Copying pencil Copying pencil A copying pencil, also indelible pencil or chemical pencil, is pencil whose lead contains a dye. The lead is fabricated by adding a dry water-soluble permanent dye to powdered graphite—used in standard graphite pencils—before binding the mixture with clay. Copying pencils were introduced in the 1870s and were originally marketed for copying documents, especially for making permanent copies of a permanent original. This was achieved by creating a hand-written document using a copying pencil, laying a moist tissue paper over the document and pressing down with a mechanical press. The water-soluble dye in the writing would be transferred
Lead every alternate layer of oxygen atoms absent. Negative oxidation states can occur as Zintl phases, as either free lead anions, as in BaPb, with lead formally being lead(−IV), or in oxygen-sensitive ring-shaped or polyhedral cluster ions such as the trigonal bipyramidal Pb ion, where two lead atoms are lead(−I) and three are lead(0). In such anions, each atom is at a polyhedral vertex and contributes two electrons to each covalent bond along an edge from their sp hybrid orbitals, the other two being an external lone pair. They may be made in liquid ammonia via the reduction of lead by