Do I correctly assume that you use a heat gun to speed up the drying of the printer's ink?Another way of doing this technique is to once you transferred the clay image to the metal, build a clay dam around the area.
Now dilute the cold blue about 50-50. This slow down the coloring and makes sort of a dye out of it. Pour the solution into the dammed area and watch it carefully. As soon as you see the image appear with the blue, Dump it out.
This eliminates the possibility of smearing the clay as you brush the blue on it.
Nowadays i just find using printing ink and tape a whole lot faster and easier