[mikethedruid]

Without seeing exactly what you are talking about it is hard to say exactly; but, from your description, and the fact that the tube works at all, it sounds like what you are describing if the "getter." The getter is installed in a tube to burn off and consume the very last of the oxygen which might remain inside the tube after the vacuum is drawn. It usually has a tiny amount of mercury and a filament on it, and when the tube is finished being made, a current is run through it which heats up the mercury (or other metal) to high incandescence, vaporizing the filament and allowing it to combine with any remaining oxygen atoms. This is what leaves the silver you see on the inside of the glass envelope. It is a normal part of the manufacturing process.