An eraser is a object that is used to remove marks from paper. Most erasers are designed to remove pencil marks. Other erasers are designed to be used on typewriter marks. Some special pens contain erasable ink that can be removed by erasers. While some erasers are sold separately in the form of wide, slender blocks, many more erasers are found permanently attached to pencils. Other erasers are made to temporarily attach to pencils. Some erasers are enclosed in wooden cases that resemble pencils. These erasers, designed to be sharpened like pencils, often have a brush attached. This is used to brush away small pieces of the eraser left behind after it removes a mark. This type of eraser is usually used to remove typewriter marks.
The first erasers were pieces of bread. There was no better substance for removing pencil marks until rubber was available in the Old World. Rubber was known to the inhabitants of Central and South America long before Europeans came to the New World. As early as the eleventh century, it was used to coat clothing and to make balls. It was also used to make footwear and bottles by pouring the liquid form on earthen molds and allowing it to dry.
In 1735, the French scientist Charles de la Condamine described a substance known as caoutchouc and sent samples to Europe. Caoutchouc was derived from a fluid produced under the bark of a tree found in tropical areas of the New World. This milky liquid, known as latex, is still used to make natural rubber.
Caoutchouc was first suggested for use as an eraser in the Proceedings of the French Academy in 1752, probably by Jean de Magellan. In 1770, the English scientist Joseph Priestley suggested that caoutchouc be named rubber, because of its ability to rub away pencil marks. He also told readers of his book Familiar Introduction to the Theory and Practice of Perspective where to purchase "a cubical piece, of about half an inch, for three shillings." In the United Kingdom, erasers are still known as rubbers.
Until the late nineteenth century, pencils and erasers were always separate. In 1858, Hyman Lipman of Philadelphia patented a pencil with a groove in the tip, into which an eraser was glued. By the early 1860s, the Faber company made pencils with attached erasers. In 1862, Joseph Rechendorfer of New York City patented an improvement of Lipman's design and sued Faber. The United States Supreme Court determined that the idea of combining a pencil with an eraser could not be patented. The reason for this decision was the fact that combining the pencil and the eraser did not change the function of either. This decision opened the way for numerous companies to make pencils with erasers.
In 1867, a hollow eraser, into which a pencil could be inserted, was invented by J. B. Blair of Philadelphia. Earlier versions are also known to have existed. In 1872, the Eagle company made pencils with erasers inserted directly into the wooden case of the pencil. Other companies soon made similar pencils, which became known as penny pencils because they were inexpensive. The availability of pencils with attached erasers in schoolrooms was at first controversial. It was believed that the ability to correct errors easily would make students careless. Despite this concern, pencils with erasers were extremely popular. About 90% of modern American pencils are made with attached erasers. Pencils without erasers are somewhat more common in Europe.
The most important raw material in an eraser is rubber. The rubber may be natural or synthetic. Natural rubber is obtained from latex produced by the rubber tree (Hevea brasilienesis). Synthetic rubber exists in a wide variety of forms. The most common synthetic rubber is derived from the chemicals styrene and butadiene. Styrene is a liquid derived from ethylbenzene. Ethylbenzene is usually made from ethylene and benzene, both of which are derived from petroleum. Butadiene is a gas, derived either directly from petroleum or from substances known as butanes and butenes, which are derived from petroleum.
Other ingredients added to rubber include pigments that change the color of the eraser. White can be produced with zinc oxide and titanium oxide. Red can be produced by iron oxide. Many other colors can be produced with various organic dyes.
An important ingredient added to almost all rubber is sulfur. Sulfur allows rubber to be vulcanized. This process was invented by Charles Goodyear in 1839. It uses heat and sulfur to make rubber more durable and resistant to heat.
Various other ingredients may be added to rubber. These include vegetable oil, to make the rubber softer and easier to shape, and pumice, a natural mineral which makes the eraser more abrasive.
The manufacturing of erasers is highly automated, with reliable products made in the millions each year. Experienced eraser manufacturers have refined the techniques used to the point where extensive inspection is not necessary.
The raw materials shipped to the manufacturer are supplied by companies that are known to provide substances with the proper characteristics. If a new substance is supplied, or if it comes from a new company, the eraser manufacturer may inspect it to be sure it meets all specifications.
Only a very small percentage of erasers need to be inspected to ensure that they have the proper physical properties. Flats must be the correct size to fit into boxes. Plugs must have the correct dimensions to fit into ferrules. The hardness of erasers is critical to how well they will work. Experienced inspectors can easily tell if an eraser is too hard or too soft.
Erasers have remained mostly unchanged for many years. Improvements in eraser technology are likely to be made in the way rubber is produced. New chemical formulas are constantly being developed to produce synthetic rubber in ways that are more efficient, less costly, and which result in products with more useful properties. Genetic engineering may result in rubber trees that produce more latex, or trees that produce latex with physical properties that would make natural rubber production more efficient.
A hint of the future of eraser design is seen in the Ergoraser, a unique eraser from Levenger, a company specializing in very high quality writing supplies. The Ergoraser, developed after two years of research, is oval and curved, much like the shape of a spoon.
The thumb fits inside the curve during use in a way which is designed to be comfortable and efficient. Although extremely expensive compared to ordinary erasers, the Ergoraser promises to play an important role in the future for those who demand the highest quality in simple objects.
Petroski, Henry. The Pencil. Knopf, 1990.
"Eraser Certification." http://www.wima.org/consumer/c-obcertprograms/eraserprog.html/ (February 17, 1998).
— Rose Secrest