Colored pencil Colored pencil A colored pencil (US-English), coloured pencil (UK-English, Canada-English), pencil crayon (UK-English, Canada-English), lead or coloured/colouring lead (Newfoundland-English) is an art medium constructed of a narrow, pigmented core encased in a wooden cylindrical case. Unlike graphite and charcoal pencils, colored pencils’ cores are wax- or oil-based and contain varying proportions of pigments, additives, and binding agents. Water-soluble (watercolor) pencils and pastel pencils are also manufactured as well as colored leads for mechanical pencils. Colored pencils vary greatly in terms of quality and usability; concentration of pigments in the core, lightfastness of the pigments, durability of the colored pencil, and
Lead of uranium-235, thorium-232, and uranium-238, respectively, so traces of all three of these lead isotopes are found naturally. Minute traces of lead-209 arise from the very rare cluster decay of radium-223, one of the daughter products of natural uranium-235, and the decay chain of neptunium-237, traces of which are produced by neutron capture in uranium ores. Lead-210 is particularly useful for helping to identify the ages of samples by measuring its ratio to lead-206 (both isotopes are present in a single decay chain). In total, 43 lead isotopes have been synthesized, with mass numbers 178–220. Lead-205 is the most stable