Abstract: A design for sealing metal-to-metal, of sections of rocket shell with fusible vitreous inorganic "glass-ceramic" compositions, which will not burn-out from high temperatures of rocket-exhaust, is disclosed. The design is intended to set up a thermal-gradient across the cross section of the sealed metal flanges. The thermal-gradient utilizes the useful property of the vitreous state of the seal, viz., the continuous viscosity change from the relatively low viscosity of molten glass at high temperature, to a very high viscosity of almost solid state at lower temperatures. This mechanism achieves a leak-proof "glass-ceramic" or glass seal between the metal flange joints of sections of rocket-shell. The vitreous seal is capable of withstanding a wide range of temperature inside the rocket, of -50.degree. C., to over 1000.degree. C., without failure when the rocket is fired.