Dave, haven't visited the page you provided yet, BUT, as a first impression, "...printing photographs on porcelainized plates using a pigment process..." sounds very much something like enamel photography to me...
Thanks for the link Loris, did they use platinum and palladium for that technique? Penn seemed quite interested in it there is almost 80 pages of notes.
P.S Still have not got around to trying that paper you kindly sent me!! Sorry about that. Is it still working well for you?