Removing Reticulation with Formaldehyde and FIRE?

I was reading through an old photography manual issued by the US Air Corps / War Department in July 1941, and came across the section about reticulation:

(3) Remedy. - Keep all solutions cool and at uniform temperatures. Under tropical conditions, use a concentrated developer and short development. The reticulation effect may sometimes be removed by placing the negative in a 10 percent solution of formaldehyde for a few minutes and drying in front of a fire. Use ample ventilation in drying negatives.

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Can anyone clarify for me what this does (how it works), particularly the part involving fire?

Is there some characteristic about the fire that this process needs? For what it is worth, this book seems to assume the availability of at least modest darkroom equipment, so I would think that more conventional drying methods would be available. In other words, this isn't a "developing film in your helmet while being shelled in the trenches" book.

Me thinks the Air Corps like to watch things blow up??

In 1941, motion picture stocks, at least those used by the entertainment industry, were still on nitrate base. Pretty much everything else was on safety film base, or at least that's my understanding.

The only way I could think of to cure reticulation would be to heat the emulsion to the point it starts to melt. I guess that's where the fire would come in. I'm also guessing the formaldehyde solution makes the process a little more controllable. I'm guessing still, that if the negative got a little too hot, it would be ruined, and the chances of this process succeeding probably weren't very great.

That's a good theory. You are right that it is risky though - if you screw up, your negatives are definitely ruined!

I found this process interesting though, because it's the only place I've ever read a method for *fixing* reticulation. There are plenty of books which explain what it is, why it happens, and tell you how to avoid it... but never any method of undoing the damage.

I looked up the flammability of formaldehyde (formalin):
http://www.geneseo.edu/~ehs/Lab and Art Studio Safety/Fomaldehyde.htm
It sounds like formalin is flammable, and formaldehyde gas is extremely flammable. The link also includes this note: "Formaldehyde should be used only in areas free of ignition sources."


So I'll take it that the advice in this book should not be followed... but at the same time, I would still like to know how it works.

I looked at the data sheet. The flammability info is for commercial formalin, which is 37% percent formaldehyde gas dissolved in water with about 15% methanol to stabilize it. This commercial formalin is usually diluted to 10% its original strength for use in preserving biological specimens. This recipe calls for 10% formaldehyde, which would be the commercial solution diluted about 1:2. At that strength, it probably won't catch on fire, but the fumes would burn a person's nasal passages severely.