The dark black thing that you see inside the pencils is graphite. Graphite is one of the forms of the element carbon. Wood is the protective outer covering surrounding the graphite lead so that it doesn’t break easily. Pencil lead is made of a combination of finely ground graphite and clay. The mixture is then mixed with water and pressed together at high temperatures into thin rods.
The graphite lead leaves behind a mark on white paper while writing or drawing. The particles of graphite cling to the particles in the fiber of the paper. Traditionally, rubber was made from natural latex rubber. Though natural rubber erases well, it smears graphite and causes an allergic reaction to some people. That is why synthetic rubbers entered the market in mid 50s. Nowadays they are made from polymers like polyvinyl chloride. The particles of the constituent compounds of eraser are stickier than paper. So when we rub pencil markings with an eraser, the graphite particles stick to the sticky components of eraser instead of paper. Stickier the particles of rubber are, cleaner is the result.
Erasers come in many shapes and sizes. There are many types of erasers like kneaded erasers, white vinyle erasers plug erasers and few more. The soft white vinyl erasers are what we commonly use. They erase more cleanly than other kinds because they are made of softer vinyl. Kneaded type of erasers is art eraser that absorbs graphite particles without friction leaving behind no debris or smudges. Plug erasers are those erasers that are found at the back of the pencils.