The softness and hardness of the so-called pencil refers to the refill, which is usually marked on the pen with Latin letters and numbers. The letter "H" means hard, "B" means soft, BH means moderate hardness, medium blackness. "F indicates the hardness between HB and B. The higher the number of H, the harder the lead is, which is suitable for engineering drawing, multi-layer copying, etc. The larger the number of B, the softer the lead, which is mostly used for painting. Ordinary pencil There are several kinds of hardness such as HB, B, 2B, 38, etc.
Why are pencil leads soft and hard? The raw materials of the lead core are graphite and clay. Soft lead contains a large amount of graphite, and hard lead contains a large amount of clay. Graphite is a kind of carbon black, and its chemical properties are very stable. The function of cypress is to make the graphite stick together and increase the hardness of the refill. For example, a 6H pencil has a refill with about 40% clay, a HB pencil with 22%, and a 9B pencil with only 10% clay.
