Thank you to everyone for your comments above or via private message. I'm fairly confident that it isn't contamination of the developer by blix (but of course it might be...). I also don't use a safelight. I constructed a kind of cradle that sits on top of the processor that helps me get the paper in the right slots in the dark, so I know I'm not sticking it in the blix and then in the developer!
I'm going to insulate the sides of the Nova processor to make sure that the dev and blix slots are the same temperature and I will try replenishing at 10ml for each 10x8 sheet that I've already done. I will do without a stop bath until I can find an acetic acid one. (Is it possible for the stop bath to poison the blix?).
If that doesn't work, I'll chuck out the developer (well, give it to the haz-chem man) and use some more from the 5L that I mixed initially, as an experiment. Then I'll do the same with the blix. Failing all of that, I'll make up some fresh and start again.
I'll report back.
I said I would report back, so here goes...
To cut a long story short, the problem has gone away; the long story is as follows. Note that all the scanned prints given as examples below are scanned against a sheet of white paper as a reference:
(a) Initially, prints looked like scan0001.jpg. This is a border-less test print, held in place by hand. It was as though the natural colour of the Fuji Crystal Archive paper had not been removed.
(b) Over the course of time (a few days, maybe, with the same chemicals remaining in the Nova slot processor), the strong cyan colour disappeared on subsequent prints so that prints then looked like scan0002.jpg. This is also a border-less test print, held in place by hand. Note that this is without changing chemicals or filtration from scan0001.jpg. The prints were developed in a vertical slot processor and the bottom edge of the prints is to the left, where there is still a cyan line, as though chemicals have been caught on the edge of the paper rather than draining off.
(c) After a few more days, the cyan problem largely disappeared but there remained an overall greeny-yellow cast as seen in scan0003.jpg. The bottom edge is to the left and the colour cast increases in intensity towards the left.
(d) At this point, I made the first post in this thread. After considering all the comments, I decided to insulate the Nova tank (the developer was in an outer slot and so slightly less warm than the stop bath and blix) and I decided to omit the stop bath altogether since it was citric acid based. I also replenished the developer and blix by draining off 250 ml of each and replacing with more of the original 5 litres (I'd done about 20 10x8 sheets, not 40 as stated previously). Each slot holds about 2 litres. The next time I began printing, I made a complete hash of getting the paper from the developer into the blix (no stop bath), so that in total it was in contact with developer for about 1 minute 30 seconds rather than the recommended 45 seconds at the temperature I was running at. The resulting print had mucky and stained borders and looked a mess. But this suggested that I might have been giving prints too much development and a 45 second development time (including draining which had been taking longer than I thought) produced spotless white borders with no stop bath. I have since replaced the stop bath with Kodak's acetic acid based one and now get good colours and white borders as in scan0004.jpg (the scan makes them look less white than they are).
So I'm inclined to conclude that the problem was some sort of chemical staining, but since I was able to get staining as described above without any stop bath it's not clear what additional effect the citric acid stop bath might have had. What I can say is that by following recommended developing times and temperatures as accurately as I can and with an acetic acid stop bath, I haven't (yet) had any more problems.
I'd still be interested to know why there was such a strong cyan stain initially. Did I not mix the chemicals well enough to start with?
I echo what PE said. Maybe your developer is not contaminated by blix but when the print is INTRODUCED into the blix there might be some developer left on it. Color chemicals are very unforgiving. And, also from PE: watch your safelight as color paper is amazingly sensitive to, especially, the red spectrum. Those trained in B&W have to learn new, much more disciplined, rules.
Edward S: provide an area of the print that received NO exposure, like the area provided by a (held down firmly) coin. If you do not do that we might be inclined to think that you merely filtered incorrectly. The unexposed base tells the whole story. - David Lyga
Thank you for pointing put an important omission. I edited my post above after initially posting to say that that scans 0001 and 0002 were borderless (apart from areas formed by hands holding down the paper at the corners) but then forgot to add that scans 0003 and 0004 do have proper borders to them where the paper was trapped under the printing easel.
Also, I don't use any safelight - the room is completely dark when the paper is out of the box so I think we can rule that out.
I did subsequently get a good print of the picture that is in scans 0001 and 0002 so I'm confident filtration isn't to blame. This is why I'm a bit puzzled because the usual culprits don't seem to be the answer in this case!
I use trays, do not use any stop between developer and bleach-fix, and never have any problems. I do, however agitate the print vigorously as soon as it is put in the bleach-fix.
Is the developer you are using straight developer or replenisher? If it is replenisher, the cyan cast you initially experienced may be due to the fact that you did not use starter. Replenishers lack chemicals (bromide and/or chloride) that is necessary to inhibit fog formation that straight developer will have. I have mixed my own home-brew RA-4 chemistry before without any sodium chloride (the fog-inhibiting restrainer, which would found be in the starter) as an experiment and got a cyan cast. After adding the chloride the cyan cast went away. As development takes place, the chloride ion is produced as a by-product of development and slowly builds up in the developer, and eventually the cyan would go away on its own. Sounds like what happened to you.
I use Kodak RA-RT replenisher without any starter and have no problems, but use it at room temperature and have not used your developer. At higher temperatures the starter may be needed.
RPC: This is interesting: you are saying that 'table salt' (sodium chloride) is a restrainer for color chemicals? I thought that the starter's restraining action was due solely to the bromide in it (just like benzotriazole is also a restrainer). Can you or someone else elaborate?
Yes, you are correct RPC, in that you really can get clean whites going directly from developer to BLIX. However, do not attempt to do directly from developer to BLEACH (ie, without the fixer). You WILL get serious fog.
I do not know what is the problem within Edward's dilemma but I assume that in his processor there is a contamination. This is SO easy to do in color work; so easy that I use 'one shot' for everything and use trays only. Decades ago when I used to use a motor drum I often had cyan fog throughout the print. I wish I could test your color developer and paper. - David Lyga
Chloride can be a restrainer for some color papers as they are made from AgCl (Silver Chloride) emulsions. In any event, Chloride does tweak the curves a bit.
You can use RA-RT Dev-Replenisher without the starter. I do all the time. I use 2' at 68F in a tray or 1' at 100F in a drum. In the drum, I always use a prewet. I also use a stop with the drum but not with trays. The stop insures uniformity and low Dmin.
This is all with EK chemistry and paper. I have reports that Fuji CA does not behave as well with these conditions, especially at lower temps.
Thank you for the info, PE. I never use starter, either, but I just wonder if the starter is provided not only to maximize consistency but also to slightly prevent a very low fog level. After all, starter is restrainer. - David Lyga
I have wondered why the RA/RT replenisher seems to work well without starter. Perhaps it has some restrainer in it already. I have looked at the starter label and it says it contains chloride (usually potassium chloride) and other ingredients such as carbonate (pH adjustment?). IIRC Kodak says to make a working solution out of the replenisher, you must add water and starter.
At the lab I work at, at one time we used Trebla replenisher to make working solution. If you didn't add the starter to the replenisher when making the working solution the control strip would give an out-of-control reading. RA-RT replenisher does not seem to have this problem. But just what is the case with the RT/LU used by the OP?
If you are running a replenished process, the process "seasons in" and changes the curves and color balance. The starter contains the chemicals that do this seasoning, and so if you dump your seasoned tank, you use replenisher + starter to bring yourself back to the seasoned tank characteristics.
IDK about Trebla, but I do know that it is a reputable company with many former EK people working there.