Re: APIS, hydroquinone hardening

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: "alt-photo list" <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, July 14, 2005 10:45 PM
Subject: Re: APIS, hydroquinone hardening

> Oxidized metol, especially in presence of persulfate, peroxide,
> percarbonate, etc. can be an effective bleaching agent(*), but I don't
> think oxidized metol can be an effective hardening agent. Generally,
> effective tanning developing agents have multiple hydroxyl groups
> available for reaction. Metol has only one and is said to give little or
> no hardening effect.

Maybe, maybe not, that's why I suggested to give it a (practical) try. As
e.g. the highly disputed subject of chrome hardening-crosslinking-tanning
suggests, there seem to be areas where theory may be way behind practical
tests.
Maybe oxidized metol is different from what the theory about "tanning
development" predicts. Incidentally, I am aware of at least one case where a
metol/ascorbic acid developer was said to harden a silver halide emulsion.

> There are other kinds of tanning developing agents,
> which have substituted groups that release a hardening agent (such as
> aldehyde) upon oxidation of the developer. One example is
> 1-phenyl-4,4-dihydroxymethyl-3-pyrazolidone disclosed in US Patent
> 3453109.

Yes, that's an nteresting patent.

> Bleaching and tanning are different chemical reactions and I request
> that clear distinctions be maintained if you continue this discussion.

So what do we do about "tanning development"?

Martin

> On Thu, 14 Jul 2005 18:55:43 +0200, "MARTINM" <martinm@SoftHome.net>
> said:
>
> > OK, you may give it a try all the same. I don't know what's exactly
> > formed
> > by oxidizing Metol but it's surely less toxic than Quinone.
>
> Oxidized metol, especially in presence of persulfate, peroxide,
> percarbonate, etc. can be an effective bleaching agent(*), but I don't
> think oxidized metol can be an effective hardening agent. Generally,
> effective tanning developing agents have multiple hydroxyl groups
> available for reaction. Metol has only one and is said to give little or
> no hardening effect. There are other kinds of tanning developing agents,
> which have substituted groups that release a hardening agent (such as
> aldehyde) upon oxidation of the developer. One example is
> 1-phenyl-4,4-dihydroxymethyl-3-pyrazolidone disclosed in US Patent
> 3453109.
>
> (*) It is known that oxidized developing agents of p-aminophenol type in
> the developer, if not removed by sulfonation or other means, may bleach
> some latent image or development centers and affect sensitometric
> properties. This can be very cleanly explained by electrode process
> model of development.
>
> > Well, sorry for being unclear about that, my "hardening/bleaching"
should
> > have read "hardening-bleaching", the way I referred to Quinone, was
> > limited on its use as a bleaching agent.
>
> Bleaching and tanning are different chemical reactions and I request
> that clear distinctions be maintained if you continue this discussion.
Received on Fri Jul 15 00:39:39 2005