[pure-silver] Re: Development modifications for higher sharpness

----- Original Message ----- 
From: "Ryuji Suzuki" <rs@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, April 27, 2005 5:57 PM
Subject: [pure-silver] Re: Development modifications for 
higher sharpness


> From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
> Subject: [pure-silver] Re: Development modifications for 
> higher sharpness
> Date: Wed, 27 Apr 2005 13:10:40 -0400
>
>> Perhaps "energetic" would be better than high energy. 
>> But still
>> somewhat vague.
>
> What's energy in general?
> What's energy in the context of developers?
> What changes energy in developers?
>
>> I have seen the following statements concerning the 
>> addition of iodide
>> to the Beutler formula.
>>
>> 1. Addition of iodide can emphasize flare and lens 
>> aberations.
>> 2. Not needed for modern emulsions.
>> 3. Never did anything anyway.  The amount has been 
>> described as being
>> homeopathic.  (I particularly liked that comment about 
>> homeopathy, ie,
>> quack medicine.)
>
> Sure, all sorts of things are said about virtually 
> anything in
> darkroom literature. The question is what is correct, what 
> is
> relevant, and what is practically useful.
>
> Influence of iodide in developer solution depends on the
> concentration.  In a very small dose, on old fashioned 
> emulsions, work
> as anti-restraining agent. So your number 1 can be in 
> operation in
> this case. In light of various techniques used in 
> emulsions to
> facilitate development reaction in modern films make the 
> number 2 more
> plausible. I disagree with the number 3.
>
> If you want to take advantage of increased adjacency 
> effect by
> adjusting the iodide level, I might add that the window of 
> useful
> iodide concentration can be fairly narrow and emulsion 
> dependent.
> Similar effect can be achieved by careful adjustment of 
> developer pH
> in DS-12 type developers. But no matter which technique 
> you choose, if
> you make film develop on the edge, the result becomes 
> erratic. I
> seriously suggest that kind of risk and frustration is 
> unnecessary in
> serious darkroom operation. If you seek exaggerated 
> effects, digital
> manipulation is a more effective approach than trying to 
> make a
> complicated chemical system work near a critical point.
>
> --
> Ryuji Suzuki
> "Keep a good head and always carry a light camera."

  Potassium Iodide is found in a couple of old developer 
formulas. These formulas are for scientific photography. One 
reason for the addition is to suppress the effects of 
bending or abrasion (this is from Mees I think. After 
reading this stuff for decades I can't always remember 
exactly where I've seen something). It may be there for 
other purposes also. An example of such a developer is a 
variation of D-76 called by Kodak D-76c. It is described as 
a low and normal contrast developer for Wratten "M" and 
Metallographic and Spectrographic plates. "M" plates were 
for microscopy. The formula is the regular D-76 formula with 
the addition of:

Potassium Iodide, 1% solution, 1.0 ml / liter
and Potassium Bromide, 2.5% solution, 10.0 ml / liter

   If Iodide tended to prevent edge/border effects in older 
type emulsions that could explain its presence in this 
formula. I also have a very vague memory of reading that 
Iodide could concentrate development near the surface of the 
film. Again, if this is so it would be reasonable for the 
applications above where maximum _resolution_ and minimum 
distortion of the image are important.
   All of this may be obviated in modern thin emulsions.
   Iodide is also sometimes added to developers or fixing 
baths for microfilm since a trace tends to prevent oxidation 
of the image. (Pope, et.al. you have the references Ryuji)

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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