Mechanical pencil is a pencil that has a mechanism that extends solid pigment core called a lead which is made of graphite or a solid pigment. This pigment core is not bonded to the outer casing and replaceable. While called a “mechanical pencil” in the United States it is called “propelling pencil” in the UK and “pen pencil” in India. This pen is mainly used for technical drawing and writing, but it can also be used in fine art. They do not have to be sharpened to be used and because of that are very popular with students.
First, rather a primitive, mechanical pencil (or more of leadholder pencil) was invented in 1565 by Conrad Gesner, a Swiss naturalist, and bibliographer. His leadholder pencil had to be manually adjusted so it could be sharpened. When HMS Pandora, which sank in 1791, was found in 1977, aboard her was found a mechanical pencil.
The first mechanical pencil that had a mechanism that propelled the lead and whose lead could be replaced was patented in 1822 by Sampson Mordan and John Isaac Hawkins in Britain. Mordan changed business partners few times until, in 1837, he decided to start manufacturing mechanical pencils alone in his "S.Mordan & Co." company. He (and his company after him) continued to make mechanical pencils until the Second World War when his factory was destroyed by the bombing.
Others continued to improve these pencils and between 1822 and 1874 more than 160 patents were registered that did just that. Spring-loaded mechanical pencil appeared in 1877 while 1895 saw the first twist-feed mechanism. In 1915, Tokuji Hayakawa, a newly employed metal worker, improved mechanical pencil and called it “Ever-Ready Sharp Pencil”. When companies from Tokyo and Osaka made large orders of his pencil, he started selling them in large numbers and opened his business that took the name from the pencil “Sharp”. At the same time in America, Charles R. Keeran was developing a similar pencil but ratchet-based while Hayakawa's was screw-based. Very thin leads appeared in 1939, and the first one had a diameter of 0.9 mm. Next were 0.3, 0.5, 0.7, 1.3 and 1.4 mm. Today we have 0.4 mm leads and even 0.2.
Mechanical pencils today work on three principles. Ratchet-based pencils have two or three small jaws inside a ring at the tip, which hold the lead. When though button on the end of the pencil is pressed, jaws move forward and open pushing the lead forward. Released button closes the jaws, but lead stays at the place because a small rubber device holds it. Some ratchet-based pencils have a weight that moves back and forth and operate the mechanism that pushes the lead forward. Screw-based pencils have a screw which when is twisted moves a slider down the barrel of the pencil which, in turn, advances the lead. Some of the screw-based pencils have a locking mechanism which allows the lead to be pushed back into the pencil. Clutch pencils (also known as leadholder) are a variant of ratchet-based pencils because they also have two or three small jaws and these, when the button on the other end is pressed, also open, but they don’t have a mechanism that will hold the lead. Lead can be moved freely when the jaws are open, in and out of the barrel of the pencil. Clutch pencils use thicker leads (from 2 to 5.6 mm) and usually hold only one piece of lead at a time while other types of mechanical pencils with thinner leads can hold more in reserve. Leads for mechanical pencils can also be made in different colors and can be made to be erasable and non-erasable.