reduction

Reduction is a type of chemical reaction. The term refers to the loss of particles. When iron ore is refined via heating with a fuel like charcoal, it loses its oxygen molecules, and its impurities in turn become slag and come to the surface of the molten metal, thus purifying the metal. Similarly, in oxyacetylene welding, reduction occurs due to the flame's coming into contact with the base metal.  The resultant creation of carbon dioxide shields the weld from the atmospheric gasses nitrogen, oxygen and hydrogen.