Re: DuPont Velour Black AND POP

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, July 18, 2005 8:56 AM
Subject: Re: DuPont Velour Black AND POP

> From: BOB KISS <bobkiss@caribsurf.com>
> Subject: RE: DuPont Velour Black AND POP
> Date: Mon, 18 Jul 2005 09:02:08 -0300
>
>> For example I have decade old Azo paper which appears
>> fogged when
>> developed in Dektol but not in Formulary 130.
>
> I suggest to add a gram of bromide to Dektol diluted 1+2
> for this
> purpose. Some people reported that my DS-14 (a print
> developer of
> Dimezone S and ascorbic acid at pH of 10.4) worked well
> with Azo as
> well as many other paper.
>
>> I am guessing this has
>> to do with whether the developer works on the latent
>> image sites on the
>> surface of the silver halide crystals or if it has a high
>> concentration of
>> Sodium Sulfite, a complexing agent, which dissolves some
>> of the crystals
>> allowing for development of internal latent image sites.
>
> You are referring to surface v. internal development. This
> technique
> is used to study surface sensitivity and internal
> sensitivity of an
> emulsion. For example, undigested AgCl emulsions often
> have high
> internal sensitivity but with low surface sensitivity. An
> optimal
> sulfur sensitization would bring up the surface
> sensitivity.
>
> AgCl emulsions can be developed very rapidly and they
> don't season
> developer solution as much as AgClBr or AgBr emulsions, so
> they are
> commonly used for color printing paper. Cost of operating
> machines
> could be reduced because of shorter operation time and
> reduced
> chemical waste. (Since 1990s, photographic chemical wastes
> may no
> longer be dumped to the ocean and disposal cost went much
> higher.)
> However, AgCl emulsions are full of difficulties like high
> intensity
> reciprocity failure, fog, difficulty with sensitizing dye,
> etc. and
> much improvement was made in last 10-20 years.
>
> Application of rehalogenating bleach before exposure can
> remove fog
> centers but it can also affect sensitivity centers created
> during
> emulsion production and sensitometric property may change
> significantly.
>
  In regard to Printing Out Paper, the image is photolytic
silver generated directly by exposure to intense light. POP
develops fog over time in the form of metallic silver which
appears in the dark. I don't know what the chemical
mechanism is for this fogging. However, given that the
emulsions for POP are different from that of DOP I wonder if
salvage, if possible at all, must be done in another way.

   BTW, it seems to me, after seeing the above, that the
method of treating age fogged paper using a re-halogenating
bleach has been suggested in some very old books with the
same warning Ryuji gives above, namely that sensitometric
properties will be significantly affected. Again by
unreliable memory I think this may have been in "Photogaphic
Ammusements" a book published by the American Photographic
Book Publishing Co, which went through many editions. The
original was edited by E.J.Wall but later editions bear the
name of Franklin I. Jordan.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com