The "grade" or "hardness" of a pencil is determined by the ratio of graphite to clay in its core.
Here's a breakdown:
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Graphite Content: A pencil with more graphite will be softer, produce darker lines, write more smoothly, and smudge more easily. However, it won't hold a sharp point for very long.
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Clay Content: A pencil with more clay will be harder, produce lighter lines, and maintain a sharp point longer.
In essence, the pencil grade tells you how much graphite versus clay is used in the pencil's core. The more graphite, the softer the pencil; the more clay, the harder the pencil.
