Re: APIS, hydroquinone hardening

From: Ryuji Suzuki ^lt;[email protected]>
Date: 07/14/05-02:45:01 PM Z
Message-id: <>

On Thu, 14 Jul 2005 18:55:43 +0200, "MARTINM" <>

> 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

(*) 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 Thu Jul 14 14:45:18 2005

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