Carbon pen is one of the most stable substances, graphite, which is composed of graphite. Carbon pen writing can not become confused because of long storage time. The pen itself is made of tap water and water-soluble ink, so the pen is water-based. The liquid in the core of ballpoint pen is oily. So the liquid in the core of ballpoint pen is oily pen. The liquid in the neutral pen is different from both the ink and the oily liquid in the core of ballpoint pen, but an organic solvent, so it is called neutral pen. Neutral pen is a new writing tool which is popular in the world at present. Neutral pen is a kind of writing tool which belongs to ballpoint pen. Ball pen is a writing tool that uses balls to roll out the writing medium (ink or ink). Its medium of writing is oil-based called ballpoint pen; its medium of writing is water-based called water-based ballpoint pen (water-based ink pen), also known as ball pen, jewelry pen; its medium of writing viscosity between water and oil is called neutral pen. Therefore, ball pen and neutral pen belong to a kind of writing tool of ballpoint pen. Neutral pen contains an organic solvent, its viscosity is lower than that of oily pen and ink, and it is thicker than that of water-based pen and ink. When writing, the ink will change from semi-solid to liquid through the pen tip. The greatest advantage of neutral pen and ink is that each drop of ink is used on the pen tip, and it will not volatilize or leak, so it can provide a silky sense of smooth writing and smooth and stable ink flow.