Large tonal swings with different negs but same values – Pd/Na2

[JakeG]

I am trying to pin down my digital negative creating for palladium/Na2 printing. The problem that keeps creeping in is getting a QTR negative that is near ideal (based on Yule-Nielsen curve), then on the next negative, with the same settings, all of the mid-tones go very light – even with a higher Dmax!


Please see the graphs here:
https://www.flickr.com/photos/fallriver1/14252093588/



Here are the particulars:
QTR software – single curve with K adjustment curve, LK(as gray) separate for Black Boost

Printer: Epson 7900
Neg substrate: Pictorico Premium
Paper: Torinoko Gampi 17gsm
Coating: 6+6+1 Na2 ratio every time
Ultrasonic humidifying of paper after complete drying
Exposure: 15 minutes
Vacuum print table: handmade - uses Kreen film instead of glass
Same developer, PO at 110F, and clearing baths every time.
Working humidity has been in the mid 40s lately.
Using densitometer instead of scanner because Gampi scans too glossy in blacks.


Here is a 4x5 image made when things were working fairly well and the step-tablet mid tones were only half as light as the first link:
https://www.flickr.com/photos/fallriver1/14230084998/



1. Can the Epson and the negatives can be ruled out based on the UV density readings?
(The first one was made the night before and the other was dried with a combination of hair dryer/ drying cabinet for 10 minutes total but the density values are near identical.)
2. What about variations in pre-exposure humidifying?
3. Coating technique inconsistent?
4. Is there something obvious that I'm missing?

 

[pschwart]

If the negative densities are truly identical, your light source is providing consistent output, and you are using the same chemistry, this suggests the coating/humidifying is the culprit.
Nice print

 

[JakeG]

Thanks, Philip. This afternoon I ran another test print whose negative was printed last night. The graph shows near ideal again. It seems any time I leave a neg to dry overnight I get good results. Even though the UV density does not appear to change compared to quick drying, I wonder if there is something else going on during longer curing times which affects the final print? OR . . . it could be my hand-steaming technique has too many variables as you suggest.

 

[pschwart]

Unless you are using a UV densitometer like an X-Rite 361T your readings are not going to be suspect.
I use a hair dryer on my negatives for about 45 seconds and they print consistently, so you might give that a try. I would suspect the humidifying first as that can have a dramatic effect, and it can be difficult to control and measure.

 

[JakeG]

Yes, the X-Rite 361T is what I use for measuring the negatives. Also, I was speaking to Melody Bostick this afternoon about details of their "Platypus party" coming up when the subject of pre-exposure humidifying came up. She suggests that such thin paper may not need it. I will make some comparison prints on my next days off. At least for now I am ruling out variability of my negatives.

 

[pschwart]

Do you use a backing sheet behind your paper in the vacuum frame? This can help retain moisture and add some consistency.

 

[JakeG]

Yes, I'm now using a sheet of orange masking film under the paper. The vacuum table I built has a black, textured rubber base, but I have suspected the slight texture might also be a channel for humidity to escape. Also, I cover the sensitized tissue with a single layer of Clear Bag film to protect the negative. I've seen no loss in detail. The cover is not glass but Kreen. I modeled it after the plate burner we use at work for polymer plates.

So the sandwich consists of masking film, paper, Clear bag layer, negative, then I unroll the Kreen and kick on the vacuum.