Graflex.org

[Mr. Calumet]

I am looking for ANY information or contacts for people who can help me figure out what the exact composition of a press 25 flashbulbs is. The filament is the big question and are flashbulbs gas filled or vacuum???

Regards

[t.r.sanford]

The prevailing belief, c. 1960, was that the filament was magnesium wool, and the bulb was filled with oxygen.

If it weren't filled with oxygen (or perhaps just air), the metal foil wouldn't burn; you'd need something that contributed oxygen, like the potassium nitrate in gunpowder. I think some sort of pyrotechnic mix was used for "flash paper," but I think that was kind of a blind alley that diverged from the main course of development.

If someone said that the filament was aluminum, not magnesium, I couldn't prove otherwise. But powdered magnesium was used as "flash powder" prior to the invention of flashbulbs, and I see no reason for them to change to something else when they found a way to contain the smoke and protect the photographer's eyebrows.

You might drop Cress Photo a line; he is an authority on flashbulbs.

[t.r.sanford]

Btw, the "Focal Encyclopedia" says that modern flashbulbs (this was three decades back) are filled with aluminum --"aluminium," in London -- and the newer, smaller ones are filled with zirconium. Specifically,

"The flash bulb consists of a glass envelope shaped like an electric light bulb the end of which carries two electrical contacts.

"Inside the bulb, the contacts are joined to a thin wire filament covered with a primer of explosive paste. The rest of the envelope is filled with a loose mass of fine aluminium wire in an atmosphere of oxygen at a reduced pressure...

"...Modern ultra-small flash bulbs use zirconium wire filling, providing the same light output from a smaller quantity of wire. At one time flash bulbs also used to be filled with aluminium foil or with an extra large quantity of primer paste and no wire at all."