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  1. #1

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    Help with fogging for pt/pd printing (dichromate contrast control)

    Greetings,

    I am having problems with fogging (gray mottling) in my highlights of pt/pd prints. I am using potassium dichromate in my potassium oxalate developer for contrast control. In the past, I used NaPt for contrast control with no problems for straight Pd printing. This is my first foray into printing with both Pd and Pt. Do I need some type of restrainer in my metal solution? Currently, I am using the following for an 8x10 print:

    1 ml FO (relatively fresh ~1 month)
    0.5 ml Pt
    0.5 ml Pd

    developed in potassium oxalate (1L + 2ml of 10% potassium dichromate)

    Exposures are ~400 units on a Nuarc and I am getting mottled highlights even when I cover the coated paper with foil. The degree of mottling seems to coincide with how long the coated paper sits out suggesting it may be sensitive to spurious UV in the house.

    Any thoughts or ideas?

    Cheers,

    mitomac

  2. #2
    dpurdy's Avatar
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    I am not sure why fogged highlights would be mottled. Mottling is more a problem with the paper PH or with it's humidity. One thing that would probably change if you leave your coated paper sitting around is it's humidity.
    One reason I have never tried to adjust contrast by adding stuff to the developer is because it seems to me it would leave questions about what the developer is doing. I adjust contrast with Pt/Pd by variously using hydrogen peroxide or Na2 or classic part B.
    Another thing in my experience is that the more platinum you use in the mix, the more likely you are to have mottling or grain problems. I keep my platinum content down to 10-15%. It only takes a little bit of platinum to improve the density of your blacks over pure palladium.
    You can make a print with quite a lot of ambient light but I work in my basement and use 25 watt lights and if I leave a coated paper sitting around awhile I will either put it face down or on a dark shelf.
    Try putting 1 drop of hydrogen peroxide in your mix to see if it clears up your highlights.
    Dennis

  3. #3
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    What paper are you using?

    just as a warning/clarification - NA2 does not work as a contrast control when doing blended pt and pd. It does not affect overall contrast, just highlight exposure.

    As a precaution, I'd reduce the overall ambient light in the room where you coat if you can, and I'd coat just-in-time - don't have pre-coated paper sitting around waiting to be used. This eliminates humidification as an issue in printing - the paper is still highly moist from the fresh emulsion so long as the overall room humidity remains above say 40%.

    I'd also switch from adding dichromate to the developer to adding it to the emulsion, the way you would add NA2.

  4. #4

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    I'm not really into chemistry but this is what I have used successfully for many years... 1/2 to1/4th pt as to 1 pd and 1/10 gold chloride, 2 FeO I to 1 FeoII (from Bostick & Sullivan) diluted with distilled water 1 part to 6 of the emulsion combination. I generally mix enough for several prints measuring with pipettes in 0.1 ml's. I keep it in a covered shot glass and coat one paper at a time. Two 15watt bulbs illuminate the room plus very little ambient light. If additional contrast is needed I add hydrogen peroxide for that particular coating. In south Fl it is usually pretty humid although I work in air conditioning. When I was getting some voids in coating I pre-wet the paper with brushed on distilled water and let it dry but until it almost felt not quite dry dry. Ammonium citrate is my developer which I keep and add fresh as needed for volume. It has worked so I haven't messed with it.

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  5. #5
    Ian Leake's Avatar
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    Quote Originally Posted by mitomac View Post
    ... I am getting mottled highlights even when I cover the coated paper with foil. The degree of mottling seems to coincide with how long the coated paper sits out suggesting it may be sensitive to spurious UV in the house.
    Potassium Dichromate shouldn't cause any highlight problems unless you are using way too much of it. And then it's less of a mottling and more of a sort of flat graininess - a bit like if you had over-brushed the paper. Are you sure that you are using a 10% solution of Potassium Dichromate? The proportions that you've quoted (2ml of 10% in 1L) are what I (and many others) call 'Grade 2'. This is fine and doesn't cause any problems. I have seen problems when I've used 30ml or more of 10% per litre of developer and this has been coupled with excessive drying.

    What is your developer temperature? This effects all sorts of things, but so long as it's in the normal range then it shouldn't be the cause of your problems.

    You don't have enough Platinum in your sensitiser to see any graininess/grittiness from it. You only really see this when you're using Potassium Chloroplatinite on its own without _any_ Sodium Chloropalladite. I used a 50:50 mix for years with Potassium Oxalate/Dichromate, and nowadays use an 85:15 Pt:Pd mix. It's only with 'pure' Platinum that I've seen grittiness.

    Three other thoughts occur: (1) As Dennis posits there may be something strange going on with your drying process; (2) You may be damaging the paper when coating it; and (3) There may be something wrong with your Ferric Oxalate.

    First I'd confirm that the problem isn't in your Ferric Oxalate. This is easy to test by mixing a sensitiser solution using fresh Ferric Oxalate. One, probably daft, question re. your Ferric Oxalate: you are using Ferric Oxalate #1 aren't you? If somehow you've got mixed up and are using #2 then the high level of Potassium Chlorate in #2 will definitely cause mottled highlights.

    Assuming that you haven't changed your paper, paper storage method or your coating process (sensitiser volumes, brush/rod, times, etc.) then I would discount that for now. If you have changed any of these variables then I would go back and test these with your old process.

    That leaves us with drying as a potential root cause. Can you describe your drying method? How are you drying the paper, and for how long? What is your ambient temperature and humidity? Do you have constant ambient temperature and humidity or do you have draughts or other variables? And while you're at it, what paper are you using and how much sensitiser are you using?

    Could you post a scan of the mottling so I can see it? Oh, and another dumb question: it's not that your paper is sticking to your negative is it? You should know if it is, but a quick check of the back of your negative should show whether there's anything sticking to it.

    One last thought. Even though this doesn't sound like fogging on its own, perhaps it could be fogging in combination with another factor that accounts for the unevenness. So it's worth being aware that platinum/palladium sensitiser is sensitive to visible light, so if you are fogging your paper then it could be any light that you have switched on. So are you drying in the dark or with lights on? And if the lights are on then how bright are they?

    Quote Originally Posted by dpurdy View Post
    One reason I have never tried to adjust contrast by adding stuff to the developer is because it seems to me it would leave questions about what the developer is doing.
    Just for the record, Dennis, Potassium Dichromate works in exactly the same way as all the other restrainers (Potassium Chlorate, Na2 solution, etc.). It inhibits the laying down of Platinum and Palladium by converting Ferrous Oxalate back into Ferric Oxalate. There's nothing mysterious going on :-)
    Last edited by Ian Leake; 04-09-2013 at 02:40 AM. Click to view previous post history.

  6. #6

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    I always dry sensitized papers in a relatively light-proof box usually for 3+ hours. Of course, humidity can slow that process. I recently went from using COT 320 to Goyu Kozo, and was surprised how long the paper remained wet. I was doing a 7X17 negative and the paper had been drying for at least 12 hours. I made the mistake of discounting a somewhat moist feel to the paper, and printed without an interleaved sheet of Mylar. The print was mottled and the negative was ruined. Fortunately, I was able to retake the scene for a new negative.
    van Huyck Photo
    "Progress is only a direction, and it's often the wrong direction"

  7. #7
    Ian Leake's Avatar
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    Quote Originally Posted by doughowk View Post
    I recently went from using COT 320 to Goyu Kozo, and was surprised how long the paper remained wet. I was doing a 7X17 negative and the paper had been drying for at least 12 hours. I made the mistake of discounting a somewhat moist feel to the paper, and printed without an interleaved sheet of Mylar. The print was mottled and the negative was ruined. Fortunately, I was able to retake the scene for a new negative.
    Ouch

  8. #8

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    Many thanks to Dennis, Flying Camera, Ian, Doug and Jeffrey!

    The mottling is more of a touch of gray that is not quite uniform in the highlights (I apologize for any confusion with the term). I just wanted to make sure I wasn't missing something with the metal mixture when using dichromate in the developer.

    Stray light

    It appears that Pt/Pd is much more sensitive to stray UV then Pd with NaPt for contrast control. Tonight I will try coating a sheet of cot320 in very dim room and will be militant about keeping the sensitized paper in the dark until dry. In the past with Pd (NaPt), I was able to coat inside during daylight hours - I tried that once with Pt/Pd and got a dark gray mess.

    Humidity

    Usually not a problem in NC, but out of habit I typically steam the paper over a kettle before exposure. Starting to think this may also be contributing to the problem and some of the variability. Will try without steaming.

    Solutions

    I am biochemistry professor by day - so fairly confident my solutions are OK (although I have been known to make boneheaded mistakes - which of course I blame on my students).

    I will make up fresh FO (cheap enough to mix on demand). Given that Pt/Pd appears to be more sensitive to stray UV light than straight Pd, it may also be more sensitive to the age of the reagents .

    Development

    Almost always done between 20C and 37C

    Many thanks for all the help - despite the cost of (Pt) and my problems with the highlights - the overall tone of the prints are fantastic. My Pd prints were always a touch too warm for my taste and these are perfect. Once I dial in the 1:1 ratio I will see how low I can I dilute the Pt for the same effect.

    Cheers,

    mitomac

  9. #9
    Ian Leake's Avatar
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    Quote Originally Posted by mitomac View Post
    Many thanks to Dennis, Flying Camera, Ian, Doug and Jeffrey!

    The mottling is more of a touch of gray that is not quite uniform in the highlights (I apologize for any confusion with the term). I just wanted to make sure I wasn't missing something with the metal mixture when using dichromate in the developer.

    Stray light

    It appears that Pt/Pd is much more sensitive to stray UV then Pd with NaPt for contrast control. Tonight I will try coating a sheet of cot320 in very dim room and will be militant about keeping the sensitized paper in the dark until dry. In the past with Pd (NaPt), I was able to coat inside during daylight hours - I tried that once with Pt/Pd and got a dark gray mess.

    Humidity

    Usually not a problem in NC, but out of habit I typically steam the paper over a kettle before exposure. Starting to think this may also be contributing to the problem and some of the variability. Will try without steaming.

    Solutions

    I am biochemistry professor by day - so fairly confident my solutions are OK (although I have been known to make boneheaded mistakes - which of course I blame on my students).

    I will make up fresh FO (cheap enough to mix on demand). Given that Pt/Pd appears to be more sensitive to stray UV light than straight Pd, it may also be more sensitive to the age of the reagents .

    Development

    Almost always done between 20C and 37C

    Many thanks for all the help - despite the cost of (Pt) and my problems with the highlights - the overall tone of the prints are fantastic. My Pd prints were always a touch too warm for my taste and these are perfect. Once I dial in the 1:1 ratio I will see how low I can I dilute the Pt for the same effect.

    Cheers,

    mitomac
    From what you've said here, my suspicions fall on your kettle or developer temperature.

    Platinum is actually less active than palladium (on many papers it is significantly less active) so there's no reason why it should fog more easily than palladium. However, the level of paper moisture has a significant impact on both platinum and palladium (Dmax and contrast range). A patch of paper that has more moisture than another may well fog more quickly. if you've got a fairly normal room humidity then you should be able to use paper without having to humidify it first.

    When platinum is developed in a cold developer (e.g. room temperature) it can get a gritty look. You may want to heat up your developer a bit to see if this changes things. At 65C you should see greater Dmax and greater contrast (and if developer temperature is the problem then perhaps the mottling will go). Beware though that higher developer temperature will boost the palladium more than the platinum.

    Good luck!

    Ian.

  10. #10
    Davec101's Avatar
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    Quote Originally Posted by mitomac View Post
    Many thanks to Dennis, Flying Camera, Ian, Doug and Jeffrey!

    It appears that Pt/Pd is much more sensitive to stray UV then Pd with NaPt for contrast control. Tonight I will try coating a sheet of cot320 in very dim room and will be militant about keeping the sensitized paper in the dark until dry. In the past with Pd (NaPt), I was able to coat inside during daylight hours - I tried that once with Pt/Pd and got a dark gray mess.

    mitomac
    What batch of Cot 320 are you using? Some of the recent batches have been problematic. The majority of issues one experiences with Platinum/Palladium printing are usually down to paper. Traditionally Cot 320 is not the ideal paper when using more than 50% Platinum.

    You might want to try a fresh batch of Potassium Oxalate. What ph is your PO? Should be around 5-6. Also you might want to add a little 0.5g Oxalic acid to your fresh Ferric Oxalate.

    Also what clearing method are you using? If its stain rather than fog you are seeing you might want trying more aggressive methods of clearing.

    If all else fails try a different paper. There are a number of good papers that work well with 50/50 Platinum/Palladium mix.
    Last edited by Davec101; 04-10-2013 at 03:32 AM. Click to view previous post history.
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