Re: Silver chloride contact printing papers - not AZO

----- Original Message -----
From: "Judy Seigel" <jseigel@panix.com>
To: <alt-photo-process-l@sask.usask.ca>
Cc: <alt-photo-process-error@sask.usask.ca>
Sent: Tuesday, January 27, 2004 10:26 PM
Subject: Re: Silver chloride contact printing papers - not
AZO

>
>
> On Tue, 27 Jan 2004, Richard Knoppow wrote:
> >
> > There is another silver chloride contact paper besides
AZO... It's
> > the Centennial Gelatine Chloride Printing-Out Paper sold
in this country
> > by Chicago Albumen works.
> >
> > Judy, its important to distinguish between printing
out paper and
> > developing out paper. Centenial POP is a printing out
paper, Azo is a
> > developing out paper. While both have silver chlororide
in their
> > emulsions (I am assuming this about the Centenial paper)
the emulsions
> > are otherwise different.
>
> Yes, of course... I'm quite aware that Centennial is a
POP, in fact I said
> so. And am now editing details of just how to POP it, of
which god is in
> the toning.... (If the original query specified
*developing out
> paper* I missed that....)
>
> However, speaking of image color, the Centennial
apparently gets a neutral
> or cool tone with the thiocyanite formula for the gold
toner... and of
> course platinum toning is also cool.
>
> I'll add, though that DOP can be made into POP with a
chloride bleach...
> I think Chris Anderson, or maybe it was Liam, or both(?)
have done that
> too... You bleach it back with hydrochloric acid & (as I
recall) a
> bichromate bleach... and just leave it in the sun or
strong light and
> forget about it... You think nothing is happening, but in
a few days you
> have a brown tone quite tactile photograph. Could
probaably gold tone it
> too, if you felt the urge.
>
> J.
>
  Somewhere, in the all too distant past, I also had
instructions for making POP out of DOP. Mainly I remember
that it was treated in a solution that included silver
nitrate. I can no longer remember where I saw this but have
a vague clue that I can follow up.
  The color of the image on B&W paper is mainly controlled
by the nature of the silver particals making it up. Printing
out paper has extremely fine grains which tend to look
redish or yellowish. After exposure to the sun the paper has
a maroon color. However, the image is not permanent so must
be treated with a toner and fixed. The final color will
depend on the toner. Gold toners leave a blue black or
purplish image color. Platinum a neutral black color. There
are other toners but I think these two are the only ones
widely used. I think Selenium can be used to tone POP but
Kodak Rapid Selenium Toner has thiosulfate in it and will
tend to bleach the image before its toned. A POP image can
be fixed before toning but the fixer will tend to dissolve
some of the very find metallic silver image as well as the
excess halides, so the usual procedure is to tone first in a
toner which is selective for metallic silver and not the
halide. That leaves out sulfiding toners off all varieties
because they will tone the halide as readily as the silver.
  There are lots of toner formulas for POP in old books, but
as is often the case with ancient art, they must be taken
with some skepticism. You have written about such
precautions in using old formulae and procedures youself, so
you know what I mean:-)

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