What is the ACTUAL Meaning of "Limit a Quad"


#1

Dear All and Walker…

I have questions that has been stuck in my head for long, please help to explain it to me clearly if you can, even though i know it may not be a PiezoDN question, it maybe a “darkroom question”. (please forgive my current technical knowledge, and i am not a perfect English Speaking person)

In the menu, under Section 11PiezoDN & The Digital Negative page 80, it states:

 

<span style=“font-size: 11.000000pt; font-family: ‘Helvetica’;”>Well, PiezoDN has a curve that is built for Palladium printing so you should start your calibration process with that .quad. The second choice is to use the “master” .quad that comes with each PiezoDN printer and then limit that for your given density requirements. This second path is chosen when calibrating for wildly different processes. </span>

Walker, most of my current prints are mainly palladium print, meaning the chemical mixing ratio is 95% palladium + 2-3 drops of platinum (mainly for the purpose to avoid solarization). In my case, i should use the “master” .quad to linearize my PiezoDN system right?

If i “limit” my printer, it seems it means i am changing the density of the final print negatives (less ink on the OHP?), that will it affect the quality of negative that i am going to produce?

Harris

#2

Walker will probably give a more technical answer to your question, but here is a practical one.

The purpose of Ink Limiting is to take care of the heavy lifting of getting the .quad within the bounds of the printing process <span style=“text-decoration: underline;”>before</span> beginning the process of linearization. Since you are printing palladium with a small amount of platinum, the existing limited master curve that installs with PiezoDN is already ideal for your printing process. But what if you were printing cyanotype which has a much shorter tonal scale? If you print the 129-step target with the Master curve and find that 2 or more highlight steps (beginning with step 1) are pure white, then in order to get tone in those steps you need to adjust the ink limit on that end of the curve. PiezoDN is designed so that the maximum at step 1 remains constant, but from step 2 on down it should be adjusted for the process.

As another example, I have just this week set up a 3880 with the K7 Carbon inkset rather than the Selenium which is standard for PiezoDN. The Carbon inkset have a higher UV density than does the Selenium, so I found it necessary to adjust the Master curve to suit the inkset. It was not a large adjustment, I think I could have gone a little further, but it brought the highlight tones down enough that they could be linearized easily. BTW, I am profiling for pure palladium.

I’d also like to comment on the phenomenon of solarization that you mentioned. It is indeed something that is more likely to occur when printing pure palladium, but it is also a definitive indicator of overexposure. If you get solarization regularly, it means that you have exceeded the optimum exposure time for the materials that you are printing and the conditions in which you are printing. By conditions I mean the environmental conditions in your workspace as well as certain procedural things that may be part of your “workflow”. Temperature and humidity come into play, how you dry your coated paper, whether you rehumidify before exposure, and if so is it in a controlled way, are very relevant to whether or not solarization may happen. The relative humidity in my darkroom stays between 50-65%, but temperature can vary seasonally from 60s in the winter to 80s in the summer. I have found solarization to be much more likely at higher temperatures, and that is when I have to pay extra close attention to the drying regimen. I long ago abandoned the use of forced air to speed the drying process (except with certain Japanese papers, but that is another story) in favor of simply allowing the paper to dry until no longer damp to the touch but still slightly cool. This is generally between 5 and 10 minutes, maybe 15 on a large print.

I recently made a series of 21-step Stouffer step tablet prints of a new paper, as is my long standing practice, to characterize it’s tonal scale and contrast response. A couple of the test prints showed slight solarization between steps 1 and 2. I knew that I had been distracted and that some had dried for longer than others before exposure, so I did another test it which drying time between coating and exposure was the only variable. I used 5, 10, 20 and 30 minutes. The 5 and 10 minute intervals had Dmax readings of 1.42, but the 20 minute test fell to 1.28 and the 30 minute to 1.26 at step 1. Step 2 was slightly darker in the 20 and 30 minute tests, but still lighter than step 1 on the 5 and 10 minute tests. This shows empirically that there is a threshold level of moisture in the coated paper beyond which solarization is likely to occur.

If you see solarization regularly, first be sure that you are not over-exposing, and second pay close attention to the moisture level of the coated paper.

And finally, the entire calibration/profiling process affects the quality of the negative. That is the whole purpose. There is not one negative that is the highest quality for everything. The goal is to produce a negative that matches the characteristics of the printing process. That is the beauty of digital negatives and PiezoDN does it better, and with higher image quality, than any other method I’ve used (which is most of them including some inventions of my own). And it’s actually relatively easy once you get used to it!


#3

Dear Keith

THANK YOU VERY MUCH for your reply.

FYI, i use 1-2 drops of platinum purely because i have experienced solarization when i first learnt Pt/Pd prints early last year, and discovered that adding one or two drops of platinum can avoid the issue (I learnt this from Paul Taylor of Renaissance Press). For me, it is more like a “must” for my palladium printing process now.

Since the PiezoDN does not have a PURE palladium .quad, i have no choice but have to do the limiting (correct me if i am wrong). According to the realm pdf in PiezoDN documentation, the proportion of PT and PD is 80% & 20%…that’s why i need to do the limiting process.

I discovered that my palladium print-out of 256 patches appeared 5 additional highlights…and i want to get them back. (255-5-4=246)…and i used 246 as my limiting number.

Question: if i do the limiting process…does it mean i actually make the final negative thinner?? Or will the process make a negative thicker??

Since i am also practicing Salt Printing which a thicker negative will help.

Again, thank you very very much for your reply.

Harris


#4

Hi Harris,

What printer are you using? It looks to me like all of the printers in the latest download have .quads optimized for pure Pd. Some have more than one choice. But your results may differ from those of Walker and Jon. There are so many variables, known and unknown, in all of the hand-coated alternative processes that chance that someone else’s profile will work perfectly for you is fairly small. You may get something close, but customization will be needed to get the best results. The PiezoDN linearization process is well worth the effort.

If adding a drop or 2 of Pt solves the solarization issue for you without altering the image tone too much then it’s a good solution for you. For me, I want every bit of warmth I can get so I tend to stay away from Pt. And I use hot potassium oxalate developer too. Am I correct to assume that you are using the standard Potassium Platinum solution, not the Sodium (Na2) Platinum solution that some printers use for contrast control?

If your highlights are blocking up on the 256 step Limiter target with the Master profile then yes, you need to customize it. See pages 80-83 of the manual. In this case you will be lowering the ink limit, i.e. pulling the curve below the diagonal line. For salt it may need to be pulled upward. I suspect, though, that starting with one of the 80/20 Pd/Pt curves, and linearizing from that will get you where you need to go.

Hope this makes sense.

 


#5

Dear Keith

I am using Epson 7900 printer, and i do not use any Na or tween 20 coz i believe using a good negative is the key for good prints and i do not need contrast control anymore. PiezoDN can do everything for us. I successfully created a few contrast curve for myself using the build-in function of PiezoDN. And i only use standard palladium and platinum solution.

DO you mean i can try to use , say 4880, 4900 or other Epson printer’s curve on my Epson 7900?? please advice…

I use Ammonium Citrate as developer at the moment coz like the solid cool tone of the final print-out. Of coz, i will try to make some potassium oxalate solution very soon. A bit scare because Potassium oxalate is poisonous … : (


#6

Hi Harris,

There are several options for you in the 7900-9900-PiezoDN Curves folder. The one I would recommend for you to start with based on the information you have provided is named 79-99-PiezoDN-80pd20pt-AC.quad.

I’d like to also address a few misconceptions in your previous post. PiezoDN cannot do everything for us, though it does make by far the best digital negatives I’ve ever used.

  1. Contrast Control. It is absolutely true that a good negative is the key to a good print, and that is the beauty of well made digital negatives - they can be perfectly tuned to the printing process being used including all of your personal variables. However, that is not the only reason you may find it necessary to use a restrainer. Under perfect conditions and with a little bit of luck they are not needed, but chemical fog can occur even with freshly mixed ferric oxalate. Even if you haven't yet encountered it, it is a safe bet to say that you will eventually. You are less likely to notice it if you don't mask your edges. If you do mask your edges, you may notice a slight difference between the cleared edge and the adjacent paper white. That is fog which is caused by the presence of ferrous oxalate in what you think is pure ferric oxalate. If step 1 of your test print reads ever so slightly darker than the uncoated paper white, you have fog. The use of a restrainer can eliminate this problem without changing the tonal characteristics of the print. Sodium hexachloroplatinate (Na2) is only one option. I mentioned it above specifically because it is incompatible with the traditional platinum solution Potassium tetrachloroplatinate which you are using. My usual mix for an 8x10 inch print is 1ml ferric oxalate + 1ml palladium + 1 drop 1.25% Na2 + 2 drops Tween20. (1ml is equal to about 16 drops. 1.25% Na2 is the weakest dilution that has an effect without increasing contrast in 2ml of solution.) I can go into this in much greater detail if you are interested.
  2. Tween 20. Whether or not it is necessary to use Tween 20 (or any other surfactant such as PhotoFlo) has absolutely nothing to do with the quality of the negative. It is entirely dependent on the paper being used. In my experience, and I've been printing Pt/Pd for almost all of my work since 1991 so I have a lot of experience, almost all papers benefit from the use of Tween 20. The new Hahnemuhle Platinum Rag is a good case in point. Without Tween 20 it speckles badly, with it it is smooth as silk. If you look at the speckles closely with a loupe or magnifier, what you see is lots of bare paper fiber where your coating was not absorbed well. Another interesting example is the current crop of Arches Platine. The heavy version, which has been around for about 20 years now and has been my standard paper when I'm not using Japanese papers (another topic), has almost always worked better with Tween 20 that without it. There have been a couple of batches over the years for which that was not the case. But the new lightweight version works much better without Tween, due to its lighter sizing. On this paper, Tween causes the coating solution to soak in too quickly, making it very difficult to coat.
  3. Potassium Oxalate. From the MSDS:
    Do not ingest. Do not get in eyes or on skin or clothing. Use only with adequate ventilation. Keep container tightly closed and sealed until ready for use. Wash throughly sfter handling.Routes of entry: Inhalation. Ingestion.Potential acute health effects Inhalation: Toxic by inhaltion. Irritating to respiratory system. Ingestion: Toxic if swallowed. Skin: Toxic in contact with skin. Irritating to skin. Eyes: Irritating to eyes.

    Potential chronic health effects
    Carcinogenicity: No known significant effects or critical hazards.
    Mutagenicity: No known significant effects or critical hazards.
    Teratogenicity/Reproductive toxicity: No known significant effects or critical hazards. Developmental effects: No known significant effects or critical hazards.
    Fertility effects: No known significant effects or critical hazards.
    Medical conditions aggravated by over-exposure: None known


    This is pretty standard stuff for most photographic chemicals. They should all be treated with respect. Use tongs; don’t put your hands in it; don’t splash it around; don’t drink it! There is nothing to be afraid of here as long as you use good darkroom practices. Wear surgical gloves and a dust mask if you feel it is necessary. I don’t (except for developing sheet film in trays) but I am extremely careful and fastidiously clean in my darkroom work. If you haven’t, read Richard Sullivan’s article Platinum Green.

     

 

#7

Dear Keith

Thank you very much for your thorough reply. I do benefit a lot from your reply.

I normally do my print in square format, say 6 x 6, 8 x 8 or 12 x 12 inches. Normally, i count the drop by using the following formula:

6 x 6 = 36 drops…then divided by 2… then i use 18 drops in total. 8 x 8 = 64 drops then divided by 2…then i use 32 drops in total.

as you have mentioned in your reply, i was recommended to use Na2 and Tween 20. Would you please tell me the solution % that i should use for a 8 x 8 print out?? i do have a 100% tween in my darkroom and i will need to dilute it obviously.

And i do have a bottle of platinum Na2 as i brought it around 1 year ago and i have not use it at all. I can give a try.

If you were me, can you tell me what should be the steps that i should follow in order to get a better print-out for calibration purpose.

It seems that i should:

Step 1: print a 256 patches PiezDN negative using the 80Pd/20Pt curves, let it sit and drug for 1 day

Step 2: cost a pieces of paper using Beggar 320COT with the proportion of 80% Pd and 20% PT…(in this case, i should NOT use the traditional PT solution and replace with the PT Na2 solution right??? 1 drop will be enough for a 8 x 8 inches print?, and 2 drops of 5% tween 20?)

Step 3: darkroom print the 256 patches of the negative…and see whether it is smoother or not, and compare with my old print-out.

PS> yes… i think i should try Potassium Oxalate coz a lot of print master use it as well. I am not that scare of using it…but just a bit get used to the tone of Ammonium Citrate… i think i should open the bottle and mix some to see the warm tone of Potassium Oxalate. Can you recommend the temperature that i should use for Potassium Oxalate as the developer???

Again…THANK YOU…BIG THANK YOU to you Keith…!!! I am so happy that i can have you in the forum.

Harris


#8

While our curves are not built for NA2, others on this forum may have x900 curves that were built for NA2.

That said, I think you will probably be just fine doing the limit procedure to almost any of the the platinum/palladium .quads and then linearizing the limited one.

best,

Walker