The primary reason is the lead content of the pencil. Lead is a chemical element in which four elements have identical chemical symbols, called the four atomic numbers. Carbon, the principal element in pencil lead, is an element with an atomic number of 22. Lead is commonly known as “white stuff” or “natural lead”. Lead was used in writing in the form of paper or crayons for thousands of years because it had the same use as the older form of printing paper. Lead can be used for purposes such as binding and inscribing. Because of the nature of their usage, lead pens are yellow.
In addition to the natural color of the pencil lead, the color is formed by adding a pigment known as pigments, including lead salts, to the oil and water of the pencil. These particles create a yellow dye, which is absorbed by the human eye and converted to color. The presence of lead pigment and or the presence of paint is the most likely explanation of why the color is yellow. A few natural compounds, such as linseed oil and linseed oil dyes, contain yellow oxides of lead, but this is the only example I know of where an additive has been identified. One other factor is probably significant: the oil used in the manufacture of lead pencils is a vegetable oil that may contain lead. In recent times lead has been banned from food packaging because the use of leaded-tobacco cigarettes in the 1950s and 1960s led to the decline of their use in that country.
Lead is a powerful pigment and is the primary source of pigments in pencils. Pigments do not have a color, but they have the ability to change from red to yellow, from red to green, or from green to blue. If a pigment contains an oxide, such as the lead in the pencil, the oxide may change color depending on the presence or absence of other substances present in the pigment. Because pigment is created from a chemical reaction involving carbon, water and sulfur, it is important to understand the chemical properties of pigments before using them to color paper.
Oxygen The oxygen that is present in pencil lead is the simplest component of paint. Like pigments, oxygen acts as a catalyst to the formation of chemical compounds. The process of using oxygen in paints and pencils begins with the addition of carbon and other elements. For most colors on paper, however, the solution of carbon, oxygen, water and some sulfuric acid (the primary component