Dmax for COT 320 using palladium

Discussion in 'Alternative Processes' started by mikepry, Feb 7, 2005.

  1. mikepry

    mikepry Subscriber

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    While we are on the the subject of COT 320... I am trying to boost my DMax and have only been able to come up to 1.23 using pure palladium. Would you consider this weak?
    I remember reading somewhere it should be a little more than that, I think.
    I'm using a glass rod for 8X10 as follows;

    18 palladium/18 Ferric Oxalate Drop Count
    PO @ 110
    Clearing using Kodak HCA 1:4, 2 baths at 5min. ea.
    20 min wash

    Also tried double coating using 9 drops palladium/9 drops distilled water on first coat and ditto on the second.....no difference, still at about 1.23.

    I don't think an oxalic acid presoak will help as I've done that in the past and side by side comparisons show no difference at all.

    I started out using a 14/14 drop count and was coming in at 1.17 so by the additional 4 drops all I can see is a marginal increase. Having said that, I have a couple prints that look really nice and when I measured the unmasked portion of the print I see an 1.17 on that and it does again, look very nice. See attached. I have the second edition of Dick Arentz's book and he recommends a 48 drop count for an 8X10! Am I being to frugal here? I can't see spreading 48 drops w/the puddle pusher as I make quite a few trips back and forth with 18/18! Any help would be really appreciated. I have a feeling one of the things I'm going to hear is start using a brush...

    Mike
     
  2. clay

    clay Subscriber

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    I generally double coat the stuff, and I get a dmax of 1.45 to 1.5. What sort of humidity are you experiencing right now? If the humidity is really low, it can make your prints anemic and prone to solarization (bronzing or density reversal with exposure). I live in a palladium printers paradise in Houston texas where it is humid most of the time, so I don't have to deal with this problem that often.

    And yes, that drop count sounds a little low to me. I use pipettes, and my rule of thumb is .1 ml of each solution per 10 square inches. So an 8x10 would take .8ml of palladium and .8ml of FO. I get serious increase in density by double coating also. It goes from something around 1.25 to 1.45. I always tell workshop participants that skimping on solution is false economy, since you end up with prints that you throw away with both valuble metal AND paper costs down the tube.

     
  3. mikepry

    mikepry Subscriber

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    Clay,
    My humidity is right at 55% in my darkroom at present. This should be okay shouldn't it? And as far as the pipettes go I'm not familiar with the increments of them.....how many drops are .1 ml, etc? Thanks heaps.
     
  4. Michael Mutmansky

    Michael Mutmansky Member

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    Mike,

    55% is perfect. I won't print until mine is over 40% and under 60%.

    When you double coat, you need to use full strength solutions for both coats (or at least the last coat). I use a 1/2 strength mix for the first coat, and then do a full strength mix for the second. I found through rigerous testing (yeah, right) that this approach gives nearly the same boost in dmax as two full strength coats.

    As Clay says, it is false economy to be frugal with the solutions as the paper costs as much as the solution, and may be more, depending on the paper.


    ---Michael
     
  5. donbga

    donbga Member

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    Hi Mike,

    Your measured DMAX of 1.23 is a bit low by my experience. Clay's mark of 1.45 is a good aim point. I've never gotten a measured DMAX above 1.47. Cot 320 shouldn't need any acidic pre-treatment before coating. You could probably get by with as little as 1.35 DMAX since that is about 90% of 1.45 (convincing black as Arentz writes.)

    As for your drop count, using Clay's figure of .1 ml per 10 sq. inches is about right by my math. The volume of 1 drop from a plastic dropper is approximately .05 ml so for an 8x10 coated area that would work out to about 40 drops total of FO and metal. So as Arentz suggests he errs a little on the extra side for sensitiser and metal.

    I use a cheap Radio Shack electronic meter for measuring RH and also a wet bulb - dry bulb thermometer and it has been my experience that the Radio Shack device measures a little low. I have much more faith in calculating RH with a psychrometric chart and a wet/dry thermometer.

    So it would be my guess lack of humidity orlack of moisture in your paper may the cause of your low DMAX. Also is your FO mixture fresh and up to snuff?

    Michael Mutmansky made a good point in another thread about lay your paper on drying screens over night to humidify rather than stacked together. That does make a difference.

    Good luck,

    Don Bryant
     
  6. mikepry

    mikepry Subscriber

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    Are you guys using the Plotter program for your testing? If so are we taking the IDmax number given on the analyze tab or are we reading the total densitiy on the y axis?
     
  7. clay

    clay Subscriber

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    I'm talking max-max-max black - not the IDmax, which can be set at whatever %black you want. I find that double coated cot320 has such good shadow separation that I can use a 95-97% black and still see some value separation in the shadow areas.

     
  8. mikepry

    mikepry Subscriber

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    If that's the case then I'm showing a reading of 1.42 at steps 20 and 21. I did double coat using 18/18 each time and that did the trick. I have in fact ordered a 9010 brush as the glass rod is abrading the paper surface due to the ammount of passes needed with that ammount of chemistry. Thanks for the help everyone...just trying to get dialed in here.
     
  9. Michael Mutmansky

    Michael Mutmansky Member

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    IDMAX is an arbitrary assigned value, so it is somewhat meaningless to others unless everyone is on the same page. However, the dmax of the print is not, and that's what Clay's numbers above are.

    Let me also say that there are other ways to push the dmax over 1.45-1.5, but we are then getting into much more complicated additives and procedures, like double printing, waxing or other surface treatments, possibly using some PVA in the coatings, etc. The paper selection can be very important for this also.

    I've gotten up to about 1.7 (IIRC) in tests using a variety of these methods, none of which I would use for normal printing. Some of these were academic exercises to satisfy my curiosity. I think the practical limit for normal pt/pd printing is about 1.45D to 1.5D.

    Oh, and Mike, start using a brush if you want to improve dmax. I used a rod for a long while, thinking that I could be more efficient with the palladium, and I finally accepted that I was not getting the best dmax I could out of the prints, which didn't fit my printing style. I think I was topping out at about 1.3d using the rod, and I was never able to get a double coat with a rod that had the smoothness of tone I was looking for, so I was stuck with single coating.

    I switched to a brush and double coating, and the improvement in dmax was substantial. A magic brush, to be exact. I've never liked the results with the hake brushes, as I would sometimes get a little streaking with them. I suppose I should try them again sometime, but until my MB dies, I'll stick with that.


    ---Michael
     
  10. mikepry

    mikepry Subscriber

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    As far as rod coating goes I mentioned earlier that I noticed it was abrading the surface and I can see white paper fibers that are present on the exposed step wedge. What I'm assuming is the grainy look. Anyways I think that these white fibers showing may also lead to erroneous readings on the densitometer as well. I am happy where I'm at now as far as the DMax goes and once again, thank you for the help.
     
  11. photomc

    photomc Member

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    Find this thread really interesting, and hate to ask such a newbie question but how are you reading DMAX? With a densitometer? As an aside can relate that at least with the Zia's I've been working on that HUMIDITY was a major factor with what I have done..like if it was to low, sometimes nothing would happen..just faint images. Only recently started using COT320 and have found the paper very nice, was using Cranes Kid finish - read really thin paper, but when things came together the blacks were really nice. Just not something I have been able to reproduce each session.

    Sorry for the interruption, but you read and hear so much about DMAX, had to ask.
     
  12. Michael Mutmansky

    Michael Mutmansky Member

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    Sorry Mike,

    You must have been entering your response to Clay as I was typing in mine. That damage you mention is part of why I switched to brush coating. The other reason is a mottling of smooth tones (sky areas showed it most).

    Those both went away once I left the brush behind.

    I was able to get great single coats with the rod, but never able to get good double coats at all.


    Good luck to you.


    ---Michael
     
  13. nze

    nze Member

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    HI all
    I use rod or rush on Cot whitout any problem , even when I double coat to get more separation in the black. As wrote Clay the double caot give more seperation in the black of the print really interesting in low key image . When the image is mostl gray it do not bring a lot but with dark tone image it's great.

    I also agree with Michael about the way to produce higher Dmax with platinum print.
    The only way I find easy is multi coating and exposure ziatype. By this I mean I coat once , expose, coat another time expose again and his another time.

    It work nicely with ziatype . The total exposure of the 3 layers should be the total equivalent o the time needed for 1 exposure. The funny thing of the proces is that the contrast could be control with any of the layers.The first time I use this method I start with the low contrast and ended with higher one.But now when I use this I start with high cotrast to set the black line and then bring the gray level. With this procedure I can get Dmax betwen 1.7-1.8 depending on the paper.

    regards
     
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  15. Michael Mutmansky

    Michael Mutmansky Member

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    Christian,

    Do you clear between the exposures, or do you slap on another layer of solution without clearing? I haven't tried the Zia mthod of pt/pd, so I don't know which approach would make the most sense.


    ---Michael
     
  16. nze

    nze Member

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    Hi Michael

    I just don't clear between the exposure. So there is no shrinking problem . Crane's cover or platinotype give me better result that COt or arches platine with this modus operandi. Gold can't be use with his method as it is so unnstable that it turn purple as there is a new layer. But I tryed with other voponent like platinum, tungstate , caesium and it work well.

    I never try with traditional, I wil make a try tonight.

    CHristian
     
  17. Jeremy

    Jeremy Member

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    I have an extra 2 hours before work today and I really don't want to delve into Catullus or Virgil just yet so I'll give this a shot. Using traditional pd only I'll coat once, expose, coat again, expose, and then develop. I have the same print dry so I'll see if there is any difference. I'll post back when the results are in.
     
  18. mark

    mark Member

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    How do you keep the registrations exact with this method?
     
  19. nze

    nze Member

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    If you got black border the registration can be done this way

    But as I don't clear the print between the caot I just use to stick my negtive to a sheet of mylar or what ever transparent and stick this sheet of mylat to my paper. So I make the first print lift the negative which stay fixed to the paper , dry, then put back the negative in his positiion. that the easier way .

    CHristian
     
  20. Jeremy

    Jeremy Member

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    I know I read this, but for some reason my hand just cranked the timer to 15 minutes intead of 7.5 both times.

    edit: I just dried the print in the microwave to speed things up and I can't see any difference in the dmax. This is on Stonehenge Rising extra white.
     
    Last edited by a moderator: Feb 8, 2005
  21. nze

    nze Member

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    I mean with black border you can register the nagtive and the print with the black border.
     
  22. mikepry

    mikepry Subscriber

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    While doing allot of reflection on all the possible variables involved with boosting Dmax I did notice the usage of PVA in the sensitiser. Is Liquitex PVA? The artist gloss medium to be exact. I saw that in the second editin of Dick Arentz's book as well as in a paper that Phil Davis sent me (in fact Phil stated he used a diluted formula to Size the paper adjunct to the addition of it to the emulsion itself). I am considering switching clearing agents as well for fear I may be getting a slight bleaching as well. I will try a 1% Oxalic acid as well as Perma Wash ala Jorge. This has been really informative for me and gives me a renewed sense of appreciation for the work Sean has put into this site. VIVA LA APUG!
     
  23. Donald Qualls

    Donald Qualls Member

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    Assuming PVA means polyvinyl alcohol, that's the working ingredient in modern white glues like Elmer's and "tacky" craft glues. I don't think it's the same as gloss acrylic medium, because PVA is white in solution and dries only semi-clear; a painting medium needs to be colorless and transparent, both wet and dry. I *think* Liquitex is a water based acrylic similar to Future acrylic floor "wax", and to the "ModPodge" decoupage kits from the 70s; it's the same as the dispersant in acrylic artist colors, but without pigment.
     
  24. colrehogan

    colrehogan Member

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    Okay, I haven't been doing this for very long so forgive me if I'm wrong.

    I have used gold in one of my ziatypes on COT paper and I didn't see any purple coloration. Gold isn't unstable. According to the Sullivan book, the purple coloration in a ziatype containing gold is supposed to arise from when you're using a mixture where gold is 80% of the metal drop count in your mixture. I suspect that due to your multi-coat technique, you are introducing too much gold into your print, hence the purple color. (Incidentally, I'd love to make one of these purple prints sometime, it sounds like it would look cool!) :D

    Perhaps if you only used gold in your final coat instead of all three, you could use it? Or you could reduce the drop count in each solution to prevent you from introducing so much gold into the print? Just my $0.02 worth.
     
  25. Michael Mutmansky

    Michael Mutmansky Member

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    There's two PVA out there that are used in the realm of alt photo. One is polyvinyl alcohol and the other is polyvinyl acetate. I'm talking about the alcohol, not the acetate. I haven't tried the acetate, except in gum printing. It may work out similarly.

    The alcohol is a clear, fairly thick liquid that dries clear, and can be used to thicken the coating solution so it does not soak into the paper as far. Keeping the solution on the surface can increase the dmax a bit, but I didn't like the shift in color that I saw with the use of the PVA, so I don't use it.

    That's all academic anyway, unless you subscribe to the belief that the dmax of the print must be 2.35 for the print to be a 'good' print. About 1.3 is all that is required to achieve a convincing black, and while a 1.5 dmax does look better in comparison, taken on it's own merits, a print with 1.35 or so will be percieved as a 'full range' print.

    ---Michael
     
  26. nze

    nze Member

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    Hello Diane

    in fact I also try to add the gold in the lats coating with a lithium feric salt which help to avoid gold stain. But there are free ferric salt which react with gold.
    for the purple print I made some of them , blue , pink or purple you just need a low Drange negative as these mixture are quite contrasty. you should also work in a 50% Rh as if there is to much humidity the print will turn neutrel cold.

    As for your question on BS forum. I try to add gold and platinum to ziatype, it sometimes works and others not. the more gold I use the less it works.