[pure-silver] Re: PMK was Re: Tri X film versions and sizes
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 16 Feb 2005 14:51:22 -0800
----- Original Message -----
From: "Ryuji Suzuki" <rs@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, February 16, 2005 2:20 PM
Subject: [pure-silver] Re: PMK was Re: Tri X film versions
and sizes
> From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
> Subject: [pure-silver] Re: PMK was Re: Tri X film versions
> and sizes
> Date: Wed, 16 Feb 2005 15:52:26 -0500
>
>> Even so the superadditivity ratio of Metol to
>> hydroquinone is around 1:3 or 1:4 and I would suspect
>> that it would be
>> in the same range for pyro.
>
> What's your definition of superadditive and "superadditive
> ratio?"
>
>> In PMK the ratio is 1:20 which does not appear to be
>> optimum.
>
> Does that make it non-superadditive?
>
>> Metol has traditionally been added in small amounts to
>> pyro
>> developers to improve shadow detail and gradation. Any
>> synergy
>> between Metol and pyro in PMK is a lagniappe.
>
> Does that make metol-pyrogallol non-superadditive?
>
> --
> Ryuji Suzuki
> "Keep a good head and always carry a light camera."
>
In developers like Kodak D-7 the Metol appears to
function as a preservative for the Pyro. D-7 is an ABC type
Pyro developer but it has much longer life. Kodak states
that in deep tanks it will last several weeks where ABC Pyro
like Kodak D-1 last only a few hours. From the limited
information given the two appear to be similar in activity
(development time). I think one would have to make
sensitometric tests to see if the Metol had any effect on
curve shape. The formulas are a bit long to copy them here
and are readily available.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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