[pure-silver] PMK and BTZS

A friend here in Australia asked for help establishing correct densities for his negatives in PMK which has opened a very interesting series of experiments over the past week or so.
To do the testing I dismissed using the BTZS tubes which are my normal method of developing 5x4 film based on the comments of many on the net regarding PMK. I also didn't initially use BTZS testing methods as I had also read that PMK oxidised rapidly and needed to be changed half way through a longer development cycle. This was impractical from my stand point with tubes.
I helped my friend establish his densities using his Jobo and at the same time for an experiment exposed a sheet of my normal film [Efke 100 5x4 sheet film] which is different to his, at a guessed exposre index and processed it in a BTZS tube for 8 1/2 minutes using my normal snap finger agitaition method. Perfect result. Much to my suprise, not streaks or uneven development. I now faced a dilema did I follow the flame of pyro so to speak?
I bit the bullet and got the actual chemistry and mixed PMK with EDTA as per the book of Pyro and proceeded to test based on the proven methods using BTZS.
I altered the dilution rate to 1.5/2/75 and did a series of tests and read them with the blue channel on an Xrite 810. I chose the dilution above to give me a particular g value at 4 minutes in the hope the developer might get to 16 minutes.
The PMK in the tubes had no problems at all with the constant snap rotation method. The curves spread evenly as I had hoped and to my surprise [blue channel reading] had a maximum density of 2.32 at 16 minutes. Based on that 16 minute density I could happily use 1.5/2/100 with the BTZS tubes.
Another major suprise was the very low base fog levels. Very little different to the same film in D76. Even at 16 minutes the base fog had only risen about an additional .03. This I think indicated that aerial oxidation in the tubes isn't [or wasn't for me] a problem
I appreciate that the blue channel is not as accurate as Visual with normal silver films but it has allowed me excellent base information to apply small corrections in Winplotter prior to exporting to expodev. 

Some observations:
The staining has been perfectly even in the BTZS tubes. No problems have been caused by the film back not having full contact with the PMK. And the base fog levels are no more than I would expect normally. No uneven development has been caused by not pre soaking the film. I follow a method of a very energetic some would say violent shaking of the tubes for 10 seconds and then snap agitation from then on. My agitation method has been exactly the same as the same film in D76 with the same wonderful even development. I diluted the stop bath to half strength and use normal non hardening fixer. Doing the film tests was a busy time as I decided not to allow the film to remain in the SB or the fixer for any longer than a film would be in a "conventional" system. 60 seconds [max] SB and 5 minutes in the fixer. 

Real film speed in either developer is almost identical.
The highlight control of the PMK "appears" to be just marginally better than the same D76 negative -- but -- the PMK image looks a touch flatter so needs a bit more contrast.I presume this is the compensating effect of the stain with VC papers. I haven't reached a verdict on the choice yet but for harsh Australian summer light I feel perhaps I would choose the PMK. For subtle shadow detail - that is yet to be answered.
I personally found there are subtle differences, and to some people and in some circumstances they may well be important. Those differences may just as easily be provided by using a different conventional developer correctly tested.
I am constantly amazed at the brilliance of BTZS, I settled in my mind, in 1.5 hours, with 5 sheets of film a curiosity I have held for many years about PMK. 40 minutes later I had shot and developed,dried and printed a test neg.
Would I change to PMK or a pyro style developer? Not completely but I now have real data if I wish to use PMK in a particular photographic setting. I found no technical reasons to not use PMK in BTZS tubes. 

I share my observation not to sway anyone either way.
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