TECHNOLOGY FOCUS - CERAMICS AND GLASS - Preferred Composition: The glass composition is constituted of an amorphous glass phase after preparation and before any heat treatment. The glass composition comprises greater than 50 wt.%, preferably 100 wt.% of crystalline phase, after maintaining at a gradient temperature of 600-1000 degrees C, preferably 800-850 degrees C, for a duration of greater than 1 hour, preferably 50-100 hours, where temperature gradient is reached by observing one or more ramps of temperature increase at a rate of 0.5 at 3 degrees C/minute. The composition (A) is compositions A1-A12 as given in the table specification. The composition (B) is compositions B1-B10 as given in the table specification. The composition (C) is C1-C7 as given in the table specification. The glass composition is present in the form of a powder. Preferred Process: The assembled parts and the glass composition is maintained at a T2 temperature gradient of 600-1000 degrees C, preferably 800-850 degrees C, for a duration of greater than 1 hour, preferably 50-100 hours. The contacting parts with the glass composition is made by forming a powder of the glass composition, the powder having a particle size of less than 20 mu m, by suspending the powder in an organic binder to obtain a paste, and by coating at least one surface of parts to be assembled with the obtained paste. The process comprises, before reaching the temperature T1, maintaining temperature gradient T3 sufficient to remove the organic binder, e.g. at a temperature of 300-500 degrees C, 400 degrees C, for a duration of 60-180 minutes, e.g. 240 minutes. The process comprises, in a step (b), preparing the following protocol raised to 0.5 degrees C/minute from the room temperature, set at 400 degrees C for 120 minutes, raised to 3 degrees C/minute, to obtain 400 degrees C; set at 800-950 degrees C for 50-120 hours, descends at a rate of 3 degrees C/minute to obtain room temperature or operating temperature. The contacting parts with the glass composition are made by preparing a glass part having the form of the joint to be formed and then placing the part between the surfaces of parts to be assembled. Preferred Components: The glass part is prepared by compacting then by sintering a powder of the glass composition in a mold conforms to the shape of the glass part. The glass part is a solid glass block prepared by direct casting of the molten glass composition in a mold according to the shape of the glass part. The parts to be assembled are made of a material such as metals, metal alloys, ceramics, and composite materials comprising the materials. At least two assembled parts are different materials. At least two assembled parts are parts of a high-temperature electrolyser or a high temperature fuel cell. EXAMPLE - Typical composition comprised of (in %): silica (60); aluminum oxide (40); calcium oxide (50); and chromium oxide (0.8).