wonderful video on the ceramic arts daily blog from the artist Kristina Bogdanov. She said to use soft leather hard clay. That was my first mistake. I am impatient, and I am doing this in the ceramic studio of the Phoenix Center for the Arts, where it is only a three hour session each week. So at the beginning of "class" I rolled out a few slabs of clay and let them air dry for about 2 hours. Kristina also said to make the "ink" the day before. I made mine that morning. That was the second mistake. So after following the steps of using gum arabic as a resist and inking up my xerox "plates" I placed the wet paper onto the mostly wet clay. She said the paper would start to look dry and I could then burnish it and pull it off. It never got the dry look. I even took them home to dry longer. After burnishing, while pulling off the paper, all there was left was a faint trace image and lots of stuck on paper.
In the second try, I let the clay get leather hard and the ink set for two days. I had excellent success with the transfer. Of course, now I have to wait for them to be fired. I'll keep you posted.