OK. A bit of background. The BTZS Plotter has been around for probably 30 years or so. I’ve been using it since the early 90s myself, but mostly for printing from original large format negatives. If you have read Dick Arentz’s Platinum & Palladium Printing you may be somewhat familiar with the concept even though I know you are not a film guy. Phil Davis, the author of Beyond the Zone System and it’s associated apps was Dick’s teacher at the University of Michigan in the 70s.
Recently, since most of my work these last few years has been with digital negatives, I’ve wondered how the concepts in the Plotter could be applied to digital negatives. The analysis part is clearly different since digital negs are not constrained by the characteristic curve of the process the way analog negs are. The reason the default Emax setting in Plotter is 90% is that this is the ANSI/ISO standard for black and white printed on gelatin silver paper. Same for the Emin setting of 0.04 over paper base white. These settings work well for Pt/Pd for printed from analog negs too. But for digital negatives we have the ability to linearize the entire exposure scale and thus eliminate the toe and shoulder. In theory this means we can set the Emax to 100% and the Emin to zero. Plotter allows us to set the Emax, but Emin is fixed at 0.04 over paper base. I’d like to be able to adjust both ends.
The spreadsheet that I recently shared with you ( and will be sending to you too Walker) is my first attempt at creating a more flexible analysis tool, and also one that can work with Luminosity (L*) values rather than (or along with) density. The Density part is easy since I know the formulas, but for the L* analysis I had to come up with something that produced similar results, but because the scales are so different, and my math skills very rusty and crude, I’m doubtful that they will work with all data sets. I also had to select the cells to use to define the white point manually which will change once I figure out how to automate it.
Back to your immediate situation. A typical ES for Pd with an IDmax setting of 100% is typically around 2.40-2.50, though I’ve seen a few papers a bit higher and lower. This is about 2.5 stops more range than your New Cyanotype (NC) test is showing. This means you need to limit the master curve by a substantial amount. The procedure for doing that is in the manual. It’s a little tricky the first time, but I think you can handle it. Or you could try the Cyanotype curve for your printer and inkset. (P400 & K7 Se?) I think the supplied cyanotype curves are for the classic formula, so it may even be too low contrast for NC, but it’s worth a try.
Didn’t we go through limiting for NC early last summer?
Enough for now. See you in Tucson next week.