What Is the Main Ingredient in Pencil Erasers?
Pencil erasers are typically affixed to the opposite end of a writing utensil. These erasers are useful for erasing errors and correcting mistakes by effectively removing any pencil markings. To understand how erasers work, it is important to first understand what materials compose common pencils and erasers.
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Graphite
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The part of a pencil that makes a mark on a piece of paper is typically made of graphite. Graphite is a soft mineral that is distinct from lead, which is a metal. Although the marking portion of a pencil is sometimes referred to as a lead, most pencils no longer use lead as the writing instrument.
Erasers
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Erasers are typically made from rubber. Some erasers are blended with pulverized pumice to make them more abrasive. In order to make the eraser more durable, the rubber is vulcanized or cured using heat and adding sulfur.
The common pencil eraser is usually stiff and flakes away when used on paper. Other types of erasers include art gum erasers, which are made from a softer, coarser rubber, gum or plastic, and kneaded erasers, which are malleable and take on a putty-like consistency. These are also made from rubber.
Pencil erasers can also be made from vinyl. Vinyl erasers are less abrasive and will cause less damage to the paper, but also may smear pencil markings.
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Function
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When a graphite pencil makes a marking on a piece of paper, it is leaving particles of graphite that adhere to the surface of the material. The ingredients that compose an eraser, however, adhere to graphite better than the paper. In a sense, the rubber is "stickier" than the paper. When you rub an eraser across a pencil marking, the particles of graphite stick to the eraser instead and are thus removed from the paper.
History
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In his book, "The Pencil: A History of Design and Circumstance," Henry Petroski wrote that the earliest erasers were actually bread crumbs. The first mention of a rubber eraser is credited to Joseph Priestley's 1770 publication entitled "A Familiar Introduction to the Theory and Practice of Perspective." While Priestley is often cited as the inventor of the rubber eraser, he actually only noted that he had "seen a substance excellently adapted to the purpose of wiping from paper the marks of a black-lead-pencil." Later, in J.R Partington's "A History of Chemistry," published in 1962, this substance being referenced was identified as being rubber.
Considerations
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Because of the abrasiveness of erasers, the paper is typically damaged when markings are erased. The use of a soft or kneaded eraser can reduce this damage, though this type of eraser does not remove pencil markings as completely. Repeated use of an eraser on a piece of paper may result in ripping or tearing of the page.
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