B&W Dry Runs
Since I was unfamiliar with most of the equipment used for Ilfochrome processing, I decided to spend some time with B&W dry runs of the process. This helped me figure out many steps and also taught me how to do these steps in total darkness. I cut B&W paper to size, placed it under the enlarger, enlarged random negatives or slides on the strip and placed it into the print drum, then ran it through the regular B&W process.
I practiced running the process in a fully repeatable fashion, every step at a controlled temperature for an exact time frame. How long does it take to change from one bath to the next with this drum processor? How long does it take the processor to reach its set temperature? How much chemistry is the bare minimum? Can I do some tasks while the bath is active which could save time later in the process? How to I prepare exposure series in total darkness? Where do I place items so I can find them when I need them in the dark?
Some folks may be natural talents, others may already be experienced from RA4 printing. I am neither so I spent an evening in the dark room performing these dry runs until I was confident I could to all these steps reliably with Ilfochrome sheets. Fortunately all the hazardous steps can be done in day light, especially those steps involving the (nasty&smelly) Ilfochrome chemistry.
Since batches of Ilfochrome sheets have slightly varying color balance, a label on the box/envelope gives printers initial filter setting to start with. Once you switch from one batch to the next, and if you keep the rest of the process constant, you can guestimate the new filter values by subtracting the filter values printed on both batches and adding the difference to your last actual filter settings (which may be quite different from the values printed on the box).
With this information we can dial in initial filter settings, but we still don't know about exposure. Not only that I did not find anything useful online, the bigger problem is that different slides may differ in mid tone density by quite a bit, sometimes because of less than perfect film exposure, other times because different slide films have different contrast. So every time I switched slides I took a measurement with my density meter (since you only need to know the difference in densities, a simple light meter could probably be used here if you don't have a density meter for your enlarger).
Since Ilfochrome CLM.1K paper has a contrast of about 1, any difference in paper exposure will be faithfully reproduced by the paper. This allowed me to accurately nail Ilfochrome exposure reliably for very different slides with the density meter. I may have been hysterical about this, but I have read multiple reports about nasty reciprocity failure of Ilfochrome paper. In order to avoid running into this issue even after changing sheet format, I tried to cover most of the calculated exposure difference with the lens aperture and changed exposure time only to cover the small remaining difference.
Anyway, there is no substitute for an exposure series. Since we can run several test strips per dev run with little extra cost, it might well pay off to run fine grained exposure series, chances are high we nail exposure right after the first test run. So there we have it: we know optimal exposure from the test run and once the test strip has been fully washed and dried, we can see whether we need to correct color balance. This is most likely the case since color balance depends on process parameters and chances are the paper maker ran with different parameters than what you will use.
After establishing correct exposure settings I went on to achieve correct color balance. The most difficult aspect of this is that it takes so long to find out how the color balance came out. Remember, you need to let the paper dry completely before you start judging its colors. Since we want to do the absolute minimum number of test runs, I recommend you expose several sections of your test strip with different filter settings, starting with the filter settings printed on the box of the paper stash. If necessary, make multiple test strips, as long as you can fit them in the same drum.
Be sure you know what the filter settings on your color enlarger head really do. Magenta looks a lot like red to my eye, but it isn't just red, it's red and blue. If you think you can compensate a red cast with the magenta filter, you'll end up wasting a lot of test strips. You will learn (or already know) that the complementary color of magenta is green, so you use the magenta filter for increasing and decreasing red+blue versus green in your final image. Same thing applies to the yellow filter. Yellow is the additive mix of red and green, the complementary color is blue. Use yellow to increase and/or decrease red+green versus blue.
If your color balance is indeed off (and it will be, trust me), take your time and look very carefully which color needs increase or decrease, and think carefully which color filter achieves the desired change.
If you have done lots of dark room printing and possibly also some RA4 and used print drums for these processes, Ilfochrome should be a piece of cake for you, at least on amateur level. After my first successful experiments I have a lot of respect for professional Ilfochrome labs which do perfect color matching and contrast masking and whatnot to reproduce every imaginable source material thrown at them. I, however, do not compete in this league, but I have found a way to print Ilfochrome from most of my slides with "good enough for me" color balance. The aim of this article is to encourage others to try this incredible process and maybe share some of their own discoveries.