What happened with the link to the pyro article is that the close parenthesis became part of the URL. Here is the URL again: http://unblinkingeye.com/Articles/Pyro/pyro.html.
In response to Tom Duffy's question, I believe pyro offers better tonal separation at both ends of the tonal scale. This is particularly apparent when enlarging--see http://unblinkingeye.com/Articles/Pyro/Fig...4/figure_4.html --but is also evident to a lesser degree when printing with either platinum or Azo.
For these tests Herbst was using negatives developed in his own variant of the Wimberley WD2D formula. It all started with Herbst's article on the use of pyro negatives for platinum printing. He did a comparison that showed clearly that pyro negatives offered a longer printable tonal range for both platinum and silver. Dan Smith and I approached Herbst to run the same test on Azo, since Michael Smith had suggested (somewhere) that Azo might have a longer tonal scale than platinum. Herbst's results show that Azo has at least a nearly equivalent tonal scale, which is a very significant finding. --So much so that Herbst plans to use Azo and amidol for making fine prints in the future, in addition to his platinum work.