Vulcanization is the name originally given to the process Charles Goodyear discovered by mixing sulfur with natural rubber and subjecting it to heat to transform a plastic substance into an elastic substance. Years later it was learned that the sulfur actually crosslinks the chains of the rubber molecules. Eventually chemicals other than sulfur were used to crosslink elastomers, resulting in the term crosslinking to become synonymous with vulcanization. Vulcanization is normally achieved with time and temperature activation of specific chemicals which react with polymeric materials, producing a crosslinked network of molecular chains with visco-elastic properties. Sulfur-bearing accelerators make the sulfur-vulcanization process safer and more efficient. Crosslinking is also achieved by organic peroxides, which may be made more efficient thru the use of coagents.