It should be ok. As long as you don’t see lines or dots or any other artifacts in your image.
You have at least 3 channels printing through every tone of the image at rather high ink limits. PiezoDN negs are built with roughly even ink limits all the way across with the idea in mind that if a neg needs to be stretched like this, the same amount of nozzles are still firing no-matter which nozzles they are.
Best,
Walker
That’s a lot better, Art, but I suspect you are still overexposed. You shouldn’t need that much ink at the shadow (thin) end of the negative for Pt/Pd. (Maybe for salt or albumen, though!)
The Curve View screenshot is informative, but secondary. I still need your measurement text files, as before, to make a proper diagnosis. Scans (or pictures) of the printed targets are helpful too. Those are plural because I’m assuming you reprinted the Master at a shorter exposure time, then made a new -lin curve and negative, and printed the -lin negative. I’d like to see the measurement files from both, and images.
Also, what were your exposure times for both rounds of tests?
And I’m sure you’ve mentioned it in another thread, but what is your exposure light?
We also were thinking it was still a little over.
The last exposure time was 4 minutes. The time before was 8 minutes.
We are using a vacuum printer with a 2kw diazo bulb.
What brand is your printer? NuArc? Olec? Something else? Do you know the exact bulb designation, model #, etc.?
It’s necessarily relevant to your original question, but I think I’m starting to see a pattern related to exposure light and how the Master curve prints. I’d like to start keeping notes on it for future reference.
I have an Olec AL15, but it is in storage since it’s so big and loud and I no longer live alone! If I ever have a separate studio space again I’ll set it up.
Those text files would be really useful. 
The bulb is Diazo 1406-1, and the vacuum printer is Berkey Ascor. I’ve been looking for documentation on the vacuum printer, do you happen to know where I can find the manual for it?
I’m going to try a shorter exposure time, and will post the text files later.
Looking at some old Olec info in my files, it looks like Diazo bulbs tend to have peak output in the 400-420nm range, while Photopolymer bulbs peak at around 360nm. My fluorescent UV BL bulbs peak at around 360. It is very possible that this is source of the differences we get when printing the Master curve. Some of us, including me, find it skews light; others, like you, find it skews dark.
Here’s a link that I just found that might be useful to you. They have your bulb (and mine) but I haven’t found any spectral output charts. I’ve also attached an old Olec lamp chart for reference.
http://www.caprockdev.com/photopolymer.htm
By the way, I’m not at all suggesting that one is better than another. Just that it might explain that one particular difference that we have seen several times.
Olec-lamps.pdf (38.3 KB)
Art asked how I came up with the adjusted Master curve for the peculiar response with Metal Halide exposure light that I suggested Gilles try.
First I looked at the curve of the initial Master target print and analyzed it. I divided it into highlights, mid-range, and shadows. I set the divisions somewhat arbitrarily at 25% and 75% which are represented by the horizontal white lines added to the graph. The horizontal axis of the graph, which represents the steps of the 129-step target, can also be thought of as ink density. You can see that much more ink is needed to block the light and bring the Pd (in this case) response up to linear. The shadow region, especially the lower half of the shadow region, has very little separation between adjacent tones. So I need a curve adjustment that will correct for this. It does not need to be perfect - that is the job of the Linearization process that we do with the Smoother tool - just close enough to not overload the Smoother.
[attachment file=26248]
For this process I used the Curve Adjustment Tool. First I made a model, in a Photoshop Curve window, of what I wanted to accomplish based on what I think is the most critical part, the shadow region. I selected a point on the curve where the toe begins and drew a horizontal line, represented by the red arrow, left to where it intersects the linear Target line. This will be my first control point on the adjustment curve. Experience tells me not to overdo the correction curve, so I don’t make it quite as dramatic as it look like it might need to be. From there I use the remaining 3 control points to bend the rest of the curve to approximate a mirror image of the Master. I am not concerned with making it perfect, since anything above the line is going to be an improvement, but I want it to be reasonably close and I want it to be smooth.
[attachment file=26249]
When I have something I think will work I transfer the 4 input/output pairs to the Piezography Curve Adjustment Tool and follow the procedure for making adjusting the .quad.
[attachment file=26250]
I would name the new .quad MH-Master (for Metal Halide) or something like that. Then test it as you would with the regular Master, and make a linearization from the results of that.
The reason Art started this thread was his concern about what he was seeing in the CurveView of the .quad curves he was coming up with which show a lot of ink in the dense region of the negative. This is directly related to the amount of density needed to block UV light to create a linear result. There is something about the interaction of the printing process, the ink on film, and the exposure light that is having a very unusual result. I don’t know what it is. I can say that I have in the past worked with a similar metal halide light (Olec AL15 w/ L-1250E lamp - similar spectral output to those used by Art, Gilles, Rafael, etc.) side-by-side with a BL fluorescent (350nm peak output). With traditional large format film negatives there was no significant difference in the way Pt/Pd prints responded. I never used the Olec with digital negatives though.
I’m pretty sure that eventually Walker will come up with a better way of making a Master tuned specifically for these metal halide units, but until then I hope this will help make the linearization process a little easier for those of you using them.
Thanks Keith
Ignore the attached files.
PiezoDN-129step-i1Pro2-HahnPtPd4min-12072016-1.txt (2.11 KB)
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