Pencils come in many different varieties. Basic pencils are graded by the hardness or softness of the graphite used in the pencil. The amount of clay mixed with the graphite determines the hardness of a pencil lead. More clay means a softer pencil lead. A softer pencil lead leaves a darker mark. The harder the graphite lead, the lighter the mark the pencil makes.
Soft-lead pencils are made with a high clay-to-graphite mixture. Many graphic artist pencils have a thin wax added to the mixture to provide the heavy, soft stroke. If you desire soft, fat stokes, then a soft pencil lead is the choice.
Medium Soft Lead
Medium soft leads have slightly less clay mixed in with the graphite. The medium-soft pencil lead leaves thinner and lighter stokes. This pencil style is the model parents are asked to buy when selecting school supplies.
Pencil leads are graded by the individual manufacturer. There is no industry standard, as each company has its own grading standards. In general, pencils are numbered or graded to inform the buying public of the hardness of the pencil lead. In the United States, most companies use a numbering system of 1 to 4. Pencil leads also have subgrades that are used mainly by graphic artists: 4H, 2H, H, HB, F, B, B2 and the softest being B4.
Hardness and Darkness
The higher the number, the harder the lead and the lighter the marking left by the pencil lead. In the United States, the number 4 pencil is the hardest lead grade. Hard pencil leads leave thin stokes and are not recommended for fragile quality paper.