graphite

An allotrope of carbon with many interesting physical properties. Graphite consists of carbon atoms, chemically bound into covalent lattice sheets, exactly one carbon atom thick. Substantial graphite deposits consist of many of these lattice sheets placed one atop of the other and scrunched together. The only thing holding these sheets together are intermolecular forces, much weaker than an actual covalent bond. Thus, it is very easy to shift these sheets in relation to each other with little friction. This ease in slipping the sheets of carbon relative to each other makes graphite an excellent lubricant. This ability also makes graphite easy to write with. The intermolecular forces between most substances and the lattice sheets are stronger than between the lattice sheets themselves. When graphite is rubbed against a substance, sheets come off of the structure and deposit themselves on the surface that is being written on.

Graphite exhibits many interesting chemical properties as well. Unbound carbon atoms exhibit 4 valence electrons. To become graphite, these carbon atoms undergo sp2 hybridization to form three sp2 orbitals that rest in a roughly triangular fashion around the atom. Additionally, one 2p orbital still exists perpendicular to the plane of the sp2 orbitals. This configuration can be visualized as a flattened tripod with a camera sticking up on it. The legs, flat against the floor, are like the sp2 orbitals. The base of the tripod is akin to the carbon atom"s nucleus and inner electron shell. The camera sticking up is like the remaining 2p orbital. When the carbon atoms bond to each other, the sp2 orbitals mesh together forming sigma bonds. At the same time, the 2p orbitals overlap at their boundaries, forming non-localized resonating pi bonds. The whole shebang looks something like this:

         \   /   \\  /
          C-C     C-C
         //  \\  /   \\
       -C     C-C     C-
         \   /  \\   /
          C=C     C-C
         /   \   /  \\

This is just one possible resonance structure of the carbon sheets; the pi bonds are delocalized, so the double bonds resonate. The delocalized nature of these pi bonds makes graphite an electrical conductor, although a weak one: electrons are free to flow from atom to atom through their overlapped 2p orbitals.

Most people aleady know that the "lead" in pencils has been made of non-toxic graphite for some time now. A more obscure story is that the Mad Hatter depicted in Alice in Wonderland is based on the tendency of many hatters to go insane after handling so much mercury in the hat making process.¹ How come we never hear of the Sickly Scribe? Most likely this is because the lead does not permeate the skin as readily as mercury. With the discovery of graphite, pencils evolved in two ways. First, they stopped killing you or making you sick and, because the graphite was more brittle than lead, they were encased in first string and then wooden rods that had to be hollowed out by hand. They left a darker mark and were easier to handle.

Graphite also has a history apart from pencils. It's discovery was made, not by scientists, but by shephards after a severe storm in Borrowdale, England in 1564. Encountering a large deposit of a black substance that wouldn't burn like coal, the shepherds were baffled. They soon discovered that it was an excellent way to mark their sheep. The English government soon found uses for it, chiefly for cannonball molds during the reign of Elizabeth I. It was termed 'Wad' and the smuggling of this useful substance was deemed a felony in 1752 by parliament.

As an artistic medium graphite is cheap, readily available, and one of the easier mediums to use. Like most artistic endeavors, to master it requires stringent discipline. Like watercolor, the use of graphite is heavily influenced by the type of paper used. Although graphite can be applied to canvas, this is usually only to create a guide for the application of another medium such as oil or acrylic. Personally, I find that watercolor paper allows for the greatest range of expression with a pencil, though at times it is hard to get the darkness afforded by other papers. Unlike watercolor, however, graphite allows for the representation of the most minute detail.

Graphite pencils come in a range from very hard to very soft. This large range is possible because of the Conté Process, where a ratio of clay particles and graphite are mixed. More clay equals a softer and darker pencil. The full range is designated using B for black (or soft) and H for hard, and goes from 9B to 9H. The #2 pencil that standardized tests are so fond of reside in the middle with an HB grade. There have been variations on this scheme though, incorporating the letter F as well. Because of this extreme range, a graphite drawing can take on photo-realistic qualities in the hands of a master.

Graph"ite (?), n. [Gr. to write: cf. F. graphite. See Graphic.] Min.

Native carbon in hexagonal crystals, also foliated or granular massive, of black color and metallic luster, and so soft as to leave a trace on paper. It is used for pencils (improperly called lead pencils), for crucibles, and as a lubricator, etc. Often called plumbago or black lead.

Graphite battery Elec., a voltaic battery consisting of zinc and carbon in sulphuric acid, or other exciting liquid.

© Webster 1913.