The silver area inside the vacuum tubes were called "getter flashes" and
were left when a chemical coating was burned or flashed from a small element
inside the tube in the manufacturing process. That process removed the
remaining air in the tube. If the tube is cracked, the getter flash will
turn white and flake off the glass.
As for why the tubes were placed back in boxes, (1) It was the safest way to
transport them without breakage (2) There was often a market for marganal
tubes among hobbyists (3) A common practice with intermittent problems,was
to "shotgun" or replace all the tubes that might cause the problem.Many of
the ones removed were good. The repair shops would often use those tubes (
after testing) to repair used sets for sell. The bad side is that many techs
would sell these questionable tubes as new. It sure did a lot of harm to the
image of the honest wrote in message
...
A couple days ago I picked up several hundred tubes at an estate sale,
for $10.

The estate was that of a fella in town who used to repair televisions.
He died a couple months ago and his family is cleaning out a huge barn
in which he had much of his old gear from his repair days.

The tubes are still in their original boxes. Other than using a tube
tester, is there any way to check to see if they are any good?

For instance, a couple I have looked at have dark spots on opposing
sides. SOme have a dark spot on just one side. Does this indicate the
tube is dead, or is it how the tubes look new?

Would it be common practice to put the old tubes in the boxes the new
tubes came out of? Do tv repairmen have any reason to keep dead tubes?

I suppose I could open the back of an old working tv and compare those
tubes with the tubes I bought.