Today I developed my Azo in Donald Miller's Phenidone, pyrogallol, pyrocatechol developer (PPPD), with and without KBr.
Without KBr I got good tonality and very dense, warm blacks (with a slight reddish tone). The developer was very active without KBr!
After developing 8 8x10s I added KBr (twice as much as I intended - and the formula calls for). The printing time increased by a factor of 5. The effective paper contrast dropped to about Grade 1. In spite of all this, I managed to get one quite good print.
When I developed the next print, I found that the developer was dying (after 16 prints from 1 liter of working solution). I threw in a teaspoon of sodium carbonate and tried another print - could only get a very weak image to appear.
I'll try again - with the right amount of KBr this time.
The PPPD developer heavily stained my (white Cesco) developer tray.
I am comparing the blacks and tonality of my Azo prints against the blacks in George Provost's Azo/Amidol print "Roots."
My best prints so far are the ones I developed in Ansco 130 with 1 gram of KBr added to the working developer. George Provost's blacks are better - almost 3 dimensional.
I will make one more run with PPPD, then on to Michael Smiths Amidol formulation.