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During the course of developing digital projectors, one attempt was to use a CRT "light valve".  

The light valve CRT included a very thin layer of Mica that was held positioned a few thousands of an inch inside of the CRT.  Liquid crystal was placed between the Mica and the face.  As an e-beam scanned over the area of the mica, pulses caused the liquid crystal to block light from traveling though the light valve.   By rapidly scanning and "projecting Red, Green, and blue lights through the light valve, with appropriate lenses, digital images could be displayed.

The liquid crystal material needed to be inserted after the light valves were under full vacuum.  A port was developed (shown to the right) to allow the material to be inserted and then sealed.  The Port, and the insertion station were developed.

The final step was seal the high vacuum port with a solder seal.  A a major concern was the potential that the solder flux could contaminate the liquid crystal material.    

Experiments on numerous materials were made, including Titanium, Stainless Steel, and Aluminum.  Several cleaning processes were reviewed, including gold plating and hydrogen firing.  Various fluxes were also evaluated.  The conclusion of the study determined the most reliable solder seal system/ process.