<P> Historian Henry Petroski notes that while ever more efficient means of mass production of pencils has driven the replacement cost of a pencil down, before this people would continue to use even the stub of a pencil . For those who "did not feel comfortable using a stub, pencil extenders were sold . These devices function something like a porte - crayon...the pencil stub can be inserted into the end of a shaft...Extenders were especially common among engineers and draftsmen, whose favorite pencils were priced dearly . The use of an extender also has the advantage that the pencil does not appreciably change its heft as it wears down ." Artists currently use extenders to maximize the use of their colored pencils . </P> <P> Residual graphite from a pencil stick is not poisonous, and graphite is harmless if consumed . </P> <P> Although lead has not been used for writing since antiquity, lead poisoning from pencils was not uncommon . Until the middle of the 20th century the paint used for the outer coating could contain high concentrations of lead, and this could be ingested when the pencil was sucked or chewed . </P> <P> The lead of the pencil is a mix of finely ground graphite and clay powders . Before the two substances are mixed, they are separately cleaned of foreign matter and dried in a manner that creates large square cakes . Once the cakes have fully dried, the graphite and the clay squares are mixed together using water . The amount of clay content added to the graphite depends on the intended pencil hardness (lower proportions of clay makes the core softer), and the amount of time spent on grinding the mixture determines the quality of the lead . The mixture is then shaped into long spaghetti - like strings, straightened, dried, cut, and then tempered in a kiln . The resulting strings are dipped in oil or molten wax, which seeps into the tiny holes of the material and allows for the smooth writing ability of the pencil . A juniper or incense - cedar plank with several long parallel grooves is cut to fashion a "slat," and the graphite / clay strings are inserted into the grooves . Another grooved plank is glued on top, and the whole assembly is then cut into individual pencils, which are then varnished or painted . Many pencils feature an eraser on the top and so the process is usually still considered incomplete at this point . Each pencil has a shoulder cut on one end of the pencil to allow for a metal ferrule to be secured onto the wood . A rubber plug is then inserted into the ferrule for a functioning eraser on the end of the pencil . </P>

When did they stop using lead in pencils