Woe is me. Woe is me. DMax won't top 1.3

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Joe Lipka

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After talking with Kerik and some other folks at Photolucida last year, I found out my technique was lacking in terms of creating "a convincing black" to someone other than a close relative. From the description of my process, I felt the problem was too much time between coating and exposure. The keen eyes among the group thought my images looked "veiled" and seemed to be somewhat below the surface of the paper. This appealed to my thought that the paper sucked up the sensitizer instead of setting atop the fibers.

The remedy, I thought, was to reduce the time between sensitizing and printing. I tried that this weekend. The paper was Weston Diploma Parchment. An 8 x 10 area was marked off and bombarded with palladium sensitizing solution (18 drops FO, 18 drops Pd and 4 drops of 2.5% NA2), not once fellow hybrid practicitioners, but twice! I coated once, waited until the paper had a damp look and coated it again. When the paper looked damp again, I printed the trusty red green array to find my new blocking color. I exposed, I developed (Pot Ox at 100F). I was convinced the black was black. But, my trusty X-rite 400 disagreed with me.

I found the new blocking color and a DMax of 1.3 to 1.32. Is this as good as it gets with this combination of sensitizer? This is really, really weak as far as blacks go.

Any suggestions?
 

keithwms

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Probably a dumb and insulting question, but.... is this perhaps an issue of base transmission of your negative? If you expose the paper directly (no neg), do you get the blacks that you desire? I didn't quite get the meaning of "I printed the trusty red green array to find my new blocking color," perhaps your answer to my question is in there somewhere.
 

clay

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Joe,

The two things that immediately spring to mind when I hear about this are:

1) humidity - a print exposed at 50% ambient RH (and with some mylar underneath to keep the vacuum frame from removing the humidity) will have better dmax than one exposed at 20-25% RH.

2) Coating volume. It looks like you are using plenty. What brush are you using? This is a problem I always run into in workshops where people get penny-wise and pound foolish and try to get by with the bare minimum of solution


As for that particular paper, I found it pretty easy to get a 1.4 Dmax with single coating - as long as I used enough solution and dried it after a one minute 'rest' with a hair dryer. Then I let it sit under a cool fan to get the humidity back to 40-50% (ambient RH)

One of the problems with Weston is that it sort of 'roughs up' on the surface when you coat, expose and process. This can reduce your dmax a little.

One final question: what are you printing your negatives on? If it is the Pictorico OHP ultrapremium, I have noticed that it is damn near impossible to get a completely solid black through the stuff.
 
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keithwms

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One final question: what are you printing your negatives on? If it is the Pictorico OHP ultrapremium, I have noticed that it is damn near impossible to get a completely solid black through the stuff.

That's what I was thinking about in my response... I posted a transmission spectrum of OHP here some time ago and it really cuts off too high for some light sources. My theory is that this result in lack of good contrast in the print, i.e. small Dmax minus Dmin.

Regarding roughness, this will affect the measurement of the DMax greatly, no?
 

clay

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Keith, I finally used up the last of my cursed OHP ultra premium a few months ago. I got it to work, but the print times were longer, and I never could get the same black as you might see in a border area that was not covered by the clear edge of the OHP film negative.

And yes, roughness will have some effect on Dmax. Thus the huge difference between matte and glossy papers when silver printing.
 
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Joe Lipka

Joe Lipka

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Thanks for the comments, gang. Here are the answers to your questions, taken straight from the top...

Keith - D'oh! Slaps forehead. That basic question, DMax without anything between the light source and the sensitizer. That would quantify the "film base plus fog" effect of the Pictorico film. A worthy experiment to try. The question about the red-green array is a good one. Our fellow member, mkochsch came up with a clever way to find a negative color layer which can be used to modulate the contrast for a digital negative. (click on the links on his post right above this one!)

I measure the DMax at more than one place. The Richeson brush is very gentle on the paper surface.

Clay - Humidity is no problem here in North Carolina. The local atmosphere is not the consistency of a thin milkshake (like Houston) the humidity during the summer months is pretty high. The use of a vacuum easel would reduce the humidity along with the air pressure. My vacuum easel is a NuArc run off a Gast vacuum pump, not one of those metal tables with a bunch of holes drilled in it. So, it is very likely that I am drying out the paper during the exposure of 6 minutes.

The coating is done with the Richeson 9010 "magic brush."

Yes, I am using the Pictorico Premium OHP material.

Michael - The color that seemed to work for me the best this time was a R=96, G=208 combination. It's kind of a lime green hue, reminiscent of Bartholomew and the Oobleck (for you Dr. Seuss fans out there) with a six minute exposure. That little square measured a 1% reflectance and was the lowest reading of the entire array. That point is a little bit under the capability of the x-rite 400, so I chose that combination.

Your suggestions have given me pause to consider some more experiments (Let it be known that I despise experiments over creating photographs) to answer some great suggestions y'all have made. To wit:

1. An exposure of sensitized paper with out a negative and not under the vacuum easel. - Measure the "true" DMax.
2. Expose sensitized material without OHP in the vacuum easel.

I can compare these two tests with the previous exposed step wedge in the vacuum frame under the OHP material. The test I have completed have plenty of material between the light source and the sensitized material. Maybe the combination of the two is a killer for my DMax. I shall find out and let you all know.

If you can come up with some other ideas between now and the weekend, post them here and I can try them. I have some vacation next week and between a trip to the Beach and various golf courses I hope to answer this question.

Thanks again for your help. You folks do know what you are talking about.
 

clay

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Joe,

I think you may be little surprised at the with/without test for the OHP. It is very hard to get a solid black with the ultra/premium OHP. The next roll I bought was the regular OHP, (TPK-2466/20) and it is a lot better. More like the imagesetter negs I used previously in terms of clear base transmissivity (is that a word?).

I routinely now keep a piece of mylar on the rubber bed of my exposure unit., one which I lay the coated paper and negative. It will seal up the package nicely and retain the humidity in the paper instead of sucking it out. This hit me a few years ago when I noticed that my longer exposures of images made from in-camera negatives were always warmer in tone. Then the 'aha' moment, as you say. The long exposures were giving the vacuum time to dehumidify the paper tremendously, which will yield a warmer tone.

Thanks for the comments, gang. Here are the answers to your questions, taken straight from the top...

Keith - D'oh! Slaps forehead. That basic question, DMax without anything between the light source and the sensitizer. That would quantify the "film base plus fog" effect of the Pictorico film. A worthy experiment to try. The question about the red-green array is a good one. Our fellow member, mkochsch came up with a clever way to find a negative color layer which can be used to modulate the contrast for a digital negative. (click on the links on his post right above this one!)

I measure the DMax at more than one place. The Richeson brush is very gentle on the paper surface.

Clay - Humidity is no problem here in North Carolina. The local atmosphere is not the consistency of a thin milkshake (like Houston) the humidity during the summer months is pretty high. The use of a vacuum easel would reduce the humidity along with the air pressure. My vacuum easel is a NuArc run off a Gast vacuum pump, not one of those metal tables with a bunch of holes drilled in it. So, it is very likely that I am drying out the paper during the exposure of 6 minutes.

The coating is done with the Richeson 9010 "magic brush."

Yes, I am using the Pictorico Premium OHP material.

Michael - The color that seemed to work for me the best this time was a R=96, G=208 combination. It's kind of a lime green hue, reminiscent of Bartholomew and the Oobleck (for you Dr. Seuss fans out there) with a six minute exposure. That little square measured a 1% reflectance and was the lowest reading of the entire array. That point is a little bit under the capability of the x-rite 400, so I chose that combination.

Your suggestions have given me pause to consider some more experiments (Let it be known that I despise experiments over creating photographs) to answer some great suggestions y'all have made. To wit:

1. An exposure of sensitized paper with out a negative and not under the vacuum easel. - Measure the "true" DMax.
2. Expose sensitized material without OHP in the vacuum easel.

I can compare these two tests with the previous exposed step wedge in the vacuum frame under the OHP material. The test I have completed have plenty of material between the light source and the sensitized material. Maybe the combination of the two is a killer for my DMax. I shall find out and let you all know.

If you can come up with some other ideas between now and the weekend, post them here and I can try them. I have some vacation next week and between a trip to the Beach and various golf courses I hope to answer this question.

Thanks again for your help. You folks do know what you are talking about.
 

keithwms

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Oh I didn't realize that there were different pictorico OHPs. Well if anybody has some scraps they want me to check, just mail them and I can put them in my spectrophotometer and post the transmission curve. The OHP that I checked before was definitely unsuitable for some light sources- it's about as transmissive as a lead brick at ~325nm and below, thus missing several important UV mercury lines....

pictorico.jpg
 

Donsta

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Joe

My 2 cents...

I think paper humidity is key to Dmax - provided the ambient humidity is above 50% and the paper itself is humid all the way through, you should not have Dmax issues. Personally, I have use a "chamber" for humidifying paper before use and my consistency has improved dramatically as a result. I place a sheet before sensitizing into the chamber for 30 minutes and then leave it to rest outside in the ambient 60% RH darkroom for 10 minutes prior to coating. My "chamber" is a pair of trays - the top one inverted as a lid with another smaller tray place inverted into a layer of water in the bottom tray - this acts as a "table" onto which the paper is placed.

I also suspect that you may be drying out the sensitizer too much on your paper. I hit mine with a hand drier immediately once their is no more visible "pooling" on the paper surface for about 90sec - I then let the paper rest for 20 minutes and print. According to your website, you use a large amount of vacuum on your easel - at that level of vacuum, I'd have moisture seeping out of my paper onto the negs. Try printing "wet" so to speak with much less suction and see if that picks it up.

IMO, convincing black seems to happen around 1.4 on most papers - I print almost exclusively on Arches Platine and get 1.4+ very consistently with a similar mixture in the same developer and developer temp.
 

sanking

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I found the new blocking color and a DMax of 1.3 to 1.32. Is this as good as it gets with this combination of sensitizer? This is really, really weak as far as blacks go.

Any suggestions?

Convincing black can be deceptive. I think there are many people who are perfectly satisfied with their pt./pd. print but if you actually measure the reflective density it will not be over about 1.35. It is definitely possible to get more. Most of the time I have no problem at all getting a reflective density of about 1.42- 1.47 with the Weston paper. A couple of times I have even gotten
over 1.50. I don't know that there is any one secret, but here are some of the things I consider best practice.

The keys to good Dmax at my place are:

1. Humidity of 60% or more. Since that does not exist without help at my home I use a local humidifier in the room where I coat and dry the paper.

2. Good humidity in the room where the paper is stored.

3. Good choice of paper. Cot 320 and the Weston paper both give good Dmax.

4. Fresh ferric oxalate, and at pH of about 6.3 or lower. You want to be sure to have a slight excess of oxalic acid.

5. Set the emulsion on the paper after you coat it with air from a fan.

6. Dry the sensitized paper no longer than necessary. I always expose within 30 minutes or less of coating.

7. Apply a coating of slighlty acid (pH 6.0 or so) water and dry before coating the emulsion. Or double coat with a second coating diluted 1:1 with distilled water.

8. Use a lot of solution to coat. I use on average about 3.0 ml of solution per 8X10 print.

9. Fairly fresh developer at pH of around 6.0.

Even with all of this there are times when Dmax drops to the 1.30 - 1.35 range, for no reason that I can figure out.

Sandy Kinig
 

keithwms

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Well, now, I suppose paper roughness is probably the biggest determining factor in the DMax you measure. Rough-textured paper simply reflects light off in too many directions to achieve a high DMax. My recollection is that, everything else being equal, a smoother paper can achieve several stops' higher Dmax than a rough surface. So... (maybe a dumb question) what about coating the completed fiber print with a resin-like material; that should boost DMax.
 
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