Ctein - please remember you were working with official Kodak papers. Those of us mordanting our own paper have somewhat different parameters. I certainly don't have enough track record yet to pin down all the relevant variables, but the dyes don't seem to "anchor" to hand mordanted papers in quite the same way. Even the time between mordanting and actual printing seems to be an important factor, just as is was in the early days when things like M-1 alum mordanting was common. I have no idea what is specifically being done with the current German transfer paper, but I'm pretty certain that the actual manner in which Kodak installed the thorium nitrate into their commercial paper had a lot to do with its storage properties for convenient use. Adding uranyl nitrate right at the time of mordanting seems to help, but it certainly isn't the same thing.