1. What a Pencil Core Is Really Made Of: Graphite and Clay, Not Lead
When you look at a pencil core, it appears shiny, black, and heavy, like a metal. However, science explanations state that the core is made mainly of graphite and contains no lead; it is made of carbon [1]. Graphite is a mineral made only of carbon. Dictionaries describe it as one of the "allotropes of carbon," a term for substances made of the same element but with different atomic arrangements [2]. It is used in pencils and as a lubricant to make things slide easily.
Actual pencil cores are made by mixing graphite with clay. According to explanations from Mitsubishi Pencil, the hardness of the core is determined by the ratio of clay to graphite [11]. This raises a question: if there is no lead, why is it called a "lead pencil" in Japanese?
2. Why People in the Past Mistook Graphite for Lead Ore
In the past, graphite was called "black lead" or "plumbago" in English. The word "plumbago" comes from the Latin word for lead, plumbum. Both names are said to have arisen from a confusion with lead ores, especially galena, because they looked very similar [4]. Galena is an ore used to extract lead. Although their contents are completely different, they were grouped together as "lead" because of their appearance.
The problem is that the name stuck. In English, the black core of a pencil is still called "lead" today. It is explained that the core has never actually contained the element lead [7]. The similarity in appearance alone invited the same name.
3. How Scheele Showed Graphite Was Not Lead and Werner Gave It Its Name
A turning point came at the end of the 18th century. In 1778, the Swedish scientist Scheele showed that graphite, molybdenite, and galena were each different minerals [4]. This showed that graphite, molybdenite, and galena were different minerals. The following year, in 1779, mining materials report that he showed graphite becomes carbon dioxide when oxidized, revealing it is made of carbon [5]. These are separate achievements in 1778 and 1779.
Then, in 1789, the German mineralogist Werner named it "graphite," after the Greek word graphein, which means "to write" [6]. He named it after its use: "the stone for writing." Even though it was proven not to be lead and given a new name, the "lead" character remains in the Japanese word for pencil.
4. How the Layers of Carbon in Graphite Slide and Leave Marks on Paper
In graphite, carbon atoms form hexagonal rings that spread out in flat planes. These planes stack on top of each other. Dictionaries call this a "layered structure" [2]. According to an announcement by the Japan Science and Technology Agency (JST), we can write smoothly with pencils because the layers slide over one another and peel away easily [3].
Graphite is one allotrope of carbon, and diamond is another. Even though both are carbon, their properties are completely different just because the arrangement of atoms is different [2]. Pencil cores write because graphite has layers that can peel away. It makes sense to think that the line drawn on paper is what remains when layers peel off as the pencil moves.
5. How the Ratio of Clay to Graphite Decides a Pencil Core's Hardness
The hardness of a pencil core is determined by the ratio of graphite to clay. For example, an HB pencil has a ratio of 7 graphite to 3 clay. This is just one example; other hardness levels have different ratios [11]. The more clay there is, the harder the core becomes, and the lighter the color.
H stands for Hard, and B stands for Black. The higher the H number, the harder and lighter the mark; the higher the B number, the softer and darker the mark [10]. The person often credited with this method is Conté from France. In 1795, he devised a method of mixing graphite with clay and firing it, finding that changing the mixing ratio changes the hardness [9]. This is the basic method for modern pencils. However, there is also a theory that Hartmuth from Austria found a similar method slightly earlier [10]. It cannot be said that it was Conté’s invention alone.
6. How Pencils Came to Japan and Why the Japanese Word Includes "Lead"
Dictionaries state that the "lead" in the Japanese word for pencil comes from the fact that lead was used in the past [10]. In the late Edo period, pencils were called "stone pencils." This was a translation of the Dutch word potloot (meaning potter’s lead), which was originally a product name for Spanish graphite [10]. The Kunozan Toshogu Museum holds a pencil about 6 cm (about 2.4 inches) long, said to be a relic of Tokugawa Ieyasu. There are no records of how it arrived [9].
Masaki Jinroku challenged domestic production. After seeing pencils at the 1878 Paris World’s Fair, he aimed to produce them in Japan. In 1887, he opened the Masaki Pencil Manufacturing Company in Naito-Shinjuku, Tokyo [12]. This became Mitsubishi Pencil. Mass production technology did not exist in Japan. He tried making cores by mixing graphite with clay and firing them on his own. It is said that it took about 10 years from deciding to make pencils in Japan to producing usable ones [12]. Some sources list the founding year as 1886, showing discrepancies in records.
7. A Simple Experiment: Checking a Pencil Line on Paper with Your Fingers and Eyes
Prepare a pencil and paper to try the following. First, press the pencil hard on the paper and shade it black. Lightly rub the shaded part with your finger. Black powder will stick to your finger. This lets you verify with your fingertips the story that graphite peels off easily in layers.
Next, draw lines of the same length with H and B pencils and compare their darkness. Compare the lines, and consider whether they fit the explanation that cores with more clay are harder and lighter in color [11]. If you have a magnifying glass, look closely at the ends of the lines. Write down what the lines look like in a notebook.
If you want to learn more, you can start with the dictionary entries for "graphite" and "pencil" [2][10]. The official Mitsubishi Pencil website also has information about cores [11].