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A Novel Method for Cleaning Reaction Vessels.The objective of zeolite synthesis is the production of pure phase material and a study by Lowe et al. showed that small and possibly significant amounts of template remaining in supposedly clean vessels could influence the crystallisation of subsequent gels. Two cleaning methods are widely used to clean the synthesis reaction vessels i.e. hydrofluoric acid or a solution of sodium hydroxide at reaction temperature, but their efficacy has not been tested. Zeolite omega was synthesized with both organic and inorganic templates and, following synthesis, the reaction vessels were cleaned by a novel method, described here, using hydrofluoric acid, crown ethers, and ultrapure water. This new method was compared to the standard methods by using a ‘scavenging gel’ to test the cleanliness of the vessels. The ‘scavenging gel’ produced some crystalline material when used following conventional cleaning whereas, when the vessels were cleaned using the method described here, the gel failed to crystallise. Conductivity measurements have proved a reliable index to the cleanliness of the reaction vessels.