Report on various methods of cleaning: mechanical, chemical and ultrasonic. A chemical cleaning process (solution of thiosulfates and sodium pyrophosphates) was found effective for removing a weathering crust composed of gypsum and syngenite when the corrosion of the underlying glass was uniform. In the case of unevenly damaged (pitted) glass, the only effective procedure is ultrasonic cleaning. If the painted decoration is in good condition, it is not attacked by the solution of thiosulfates and pyrophosphates or by ultrasonic vibrations.