Despite the commonly used term 'lead pencil', pencils have never contained lead but consist of a form of carbon - graphite. When this material was first discovered in England and its usefulness for mark-making established, it was mistaken for lead and, despite its true composition being identified in the late 18th Century, the name lead pencil stuck.

The region of England in which the graphite was mined was Barrowdale near Keswick in Cumberland and a thriving industry grew in the area. Today the Derwent Cumberland pencils are still made in the area and a pencil museum is sited there.
The process that was used in the very early years of this industry was to take the graphite and wrap it a continuous length of string which could be peeled away to reveal the drawing material as needed. The next process to evolve was to mix the graphite with extenders into a paste and mould it into groves cut in wood, usually cedar wood. Another piece of grooved cedar was then glued on to 'sandwich' the graphite mixture. At the same time, metal 'portes' or holders were in use that were something similar to the modern propelling pencil.
The word 'pencil' comes from the Latin 'pencillus' meaning 'little tail' as a result of the medieval mark-making implement which was a small brush dipped in ink. The Romans, themselves, had used a stylus - or lead rod - to scratch the surface of wax tablets.
Styli remained in use and by the Renaissance, many artists used a form of stylus to produce beautifully detailed drawings. The name of this method was Silverpoint and comprised of a rod made from an alloy of lead and tin marking a specially prepared surface of gesso. Bread was used to remove errors and chalk to add highlights.
All the great Renaissance artists - da Vinci, Durer and Raphael - used Silverpoint but advances in paper-making were gathering pace during their lifetimes and pencil became popular as it cut out the need for preparing a surface.
However, graphite had always been relatively scarce and when Continental Europe was affected by an embargo on English graphite in the late 1700's, Nicolas Jacques Conte was given the task of providing a substitute. He soon came up with a process of mixing lower quality graphite with powdered clay which enabled manufacturers to control the hardness of the graphite and led to the modern process and the modern graphite scale of 9H to 9B.

The H stands for hard and the B for black. The harder pencil leaves less graphite on the surface resulting in lighter mark-making. The pencils classed as B, on the other hand, are softer and leave much more graphite on the surface. Hence, the marks are blacker. For both types, the higher the number, the harder or blacker they are. There are also HB pencils, which fall in the middle of the scale and are used as much for writing as drawing and F pencils which are firm.
There may be a tendency for many users to press too hard on their pencil in an effort to increase intensity causing the paper to suffer. It is, therefore, important to use the correct pencil for the effect required and to use the correct surface. Smooth papers and Bristol board take soft 'leads' well whereas the harder 'leads' work effectively on textured paper such as watercolour and ingres papers.

Techniques

Pencils are the most versatile of drawing media because of the variety of marks that can be made. Marks can be subtle and delicate or bold and vigorous. A few bold strokes can capture movement whilst tonal shading can define form. A great characteristic of pencil is that line and tone can be combined in one drawing.
When executing a line drawing, the look of a line depends on several factors. These are the grade of the graphite used, its sharpness, the pressure applied, the speed with which the line was drawn and the texture of the paper. There are no rules governing this - it all depends on your style of drawing, the subject matter or atmosphere that you are seeking to create.
Tones can be achieved in a number of ways. The classic technique goes back to the time of Silverpoint and involves drawing closely juxtaposed lines that become lighter and fainter as they move out of shadowed areas into lighter ones. Other methods used to express tone include cross-hatching - two layers of crossing lines - dots and smudging the graphite with fingers, stumps or rubbers. Interesting tonal areas can also be achieved by rubbing the pencil over paper that has been laid on a textured surface.
For detailed drawings, erasers can lift any errors. For sketching, however, rough lines and random marks can add to the piece and so rubbers should not be over used.
Some artists, however, create very interesting pieces just using a rubber. Having laid down a base of tonal areas, the form is picked out by the careful removal of the pencil allowing the image to emerge from the darkness.