Abstract: A method of securing a window of crumbly material in the end of a tube so as to effectively prevent leakage during temperature cycling, first involving the step of selecting a window having a small clearance when placed inside the end of the tube. Any contamination is removed from the periphery of the window, and then a thin metallic layer that will accept nickel plate is vapor deposited around the periphery of the window. Subsequently, a hoop of tensilely stressed nickel plate is applied over the thin metallic layer, after which the window and tube are sweated together by the application of suitable amounts of solder and heat. Significantly, the hoop of nickel serves to keep the window in continuous compression, such that leakage between the window and tube is effectively prevented.