Method of making a vaccum vessel with infrared radiation portal

A method of making a double-walled vacuum container with an infrared portal, comprising:

• a. forming from a gas-impermeable, infrared transmissive or absorbent material a double-walled container with inner and outer walls of the container disposed in spaced-apart relationship to one another and enclosing an interior volume, with lacuna between the inner and outer walls which is in communication with the surroundings through a flow passage;
• b. placing the container in a position where the center of that portion of the inner and outer walls which is to form the infrared portal is at an upper elevation;
• c. introducing into the lacuna a solution containing an infrared opaque, reflective coating constituent, in an amount sufficient to coat the interior container walls except for portions thereof at the upper elevation;
• d. retaining the solution in the container until its ability to deposit the coating is exhausted;
• e. removing any remaining deposition liquid from the lacuna through the flow passage;
• and
• f. evacuating the lacuna and sealing the flow passage.