The best UV Blocking-Color for the Digital Negatives ?

Discussion in 'Digital Negatives' started by Dan Pavel, Jan 4, 2018.

  1. Dan Pavel

    Dan Pavel Member

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    Till yesterday for my DNs I've used some UV blocking-colors recommended by others in their posts on different sites. Yesterday I have decided to see myself what the best UV b-c is for my printers. I printed Mr. Peter Mrhars' HSB grid on a sheet of Pictorico with an Epson SureColor SC-P600 printer and made a VDB print of it with a 3min exposure time on a sheet of Bergger COT32. The result was not satisfying: a too short exposure to clearly see the best UV b-c.
    I did it again with anothe sheet of Bergger and with a 5min. exposure - again too short. This time I re-aligned the negative and gave it 10 min more UV. exposure - not enough again! I re-aligned the DN again and gave it another 10 min of exposure. This time it was a bit over-exposed (25 min exposure!), exactly how I wanted, and the best UV b-c could be clearly seen. It was quite close to what I use for VDB.

    Blocking color.jpg

    Today, watching the 2 prints, I realized that I can't understand why that color is considered the best UV b-c. It is, obviously, the "most blocking" UV color, but why should it be "the best"? If looking at the column of grays (well, browns..) beneath it it's clear that it will need a quite "strong" correction curve when used for a DN (quite distanced from diagonale). On the other hand other colors would need a more close to diagonal correction curve while giving a good white and a deep black (brown..), too, with the 3 min exposure time (or a bit more) instead of 25 min (or a bit less). Why is the "most blocking" color considered the best choice and not the one that needs the less corrections (while both give similar max. black and max. white, but at different exposure times)? It doesn't seam logical to me. Am I missing something?
    Look at the 2 prints how different the 2 colors are.
     
    Last edited: Jan 4, 2018
  2. nmp

    nmp Member

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    The way I do it is to set the exposure time strictly on the minimum time for maximum black/dark. Make that the process exposure time. Only then do the test for blocking color - using that exposure time. If you have a high contrast process, you may have a range of blocking colors rather than a single one - each giving a different correction curve. You can choose the one that would give the most linear curve like the one you chose in the 3 min test. But the end result should be equivalent.

    :Niranjan.
     
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    Dan Pavel

    Dan Pavel Member

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    This sounds logical. The range of useful blocking colors depends on the exposure time and the exposure time should be the min. time at which the max. black/dark appears. The end result should be, at least theoretical, echivalent with both colors because it should be equally well corrected, even by 2 different curves. But some differences may appear because the same range of grays are compressed into a larger or a shorter range of colors. I think it's worth testing it to see if any difference is sesizabile.
     
  4. Herzeleid

    Herzeleid Member

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    Another point, since your printer has 2 cyan cartridges in that printer you can not control which cyan cartridge is used when making green color. Both inks C and LC, will have different UV blocking characteristics.
    If you look at the green color column and compare it to the pure yellow, you will notice in both exposures the yellow column has smoother increase in densities.
    25 min exposure for green color has anomalies.
    Usually with epson printers Y ink is the best UV blocking color, after black inks.
     
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    Dan Pavel

    Dan Pavel Member

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    Yes, your point is valid but why is Y the best UV blocking color after the black inks? The printer uses 3 black inks for a B/W print and they may have different UV blocking characteristics, too.
     
  6. jim10219

    jim10219 Member

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    This was a problem that I ran into as well. The best UV blocking color for me (on my Epson 9880) was, obviously, rich black. That's because it combines all of the inks and has the highest density of ink. However, as you go from darker to lighter shades, the ratios of ink aren't anywhere near smooth or consistent. So it was virtually useless for alt. process negatives. I also tried straight Cyan and Magenta. I had the same issues, though not nearly as bad. This is due to having two of each of those inks, and the mix ratio between them being uncontrollable on my setup. Greens, oranges, violets, all had similar issues. Violet was actually the second best UV blocker behind rich black. Yellow didn't give me very good results either, as it didn't block UV all that well and really limited my shadow density. I even tried monotone prints in CMYK to force the printer to keep the ink ratios consistent. But that didn't work out for me. Photoshop isn't good with colors like that (or at least I couldn't figure out how to keep it from altering the ratios on it's own). In the end, I settled with standard black. I just convert all of my images to grayscale and use black ink only option in the printer's dialog box. I have no idea if that causes the printer to only use one cartridge or all three black ink cartridges, but I do know that I can get a smooth and consistent gradient across the board, post curves. If it does use three different black cartridges, they are at least similar enough to each other in UV blocking characteristics that after the curve is applied, it doesn't produce much of an issue for me.

    The one caveat being that it limits my range slightly. With a rich black, I can expose my prints for much longer, and still keep the highlights clear, which allows me to produce a very slightly darker shadow region in alt. process prints. However, that difference is very minimal, and only really noticed when comparing the two, side by side. With my current setup, I run exposures for Van Dyke's at around 3:00, and get great results (I could probably run them longer without fogging my highlights, but this works well enough for me and doesn't force me to spend all day exposing prints). If I switched over to rich black, I could run then for upwards of 30:00, and still not fog my highlights (probably longer, but 30:00 was as long as far out as I tested). But I could never get a smooth and consistent range between the two. I'll take the barely noticeable difference in shadow density with smooth and consistent gradients over extreme contrast any day.

    My curves with the grayscale black are much smoother than the curves I tried with other inks. They're typically linear except for the extreme ends of the scale. With the other colors, my curves would have funny dips and bumps all throughout. But that was just my experience with my setup. I think you have to experiment with your own setup and figure out the best method for yourself. I know for my setup, I have to change the curves anytime I switch paper, chemistry, the amount or type of size I use, preshrink the paper, coating method, or in the case of gum or other colored prints, changes to the pigment. Everything effects everything to the point that I can't make two identical prints, no matter how hard I try. And that's part of what I love about it all. But since you have different tools and working methods from me, my advice won't be all that helpful to you.
     
  7. Herzeleid

    Herzeleid Member

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    Why Y cartridge, because it is my experience with Epson printers. I have used printers with Claria inks and Epson 3880 and 9800. Yellow ink is the best uv blocking color, black inks are opaque in adequate densities.
    Strangely among my generic refill inks for Epson p50, yellow ink is the second best uv blocker.
    Maybe the reason is that yellow color is the complementary color of Violet. That is just speculation on my part.
     
  8. jeffreyg

    jeffreyg Subscriber

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    I have no "scientific" data to backup my comments. I have been making pt/pd prints for about twenty years and have also heard that yellow is a good uv blocker and film developed with one of the pyro developers works well for uv blocking. I have made very nice pt/pd prints from Delta 400 4x5 (no longer available) 4x5 HP5, 4x5 Tri-x and from enlarged negatives with x-ray duplicating film. Some of the 4x5's were developed in PMK Pyro and others in Ilford ID-11. I have not really noticed a difference as all have worked well. The duplicating film was developed in Kodak now Carestream GBX. They have also worked very nicely. Beside those, I have also made negatives on Pictorico transparent film with Epson Ultrachrome inks. For those I scanned negatives, edited as RGB, converted to grayscale then back to RGB before inverting and printing. I've done them as per black and white and also in tones that match the film developed in PMK Pyro and using Dan Burkholders curves which I had to tweak a bit.. There really hasn't been any noticeable difference in my hands.

    A few years ago I printed a limited edition series for Mario Algaze. We enlarged his 2 1/4 negatives on to the x-ray duplicating film developed in GBX.

    I wouldn't knock myself out chasing a magic solution unless you like experimenting.

    http://www.jeffreyglasser.com/
     
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    Dan Pavel

    Dan Pavel Member

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    Thanks Jeffrey, I think that's a good advice. Time is precious and it should be spent wisely. I think I'll change the UV blocking color to black inks, as suggested by most posters, and stop concerning about it.
     
  10. Bob Carnie

    Bob Carnie Subscriber

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    I have the luxury of making silver digital negatives and of course inkjet negatives.. In my darkrooms I find that inkjet cannot rival the silver if I am comparing two negatives on silver paper via contact.
    I do though feel for alt process like Carbon , Gum, Pt Pd, Cyanotype the difference is not recognizable.

    I have been thinking about how we use in PS a method of using red ruby and various opacities to work on an image.. For example make a layer, multiply then make a mask. pick up a brush and paint in the whole scene. by using the forward slash key beside the brackets that enlarge or reduce brush size , one can paint in red ruby to minimise the amount of multiply, basically a dodging brush. Also we know if you use red ruby on your plate burner it will completely block the light . So following this thinking I get where the OP is going and it is interesting that one could intensify the blocking power of given negative with application of colour at the inkjet stage. The ability to help the negative along its natural course would be an interesting adaptation.

    Now to be clear I have not gone down this wormhole of experimentation but I do believe that some smart cookie would be able to devise a colour scheme that works linearly with the lay down of density of the negative from pure white or clear on film to total black and black on film..

    This may be an area of film production that others have mastered to create a digital inkjet negative that actually can rival that of a in camera negative for silver contact.. I already know that I can do this with silver (Ilford Ortho) on my Lambda for negatives that rival in camera negatives.... But the cost is extraordinary , a roll of film 40 ft by 20 inch is over 1500 dollars plus you still have to pay for the chemistry to image it.
    This Negative Generation is the second reason I have kept my Lambda, the first is the ability to make silver prints directly from digital files. But it would be a nice breakthrough IMHO if one could create inkjet negatives that do not bleed through on silver contact process.
     
  11. nmp

    nmp Member

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    Great discussion!

    I have always wondered what the actual mechanism behind the blocking characteristic of a particular color is. Pigment inks (or for that matter dye inks as well once they are dried) are composed of finite sized opaque particles whose absorptive/reflective properties give rise to the color they display. When applied on a transparency, then, it is not like putting a homogeneous filter in the path of UV light. If it acted as such, then yellow/red theoretically should have the greatest blocking power. However, it is not always the case in practice. My first experiments for Centennial POP with Vivera inks on HP B9180 ended up having best blocking at R/G/B of 61/118/0, much better than at both pure red (255/0/0) or yellow (255/255/0) as well as pure black. After my HP B9180 stopped working recently, I got myself an Epson P400. Here the optimum turned out to be very close to black at 0/30/0 (for salt prints, not POP) - still greenish but much less so.

    That brings me to the theory that perhaps it is not the pigment color per se that is responsible ultimately to the blocking power, rather the physical area it covers. Each pixel of a particular color of R/G/B is created using dots of a combination of the multitude of inks available on a given printer. The one that results in the densest set of dots probably block the most light. Does green require greater dot density than say yellow or red? If this mechanism were to be the case, then the blocking density should be same same no matter the wavelength of the light source. Does one require separate set of R/G/B for UV based process like salt or Pt-Pd and Silver Gelatine, given the same set of inks? That would be interesting to know.

    :Niranjan.
     
    Last edited: Jan 6, 2018
  12. Bob Carnie

    Bob Carnie Subscriber

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    I would imagine that yes one would need a different set of inks for maximum effectiveness... not to mention when one starts playing with colour gum or carbon this could catastrophic if applied incorrectly , I imagine days of testing could indeed answer this.

    for example when I do tri colour or duo tone gum dichromate, it would be necessary to understand how each colour reacts to Pigment Thaylo Blue(green shade) or Indian Yellow.. ones exposure times would be compromised I would think.

    Today I understand my basic balances for these colours from my inkjet negs, once I start affecting the colour the balances will change.
     
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    Dan Pavel

    Dan Pavel Member

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    An inkjet printer obtains its compound colors not by the superposition of pure inks but rather by placing the pure ink dots close to each other and not one on top of the other. That's why the control of the paper absorbance is so important.
    If a pure ink "A" has a significantly greater UV blocking power than the other pure inks then any combination of "A" with the other inks will have a lower blocking power than pure "A" in a "dot near dot" placement. And this doesn't seam to be the case - not the pure inks are the most UV blocking, but the compound colors (the "valleys" in my sample photos).

    By looking at the printed results: the pure inks have slightly different UV blocking power (the "peaks" in the print are almost equal but still different, with black being the most UV blocking of them) but, what's more important, the most blocking colors (the "valleys") are compound colors (with probably a denser dots distribution) and not the pure inks.

    IMO your theory could be correct, Niranjan - the density of the dots distribution could have more impact in blocking the UV light than the color of the inks. Otherwise the "valleys" should appear on the pure CMYK colors and not on the compound colors, as they do.
     
    Last edited: Jan 7, 2018
  14. Miles Nelson

    Miles Nelson Subscriber

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    In my system I use an app that allows you to control the volume and distribution curve of each of the 12 colors available... I first find the best exposure time using a step tablet for the process. I Then print a color array which demonstrates the candidates for best UV blocking... I then determine that array color’s numbers. Then I use that number in the app to set the color ink and volume. In the case of Kallitype or Pt/Pd my choice involved a combination of about 90% yellow and 10% magenta and I turned off the other 10 colors...the printer output distribution for both colors was set to be linear (this is the profile unlinearized)... I then print the app’s step tablet with this profile at the predetermined best UV exposure time and process and dry... I then read the printed step densities back into the app’s linearization function which produces a linearized “profile “ for the paper/process... at this point I import the negative image that I want to make a digital negative of into the app, apply the profile and print... in practice this is a very straight forward task and the tonal quality is very smooth...Any new process I only have to use the unlinearized profile and make a print of the step tablet with that process,read and linearize. I believe this has been successful because there is no printer determined algorithms or amping up or down with pigment distributions and volumes... just operator controlled linear distribution of ink. Also the profile is performing tonal mapping which is not exactly the same as apply a somewhat aggressive curve on the image file itself... I’m use a canon iPF printer with LUCIA inks ...the big down side is that the app only works with Canon iPF printers and Apple computers ...
     
  15. nmp

    nmp Member

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    Very intersting....looks like you have created a QTR type system for Canon. Is that right? Do Lucia inks provide good UV opacity? What process are you doing?

    :Niranjan.
     
  16. Miles Nelson

    Miles Nelson Subscriber

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    From what little I know about QTR , this is much simpler and more direct control of the full printer function ... I do Pt/Pd, Kallitype, Cyanotype and Gum Bichromate...
     
  17. nmp

    nmp Member

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    I have been playing with QTR last few weeks....it definitely could use some simplicity. Not sure it is my cup of tea. Unfortunately my printer Epson P400 does not cut it for UV opacity the normal way so I thought I get better results with QTR as it allows to pile on ink density (which has it's own problems.)

    I was under the impression that only Epson allows the direct control of ink nozzles. If you are able to do that with Canon, I bet folks will be very much interested in it. Particularly someone like Cone/InkjetMall who would love to sell their custom monochrome inks to bigger market than just Epson people.

    The reason I asked about the opacity of Lucia inks is that Canon has a great sale going on right now for Pro-100 that can be had for some $120 after rebates. I thought I might consider it if I had an understanding of how opaque the Lucia inks are and whether it is possible to do colorized negative without the use of driver control as you seem to be doing. I got burnt with P400 which I bought assuming it was going to be adequate (should have done more research.) I am also doing a process that is the most demanding of the negative Dmax, i.e. Centennial POP. P400 almost works for my version of hand-coated salt prints, but it is grossly inadequate for Centennial POP. I was spoiled by my (now dead and gone) HP B9180 which was excellent for this process.

    :Niranjan.
     
    Last edited: Apr 21, 2018
  18. Miles Nelson

    Miles Nelson Subscriber

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    I can’t directly compare Canon’s LUCIA with Epson inks but it’s becoming a bit more clear that opacity as a factor in UV blocking is a more complex issue and could actually be a two edged sword... if an ink is very dense and opaque then issues show up which requires more enhanced print management techniques and file manipulating... A degree of translucency of the ink/pigment offers opportunity for improved subtleties and smooth tonal quality ... I do know that my system is capable (if not used thoughtfully) of laying down too much ink and thereby overwhelm the capacity of pictorico / ink press OHP and forming puddles...
     
  19. nmp

    nmp Member

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    Complex it is...still trying to figure out what is going on on with different inks.

    I confused Lucia inks with ChromaLife, which is the dye-based set in Pro-100, not the same as what you have in your iPF.
     
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