Quote Originally Posted by Gerald C Koch View Post
By pyro I must assume that you are asking about a staining developer. By "works best" just what do you mean? Finer grain? Xtol is a fine grain developer.

The answer is that a stain image can never have as fine grain or accutance of an ordinary image. The reason that this is true is that the stain/dye migrates away from the silver halide grain during development. The result is that the apparent size of the grains is increased by the larger dye clouds. The dye cloud also masks fine detail. This can be easily seen with the use of a microscope. Each silver grain is surrounded by a stain halo. This is why staining developers are not recommended for 35mm films.
I have to agree with Ian on your observations. In fact, you may well have your findings exactly opposite of what is generally known about developer characteristics.

Pyro based developers harden the gelatin of the film during the very first stages of reduction, grain is set at that point with relatively little change to the grain's accutance or appearance no matter the length of exposure to chemistry.

Whereas, developers with a significant presence of Sodium Sulfite do in fact promote silver migration during the last stages of exposure to chemistry. Such migration and lack of stability directly go to the accutance and impression of sharpness in the final negative / print.

MSDS information on Xtol shows a moderate amount of Sodium Sulfite makes up the formula for Xtol.

Lastly, I have never looked through a microscope at any negative, I have however seen tests done on Tri X & FP 4 developed with HC 110 and the Pyrocat HD. THese tests were conducted by a respected moderator on the LF Forum and bare out with striking clarity the thoughts I shared above.

Cheers