Page 3 of 21 FirstFirst 1234513 ... LastLast
Results 21 to 30 of 203

Thread: Obsidian Aqua, catechol staining developer

  1. #21

    Join Date
    Sep 2003
    Location
    Seattle, Washington
    Posts
    2,920

    Re: Obsidian Aqua, catechol staining developer

    Hi Chris,

    Yes, I think so, but there's some question as to whether a staining developer of any kind is the best choice for films with a lot of base fog. I suppose a staining developer can still provide a larger density range than a non-staining developer, important if one is printing in a long scale process, but staining the fog will definitely increase printing times, so it's a judgement call. But yes, if you are decided to use a staining developer, one that produces the minimum general stain is the best choice.

    Catechol itself is quite resistant to fogging, which contributes to general stain. In catechol developers that produce fog/general stain, it is almost always the secondary developing agents responsible. This is why a catechol developer that also includes phenidone requires a restrainer. Phenidone, and even metol produce fog in a pH environment appropriate for a catechol developer, and provide no benefit to justify this fault. I don't think phenidone or metol are superadditive with catechol, and perhaps not even additive. If you compare developing times for standard dilutions of Obsidian Aqua and Pyrocat HD, for example, you'll see what I mean. Even though OA contains no phenidone, and uses a lower concentration of carbonate, development times for OA are typically shorter than development times for Pyrocat HD at comparable dilutions. How can this be? Well, I don't know, exactly. There's an awful lot of reactions taking place in a Pyrocat HD working solution that are not present in OA, and some must have a braking effect on development. The same is true for Tanol Speed, which contains both catechol, and pyrogallol, along with two other developing agents, and yet development times are longer than with OA, and fog/general stain are higher, too.

    In my opinion, catechol developers are not improved by the addition of secondary/tertiary etc. developing agents, and all the other ingredients added to mediate their effects. Simply balancing the concentrations and ratios of catechol, preservative and alkali is all that is required to make a developer that does everything we want one to do, and nothing we want it not to do. All the rest is obfuscation and confusion.

  2. #22
    funkadelic
    Join Date
    Sep 2008
    Location
    Nashville, TN
    Posts
    1,250

    Re: Obsidian Aqua, catechol staining developer

    Thanks for sharing the formula for this developer. It looks inexpensive for such a large quantity, and the long shelf life is a great reason for me to conder its use. I've ordered some catechol and already have the others. I look forward to trying it in the near future.

  3. #23

    Re: Obsidian Aqua, catechol staining developer

    Any results from brush development in flat bottom trays?

    Compared to Sandy King's Pyrocat HD, what would I expect to see that you would call an improvement - and viewable in the final print?

  4. #24

    Join Date
    Sep 2003
    Location
    Seattle, Washington
    Posts
    2,920

    Re: Obsidian Aqua, catechol staining developer

    Chris, I'm always happy to share my work, and I hope others find it useful. OA is very inexpensive, and a little goes a long way. It can be a little tricky to measure out tiny volumes required for small tanks, due to the high concentration of the stock solution. A graduated pipette can make things a lot easier, and the bulb type are accurate enough for photo work. The first time you measure out 0.6ml for 300ml of solution can be a little unnerving, but after a few times, you get used to it.

    Feel free to contact me directly at:

    jdefehr@gmail.com

    with any questions or comments. Good luck!

  5. #25

    Join Date
    Sep 2003
    Location
    Seattle, Washington
    Posts
    2,920

    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by Dakotah Jackson View Post
    Any results from brush development in flat bottom trays?

    Compared to Sandy King's Pyrocat HD, what would I expect to see that you would call an improvement - and viewable in the final print?
    Brush development works very well with OA. Compared to Pyrocat HD, OA is sharper, finer grained, produces less fog/general stain, and more compensation with intermittent agitation.

  6. #26

    Join Date
    May 2008
    Location
    El Cajon, CA
    Posts
    406

    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by Jay DeFehr View Post
    Chris, I'm always happy to share my work, and I hope others find it useful. OA is very inexpensive, and a little goes a long way. It can be a little tricky to measure out tiny volumes required for small tanks, due to the high concentration of the stock solution. A graduated pipette can make things a lot easier, and the bulb type are accurate enough for photo work. The first time you measure out 0.6ml for 300ml of solution can be a little unnerving, but after a few times, you get used to it.

    Feel free to contact me directly at:

    jdefehr@gmail.com

    with any questions or comments. Good luck!
    A 1.0 cc syringe is graduated to 0.01 cc, so it should be accurate enough.

    m
    Michael Cienfuegos


    Non Illegetami Carborundum

  7. #27

    Join Date
    Sep 2003
    Location
    Seattle, Washington
    Posts
    2,920

    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by Michael Cienfuegos View Post
    A 1.0 cc syringe is graduated to 0.01 cc, so it should be accurate enough.

    m
    Yes, I use both. A syringe is more convenient for solutions in TEA or glycol, but a pipet is more convenient for aqueous solutions.

  8. #28

    Join Date
    Feb 2010
    Location
    Blue Ridge, VA
    Posts
    127

    Re: Obsidian Aqua, catechol staining developer

    This sounds like an interesting developer. However, the terms "low frequency" and "intermittent" agitation have been used here and are confusing me. Jay, can you define these terms more precisely? I assume that they mean more frequent agitation than stand (agitation for only the first 1 or 1 1/2 minutes after the developer is added) or semi stand (initial agitation plus one agitation cycle halfway through development.) Thank you in advance for the clarification, and for sharing your research.

  9. #29

    Join Date
    Sep 2003
    Location
    Seattle, Washington
    Posts
    2,920

    Re: Obsidian Aqua, catechol staining developer

    Hi Dan. I think you have the gist of it. Agitation frequency ranges from continuous at the high end, to stand at the low end, with a range of frequency in between. I consider "normal" agitation frequency to be the Kodak standard of 5 seconds every 30 seconds, or Ilford's standard of 10 seconds every minute, though this standard should not be thought of as the mean or median between the extremes. Low Frequency Agitation would be below these standards, and High Frequency Agitation above. Gordon Hutching's recommended agitation frequency of 5 seconds every 15 seconds would qualify as High frequency agitation, and all the various schemes such as semi-stand, minimal, extreme minimal, etc., would qualify as Low Frequency Agitation, meaning less frequent than standard.

    Agitation frequency can be visualized as a wave form, with rest periods alternating with agitation periods, and the amplitude of the wave as the vigor of the agitation. If, for example, we take an agitation scheme of continuous gentle inversions for 30 seconds, followed by 1 gentle inversion every 3 minutes, we could visualize this as a low frequency, low amplitude wave, and might be appropriate for a dilute developer and a high contrast scene. Another scheme might be to vigorously shake the tank for 30 seconds, and then to repeat for 5 seconds every 15 seconds, and we could visualize this as a high frequency, high amplitude wave that is typical for Technidol and Technical Pan development.

    This is probably more than you care to think about agitation, and to some extent it's more theoretical than practical, but there is a practical basis with a developer like Obsidian Aqua that is more sensitive to agitation than general purpose developers are. Visualizing agitation as a wave form with both frequency and amplitude has helped me to theorize about agitation schemes, and to test my theories, but it might be of little or no interest to anyone else. I hope I've answered your questions without putting you to sleep!

  10. #30

    Join Date
    Feb 2010
    Location
    Blue Ridge, VA
    Posts
    127

    Re: Obsidian Aqua, catechol staining developer

    I was hoping this thread would continue on as I am very interested in mixing up and trying a batch. So I will provide a bit of agitation...

    Jay: thank you very much for your detailed reply. After reading it and rereading the entire thread, I am assuming that you recommend the "geometric" agitation plan that you discussed in your original post? With that agitation, where do you suggest I begin for an N development time with Ilford HP4 Plus?

    Anyone else: have you tried this yet and what are your impressions?

Similar Threads

  1. Glycin and staining developers
    By Jarin Blaschke in forum Darkroom: Film, Processing & Printing
    Replies: 15
    Last Post: 3-Aug-2012, 04:50
  2. pyro developer, but which?
    By sergiob in forum Darkroom: Film, Processing & Printing
    Replies: 206
    Last Post: 25-May-2012, 18:06
  3. Ideal Developer for Film to be Scanned
    By Jay DeFehr in forum Darkroom: Film, Processing & Printing
    Replies: 34
    Last Post: 12-Apr-2010, 05:09
  4. Which staining developer?
    By Leonard Metcalf in forum Darkroom: Film, Processing & Printing
    Replies: 21
    Last Post: 21-Oct-2007, 08:13
  5. Old Formulas : Film
    By Paul Fitzgerald in forum Darkroom: Film, Processing & Printing
    Replies: 6
    Last Post: 19-Mar-2005, 20:31

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •