The best UV Blocking-Color for the Digital Negatives ?

[Dan Pavel]

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.

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.

 

[nmp]

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.

 

[Dan Pavel]

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.

 

[Herzeleid]

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.

 

[Dan Pavel]

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.

 

[jim10219]

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.

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.

 

[Herzeleid]

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.

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.

 

[jeffreyg]

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/

 

[Dan Pavel]

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.

 

[Bob Carnie]

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.

 

[nmp]

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.

 

[Bob Carnie]

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.

 

[Dan Pavel]

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.

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.
:Niranjan.

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.

 

[Miles Nelson]

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 ...

 

[nmp]

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 ...

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.

 

[Miles Nelson]

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.

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...

 

[nmp]

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...

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.

 

[Miles Nelson]

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.

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...

 

[nmp]

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...

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.

 

[LUIS GUEVARA]

Hi Dan Pavel. I don't have the same system that you have ( Mr Marhar ) but my understanding is that you should use the color that achieves the largest range of tones before reaching white, counting from maximum black . That is why it is important to determine the minimum time required to achieve maximum black through a clear substrate , before attempting to find the best blocking color. In your case it would be the magenta color that achieves more gray tones (10 ) than the green color that only achieves 8 ( More contrast ).

Perhaps you could describe all the steps in Mr Mrhar system so we can better understand what you are doing. Luis

 

[Dan Pavel]

Hi Luis.
Yes, my conclusion is the same : the best blocking color and not the most blocking color should be chosen. However, a lot of people recommend the most blocking color as being the best choice. See, for example, here:http://www.thesis.bilkent.edu.tr/0006299.pdf
It states:
"The resulting print shows which colors block most UV light apart from the black ink. In the print (see Figure 24) the green color shows the most resistance to UV light. We can deduce that the green color (combined from different inks) and the black ink from this specific printer can be used to create the most UV opaque negative possible."
It was not my intention to discuss Mr Mrhar system as I neither use it nor am I familiar with it. I have only used his well designed HSB color grid for printing the sample prints.

Finding the best exposure time first is a must, of course. But choosing the best exposure time is another interesting discussion. There is not a single exposure time that prints the darker possible black while keeping the white unchanged. Which of them works better? The general accepted recommendation is to use the shortest ET which fulfills the condition. But why not to choose the ET that fulfills the condition and prints the middle grey most close to the correct middle grey, for example?
My guess is that there is no significant difference and the correction curve will compensate for the differences, if any. A noticeable difference may appear from the capability of the inkjet printer to print better the differences in the darker tones or in the lighter tones. If this is the case then the best ET should be chosen in such a way to enable the use of darker or lighter Digital Negatives. I have never tested that but working lately with Gum prints, which are very demanding, raises the question.

 

[Herzeleid]

Hi Luis.
Yes, my conclusion is the same : the best blocking color and not the most blocking color should be chosen. However, a lot of people recommend the most blocking color as being the best choice. See, for example, here:http://www.thesis.bilkent.edu.tr/0006299.pdf

Well, Interesting to see my thesis quoted. I would have written it differently today. Since I have noticed the problem with that particular green color later on.
https://www.photrio.com/forum/threa...or-the-digital-negatives.156527/#post-2031200

QTR ink calibration chart is a better method to determine best possible UV blocking color combinations.

 

[Dan Pavel]

Hi Serdar.
I didn't know it was yours. I quoted it because it was the most handy for me - I keep a link to it in my browser as I could find many useful things there.

 

[Herzeleid]

Hi Serdar.
I didn't know it was yours. I quoted it because it was the most handy for me - I keep a link to it in my browser as I could find many useful things there.

Hi Dan,
It is good to hear that it has some merits. I would have changed it considerably today from technical point of view. Since I was just learning the processes back then.

Back to topic,
I would use HSB arrays as a guide if necessary but they can be very misleading. My friend had a printer with Orange and Green ink cartridges on top of regular CMYK and LMLC, there is no way of controlling how colors are mixed with default drivers. So printing an HSB array to find a UV blocking color(s) from such printer would give so many false positives.
Now I aim for the least dramatic curve possible, I adjust ink loads gamma etc in QTR, or change the ink load etc in epson drivers to make a smoother curve.

 

[LUIS GUEVARA]

Well, Interesting to see my thesis quoted. I would have written it differently today. Since I have noticed the problem with that particular green color later on.
https://www.photrio.com/forum/threa...or-the-digital-negatives.156527/#post-2031200

QTR ink calibration chart is a better method to determine best possible UV blocking color combinations.

Well, Interesting to see my thesis quoted. I would have written it differently today. Since I have noticed the problem with that particular green color later on.
https://www.photrio.com/forum/threa...or-the-digital-negatives.156527/#post-2031200

QTR ink calibration chart is a better method to determine best possible UV blocking color combinations.

Hi Luis.
Yes, my conclusion is the same : the best blocking color and not the most blocking color should be chosen. However, a lot of people recommend the most blocking color as being the best choice. See, for example, here:http://www.thesis.bilkent.edu.tr/0006299.pdf
It states:
"The resulting print shows which colors block most UV light apart from the black ink. In the print (see Figure 24) the green color shows the most resistance to UV light. We can deduce that the green color (combined from different inks) and the black ink from this specific printer can be used to create the most UV opaque negative possible."
It was not my intention to discuss Mr Mrhar system as I neither use it nor am I familiar with it. I have only used his well designed HSB color grid for printing the sample prints.

Finding the best exposure time first is a must, of course. But choosing the best exposure time is another interesting discussion. There is not a single exposure time that prints the darker possible black while keeping the white unchanged. Which of them works better? The general accepted recommendation is to use the shortest ET which fulfills the condition. But why not to choose the ET that fulfills the condition and prints the middle grey most close to the correct middle grey, for example?
My guess is that there is no significant difference and the correction curve will compensate for the differences, if any. A noticeable difference may appear from the capability of the inkjet printer to print better the differences in the darker tones or in the lighter tones. If this is the case then the best ET should be chosen in such a way to enable the use of darker or lighter Digital Negatives. I have never tested that but working lately with Gum prints, which are very demanding, raises the question.

Dear Dan and Serdar.

When a process has too many variables , all but one , have to be kept constant . Change only one of them at a time so, in this process , the minimum time for maximum Density has to be found first and then kept constant while you check or change the color variables.It is not the BEST exposure that you are trying to determine but the MINIMUM exposure that would produce black trough the clear base. It has to be the minimum because more exposure will raise ALL THE DENSITY VALUES and the upper tones of the print will be clipped as there will be too much density and not enough light will pass through, to achieve printed highlights.

After that ,when you find the best color that produces the longest tonal scale on your analog print you have already found the Black point and the White point. The maximum density should be achieved at a CLEAR base square ,with no ink deposition , so color will have no influence in its transmission properties . This should correspond to the first square, bottom left in the ChartThrob negative.

Mr Herzeleid thesis clearly pointed it out; "The exposure for maximum black (D-Max) on the print responds to minimum density on negative (D-Min)" and "When correctly established the exposure time becomes a constant in this workflow"

Mt Herzeleid test print seems to me to be OVEREXPOSED by about 3 stops and therefore exhibits too many Max Black squares and because the negative was made with too much UV blocking power it also achieves White too soon , there is about 3 stops of midtones between max black and white. See the print below. To achieve a longer tonal range it needs less Max actinic density by reducing the max ink deposition or using a less actinic color. Of course the base exposure should be reduced to expand the mid tones and leave only ONE FULL BLACK SQUARE at bottom left.

After that the next step should be working the tonal mapping in between those Black and White points so that the 254 midtones remaining , are uniformly spaced along a straight line and , consequently, will print equally spaced.

Things to keep in mind here;
-- Ink Jet Printers are designed to receive RGB COLOR images in sRGB color space , that is Gamma 2.2 . If they receive anything else the printer will convert it , on the fly , to sRGB and assign Gamma 2.2 to it so, in essence ,the printed negative will not be made according to the tonal values you sent to it. If the image was sent as Gamma 1.8 it will end up printing with an abundance of dark tones and very few highlight tones because that is the shape of the sRGB Gamma 2.2 curve.

QTR provides the most control but it require understanding of the factors involved in the Hybrid digital/analog chain. By the way If you are going to use a colored layer over the Black and White image the image should remain in sRGB color mode and all the color channels should be linearized or you will end up with a weird distribution of printed tonal values since there will be more colored ink where there is less black ink. It is best in my opinion to use just black.