Re: POP process

----- Original Message -----
From: "Loris Medici" <loris_medici@mynet.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, November 08, 2004 9:03 AM
Subject: Re: POP process

>
> I guess Mike was asking:
>
> Is there any selenium toner fomula that doesn't
> incorporate sodium or ammonium thiosulfate so that we can
> use it "after fixing" but without the fear of "further"
> image fading? Or does Selenium definitely needs some sort
> of silver halide solvent in order to work?
>
> Your answer says "yes" I understand... Where we can find
> the formulas?
>
> ITOH, isn't powdered Selenium quite poisonous / dangerous?
>
> Thanks in advance,
> Loris.
  To clarify this. One can make Selenium toner without
thiosulfate but it still tones silver halide so it will tone
everything in the emulsion. So will sulfiding toners like
Kodak Brown Toner. The bleaching is due to the exceedingly
fine grains of silver which make up the POP image. This is
why the image is reddish brown. The finer the silver
particles making up the image the more yellow they look. If
the metallic silver is fine enough the hypo will tend to
dissolve some of it along with the silver halide. Gold
toners do not affect the halide but do convert the metallic
silver. This protects it from the hypo along with
intensifying the image and changing its color. At least some
of the color change is probably due to enlarging the silver
crystals.
   There may be other, and cheaper, materials than Gold or
Platinum for toning but I don't know what they are.
   Powdered Selenium is hazardous but mainly becuse of the
danger of its becoming airborne. Selenium compounds are more
toxic than pure selenium but in a liquid solution it is both
diluted and can not easily become airborne. Kodak Selenium
toner is not hazardous unless you drink it. In its working
form its not dangerous to use. While Selenium, and some
other photo chemicals, can be absorbed through the skin the
rate of absorption is very low so there is no real hazard to
getting it on your hands. That said it is still good
practice to keep photo chemicals off your hands by using
gloves or tongs.

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