Like silk or wool, leather is a fine, natural product. With leather, each hide is unique and features its own texture, color, and natural markings. There are even differences within a single hide. Therefore, it is not unusual to see color differences, grain changes, and even scars or brand marks on a piece of furniture. Different types of leather show these characteristics in different degrees, with some types of leather processed to eliminate these natural marks altogether and others left largely unprocessed to showcase them.
Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impurities which allow cracks to pass straight through, grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks, and ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing.