Abstract: The invention provides a powder of fine semiconducting vitreous enamelling particles, such as alkali-boro silicate glass frit, especially applicable to an electrostatic powder coating process, for providing improved electrostatic adhesion to a base metallic surface. The preferred powder treatment is to expose the dried powder to tri-chloro-silane vapor which reacts with the hydroxyl surface groups on the particles to form a surface layer which is then exposed to water vapor producing a hydrophobic cross-linked silicone structure. In the final firing stage of the enamelling process excess organic groups are driven off, and the enamel is not contaminated.