I found the old post on bulb coating

[pete <peteray@xxxxxxxxxx>]

Here it is:

Good morning all. From a 1970 photo-lab-index, "BLACKOUT COATING for
flashbulbs:

Eosin 2524......................60 grains................4.0 grams
Tartrazine N. 250...............88 grains................6.0 grams
Coomassie Violet RS.............60 grains................4.0 grams
Lissamine Green................146 grains...............10.0 grams
Gelatin (hard)...............6+3/4 ounces..............200.0 grams
Glycerin.....................3+1/4 fl. oz. ............100.0 cc
Add cold water to make..........32 ounces................1.0 liter

"The gelatin is first soaked in half the quantity of water for one hour,
then warmed to 120 degrees F (49C) and stirred until dispersed. The dyes
are dissolved separately in small quantities of water at not above 150
degrees F (65C). Each dye is mixed with a small quantity of the gelatin
solution to prevent precipitation when they are later mixed. The glycerin
is diluted with another small portion of water, then all ingredients are
mixed and brought to the final volume with water at 120 degrees F (49C).

"If necessary the mixture is filtered through two layers of muslin to
remove air bubbles, then cooled to 96 degrees F (36C). At this temperature
the flashbulbs are dipped in the mixture until completely covered. On
removal from the solution they are drained for a few seconds, then inverted
and the remaining solution is permitted to spread back over the surface
rather than draining. They should appear almost black and it should be
impossible to see within the bulb. Drying takes about 24 hours. These bulbs
may then be used with any regular infrared film for photography in complete
darkness.

"The  formula above is a British formula and the dyestuffs mentioned are of
British manufacture... American dyes are..."

Then it lists different companies with some equivalent products. I'm a
couple blocks from Aldrich Chemical Co. and they carried all the stuff.
Based on quantities that were available it would cost about 100 bucks. I
wonder if there is somewhere to buy the dyes at lesser purities. Anyway
here are some equivalent dyes that are listed then in the book: Tartrazine
N. 250 = Tartrazine Conc. or Wool Yellow X Conc.; Coomassie Violet RS =
Pontacyl Violet 4BL, Conc. 125 percent or Formyl Violet S4B or Wool Violet
4BN; and Lissamine Green = Pontacyl Green SN Extra or Wool Green S. All the
"wool" colors were supplied by National Aniline Corp in NY. I kept the
capitalization and abbreviation the same as the text pretty much, so thats
all the clues you get. Are there any chemists in the crowd?

End of original post.

Well, glycerin and gelatin are common, cheap and safe enough. I wouldn't
think that dyes would be that expensive, but the ones from chemical supply
houses are very pure and somewhat expensive. Maybe a mixture of common
clothing dyes would work... or maybe one part lime jello, one part grape
jello and...

pete



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