A modified version of an indium seal with a very small loss area, in which pure In solder is used instead of pure In wire, has been tried for a glass window of 20mm in diameter. It has turned out that this seal is vacuum tight against the liquid helium at 4.2K. A seal of a 10mmφ sapphire window with STYCAST 2, 850GT was also successfully tested at 4.2K.
