Pencil cores are commonly made from graphite mixed with clay and other materials. Despite the name lead, modern cores are not made of metallic lead, and their composition affects hardness.
A wooden casing makes the core easier to hold and protects it. Different hardness grades offer different line qualities for writing, drawing, and art.
Graphite deposit discoveries
As a technique for drawing, the closest predecessor to the pencil was silverpoint or leadpoint until, in 1565 (some sources say as early as 1500), a large deposit of graphite was discovered on the approach to Grey Knotts from the hamlet of Seathwaite in Borrowdale parish, Cumbria, England. This particular deposit of graphite was extremely pure and solid, and it could easily be sawn into sticks. It remains the only large-scale deposit of graphite ever found in this solid form. Chemistry was in its infancy, and the substance was thought to be a form of lead. Consequently, it was called plumbago (Latin for "lead ore").
Because the pencil core is still referred to as "lead", or "a lead", many people have the misconception that the graphite in the pencil is lead, and the black core of pencils is still referred to as lead, even though it never contained the element lead. The words for pencil in German (Bleistift), Irish (peann luaidhe), Arabic (qalam raṣāṣ), and some other languages literally mean lead pen.
The value of graphite would soon be realised to be enormous, mainly because it could be used to line the moulds for cannonballs; the mines were taken over by the Crown and were guarded. When sufficient stores of graphite had been accumulated, the mines were flooded to prevent theft until more was required.
The usefulness of graphite for pencils was also discovered, but initially it had to be smuggled out of England. Because graphite is soft, it requires some form of encasement. Graphite sticks were initially wrapped in string or sheepskin for stability. England would enjoy a monopoly on the production of pencils until a method for reconstituting graphite powder was discovered in Germany in 1662. However, the distinctively square English pencils continued to be made with sticks cut from natural graphite into the 1860s. The Derwent Pencil Museum commemorates this manufacturing history in Keswick. In 2008, Derwent moved its pencil factory from Keswick to Workington, also in Cumbria. The meaning of "graphite writing implement" apparently evolved late in the 16th century.
Wood encasement
Around 1560, an Italian couple, Simonio and Lyndiana Bernacotti, made what are likely the first blueprints for the modern, wood-encased carpentry pencil. Their version was a flat, oval, more compact type of pencil. Their concept involved the hollowing out of a stick of juniper wood. Shortly thereafter, a superior technique was discovered: two wooden halves were carved, a graphite stick inserted, and the halves then glued together—essentially the same method in use to this day.
Graphite powder and clay
The first attempt to manufacture graphite sticks from powdered graphite was in Nuremberg, Germany, in 1662. It used a mixture of graphite, sulphur, and antimony.
English and German pencils were not available to the French during the French Revolutionary Wars; France, under a naval blockade imposed by Great Britain, was unable to import the pure graphite sticks from the British Grey Knotts mines – the only known source in the world. France was also unable to import the inferior German graphite pencil substitute. It took the efforts of a French military officer to change this. In 1795, Nicolas-Jacques Conté discovered a method of mixing powdered graphite with clay and forming the mixture into rods that were then fired in a kiln. By varying the ratio of graphite to clay, the hardness of the graphite rod could also be varied. This method of manufacture, which was discovered earlier by the Austrian Joseph Hardtmuth, the founder of Vienna's Koh-I-Noor company in 1790, remains in use. In 1802, the production of graphite leads from graphite and clay was patented by Koh-I-Noor.
In England, pencils continued to be made from whole sawn graphite. Henry Bessemer's first successful invention (1838) was a method of compressing graphite powder into solid graphite, thus allowing the waste from sawing to be reused.