Abstract: This invention relates to a process for producing on the outer surface of a glass volume, such as a bottle or flask, an indelible decoration consisting of fine particles of enamel each fused in situ with the surface layer of glass of the volume. The process consists in spraying onto the said outer surface a frit of enamel particles having a melting point lower than the softening point of the glass and a coefficient of expansion close to that of the glass, under conditions such that the frit remains temporarily in place on the surface and, while the frit is in place in this way on the surface, it is fired by heat treatment at a temperature such that the frit particles melt on the surface while fusing with it, but retain their individuality without associating together to form a continuous film.The frit is used in a suspended state in an oil-aqueous binder so as to constitute a slip which is sufficiently viscous to adhere to the outer surface of the bottle.