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.
Received on Mon Jul 18 09:57:02 2005