UV Density of Inkjet Inks
Posted 12 January 2011 - 01:10 AM
It seems that if one knew the transmission/absorbance spectrum of each of the inks in a given printer system, coupled with the range over which a given process chemistry is sensitive to light (e.g. dichromate is most sensitive in the 360-380nm range, I believe, but I don't know about others like cyanotype or Pt/Pd), it should be relatively trivial find a near-optimum blend of colors for your negative for a given process, at least in a case where you have direct control over inkjet nozzles, like QTR.
For example, one might infer that yellow would be a good blocking color for virtually all of the UV spectrum, and that cyan would be a poor color, since it is expected to have high transmission in the blue part of the spectrum. Yet many people feel that shades of green are a good choice for colorized negatives.
Based on some data collected by Alberto Novo on the alt-photo-list:
Yellow ink's UV absorbance falls precipitously below 400nm, while cyan's starts to rise below 400, to the point where C and Y have about the same absorbance at 370nm. Looking at his graphs, you might say that equal parts C+Y+K could make for very smooth negatives for a process with peak sensitivity near 370nm, as you have 3 different colors, a 3-part color (K,LK,LLK), a 2-part color (C,LC) and a 1-part color (Y), with differing crossover points. For a process that peaks at 400nm, though, the cyan inks would be virtually worthless.
His curves were collected with outputs from the Epson driver, not QTR, using an R2400. This uses K3 inks, so the Y, C's and K's are the same as the other K3 printers currently in production. So some of the data is useful, and applicable beyond just the R2400.
It would be an interesting exercise to extend this to other printers, like the R1800 and R1900, the 1400 and others.
I suppose it's as much an academic curiosity as anything else. I doubt the data would be useful beyond a fairly narrow group of die-hards, but if I had access to a UV-VIS spectro, I'd do it myself.
Anybody else have access to the tools and interested in collecting the data? I can offer samples from a 3880 and an R1900.
Just wanted to share some late-night ramblings.
Posted 20 January 2011 - 02:02 PM
Posted 21 February 2011 - 02:29 PM
- A different Evan
Posted 21 February 2011 - 02:44 PM
- A different Evan
To quote Dan
When I wrote Making Digital Negatives for Contact Printing, the Epson Photo EX was state of the art. With that printer and Epson’s own Transparency Film, making a colorized negative produced the best results for platinum printing. When I teach workshops in Mexico, where they still use the Photo EX printers and can only get Epson’s transparency film, I still make negatives just as outlined in the book.
Printers after the Photo EX—along with better transparency materials like the Pictorico OHP—allow us to apply heavier neutral-color ink loads on the film.
With the 1270 and Pictorico OHP Film, I get smoother results when using all six inks and not colorizing the negative at all.
For the Epson1280, I have returned to the Colorize method to create an orange negative for platinum printing. More Epson 1280 info can be found below.
These "when to colorize" issues are covered in depth in The Inkjet Negative Companion.
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