Researchers studying ancient Japanese coins have for many years advocated that there was no direct relation between the production of copper and Wadokaichin coins, and that as methods for minting coins already existed the word "wado" was used for political reasons as it was viewed as a good omen for commencing coin production. Our analysis using natural science methods also supports this contention. Lead contains a mixture of four atoms (isotopes) which have the same properties and vary slightly in weight. We analyzed the Twelve Imperial Coins to determine the regions of origin of the raw materials using the lead isotope ratios of the coins, which reflect the surrounding geological conditions and vary according to mineral deposits. We found that the lead isotope ratios of nearly 80% of coins from the Shinwado onwards were concentrated in a certain numerical range. We then analyzed samples taken from mines where copper and lead were mined and smelted during the same period and from nearby archaeological sites. This revealed that the measurements for the coins matched those of items taken from the Naganobori mine and the nearby Hirabaru site in Yamaguchi Prefecture and from the Sakabe site near the Zoumeki mine. In other words, there is a strong possibility that these mines supplied the main raw materials used to make the coins.

Most of the measurements taken from the Kowado coins did not fall within this range, and regions of origin of their raw materials have yet to be sufficiently narrowed down. But since in both cases we did not find any coins that displayed similar values approximating those of the Chichibu mine, for the time being it is unthinkable that there is a direct link between "wado" copper and Wadokaichin coins.

皇朝十二銭
Twelve Imperial Coins (Museum collection) The change in size is clear

The minting of coins was carried out by an organization called the "Chusenshi", which in those days was called "Juzen no tsukasa". Records show that it was located in Kawachi, Nagato and Suo. Although there are no records that mention the quantities issued for each type of the Twelve Imperial Coins, a comparison of quantities that have been excavated shows that an overwhelming number are Wadokaichin coins. Also, coins that have been excavated comprise mainly of the Man'nen Tsuho, Jingo Kaiho, Ryuhei Eiho and Fuju Shinpo types issued from the Nara period through to the early Heian period, while there are lesser quantities of later Jowa Shoho through to Kengen Taiho coins. Coins gradually became smaller in size due to a shortage in copper, the need to cut back on minting costs and the diminishing value of the coins caused by the successive issuing of new coins. The quality of the coins deteriorated and they contained more lead, as mentioned earlier. This gave rise to a vicious cycle which caused inflation and made people no longer like the coins. The fall in the value of the coins made them less useful as currency, and this coincided with the disappearance of large state-funded infrastructure projects, making the issue of coins less important. The minting of the Twelve Imperial Coins ended with the issue of the Kengen Taiho coins in 958.

Although coins were used in large quantities during the medieval period which followed, this had nothing to do with the power of the state, but came about as the result of brisk trading activities. These coins were not issued by the government, but were mainly so-called "foreign coins" such as Sung and Ming dynasty coins which were imported to Japan from China. Japan did not resume the large-scale issuing and distribution of coins on its own until the creation of the Tokugawa shogunate's three-currency system in the Edo period.

Tsutomu Saito (Science of Cultural Properties, Research Department)