Any chemical or other substance that increases the rate at which a chemical reaction takes place, but which itself is consumed and/or altered by the reaction. In printing inks, driers are added as catalysts, as they facilitate the chemical reactions (such as oxidation and/or polymerization) that cause an ink to dry. A substance that increases the rate of reaction but which is not affected by the reaction is called a catalyst. A substance which acts to retard the rate of a chemical reaction is called an inhibitor.
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