Re: Silver chloride contact printing papers - AZO

----- Original Message -----
From: "Loris Medici" <loris_medici@yahoo.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, January 26, 2004 9:05 AM
Subject: Silver chloride contact printing papers - AZO

>
> I was reading an article about AZO paper and in the
article it's written
> that AZO is a silver chloride contact printing paper.
AFAIK, salted
> papers and albumenized papers also are silver chloride
papers. The AZO
> article also mention developers like Amidol, Dektol...
that's where I
> got confused; according to my limited knowledge, salted
and albumenized
> silver chloride papers are POP papers - there's no
development involved
> but only a wash to get rid of unexposed silver chloride,
then toning and
> fixing. So, what is the main difference - in the emulsion,
not the
> support - between salted / albuminenized paper and AZO
paper? BTW, the
> look of AZO prints doesn't resemble even a bit to salted
paper and/or
> albumenized paper - from what I get from the reproductions
of both
> mediums.
>
> Thanks in advance,
> Loris.
>

  The difference between Printing Out Paper and developing
out paper is the way the emulsion is treated before coating.
Printing Out Paper has excess salts in it which are washed
out of developing out emulsions before coating. There are
other differences but this is the main one.
  The image on POP is produced by photolytic silver. That
is, silver generated by the direct action of light on the
emulsion. All emulsions will produce some photolytic silver
when exposed to light, but the amount is too small for image
formation in developing out materials.
   Azo has a completely conventional emulsion. According to
Kodak it is all silver chloride rather than a mixture of
chloride and bromide as is most enlarging paper. Silver
chloride is very slow so it is suitable for use in a contact
printing paper intended to be used with strong light
sources. The ratio of speed between Azo and typical variable
contrast enlarging paper is about 100.
   At one time every manufacturer of printing paper made at
least one contact paper, Kodak made at least three, plus a
couple of special purpose papers. Azo was a general purpose,
neutral image color, paper. It is now the only contact speed
paper made.
   Amidol tends to produce neutral or slightly cold toned
images. The maximum density of the image is determined by
the emulsion rather than the developer so Amidol blacks are
no denser than those produced by other paper developers such
as Kodak Dektol but the image color tends to make them look
dense. Phenidone paper developers, like Ilford Bromophen,
also tend to produce neutral or bluish image color so are
probably as effective as Amidol without the cost.
   While many consider Azo a "magic" paper, in fact, its
published curves are very similar to Kodabromide, the
discontinued neutral tone enlarging paper.
   Azo is handled like any other developing out paper. It
can be toned to increase density or to change image color
but does not need toning to make the images permanent. By
permanent I am refering to immediate darkening, as with POP,
not to archival protection.
   Silver Gelatin printing out paper must be washed to get
rid of the excess salts and then treated in a toner and
fixed. Because the image silver is so finely devided (which
also accounts for the sepia color) even a weak fixing bath
will tend to bleach some of it away. The usual process is to
treat it in a toner which affects the silver image but does
not tone the remaining halide, and then remove the halide
with a fixing bath.
  Michael Smith and Paula Chamlee have contracted with Kodak
to provide the minimum sales to keep Azo in production. I
strongly suggest buying Azo from them. Their stocks are also
likely to be fresh. They have a number of suggestions for
using Azo on their web site including some good Amidol
developer formulas. Their prints look wonderful but I think
that is largely due to their making very good negatives and
being very good printers although they attribute at least
some of the quality to the paper itself.
  Salted paper is also a printing out paper but does not
have an emulsion. Rather, the sensitive salts are coated
directly on the paper. However, it is processed much like
silver-gelatin POP.
  The name "Azo" probably comes from the idea of its being a
universal paper, i.e., "everything from A to Z 'O. Like many
of its brand names this one came from a company Kodak bought
out in the days when George Eastman was creating a photo
materials monopoly around 1900.

http://www.michaelandpaula.com/mp/index.html

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