Re: Developing Lith Negs with Dilutions of PQ etc.,

[Richard Knoppow <dickburk@ix.netcom.com>]

At 09:59 AM 08/13/2001 -0400, you wrote:
Maybe I missed it, but what is PQ?  I'm just about to expose my first two 
sheets of Arista ortho litho and was trying to decide between dilute Dektol 
or LC-1.  By the way, there is a web site that gives measuring spoon 
equivalents for various photo chemicals if you want to make Soemarko's LC-1. 

John McAdam 

   PQ means Phenidone and Hydroquinone. Another name for Hydroquinone is
Quinone or Quinol.
  Phenidone and Metol are "superadditive" with Hydroquinone, meaning the
combination of the two developers is more powerful than either alone. MQ or
Metol and Hydorquinone developers are the most common of all. Nearly any
kind of developer can be made with this combination. 
  Phenidone has some advantages over Metol. It is less toxic to the skin
and is less affected by dissolved bromide in the developer, meaning PQ
developers generally have a larger capacity than their MQ equivalents. 
  Phenidone, by itself, is a very low contrast developer. Its used as the
sole developing agent in special very low contrast developers like POTA and
Kodak Technidol. For normal contrast use it must be combined with another,
superadditive, developing agent, like Hydroquinone or Ascorbic acid. 
  Kendall of Ilford developed a practical method of manufacturing Phenidone
in the late 1940's. Ilford began exploiting this developing agent and makes
a number of developers containing it and also published formulas for
several type of Phenidone developers, including a lithographic developer. 
  Commercial packaged developers with Phenidone or one of its newer
derivatives are:
Ilford Microphen (a PQ version of D-76)
Ilford Bromophen (PQ Dektol)
Kodak Xtol (P and Iso-Ascorbic acid)
  There are many other examples. The patents on Phenidone expired long ago. 
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com