Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 68,766   Posts: 1,484,117   Online: 926
      
Results 1 to 4 of 4
  1. #1

    Join Date
    Nov 2002
    Location
    Melbourne, Australia
    Shooter
    Medium Format
    Posts
    950
    I have been using some home made Pyrocat-HD, made of chemicals from Vanbar in Melbourne (Australia) who are generally pretty good with their source of bulk chemicals. Results have been promising, but shadow detail has been unexpectedly low. So I've done a proper Zone test on 120 HP5+ (I know I should have done it in the first place) and have found speed to be under 100. Contrast in Zones 3 and beyond is quite high (not a worry at the moment). I'm using 1+1+100. Non-rotary tank.

    I suspected that the phenidone might have been stale (it was a bit brown) but the chemical guy at Vanbar said that some POTA had recently been made with that batch and it had been fine. This seems a good enough test to me.

    I am pretty careful with measurements, but it's not beyond possibility that I made a mistake. Would adding too much potassium bromide be a cause of depressed shadows combined with minimal effect at higher zones? I intend to mix another batch very soon.

    I've been a PMK user for a while and I've enjoyed the long shelf life of mixed PMK. The phenidone in Pyrocat-HD does give it a shorter shelf life. Also, I understand that phenidone usually requires a restrainer to control fog.

    If I use metol (25g/Litre of Part_A) instead of phenidone could I dispense with the bromide altogether? If using metol costs me 1/3 of a stop I don't mind. I don't do rotary processing, and don't get much general fog from PMK, although the negs don't look as clean as the Pyrocat-HD ones. Would doing this affect the qualities of Pyrocat-HD when used with minimal agitation?

  2. #2

    Join Date
    Mar 2003
    Location
    Greenville, SC
    Shooter
    Large Format
    Posts
    4,813
    Images
    5
    [quote="john_s"]

    "I have been using some home made Pyrocat-HD, made of chemicals from Vanbar in Melbourne (Australia) who are generally pretty good with their source of bulk chemicals. Results have been promising, but shadow detail has been unexpectedly low. So I've done a proper Zone test on 120 HP5+ (I know I should have done it in the first place) and have found speed to be under 100. Contrast in Zones 3 and beyond is quite high (not a worry at the moment). I'm using 1+1+100. Non-rotary tank."

    Something is very wrong here. Pyrocat-HD give full emulsion speed with HP5+ so your effective film speed is off by about two full stops.

    "I suspected that the phenidone might have been stale (it was a bit brown) but the chemical guy at Vanbar said that some POTA had recently been made with that batch and it had been fine. This seems a good enough test to me."

    Probably not the cause of the very low EI. Even without the phenidone the pyrocatechin in the formula has enough punch to get close to emulsion speed.

    "I am pretty careful with measurements, but it's not beyond possibility that I made a mistake. Would adding too much potassium bromide be a cause of depressed shadows combined with minimal effect at higher zones? I intend to mix another batch very soon."

    Adding too much potassium bromide could have a huge impact in depressing shadow density, and effective film speed.

    "I've been a PMK user for a while and I've enjoyed the long shelf life of mixed PMK. The phenidone in Pyrocat-HD does give it a shorter shelf life. Also, I understand that phenidone usually requires a restrainer to control fog."

    Pyrocat-HD also has a very long shelf life, definitely more than six months. Phenidone does require a restrainer because it has enormous regenerative qualities. Just a tiny bit of it, as in the PyrocaHD formula, results in a significant increase in efffective film speed.

    "If I use metol (25g/Litre of Part_A) instead of phenidone could I dispense with the bromide altogether? If using metol costs me 1/3 of a stop I don't mind. I don't do rotary processing, and don't get much general fog from PMK, although the negs don't look as clean as the Pyrocat-HD ones. Would doing this affect the qualities of Pyrocat-HD when used with minimal agitation?"

    You could substitute metol for phenidone at about 10X the amount, but I would still recommend that you include potassium bormide. The main difference with the metol substitution is slightly reduced film speed.

    Sandy

  3. #3

    Join Date
    Nov 2002
    Location
    Melbourne, Australia
    Shooter
    Medium Format
    Posts
    950
    Thanks, Sandy, for your prompt and informative reply.

    I have just made up some fresh "PMC" that was one of your earlier formulas. I mixed it without bromide, and with 25g/L metol, and got a healthy 200 speed out of HP5+.

    As soon as i can, i'll mix up some more real pyrocat-HD with phenidone and bromide.

    Could you explain why bromide gives more speed? Would varying bromide change acutance effects? I'm particularly interested in semi-stand development with half-strength pyrocat-HD. Even my faulty batch gave me brilliant, lively sharpness.

  4. #4

    Join Date
    Mar 2003
    Location
    Greenville, SC
    Shooter
    Large Format
    Posts
    4,813
    Images
    5
    [quote="john_s"]

    "I have just made up some fresh "PMC" that was one of your earlier formulas. I mixed it without bromide, and with 25g/L metol, and got a healthy 200 speed out of HP5+."

    Interesting that you found that information from so long ago. PMC stood for pyrocatechin/metol/carbonate, but it sounded too much like PMK. There is no practical working difference between PMC and the current Pyrocat-HD with metol. The PMC formula called for sodium carbonate and not potassium carbonate, but so too did early versions of Pyrocat-HD. It really makes no difference which of the carbonates you use so long at you get the same amount by weight into the working solution.

    "Could you explain why bromide gives more speed? Would varying bromide change acutance effects?"

    Bromide is a restrainer and when used in the right amount reduces fog without cutting speed. However, if you use too much bromide the result will be not only very fog free negatives but also a signficant reduction in effective emulsion speed.

    "I'm particularly interested in semi-stand development with half-strength pyrocat-HD. Even my faulty batch gave me brilliant, lively sharpness.

    You might want to look at the threads at the AZO forum on the use of Pyrocat-HD with semi-stand and minimal agitation. Quite a number of peopole have been experimenting along these lines and reporting their results.

    Sandy



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin