[pure-silver] Re: PMK was Re: Tri X film versions and sizes
- From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 16 Feb 2005 15:52:26 -0500
"metol is a much more powerful developer, gram for gram, than
pyrogallol"
It's hard to directly compare developing agents because their modes of
action may be different. However, the molecular weights of Metol and
pyrogallol are 176 and 126 respectively. You must use 40 percent more
Metol to=20
get the same stochiometric result as pyro.
"It's a pyrogallol-metol developer. It works differently than
developers using either alone."
It is said that Metol and pyro are superadditive but I have not seen any
data confirming this. 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. In PMK the ratio is 1:20 which does not
appear to be optimum. Such a high ratio is what is usually evidenced by
Phenidone in superadditive combinations.
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.
Jerry
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Jim MacKenzie
Sent: Wednesday, February 16, 2005 2:59 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Tri X film versions and sizes
----- Original Message -----=20
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, February 16, 2005 1:53 PM
Subject: [pure-silver] Re: Tri X film versions and sizes
> "PMK ..., which also largely based on metol"
>
> I would not characterize PMK as a Metol developer it contains 10 times
> as much pyrogallol as it does Metol.
True, but that's deceiving because metol is a much more powerful
developer,=20
gram for gram, than pyrogallol is. It's a pyrogallol-metol developer.
It=20
works differently than developers using either alone.
Jim=20
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