How erasers are made

Make no mistake about it: an eraser is a student’s best friend. Whether it’s attached to the top of a pencil or on its own, only an eraser can quickly rub out an error. White erasers are made of flexible vinyl while pink erasers are made of synthetic rubber.

In 1736 a French explorer observed South American native Indians using a certain tree resin to make bouncing balls. He brought this resin back home and before long Europeans discovered it could rub out pencil marks, hence the term rubber. There was just one problem after a while: rubber would rot. That dilemma was solved a century later by one Charles Goodyear, who developed a curing process to prevent rubber from rotting.

A lot of ingredients go into making a simple pink eraser. Carefully measured fillers, accelerators, curing agents, oils, colouring and the main ingredient – synthetic rubber. They start by putting a batch of rubber into a mill. The rubber passes repeatedly between large heated rollers. Then throw in any defective erasers from the last production run, recycling them into this new batch, then add sulphur as a curing agent.

Accelerators to help the sulphur do its job. Add red colouring then blend everything for five to ten minutes, until the mixture is the consistency of heavy dough. Next add vulcanized vegetable oil (that’s vegetable oil treated with sulphur). Following that regular vegetable oil is added, then calcium carbonate – this acts as a filler when the colour and thickness are just right. In a factory, workers remove the rubber, which by now is hot and soft as a result of all that milling, and leave it to cool and harden at room temperature for about half a day. When the rubber is ready, they cut out large squares, each weighing between 5 and 8 kilograms depending on the thickness of eraser the client has ordered. The squares go into a steam heated press to cure for about 20 minutes at 163 degrees Celsius and the pressure compacts the rubber while the intense heat hardens it. They trim off the excess then submerge the hot rubber squares in cold water to stop the curing process.

To make erasers that erase both lead and ink, they cut beveled strips from two batches of rubber; one pink and one blue. The blue contains pumice which gives it that extra abrasiveness to erase ink. They pair up each pink with a blue to form a two colour strip, then it’s into the steam press. After twelve minutes, workers remove the trays, trim off the excess and submerge the strips and cold water to stop the curing process. Then an automated machine chops the strip’s into pieces the size of erasers.

And back to the all pink erasers – the rubber squares come out of their cold water bath, and go through a machine that cuts strips with beveled edges, then chops the strip’s into erasers. From there the erasers drop into a giant barrel. Workers throw in some talcum powder to prevent them from sticking together, then they set the barrel spinning for three to five hours as the erasers tumble against each other. The abrasion rounds off their edges.

The last step is printing a machine stamps each eraser with the company name and the model number. It’s not the rubber that gives the eraser the ability to erase but rather the vulcanized vegetable oil that’s in it – that’s what makes the eraser crumble when rubbed on paper taking away the pencil marks with it.