墨ができるまで

Until Ink Stick is made

What is "Sumi"

Ink, simply put, is made by mixing glue (nikawa) that has been gently heated in a water bath with soot, then drying and solidifying the mixture.

Nikawa is a gelatinous substance made by boiling down animal hides or tendons to extract collagen, which is then filtered and refined. It resembles a kind of natural gelatin. You might wonder, “How is this different from gelatin?” The answer is that gelatin is further refined to remove as many impurities as possible, resulting in a highly purified product. However, when the purity is too high, it loses its moisture-retaining properties, making it unsuitable for ink-making. Nowadays, since gelatin is used in cosmetics and food products, it is often refined to a high degree of purity, making it increasingly difficult to obtain high-quality nikawa for ink.

Additionally, the glue used in Chinese ink is often derived from fish skin, which has weaker adhesive properties than glue made from animal sources. As a result, Chinese ink typically contains a higher amount of glue, making it harder.

Soot refers to carbon particles produced by the incomplete combustion of oils or pine resin. Ink made using soot derived from oil is called yuenboku (oil soot ink), while ink made from soot collected from pine resin is called shōenboku (pine soot ink). Soot can also be collected from other types of plants. Oil soot ink can be further classified into two types: one made from soot collected from plant-based oils such as sesame oil, rapeseed oil, or hemp oil; and another made from soot derived from mineral oils (like naphtha).

If the soot particles are fine (small), the ink produces a lighter tone but has good flow. On the other hand, if the particles are coarse (large), the ink appears darker but has less fluidity. Fine soot is difficult to produce in large quantities and is therefore expensive, whereas coarse soot can be collected in larger amounts, making it more affordable. Depending on what you are writing or painting, try using different inks to enjoy a variety of expressive qualities.

What is the difference between solid ink (sumi) and liquid ink?

The key difference between traditional solid ink (sumi) and liquid ink lies in the presence of additives such as preservatives and anti-coagulants. As previously mentioned, the ingredients of solid ink are simply nikawa (animal glue) and soot. In contrast, liquid ink is made from carbon black or soot mixed with a resin-based binder or nikawa, to which various additives—such as preservatives and anti-coagulants—are added.

These additives help maintain a consistent color and density, making liquid ink convenient and ready to use. However, they can damage your brushes over time. For this reason, we recommend using separate brushes for traditional ink and for liquid ink. This is especially important for wool (goat hair) brushes, which are more sensitive. Even if a product claims to use nikawa in its liquid ink, that does not mean it is safe—all liquid inks contain some kind of preservative or stabilizer, so please be cautious.

We often hear people say that they mix liquid ink with traditional ink by grinding them together, but this is strongly discouraged. The additives in liquid ink dry into a solid coating that does not dissolve, and when liquid ink comes into contact with a solid ink stick, it coats the grinding surface with preservatives. This makes it difficult, or even impossible, to grind the ink properly afterward. The same applies to inkstones—the surface may become coated and lose its grinding ability.

If you choose to use liquid ink, we recommend using an ink well (bokuchi) or a ceramic dish instead of a traditional inkstone (suzuri).

The Process of Making
Ink Sticks

collect soot

Methods of Collecting Soot Differ Depending on the Source:

Plant-Based Oil Soot, Pine Soot, and Mineral Oil Soot

● Plant-Based Oil Soot

Oils such as hemp oil, sesame oil, and rapeseed oil are poured into an unglazed dish. A specially braided wick is soaked in the oil and lit (similar to an alcohol lamp). A lid is placed above the flame, and the soot rising from the burning oil adheres to its underside. This soot is continually swept off using a feather brush and collected.

To produce high-quality soot, a thinner wick is used to create a smaller flame. The smaller the flame, the greater the distance between the flame and the lid. Because finer soot particles can travel farther, this allows finer soot to adhere to the lid. However, this method yields only a small amount of soot at a time and requires great care and time, making the soot expensive.

Today, soot is also collected using an automatic soot collection machine (also known as a "channel"). Soot collected by this machine is used in more affordable ink products.

● Pine Soot

Pine resin is burned in the center of a room enclosed with sliding paper doors (shōji) on all sides and the ceiling. The room is then sealed. Inside this sealed space, the pine resin undergoes incomplete combustion, producing soot.

Once the resin has burned out completely, the room is opened and the soot that has adhered to the shōji surfaces is collected. Because this method produces soot with a wide range of particle sizes—from very fine to coarse—large amounts can be gathered at once. However, the varying particle sizes result in ink with subtle differences in tone and color.

In the past, pine soot ink was the standard due to the abundance of soot produced. However, with the rise of mineral oil soot and carbon black, pine soot ink has become less common and is now produced in smaller quantities, making it relatively more expensive.

● Mineral Oil Soot

Naphtha, a by-product of heavy oil, is burned incompletely inside a silo. The resulting soot adheres to the inner walls of the silo. Soot that collects in the lower areas tends to have larger particles, while the soot near the top consists of finer particles.

Soot is collected and sorted based on where it settled—upper, lower, or middle areas—each with different particle sizes suited to different ink qualities.

The molding of ink sticks is typically done from early morning to late morning, during the cooler months from around October to April. In particular, the production of high-quality ink is limited to the coldest period of the year—between Shōkan (Minor Cold) and the Spring Equinox.

Recently, however, rising temperatures have shortened the window of time during which this delicate work can be performed.

Collecting soot from rapeseed oil smoke...
It’s generally dark and hard to see clearly, but a plate is placed above the flame to collect the soot.

Automatic soot collection machine...
Soot is collected by applying a flame to a rotating rod, causing the soot to adhere to its surface.

Dissolving the Glue (Nikawa)

The glue (nikawa) is dissolved by heating it gently in a water bath and then thoroughly filtered through silk. This glue is produced by specialized manufacturers separate from the ink-making process. Currently, there are few producers of high-quality glue, making it difficult to obtain.

kneading

The process of mixing soot with glue is called “neriawase” In the past, this was done in a sealed room where a small fire was lit in a stove. A large cedar board was placed over the fire, and about one kin (approximately 600 grams) of soot was spread evenly on the board. Then, about eight ryō (approximately 240 grams) of hot, well-dissolved glue was poured into the soot, and the mixture was kneaded like making udon dough until it formed a dough-like ball.

Next, fragrance materials were added, and the mixture was kneaded with force until it gradually developed a glossy sheen. The dough was then divided into three portions; two were kept warm by carrying them close to the body, while the remaining one was kneaded further.

Today, machines can handle kneading the mixture into dough balls, making the process somewhat easier. However, it used to be a very labor-intensive task.

The main fragrances used are borneol and musk, which are quite expensive, so most modern production uses synthetic versions of these substances. Additionally, red pigments are sometimes added to enhance the blackness of the ink color.

mold pressing process

Next, the ink is placed into molds. Long ago, ink molds were made of iron, but nowadays they are made from wood such as loquat or pear. The molds vary in size, thickness, and shape. Each mold consists of three wooden boards: the middle board sets the thickness of the ink stick, while the top and bottom boards are carved with patterns, designs, or characters.

A measured amount of well-kneaded ink paste is placed into the mold, and pressure is applied to form the ink stick.

Kneading Process…The soot and glue dissolved by gentle heating in a water bath are first mixed together using a mixer. Once the mixture reaches a certain consistency, it is kneaded by foot, and finally, the kneading is finished by hand.

mold pressing…The mixture of glue and kneaded soot is placed into molds. Although this work is done during the cold season, the metal plates are heated with heaters to prevent the ink from hardening prematurely. Once the work begins, it becomes physically demanding and workers often sweat profusely.

Drying

After leaving the ink sticks in the molds for a set period, they are removed and placed into a bed of clean ash free from impurities. This ash is spread inside a wooden box called an ash vat. On top of the ash, Japanese paper dyed with persimmon tannin is laid, then the ink sticks are arranged on this paper. Another layer of the dyed paper is placed over the ink sticks, followed by another layer of ash. The whole setup is placed in a wind-free location.

This daily replacement of ash is called “ash changing.” At first, moist ash is used, and gradually drier ash is added as the process continues. After one day in the ash, any flash (excess edges sticking out from the mold) on the corners of the ink sticks is carefully shaved off with a small knife. The shaved-off ink is known as “shaving ink” and is also used.

(Currently, newspaper is used instead of persimmon-dyed paper.)

Depending on the weather, small ink sticks undergo ash changing for 7 to 10 days. Larger ink sticks (such as the juttchō size) require 30 to 50 days of ash changing. Rapid drying must be avoided, so many years of experience are required to adjust the process according to temperature and humidity.

After ash changing, the ink sticks are moved to shelves for shelf drying. At Nanmatsuen, they are aged for at least three years before being sold.

Ash drying…The ink sticks are placed in moist ash and gradually dried.

Air drying…After the ash drying process is complete, the ink sticks are arranged on shelves or hung up to dry naturally.

Finishing

After the drying process is complete, the ink sticks are polished and decorated before shipment as finished products. Each ink stick is hand-painted with gold or silver according to the design, then individually wrapped in Japanese paper and packed into paper boxes or paulownia wood boxes for completion.

Polishing process…Polishing the ink sticks with clam shells produces a glossy surface. The shiny ink sticks shown in the photo on the right have undergone this polishing.