Van Dyke question
I ma ,not a Van Dyke pratician, but these techniques are similar. Perhaps you problem is coming from The PH of the water. The Ph must be acidic with frerrous salts, I add a pinch of oxalic aci or citric acid when I wash the print to come out the yellow ferrous salt. After I am using normal water to wash the photoyuqte.
You can Find this process in my e - book Palladium (new versioon) in galerie photo.com. I describe this process. (in French)
I am a french photograph. Will you excuse my bad english.