Century eggs are made by preserving eggs in a mixture of clay, ash, salt and what kind of oxide?
Century egg Century egg or Pidan (), also known as preserved egg, hundred-year egg, thousand-year egg, thousand-year-old egg, millennium egg and black egg, is a Chinese preserved food product and delicacy made by preserving duck, chicken or quail eggs in a mixture of clay, ash, salt, quicklime, and rice hulls for several weeks to several months, depending on the method of processing.
Silicon dioxide Silicon dioxide, also known as silica (from the Latin "silex"), is an oxide of silicon with the chemical formula Si O , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing as a compound of several minerals and as synthetic product. Notable examples include fused quartz, fumed silica, silica gel, and aerogels. It is used in structural materials, microelectronics, and as components in the food and pharmaceutical industries.