Re: Dreaded fungus

Is it possible to prevent dry gelatin from taking up any
moisture from the atmosphere? Is it possible to prevent
water from causing the dry gelatin layer from swelling?
(In essence, waterproofing the gelatin)

-Phillip

Ryuji Suzuki wrote:

> From: Richard Knoppow <dickburk@ix.netcom.com>
> Subject: Re: Dreaded fungus
> Date: Wed, 17 Dec 2003 22:00:06 -0800
>
> > Most hardeners of the
> > sort found in fixers harden the emulsion only when it is
> > wet. I think formaldehyde may actually harden it when dry.
>
> Note that any hardner hardens the gelatin and gelatin is hardened
> whether it's wet or dried. The difference is that the antiswelling
> effect of hardening is seen when the emulsion is wet, not when dry.
>
> Gelatin always retains some amount of water, depending on the RH of
> the air. Hardening does not affect much in gelatin's absorption of
> water at high RH. (OTOH, at very low RH, emulsion may shrink and
> become excessively curly and brittle, whether it is hardened or not.)
>
> Formaldehyde is not a very desirable form of hardening agent in
> emulsion making for several reasons, but it is a quite effective
> hardening agent. Yet, its hardening has little influence on the
> absorption of water vapor from air at high RH.
>
> Dry strength is more strongly influenced by the gelatin
> structure. When the emulsion is dried slowly at chilling low
> temperature, the gelatin is in a gel structure, while when dried fast
> at high temperature, the gelatin is in sol structure. The gel
> structure is the desired form in terms of dry mechanical
> properties. The gel structure also responds to hardening agents better
> than the sol structure. Although modern coating facility design is a
> tight trade secret, patents in this area generally describe very fast
> coating of very thick emulsion on film or paper, and the coated
> material is immediately chill set and dried in dry, cold environment.
>
> --
> Ryuji Suzuki
> "Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)
Received on Thu Dec 18 06:25:31 2003