On Sat, 20 Sep 2008 13:43:09 -0700, Roger Shoaf wrote:
This post brings me back a bit. One of my friends fathers worked for a
vacuum tube manufacturer (Eimac) and would patently explain any question
presented by one of the boys hanging out in his garage.

I remember him explaining that the silver you saw on the inside of a
tube was the last step in removing all of the oxygen from the tube.
When the tube had been pumped down and sealed off, there was a heating
element that would vaporize a but of silver and the vapor would bond
with the remaining oxygen and condense on the inside of the tube. The
term for this was a getter as it would "get" the last bits of stray
oxygen.

I don't know whether silver is ever used as a getter; the usual
getter is barium. http://en.wikipedia.org/wiki/Vacuum_tube
says zirconium is used in large tubes, and phosphorus was used in
some early tubes.

This was the same guy that thought us how to drill a hole in glass using
a copper tube and a slurry of abrasive restrained by a clay dam. He
also explained why it was a real pain to drill stainless steel and
showed us how it could be done by holding pressure on the quill of the
drill press with one hand and using the other hand to turn the pulley.
No destroyed bit and no work hardening of the stainless.

--
jiw