Iron and Steel Technology in Japanese Arms & Armors - Part 1: Iron Sources

Iron and Steel Technology in Japanese Arms & Armors - Part 1: Iron Sources

Japanese blacksmith in an Edo period print,  Switzerland, Museum of Ethnography of Neuchâtel, sources here

If you are into swords and armors to some extent, you might have fallen into archaeometallurgy and science; if this is the case and you want to go deep inside the nature of Japanese metal artifacts during the middle ages , you might found this series of articles interesting.
Although the history of Iron in Japan is rather long and old (yet not the oldest as someone claimed in the past!) this series will be specifically dedicated to the late Muromachi and Azuchi-Momoyama period (namely the 16th century).

I'm far from being an expert, and actually I'm still learning a lot in this field, so that's my disclaimer:

I might have missed something here and there, and I might be wrong since I don't have neither the experience nor the academic background to be precisely accurate. Please take these information with a "pinch of salt".
Despite this limitation, I'm using academic references that you can find throughout the article to back up my thesis.

However this has been a topic in my researches for quite a long period and I've been able to collect a lot of information and references that I'm going to share with you. I'll try to be as simplistic as possible, and if there is someone with actual experience please feel free to correct me or leave suggestions in the comment!

This article is the first part of a series which would describe the iron & steel technology found in the Japanese arms & armors.
The Part 1 would be dedicated to the Japanese iron sources.

Iron sources used in Japan

Iron is one of the commonest element found on earth's ground and is widespread all over the world. In nature is always bounded with other elements, and although it might not be the scientific terms, I've decided to call these chemical compositions "raw iron"; this paragraph will be dedicated to the raw iron sources used to create metal artifacts.

There are a lot misconception regarding the iron quality and quantity of the Japanese arcipelago.
The first one is in its raw quality; there were different types of iron ores which were used in Japan during the 16th century: iron sand called Satetsu (砂鉄), iron ore called Mochi Tetsu (餅鉄) and foreign iron/steel billets from China, India and possibly Europe generally called Nanban Tetsu (南蛮鉄). 
The domestic Satetsu is probably the most known and the most used back in the days.


Mochi Tetsu (餅鉄):

This type of Iron ore was extremely high in purity with an average iron content of 60%. It was similar to the famous Swedish iron in composition and gave a high quality reduced iron.
Its name is given by the fact that the ores that were collected resembled a mochi cake. Little to nothing is known about its production or use, but we do know that it was produced in the Tohouku region (present day Iwate region) since the middle ages, where it was found in large quantities.

This type of iron had significant advantages both quantitative and qualitative over the mainstream iron sand method.
It was also low in sulfur and phosphorus, two elements harmful to the quality of steel, although no data are available for a comparison with Iron sand.
It was far easier, faster and cheaper to obtain Kera Ingot and Zuku from Mochi Tetsu rather than with Iron sands, and the final product will be of high quality.
It was an important asset (due to all of its benefits), and was often mixed with the others types of iron sources; however nowadays nobody seems to care about mentioning it.

(Reference:
"Origin and development of iron and steel technology in Japan" by "Kenichi Iida")

An example of Mochi Tetsu

Nanban Tetsu (南蛮鉄):

As the word suggest, Nanban refers to foreign type of iron and steel; unlike the other "raw sources", this type of iron was already smelted and it came in the form of Hyoutan (瓢箪) ingots, and it was divided into different categories.
It was usually imported by the Europeans (especially by the Dutch during the Edo period) and its origin is unknown; it could be European, Indian or Chinese (or Korean too).
In respect of Chinese and Korean iron ingots, they were directly acquired by trading or by the Wokou raids and have been imported to Japan at least since the Kofun period.
As for the quality of these imported ingots, especially the one imported by the Europeans, contrary to the internet's average opinion, these type of steel and iron ingots were high in sulfur and phosphorus and thus weren't necessarily better than the native refined iron sources.
Even the well known author Sakakibara Kozan (which would be mentioned in another article) said that Nanban tetsu wasn't great for armor plates due to its brittleness (yet is fair to notice that other sources according to the same author, like the Honzou Koumoku, said that this type of steel was great for swords).
It is also important to notice that despite being imported by the Europeans, it is likely that this types of ingots didn't came from Europe, since they had centers of production in India and other regions of Asia.

However, not every single ingots of Nanban Tetsu was likely to be low quality; like anything in this world, good and bad quality items coexisted.
It is fair to highlight that the flow of this foreign resource was mandatory to meet the high demand of iron during the late Sengoku and early Edo period.
In fact, some swords and some matchlock arquebus were produced with Nanban tetsu and signed to highlight this unique "exotic" features of being made with foreign steel or iron.
It is interesting to notice that the oldest sword with this feature was made in the 1600s, which seems in contradiction with the fact that Nanban tetsu was traded at least from the 1550s.

Recent theories have also highlighted that inside this category, the famous and well known wootz steel could have reached Japan, but the field is still pretty much unexplored.
It could be possible however, since almost every sources agree on its average high carbon content, but that's far from having any serious proofs.

(References:
"Effect of Phosphorus Content of Nanban-tetsu on Forgeability of Japanese Sword Making" by "Takuo Suzuki".

"The The Connoisseur's Book of Japanese Swords" by "Kōkan Nagayama".

And for those interested here there is a project talking about Nanban tetsu!)

An example of hyoutan nanban tetsu ingots, source here

Satetsu (砂鉄):

The most famous and widespread raw iron source used in Japan, the Japanese iron sands have a bad reputation on the internet for being a low quality iron source.
As I've written before, however, this wasn't the only source of iron in Japan, and although the mainstream type, it wasn't used as much as people might think compared to the other sources.
It was only in recent times, when the "sword making art" was resurrected, that the Japanese themselves pushed a lot on the "iron sands thing" since it was quite unique to Japan, and you know, unique things sell better.
I wanted to stress it because it seems that nobody is aware of the purer mochi tetsu or that they also had access to Indian and Chinese iron ingots.

Talking about its quality: in the case of iron ore, it is determined by the amount of iron content; Japanese iron sands are usually really low, about 2% to 5% (yet it is fair to highlight that the iron sand found in the Chugoku region, which was known to be the top quality, has a 58% iron content).

However, the lowest quality iron sand was purified and harvested in a precious way to reduce the number of impurities and the final result turn out to be of good quality; in regard to this fact, compared to some European iron sources, it was lower in phosphorus.
In addition to that, some type of Iron sand was high in manganese and vanadium, which increase the strength of the steel.

So to sum it up, raw iron sand is quite low quality, refined iron sand is perfectly fine in quality.

Iron sands was found in high quantities all over the arcipelago, and it was concentrated in the Chuugoku region.
Satetsu could roughly divided into three categories: Masa, Akome and Hama.
Masa satetsu was considered the highest in quality among the three, and it was used to produce the famous Tamahagane.
The sand was "harvested" through the Kanna nagashi method, where water was set to flow down a particularly steep mountain slope to degrade weathered granite rocks containing iron sands so that the washed raw iron sources were deposited in a pond at the foot.

The process is also called Suiro hashiri, or “running the waterway.”
The concept is similar to panning for gold: ore-washing facilities would be comprised of four washing ponds with higher quality sand present after each wash.
The ore gradually sorted until iron sand constitutes up to 80% of the material collected. The lighter earth drifts downstream, while the heavy iron sand sinks to the bottom.
Extremely pure iron sand can be sorted out through repeating the process.
However it is easy to see how long the process of acquiring good purified raw iron sand could be.

(References:
"Origin and development of iron and steel technology in Japan" by "Kenichi Iida"

"Art of the Japanese Sword: The craft of swordmaking and its appreciation" by "Y. Yoshihara, L. Kapp, H. Kapp"

"Hitachi Metals Co." )

An example of iron sand "animated" by a magnet; traditional Japanese iron sand wasn't that pure because it wasn't collected with a magnet, but this is not a real issue since most of the impurities were lost in the smelting process, which would be covered in the next article of this series.

Reclaimed materials:

Last but not least, it is important to acknowledge that in every pre-industrial country in the world, recycling was fundamental, and while resources were rare and expensive, manpower wasn't.
Wasting something was not accepted and reusing old materials was a fairly common practice.
S. Kozan mentions that "Disused hoes and spades afford the best inner iron for plates". Each single fragments of steel, be it a sword's broken edge or a common nail, was recycled and mixed with raw iron sources, especially during the Sengoku Jidai were the demand of iron and steel to make arms & armors was incredibly high.



Quantity of Japanese native iron sources

Together with the quality issues (which as I have written in the previous paragraph are far from being true) another issue regarding the (in)famous Japanese iron is its quantity.

You might be already familiar with this fact; Japan is an iron poor country. And this is true, nobody could denied it. 
But things need to be put under the right context.
It is true only if we look under the perspective of a post-industrial revolution world, were the volume of products are incredibly higher compared to the past.

During the 16th century, despite the fact that the demand of iron was at its peak, the Japanese didn't run out of iron and were able to produce iron artifacts well beyond the Edo Period.
Iron (and especially high quality steel) was rare and expensive all over the world until the Bessemer method.
It is quite unfair to claim that Japan had bad iron, in low quantities when using modern days standard; because through this lens, every other nations would have had the same problem!
On the contrary, during this period, Japan had a well developed industry of arms and armor that allow the armies of this age to equip themselves with cheap and mass produced armors and weapons (together with high end examples as well), something that would not have been possible for an iron poor nation, especially when the government was decentralized and every regions had its own centre of production.
There are also some European sources from the 17th and 19th century that deal with the quantity of iron found in Japan;

A map of Japan, drawn by G. Mercator (1512-1594); By Georges Jansoone (JoJan) - artwork by Gerardus Mercator (Own photo by uploader at an art auction in Belgium) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

In the "History of Japan - together with a description of the kingdom of Siam" by Engelbert Kaempfer,written in the late 1600s, he wrote that:

"Iron is dug up only upon the confines of the three provinces Mimasaka, Bitsju and Bisen. But is found there in large quantities. It is refin'd upon the spot, and cast into Staffs or Cylinders, two spans long. Japanese Merchants buy it at the place, and export it all over the Empire."

While inside the "Recollections of Japan: with Observations on the Geography, Climate, Population, and Productions of the Country" by "Vasiliĭ Mikhaĭlovich Golovnin" who stayed in Japan from the 1811 to the 1813, there is written:

"With respect to iron, the Japanese do not posses that metal in such abundance as copper, but they have sufficient to supply their absolute wants; and if the government exchanged with the Dutch, copper for iron, this was not out of necessity, [...] If the Japanese had not iron sufficient for their absolute wants, they would certainly set more value on the trade with the Dutch"

Also, regarding the trade with the Ming dynasty in the 15th and 16th century, it was estimated by Markus Sesko that about 128.000 swords were brought to China with nine expeditions, and within the last ones, an average of 17 swords per day were made! And this is only a minimal fraction of the picture, since also spears, armors and other iron works were brought in the mission together with the swords.
Not to mention that to produce a swords, a lot of the starting material is lost in the process.

Emperor Yongle (永樂) from the Ming Dynasty, the man who started the trade with the Japanese.

The majority of the aforementioned swords traded were mass produced, and weren't product of high end quality, so there was indeed an emphasis on quantity over quality in this case, something that would not have been possible to follow for an iron poor country.
By the end of the 16th century, it was estimated that Japan was able to produce 1000 metric tons of steel per year, and even with the isolation policy followed by the Shogunate during the Edo period, which didn't see any significant improvement except few minor changes in the production system, the Japanese were able to produce 10000 metric tons of steel per year, without an huge amount of foreign supplies (according to the "Art of the Japanese swords: The craft of swordmaking and its appreciation" by "Y. Yoshihara, L. Kapp, H. Kapp").

Last but not least, there was a comparison done by "Hiroshi Arai - Iron Prices in Ancient Japan and the International Comparison" which dealt with the prices of the iron in Japan, Europe and China through out their entire history.
The outcome of that research underlined the fact that prices were similar in both countries with minimal variations. More important than that, the prices went down with time, a situation that was possible with the development of more efficient processes.

To sum it up, Japan didn't have any substantial lack of iron sources to make steel and iron artifacts until the 20th century.
During the 16th century, with native production (which was expensive and time consuming for the reasons I will explain in the next article) and foreign trade with Ming and with Europeans, the demand of iron was perfectly satisfied and even the most basic foot soldier was able to acquire cheap munition armor and cheap weapons.
In fact thanks to the amount of iron available to the country, the warlords of Japan were able to raise huge armies of Samurai and Ashigaru armed with arquebus and spears.

(Please, note that don't lacking iron sources to match the demand is not the same as saying that in Japan, during the 16th century, there was an abundance or iron and steel artifacts or that the widespread usage of munition armor implied that there was a modern day level of production; my emphasis here is to debunk the average idea of the Samurai having to use non-metallic armors because the lack of good quality iron sources, which is far from the truth as I've hope to have shown to you with all these references)


If you have any questions, corrections or advise please feel free to leave a comment, and if you liked this article feel free to share it, I will appreciate it! Thank you for coming at this line through this massive and technical article!
If you want to continue with this series,  the second part: "Smelting process" is available!

Gunbai