Pencil thereby pushing a new tip to the top. Invented by Harold Grossman for Empire Pencil Company in 1967 and subsequently improved upon by Arthur D. Little for Empire from 1969 through the early 1970s; the plastic pencil was commercialised by Empire as the "EPCON" Pencil. These pencils were co-extruded, extruding a plasticised graphite mix within a wood-composite core. Residual graphite from a pencil stick is not poisonous, and graphite is harmless if consumed. 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
Lead castle chevron edges to prevent "shine paths" of direct radiation through the gaps. They can also be made from lead produced in bespoke shapes by machining or casting. Such an example would be the annular ring castle commonly used for shielding scintillation counters. A typical lead brick weighs about ten kilograms. Lead castles can be made of hundreds of bricks and weigh thousands of kilograms, so the floor must be able to withstand a heavy load. It is best to set up on a floor designed to carry the weight, or in the basement of a building built on a concrete