PURPOSE: To provide a glass etchant for high temperature use, convenient for handling and storage, capable of forming a film decomposable at high temperature, and composed of a composition obtained by mixing an organic polymer substance with a material derived from a metal fluoride and ammonium fluoride.

CONSTITUTION: A glass etchant for high temperature use and capable of forming a film decomposable at high temperature, is prepared by compounding (A) a mixture, double salt, or complex salt of a metal fluoride (fluoride of a III-group metal or transition metal; e.g. aluminum fluoride) and ammonium fluoride, e.g. (NH4)3AlF6, (B) an organic polymer substance unreactive with the component (A), and if necessary (C) additives (e.g. diluent, filler, stabilizer, flux, softening agent, etc.). When the etchant is applied to the surface of a glass article, dried to form a solid film, and thermally decomposed at about 250W550°C, the glass surface is easily etched with the generated hydrogen fluoride gas.