Eraser

**Erasers**, also called **rubbers**, are tools made from rubber or vinyl and are used to get rid of marks made from pencils, or some types of pens. Some erasers may be attached to a pencil, while others can be temporarily removed and then added. Erasers can be used by rubbing the pencil/pen mark and it will slowly clear away. All erasers will produce some dust called debris. There are some erasers which are very soft and can erase easily. Pink erasers are often used for normal papers, while blue erasers are for thick papers. White erasers can be used for all papers. 

## History
Before the 1770s, people used to use wet bread to clean their mistakes.

Before rubber erasers used today, blocks of wax were used to erase lead or charcoal marks from paper. Pieces of rough stone such as sandstone or pumice were used to remove small errors from parchment or papyrus documents written in ink. Bread, without its crust, was used; a Meiji period (1868–1912) Tokyo student said: "Bread erasers were used in place of rubber erasers, and so they would give them to us with no restriction on amount.  So we thought nothing of taking these and eating a firm part to at least slightly satisfy our hunger."

In 1770, an English engineer Edward Nairne is said to have made the first widely sold rubber eraser, for an inventions competition. Until that time the material was known as *gum elastic* or by its Native American name (via French) *caoutchouc*. Nairne sold natural rubber erasers for the high price of three shillings for a cube with a side length of half an inch. According to Nairne, he accidentally picked up a piece of rubber instead of breadcrumbs, discovered rubber's erasing properties, and began selling rubber erasers. The invention was written about by Joseph Priestley on April 15, 1770: "I have seen a substance excellently adapted to the purpose of wiping from paper the mark of black-lead-pencil. ... It is sold by Mr. Nairne, Mathematical Instrument-Maker, opposite the Royal-Exchange." the word started to refer to the new material between 1770 and 1778.

However, raw rubber could be broken down by microorganisms. In 1839 Charles Goodyear discovered the process of vulcanization, a method that would cure rubber, making it last longer. Rubber erasers became common after vulcanization was discovered.

On March 30, 1858, Hymen Lipman of Philadelphia, United States, got the first patent for attaching an eraser to the end of a pencil. The patent was later removed because the invention was found to be a mix of two already-invented pieces rather than an entirely new product.

Erasers may be free-standing blocks (*block* and *wedge eraser*), or cone-like caps that can slip onto the end of a pencil (*cap eraser*). A *barrel* or *click eraser* is a tool shaped like a pencil, but instead of having pencil lead inside, it has a retractable cylinder of eraser material (most commonly soft vinyl). Many, but not all, wooden pencils are made with attached erasers. Newer erasers in shapes made to be funny are often made of hard vinyl, which often smears heavier markings when used as an eraser. 

## Types 
### Pencil cap erasers 
Pencil cap erasers were first made from natural rubber. Now they are made from a cheaper material called styrene-butadiene rubber, or SBR. This type has minerals inside and an abrasive (most often pumice). Also, it has a *plasticizer,* a material added to make something more flexible and soft, usually vegetable oil. They are quite hard so they can stay attached to the pencil, and are colored pink most of the time. They may also be permanently attached with a *ferrule,* in this case a group of metal rings squished together, connected to both the pencil and the eraser. 

### Ink erasers 
Ink erasers are used to erase ink. Modern ink erasers use chemicals like chlorine, hydroxide, or sulfite.  

### Chalkboard erasers
Chalkboard erasers are used to erase chalk marks from blackboards and other chalkboards. They are usually made of felt. 

## References