test step-tablet array
I’ve been experimenting with a hybrid of trichroic negative processes and Quadtone RIP. Since the ink control with QTR is so great, theoretically it should be possible to produce any color that routines like RNP or PDN can produce, but from within the QTR interface.
I thought it would be interesting to combine the smooth highlights of the colorized negatives with the even shadow gradations and the very minor necessary curve adjustments possible with QTR and the light ink set. Printing carbon transfers, highlights can problematic with QTR when using all the dark inks because the UV blocking characteristics of each dark ink are so different, which effectively exaggerates the grain and dither of the printer. It seems like a matter of just finding the equivalent proportion of CMYK inks plotted of the best highlight blocking colors in an HSL array and plugging them into the QTR interface.
My approach was admittedly a little rudimentary- take the CMYK values from HSB sample (as described in the RNP link) and use similar percentages in the QTR setup. I always has good luck with green negatives dating back to a HP 9180, so I started at a ‘known’ QTR density from previous profile for the shadows and tried a limit of 40 for yellow and 30 cyan inks for the highlights, then increased the densities until I get decent blockage at my basic exposures. Right now I’m at about a 60Y/30C mix of the dark inks and the steps are looking fairly linear already without any curving. It’s certainly not a pure translation of a sampled HSB color, but it’s workable.
I’m starting to wonder though if the ratio of the C, Y or even M inks are as important as simply leaving the K out (speaking from strictly a smoothness of rendering standpoint.) The red versions look just as smooth, but would require a lot more ink to be as effective as the cyan/yellow mix.
Given a long enough time line of testing, I bet there might be a way to extrapolate HSB coordinates empirically, but sure hope I don’t have to prove it.
Update 9/12
Really interesting results so far, very smooth and quite linear without an adjustment curve.
Some initial results, all use the same light ink mix of 35 limits on LC, LM, and LK. The dark ink blends are:
1. Cyan20 Y60
2. C15 Y70
3. >Magenta 30 Yellow60
4. M70 Y40
5. >Back to Cyan15 Y65
The C20 Y60 seemed like a good jumping off point. The reds need a lot of ink to block enough UV, to the point of pooling, so I didn’t pursue magenta inks any further.
For the profile linked below I tweaked the gamma up to 1.3 in the profile to give a bit less highlight blocking through the 5-25 steps, then the curve needed was really minor. Again, this is for printing carbon transfers. For iron-precious metal processes I suspect the highlights will need the K and K boost tweaks to get contrast in the highlights. Carbon is linear enough that the extra push of black ink in the K Boost value doesn’t seem required.
I’m using an .7% (seven tenths of one percent) pigmented tissue sensitized with a 2% ammonium dichromate (but check my math, 5ml of 20% dichromate in 50ml of total solution), exposed for 24 minutes in a bank of BL bulbs with 90mm of clearance. Not sure how this profile would work for other processes. The high load of yellow does create pizza wheels marks, but they feather out and fill in completely on drying and do not show up in the final print. Also, front loading the OHP material is a proven workaround for the pizza wheel problem.
Newcarbon_K0_C20_Y60_13gamma_Crv2
Having such fun with this right now I’m not sure what looks cooler, the prints or the negatives.
