The red "dip" is a phosphorus compound in a liquid suspension used to remove any remaining oxygen in the lamp upon first ignition. Its the least possible cost, simplest possible, getter on world's least expensive vacuum tube. Some times it has other additives.
This lets them get away with just a roughing pump on the Sealex machine and a simple piece of rubber tubing to seal around the fill stem on the carousel.
Notice they pulse the lamp on the first ignitions? That is why. To burn off any oxygen and to outgas the tungsten.
My guess is that is a gas filled lamp. Argon or nitrogen filled. Filled somewhat below atmospheric pressure so the pressure differential crushes the fill stem closed when the final set of flames heats it.
What they don't show is the machine that etches away the molybdenum mandrel that the filament is wound on, and how the delicate coiled coil filament is shipped and then oriented by the Sealex machine. Always wanted to see film of that, but the process is just not talked about to this day.
I live in part of Ohio that was surrounded by roughly a dozen GE lamp and lamp parts plants, now almost all gone save for one. All of it that was not closed went to Hungary about 15 years ago. Never got the tour, always had a college exam on tour day. You had to know some one and be over 18 to get in anyways. Mom and Dad got the linear halogen and high pressure sodium lamp tours.
I was interested, really interested, but by the time I got out of College, lamp jobs were departing. Our local science library had some real interesting lamp textbooks because of the proximity to Nela Park. My mentor at my first serious job was a former research scientist on Sodium Lamps and plasma discharges for gas lasers. Brilliant fellow, Thank You DAN for all that you taught me!!!!!
Much interesting reading here:
http://www.lamptech.co.uk/index.html God Bless him for posting much of what he knows.
Steve