'Dazzle-Free Photoflash Photography' - Infrared-Transmitting Coating for Flash Bulbs
This article was written by R.B. Morris & D.A. Spencer and appeared in the British Journal of Photography, 1940, Vol. 87, p.288-289.
I'm assuming that it's public domain at this point and it is reproduced here as a scan of a print from a micro-film reel obtained from the Spencer Art & Architecture Library at the University of Kansas.
In the article are given 3 formulae.
1) an Infra Red Filter Coating for Photoflash Bulbs
2) an Anti-Dazzle coating for photoflash bulbs used in conjunction with [panchromatic film]
3) a Formula for converting "Cellophane" photoflash safety covers into anti-dazzle filters
In addition to the well-understood invisible IR flash, this article discusses an anti-dazzle (a.k.a. non-blinding) coating for normal panchromatic films; which seems like a novel idea that is neglected in modern practice.
"For the time time being , the new fast IR material is available only on plates, and miniature camera workers may therefore be interested in an alternative system which makes use of ordinary panchromatic negative materials and a purple-coated flashbulb, and incidentally does not possess the minor drawbacks of the IR system. This system relies on the fact that to the eye the most luminous part of the spectrum of white light is the yellow and green. A filter coating which represses this region of the spectrum and transmits only the red and blue rays will, therefore, when used in conjunction with a suitable panchromatic emulsion, be much more efficient photographically than the visual appearance of the flash would suggest."
If there are any problems with the attachments, PM me and let me know. Someday soon I hope to (or if anyone else would like to!) get it converted into a text file.
keywords: infrared coating infrared dip infrared lacquer IR coating IR dip IR lacquer invisible flash IR transmitting infrared transmitting filter Jen-Dip flashbulb dip infrared flashbulb flash bulb