Sometimes you just have to live with the dirt.
Awhile back I purchased two #59 Lionel lamps which were complete, not only with their original main boxes but also with the boxes and their contents - two No. 40 light bulbs.
When they arrived I took everything out, screwed in the light bulbs and looked them over. The light bulbs were, to put it mildly - filthy. Both bulbs appeared to be frosted so I took the first bulb and gently scrubbed it with a damp cloth and mild soap. The transformation was nothing short of spectacular. The frosted bulb (on the left) went from dirty to diamond.
While the bulb on the right might not look too bad in the picture - trust me - it looked a lot worse in real life....So, given the success with the first bulb, I took the second and started to carefully clean it...
The end result is, as you can see, very clean and also very different from what it was
It turns out at some point in time Lionel shifted from purchasing actual frosted glass light bulbs to clear glass light bulbs coated with some kind of VERY water soluble white paint. Both bulbs came in boxes with identical markings so there was nothing to indicate there might have been a difference in the two No.40's.
The bulb paint was so soluble that a single pass with the damp cloth stripped away a wide swath. Since that made the bulb look even worse I just went ahead and cleaned the whole thing. It would be a simple matter to dip the clear bulb in some flat white, water soluble, latex paint but I'm going to leave it alone - my own monument to being a bit too concerned with cleanliness. 
