Catalysts are materials that remain unchanged in the curing reaction. They crosslink and solidify the primary resin. Acids, bases, salts, sulfur compounds and peroxides are the most commonly used catalysts. Accelerators on the other hand are added in small amounts to speed up the curing of adhesives. In the 19th century mostly oxides and hydroxides of inorganic compounds like lead, zinc, magnesium and calcium were brought to use. These days organic compounds are majorly used as accelerators. Accelerators have been found beneficial as crosslinking agents in influencing final performance properties. Accelerators are also known as promoters when used with polyester resins and vulcanizing agents when used with rubbers.