Customized Curve Linearization


#1

I successfully created a linearized curve using the PiezoDN-Master.quad from my printed 129-Spyder Step. I process printed the Step using the chemicals as described in the Data Sheet for the Epson 1430 (100%Pd + P.O. Developer). I was looking for prints with a bit more contrast, so I then printed my DN image with A.C. Developer but the result wasn’t much different.

In 2016 when using Jon’s older curves (51b-Lin-1_89.quad) with 50-50 Pt-Pd + A.C. developer, I was getting the exact look I wanted with a 5:00 minute exposure time.

So, the other day I took my 129 Step DN that I printed with the master.quad curve and process printed it with a bit less Pt than before - this time 70% Pd/30%Pt - and exposed it for my standard 5 minutes and used A.C. developer. The purpose of this was to create a linearized curve specific to my chemicals. But the 129 step was severely underexposed - only about half the squares were visible.

Q>Why would this print time, with me using similar chemicals as before, give me such an underexposed print? Is the 129step DN printed with the Master.quad causing this?

This time I even used a higher percentage of Pd than before, so one would assume I would get an even darker print with the same standard print time. Oh yes, I also printed a test strip to verify my print time, and the 5 minutes still looks about right.

 

thanks…

Robert

 


#2

With PiezoDN, contrast is not longer controlled by the chemistry. The chemistry is standardized and instead contrast is controlled by the image in photoshop. If you find that the image needs more contrast, print with the linearized curve but select the Default-PtPd.icc profile (this works with Mac only and PrintTool) instead of “No Color Management”

If you are on a PC, either adjust the contrast of your image in Photoshop or adjust the curve with the Piezography Curve Adjustment tool to be more contrasty.

best,
Walker


#3

In the Print Tool, I see the option for “Print Tool Managed”, then in the next pull-down menu I see PiezoDN_PtPd_Default. I’m assuming that’s the setting you are referring to.

ALSO, what about the question of the 129 Step printing so light? Is that because I used some Pt in the mixture, and not 100% Pd?

What do I do if I want to create a customized, linearized curve with my desired chemical (70/30 Pd/Pt) / developer choice?


#4

Robert - Please check your original post for typos. There are a couple of thing that seem to contradict each other. For example, you said that your initial print was 100% Pd, then you said you reprinted with “a bit less Pt than before”. But if you were using 100% Pd there was no Pt before. I think you mean Pd here since you then say you used a 70:30 mix of Pd to Pt. Then at the end you said you used an even higher % of Pd than before.

My best guess for why the second print had only about 1/2 of the steps showing is that you made an error in making up the coating mixture. Is it possible that you used “Na2” platinum rather than the standard #3 platinum solution (potassium tetrachloroplatinate)? That would certainly cause this result.

There should not be a significant difference in exposure time (may need very slightly more ~10%), and only a slight increase in contrast between 100:0 and 70:30 Pd:Pt ratios. The image color should also be slightly less warm - more neutral.


#5

Related to my comment and then also Keiths, when I say that “the chemistry is standardized” what I mean by that is that for digital negatives to work best, one must figure out darkroom technique first. Once darkroom (exposure, chemistry, paper, etc) has been figured out, the negative is calibrated for those exact conditions. That is what I mean by “standardized.” After that, you calibrate the negative/digital-end and work to keep your darkroom technique (humidity, paper, chemistry) as consistent as possible.

best,
Walker


#6

Sorry, my use of the word “before” apparently caused confusion.

In 2016 when using Jon’s older curves, (which was my “before” reference) I was using 50-50 Pt-Pd, and was happy with the result.

Last week, I DN printed the 129 Step using the master.quad, then process-printed it with 100% Pd, and generated my linearized curve. Using that curve, I printed an image with the same chemical mixture of 100% Pd. It’s this result that I wanted to change to achieve more contrast.

So, I then process-printed the same 129 Step with “a bit less Pt than before” (“before” being in 2016 using Jon’s older curves), this time 70%Pd / 30% Pt. It’s this Step that was very underexposed.

And your comment about Na2 was insightful, because just before printing I was cleaning up my workspace, and after coating the paper I noticed the Na2 bottle was not in it’s correct position in the bottle rack. So it’s quite possible I screwed that up. I’ve since relabeled the bottles for maximum clarity.

Would Na2 cause such a dramatic underexposure compared to the same amount of Pt?

I’ll reprint the Step.

thanks…

Robert


#7

Actually, I read read the phrase “less Pt than before” to be in comparison the 100% Pd that I thought you were comparing it to, so I thought maybe you meant to say less Pd. Anyhow, it looks like you edited the original post, and that we are now on the same page.

Some generalizations about Pt/Pd process that I have learned over 25+ years of working with it:

  1. platinum is contrastier than palladium
  2. a 50:50 mix will be about 1/2 stop contrastier than 100% Pd
  3. palladium responds faster to UV exposure than platinum
  4. a 50:50 mix of Pt/Pd in the coating does not result in the same ratio in the print
  5. palladium is warmer than platinum
  6. ammonium citrate produces a cooler image color than potassium oxalate
  7. ammonium citrate is slightly contrastier than potassium oxalate
  8. ammonium citrate is slightly slower than potassium oxalate
  9. all of these things are paper dependent to some degree
Na2 (sodium tetrachloroplatinate) is not interchangeable with the standard platinum solution (potassium tetrachloroplatinate). In addition, they can not be used together. "Na2" is a powerful restrainer and is used in minute amounts to control contrast. With digital negatives, the best practice is to use the minimum concentration that prevents the possibility of highlight fog without a significant increase in contrast.

Example: For a typical 8x10 image size (80 sq in) I use 1ml ferric oxalate + 1ml Pd + 1 drop 1.25% Na2 + 2 drops of Tween 20 for brush coating on most papers. If you measure in drops, 1ml will equal probably between 15 and 20 drops depending on your dropper. (Note: 2.5% Na2 would be fine here too.)

Accidentally using Na2PtCl4 rather than K2PtCl4 would absolutely cause the result you obtained. I’ve done it too! It’s less underexposure though, and more a huge increase in contrast. Try it again with the standard Pt #3 solution.


#8

Kieth, thanks for the insights and follow-up…

Robert