Re: Glyoxal?

Ryuji,

that's great, thanks Ryuji. I read somewhere that formalin was both a
"hardener" and a preservative, do you know if it's the same with
glutaraldyhyde???

Thanks again
Yves

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, January 14, 2006 4:44 AM
Subject: Re: Glyoxal?

> From: Yves Gauvreau <gauvreau-yves@sympatico.ca>
> Subject: Re: Glyoxal?
> Date: Fri, 13 Jan 2006 23:14:40 -0500
>
> > I'm not sure I understand which one to use with the recipe you give in
the
> > first paragraph. I'm surprised with all this, only 0.15 gram of the
stuff
> > for a liter of gelatine, it doesn't seem like much. I suppose as long as
it
> > does the job
>
> That amount is sufficient if you use glutaraldehyde. The amount of
> hardener molecule needed to crosslink a sufficient fraction of gelatin
> macromolecule, 0.5% weight of hardener is still more than enough. The
> reason formaldehyde and glyoxal are used in much larger quantity is
> that those agents are far slower in crosslinking reaction, and much of
> them would evaporate, oxidize, or somehow involved in other reactions
> to leave the reaction system before they get to harden gelatin. In my
> view glut is far better agent to use because (1) very small excess
> agent is needed, so there's little need to worry about large excess
> causing trouble later, as with the case with glyoxal; (2) hardening
> reaction is fast and stable; (3) crosslinking reaction is
> nonreversible, unlike formaldehyde; (4) glut doesn't fog silver
> gelatin emulsion, unlike formaldehyde.
>
> Glutaraldehyde is an excellent gelatin crosslinking agent. It was once
> as a standard hardening agent in photographic industry. It was also
> used in older color reversal processing sequence as an emulsion
> hardener. The industry replaced it with an even faster reacting
> hardeners, but those agents are toxic and they also harden gelatin
> almost instantly, and so they aren't suitable to hand coating of size
> or silver gelatin emulsion.
Received on Sat Jan 14 05:02:45 2006