1. Do you need to replenish the developer or is it sufficient to just add back what is lost during processing?
"I am confused about #1, do you mean just add water, or add more PO to make up for the loss in process? I add back more PO once my jars get too low. I keep 5 one gal solutions with varying concentrations of pot dichromate, once they get to about 2 liters I add more PO solution."
You answered my question. When working in kallitype with sodium citrate I typically keep on hand several bottles of developer with varying concentrations of potassium dichromate, but as it is used up in processing I regulary top off the developer with a fresh sodium citrate solution of the same strength as the developer, plus a few drops of dichromate as needed. If you don't replenish regulary with kallitype the prints become very hard, and eventually impossible, to clear. I assume from your answer that it is not necessary to replenish on a regular basis with pt/pd printing to clear well.
I have not seen that as far as clearing, nor have I seen the metal interfeer with the clearing, but then I dont let my solutions get too concentrated, perhaps that is the trick.
I have noticed that there is some variability to the speed and the contrast of the print that I think may be attributed to the age of the developer. I noticed this when I replenished my developer recently, and it appeared to cause a change in contrast and also a slight speed change.
So, while you can let the PO go as long as you want, and simply replenish it on occasion, I think it is much better to get a set amount of PO, and then replenish it back to that level on a regular basis.
This will cause the nature of the mix to remain a bit more stable from the unreplenished developer to the freshly replenished developer.
There have been some discussions regarding the fact that the PO does become heavily loaded with both metal salts and FO, and it does have an effect on the final print, and I think that some staining and the dreaded salt migration can be partially attributed to the amount that the PO has of FO and salts.
I have recently started increasing the replenishment rate by pouring off a few hundred ml of PO at the end of a big printing session. I have done this because I think that it may help keep the highlights clean and also help eliminate any possible staining that might occur. This is not based on direct experiential data, but is simply a hunch based on some anecdotal evidence I have.
"I have recently started increasing the replenishment rate by pouring off a few hundred ml of PO at the end of a big printing session. I have done this because I think that it may help keep the highlights clean and also help eliminate any possible staining that might occur. This is not based on direct experiential data, but is simply a hunch based on some anecdotal evidence I have."
What you describe is the way I have always worked with kallitype, and with sodium citrate developers with palladium. If you don't replenish on a regular basis with kallithype (about 100ml for every 300-400 square inches of print developed) it becomes increasingly difficult to clear the print. Perhaps it is also true with palladuim, though on a lesser scale.
But how do you deal with the accumulation of metal salts in the developer? I have heard that they fall to the bottom of potassium oxalate developers, but I have a liter bottle of a 30% solution of potassium oxalate that I have used with palladium for several months and I don't see any metal sediment on the bottom??
The metal salts are too small to filter, even through whatman paper, so I just leave it in there.
I have found that the stuff that falls to the bottom is other things, that don't have the blackness of the metal salts. I think it might be FO, and also PO that has dropped out of solution. Most people use the PO hot, so you get a bit of concentration due to evaporation, and this might result in some crystal fallout on the bottom. If you do get large green crystals, add some distilled water, as you are getting supersaturated fallout.
I also get a very fine silt at the bottom that may be contamination from the paper that gets put through the developer, but I'm not really sure. It's white-ish and I thought it may be some carbonate buffering material.
I decant the PO when I pour it out, and always try to avoid pouring any solids on the print, as you never know what they will do to the image. The grains can cause some surface abrasion, at least.
Every once in a while, I'll run the PO through a coffee filter to remove all the larger sediment, and that's about it.