Platinum/Palladium exposure issues
I just got back to alternative printing after a bit of a hiatus and am starting out with the Na2 method. I was printing yesterday for the first time with this technique and ran into a few problems.
My primary problem is very long exposure times and lack of Dmax. I am printing on COT320 (after abandoning a very uncooperative batch of Arches Platine). I am using the Pd and ferric oxalate in equal proportions with a couple of drops of Na2 5% per 8x10 for contrast control and potassium oxalate as a developer. I even double coated, but this did not seem to help much. I am brush coating with a Richeson brush. Humidity levels and temperatures are within acceptable levels for this time of year (I ran a heater and humidifier in the room). All my chemicals are fresh from B&S this week. I am using a bank of fluorescent tubes at about 6 inches (I am not exactly sure what kind, but they were marketed as under counter grow lights) and my exposure times were over an hour, and even at these levels, I am not quite getting two of the least dense steps on the step tablet to merge as black. I would blame the light source, but last year I did lots of kallitypes and they worked fine with exposures of about 30 minutes -- and this was with pyro developed negatives. The neg is sandwiched under the same glass I have used in the past and it is not UV blocking (I thought of that). Currently my negs are developed in D76 and I am pretty sure that they are well tailored for the process. (Of course, the step tablet suggests that the problem is independent of the negative.)
I fully expected that with the Na2 process and non-pyro negs my exposures would be in the 15 minute range based on my kallitype experience with pyro negs. Is palladium that much slower than kallitype? It does not seem that it should be.
Any thoughts as to what might be going on? Would low relative humidity cause these issues? I suspect that even with a humidifier my basement is a little dry. Though when I was trying to get the Platine to work I brushed it with a 10% oxalic acid bath and the paper was nicely humidified when coated and with this arrangement I was still getting hour plus exposures, so I don't think that is the issue. But if it is the lights, why would they work well for one process and not another. Very confused....
Any suggestions would be much appreciated.