1. Why Museums Light Each Japanese Sword with a Single Light
At the Japanese Sword Museum in Tokyo, each Japanese sword is illuminated by a single light source positioned above and to the front. This display method is designed specifically to help viewers see the steel grain and the blade pattern. [4] Swords receive this special attention to lighting because their patterns become easier to see when light hits them. [3]
Viewers are also encouraged to adjust their position. Exhibition guides suggest crouching or stretching to view the sword from different angles. If you have a monocular, you can see even finer details. [3] Curators note that seeing the steel grain can be difficult for beginners. They recommend looking not just from the front, but also by crouching or peering from the left and right sides to make discoveries. [4] Japanese swords are artworks that require you to move your body to find the light, rather than just standing still and staring.
However, moving around is not enough if you do not know what to look for. Where exactly are the points of interest?
2. Three Things to Look At: Shape, Steel Grain, and Blade Pattern
In 2019, the Japanese Sword Museum organized a three-part series focusing on the basics of appreciation: "Shape," "Steel Grain," and "Blade Pattern." [1] Dividing the viewing experience into these three categories is a good entry point.
"Shape" refers to the overall balance of the sword, involving factors like the curve, width, and thickness. Examining the shape provides clues to roughly determine the era in which the sword was made. [9] The recommended order of viewing is to look at the whole first, and then the details.
The "Blade Pattern" (hamon) is a line-like pattern that appears due to hardening techniques. It is categorized into types such as straight lines, gentle waves, clove-shaped forms, and alternating rounded peaks. [2]
The "Steel Grain" (jigane) is a pattern that appears in the black parts of the blade, related to processes like folding and forging the iron. Because it resembles the cross-section of wood, terms like "board grain," "straight grain," and "burl grain" are used. [2]
Among these three, the blade pattern has clear shapes and is the easiest for beginners to find. So, how do these lines appear on the sword?
3. How Clay and Heat Create a Sword's Blade Pattern and Curve
The blade pattern is created by applying a clay mixture called yakiba-tsuchi to the blade and then hardening it. The spine, where the clay is applied thickly, cools slowly and becomes a steel structure called pearlite. The cutting edge, where the clay is thin, cools rapidly and becomes hard, forming a structure called martensite. [7]
A research team including Shimane University states that this partial hardening—applying thin clay to the edge to speed up cooling and create hard martensite—is a feature not seen in other swords. The edge is hard, while the center and spine are relatively soft. This structure is considered the reason for the sword's ability to cut well without breaking or bending. [8]
Thus, the blade pattern is a mark of the hardening process. That same hardening process is also a technique to finish the edge. Beneath the visual beauty lies the ingenuity for cutting power.
Another surprise is that the difference in cooling rates is also explained as the cause of the Japanese sword's curve. [7] The curve of the shape and the blade pattern are not separate decorations; they are like siblings born from the same hardening process.
So, how is the pattern on the opposite side, the steel grain, created?
4. How Folding Iron Creates the Wood-Like Steel Grain
The origin of the steel grain pattern is the forging process of folding the iron repeatedly. An explanatory sheet from the Ministry of Land, Infrastructure, Transport and Tourism explains that steel is folded repeatedly to create a dense steel with about 33,000 layers. When polished, these layers appear as various patterns such as straight lines, waves, or wood grain. [7]
The figure of "about 33,000" is cited in the explanatory sheet. To grasp the magnitude of this number, we can calculate simply: if the number of layers doubles with each fold, 2 to the 15th power is 32,768. Therefore, about 33,000 layers corresponds to roughly 15 folds. This is a calculation to understand the scale, not a record of the actual process.
While 15 folds might sound few, the layers double each time, so the simple calculation gives roughly 33,000 layers. These layers appear on the polished surface, making them resemble patterns in a wood cross-section. This visual similarity is why wood terminology is used for the steel grain. [2]
Thus, we can see that the curve of the shape and the blade pattern are traces of hardening, while the steel grain is a trace of forging. How far can we learn about the maker from these patterns?
5. How Steel Grain and Blade Pattern Help Identify a Sword's Maker
According to a report on a sword appreciation meeting, one can narrow down the identification range: the steel grain can indicate the country or school, while the blade pattern can point to the individual maker. [5] Reading the patterns is also about looking for the habits of the person who made the sword.
There are manners to observe during appreciation. Unlike iai (sword drawing) or sword dance, viewing Japanese swords is a quiet activity. You must face the light source directly and not swing the sword left or right. This is dangerous because many people stand side by side. [5]
At appreciation meetings held by the Association for the Preservation of Japanese Art Swords, participants can hold actual swords. Because the edges are sharply polished and prone to scratches or rust, only course participants may attend, and a manners course is provided. Participation is generally for those aged 16 and older. [6]
Therefore, for children or first-time viewers, looking at swords in museum display cases under the light is the most accessible entry point. You move your own body while viewing through the case.
Is there any practice you can do at home before visiting a museum?
6. Why Steel Grains Are Named After Wood, and How to Test It with Wooden Boards
The terms "board grain," "straight grain," and "burl grain" are used for steel patterns because they resemble the cross-section of wood. [2] You can explore the origin of these terms using wooden boards at home.
Find a wooden board in your house, such as a tabletop or a wooden cutting board. Darken the room slightly and shine a flashlight from near the surface of the board at an angle. Do not use fire. Be careful not to scratch used cutting boards or furniture.
Look at the wood grain lines while changing the angle of the light and your eye position. As examples of wood grain, you may see straight lines, mountain-like curves, or swirls, and the pattern depends on the kind of board. Even on the same board, the appearance changes depending on the direction of the light. This is the same movement as crouching or looking from the left and right at a museum.
If you can go out, look for museums that display swords, such as the Japanese Sword Museum or Kyoto National Museum. You can check schedules and exhibition contents on their official websites. If you find the lines of the blade pattern under the light, know that they are traces of clay coating and hardening.
For those who wish to consult original sources, the Kyoto National Museum's sword guide and the Ministry of Land, Infrastructure, Transport and Tourism's multilingual explanatory sheet "Evaluation of Japanese Swords" are good starting points.