Re: APIS, hydroquinone hardening

From: Jack Brubaker ^lt;[email protected]>
Date: 07/14/05-03:47:59 PM Z
Message-id: <>

I hear you and Martin warning about the toxic nature of the resulting
chemicals produced by the interaction of the hydroquinone and a dichromate.
Not being steeped in chemical awareness myself can you or martin temper your
warnings with the fact that the resulting chemical would be in the hardened
sizing. Will it be toxic but locked up in the size or is it going to be
dissolving out into future water developing baths? Will it be gassing out of
the size? Is it a contact threat or a respiratory threat.


> From: Ryuji Suzuki <>
> Reply-To:
> Date: Thu, 14 Jul 2005 16:45:01 -0400
> To: alt-photo list <>
> Subject: Re: APIS, hydroquinone hardening
> On Thu, 14 Jul 2005 18:55:43 +0200, "MARTINM" <>
> 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 Thu Jul 14 15:46:51 2005

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