The platinum-palladium (Pt/Pd) process is an iron based process.  (Other iron based processes include Cyanotype and Kallitype.)  The light sensitive component of the platinum-palladium process is Ferric Oxalate.  Upon exposure to light the Ferric Oxalate is transformed into Ferrous Oxalate.  The basic difference is that Ferric has a covalence of +3 and Ferrous has a covalence of +2.  These are differences in the electrons which cause the molecule to bond differently.  A property of the Ferrous Oxalate is to reduce noble metals from their double salts and revert back to Ferric Oxalate.  This reaction is known as Brewster's Reaction.  Platinum and Palladium are noble metals.  The resulting print consists of these noble metals imbedded in the fibers of a substrate.

The Ferric Oxalate sensitizer provides for what is called a Develop Out Process (DOP).  The image prints out partially and must be enhanced by use of a developer.  Another sensitizer, Ammonium Ferric Oxalate, provides for what is called a Printing Out Process (POP).  The image prints out fully with exposure.  No developer is used.  Both of these sensitizers are used to make Pt/Pd prints and provide for differing results in the prints.

The sensitizer is most sensitive to the Ultra Violet (UV) and blue portion of the light
spectrum.  However, it must be remembered that the Ferric Oxalates will also react to heat and time.  It is a good technique to expose within four hours of coating DOP and immediately upon coating and drying POP.

Platinum and Palladium may be used interchangeably or in combination, with each scenario producing unique qualities in the photographic print.  The metals can be mixed into a solution useful for this process when they are in the form of a double salt.  The double sat is basically the nobel metal chloride (such as PdCl₂) combined with a chloride salt (such as NaCl).   The platinum double salt is typically that using Potassium, K₂PtCl₄.  However the ammonium salt [(NH₄)₂PtCl₄] is sometimes used.  The palladium double salt can be any of the period I chloride salts or ammonium.  It is important that the salt be soluble in water.

Note:  At this point, I have only tried K₂PtCl₄, Li₂PdCl₄, Na₂PdCl₄, and K₂PdCl₄,

It is important that the greatest amount of metallic salt that the sensitizer can utilize be used for optimal print quality.  Metal beyond that will only be wasted, while not enough metal will result in a weaker print.  The simplified chemical equations for the Pt/Pd process are given in the section "Process Equations" in Chapter 6, Chemistry.  Optimized formulas for the metallic salts are found in the next section of Chapter 6.

Several contrast agents can be used to increase contrast in the print, though a reduction of contrast is not always possible.  It is highly suggested that near to correct contrast (erring on the weak side) be given to the negative.

Everything other than pure metallic platinum and/or palladium is cleared from the print with a clearing solution. The final result is the platinum and/or palladium metals embedded in the fibers of the substrate.

Please note that all of the methods, techniques, items, and things within this guide have been tried and tested by the author.  Those that work are currently in use by the author, and those that don't are so stated.   Every paper, chemical, or process variation can produce a unique nuance in the print and an incredible amount of control.  It is important that various materials are tried.

Technique is the key to control.  Technique is presented fairly well in this Guide, but it is something that has to be mastered.  Only with much practice will experience develop.  Experience will then provide insight into the materials, process, and technique.  Experience becomes the key to connecting the print to the eye.

There are certainly many untried and undiscovered nuances of the Pt/Pd process.
Additions or modifications may be made to this guide at any time.  Any questions or comments can be served via E-mail.
 

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