U of S | Mailing List Archive | alt-photo-process-l | Re: Hardening With Glyoxal: One Shot?

Re: Hardening With Glyoxal: One Shot?

Hardener and biocide provide different functions.

Addition of biocide is recommended if the solution is mixed in bulk for
later use. Simply, the gelatin solution won't keep unless you sterilize
and keep it sealed.

Hardener is used to modify chemical and mechanical properties of the
gelatin. The main goal is to make the gelatin insoluble in later stages
such as coating of the sensitizer and wet processing. The hardened
gelatin also has lower swelling factor (ratio of thickness in wet and
dry conditions). Less swelling makes the gelatin layer more resistant
from damage while the material is wet.

For your purpose, I'd prepare a bulk batch of gelatin solution
containing a sufficient amount of biocide (2-phenylphenol, methyl
paraben, thymol, isothiazolinones, etc.) and other addenda you may want
to use, such as surfactant and antifoamer. Hardener (glutaraldehyde,
bisepoxides, glyoxal, etc.) should be added immediately prior to

On Mon, 07 May 2007 15:28:20 -0600, "Michael Koch-Schulte"
<mkochsch@shaw.ca> said:
> I was just thinking "whither Ryuji?"....So are you advocating using both
> a
> biocide and a hardener with gelatin? If the hardener's not a biocide are
> people fooling themselves? Should we separate biocides and hardeners into
> separate categories? My stock gum arabic I assume has a biocide already
> in
> it. I understand the purpose of the biocide but has the term "harden"
> been
> applied too loosely in the past? Hardening without a biocide presumably
> still leave the gelatin open to attack.
>  For my own purposes I'd like a method of being able to size small
>  amounts
> of paper. So ideally a stock solution of gelatin that can be rewarmed and
> then I'll add in drops of my hardener of choice, that sound about right?
> Thanks Ryuji!
> ~m
> ----- Original Message ----- 
> From: "Ryuji Suzuki" <rs@silvergrain.org>
> To: <alt-photo-process-l@usask.ca>
> Sent: Monday, May 07, 2007 1:32 PM
> Subject: Re: Hardening With Glyoxal: One Shot?
> > Gelatin solution does not keep very well even if refrigerated, unless a
> > small amount of biocide is added. A couple of days may be ok but
> > bacteria grow very well on gelatin solution. They break down gelatin
> > molecules to smaller molecules and their gelling property is affected.
> >
> > http://silvergrain.org/wiki/index.php?title=Biocides
> >
> > Compounds that hardens gelatin molecules should not be counted on
> > because they bind with gelatin molecules and not available to kill
> > bacteria. Ones that are photographically inert and don't react with
> > gelatin should be added, if the sizing solution is to be kept for later
> > reusing.
> >
> > Hardener is best added immediately prior to coating, as already
> > discussed.
> >