An aqueous conductivizing composition for conductivizing paper or other sheet material, for example for producing a conductive base for use in dielectric paper or other electrostatic imaging material, is produced by (a) removing sodium magnesium trifluoride impurity (neighborite) from a synthetic hectorite clay conductivizing agent, and (b) adding a binder. These measures reduce dust formation experienced in production or use of electrostatic imaging material incorporating a base which has been conductivized with a synthetic hectorite clay conductivising agent.
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