Dmax for COT 320 using palladium
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...
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.
Originally Posted by mikepry
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.
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.
Originally Posted by mikepry
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.
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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?
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.
Originally Posted by mikepry
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.
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.
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.