I would start by spraying a bone dry plate (or vase) down with a little water and then brush a thin layer of ash glaze over the plate. She would paint the rose and leaves and then carve lightly through the glaze to add details onto the rose and leaves. On this plate, Jane also carved a pattern around the edge of the plate. She would have to work relatively fast so the glaze stayed moist enough to keep it from chipping off when she carved.
The back of the plate is unglazed, and the plate was sprayed lightly with a bit of cobalt, using an atomizer. I remember that the thickness of her color had to be just right, otherwise the color would fade away or the color would absorb too much glaze and be dry, sometimes peeling away from the pot. The thickness of glaze and decoration in the plate above is spot on.
Thanks, Sybille, for bringing it by so I could have a look. Enjoy it.