A seal is provided for sealing a quartz envelope to a glass stem in an electron tube. The seal includes an intermediate annular metallic stress relieving ring disposed between the quartz envelope and the glass stem. The annular metallic stress relieving ring has: a radial flange portion, plated with a noble metal and sealed to a silver plated surface of the quartz envelope by a silver chloride cement; a supporting thin narrow relieving portion connected and extending substantially perpendicular to the radial flange portion; and a stem sealing portion which is sealed to the glass stem by conventional sealing techniques and which is interconnected with the annular stress relieving portion.