I've tried a bit of carving now - Celtic knotwork is flipping hard to do! - And I've got an idea for what to do to make it more successfull. It's simple, really. I just copy down the template onto a paper, fasten it to the cup, and trace with a knife.
Anyhoo, I covered one of the cups in black slip, as well as the drinking horn, and rubbed a spoon over the horn for the last bit of the lesson.
Yes. I rubbed the horn with a spoon.