SensitometryThe apparent values in a photographic print or negative can be quite different from the actual physical densities. Part of this is due to the fact that any value will influence the appearance of another value it is next to. Another consideration is that a particular value may feel right for the context of a particular image.
Knowing the density of a spot on a negative or print is not necessary for producing the highest quality Pt/Pd prints. So too is any line, curve, or number. These terms may be used to talk tough, but that's not a photograph. A d-logE curve will not provide the real information as to how the photograph is seen or felt. A densitometer will provide a unneeded number at great expense.Getting an absolute black means nothing. Claims are made that such-and-such is better because it provides a blacker black (or "it's D-max is better"). Black is not absolute. Even the deepest shadow, even in the middle of the night, is not absolute black, especially with the platinum palladium process. Let it be known right here that if a blacker black is desired, then one should try the gelatin silver process. Different papers, as well as variations in chemistry, will provide different blacks. It would NOT be wise to select a paper (or worse discard a paper) based only on its blackest value (or D-max). And, surprise, the blackest black in the print will never be the blackest possible with those materials. (Note: If not surprised, a good amount of printing experience must be at hand.)
Zones (as from the Zone System), like blacks, are also misunderstood. A Zone is a zone. Not a particular value, a Zone is a range of values. By definition the size of a Zone has been set to the range of values between the relative end points of a one stop range of exposure. The exact value is selected by the photographer for that particular print. A Zone may differ in the next print or with the next subject. Zones become useful in understanding relative increments of exposure and development and the relative placement of tonal values.
Might as well continue with a description of whites . With the platinum palladium process, many papers are available for selection. Each paper will have its own white. Optical brightening agents may alter the paper white. The platinum palladium process may not produce a white as brilliant as a gelatin silver print. If that's what is needed, print in gelatin silver. It is sometimes thought that Zone X or XI is paper white. This is not the case, especially with pure palladium. Zones X, XI, and XII may be distinguished and still not be paper white. The upper values are extremely important to a print. Finding and using the proper materials can make all the difference.
All one needs to know about the sensitometric qualities of film and materials can be had by making, fine tuning, and studying the Matrix described in the next section. Notes of the original scene at hand, the Matrix of negatives, and the Matrix of prints all laid out upon the table provide a wealth of information. From these one can see the smallest amount of density that will just separate a tone from the darkest density in the print ("speed point", zone I). It can also be seen at what density in the film the print will stop exhibiting texture ("contrast point", zone VIII) or just remain as plain as paper base ("upper limit"). If the print captures the quality that the photographer feels then it must be right. So too, the negative may be read as to containing such feeling.
Most importantly, the Matrix is based on a subject of familiarity to the photographer enabling them to intuitively grasp the nuances of the effects of exposure and development on the materials selected. To see a photograph, the photographer must know what the print looks like, and what kind of negative produced that print, and what kind of seeing lead to producing that negative. This only comes through experience and with much practice.