You can if you're just using them as art; once the pens are baked it becomes dishwasher safe, and (I believe) food safe. It says no health labeling required on the pen??
You bake it in a 325 degree oven for 40 minutes. MAKE SURE! That you put the cup/plate/whatever in the oven before you heat it up, and when it's done baking, turn off the oven and wait until it's completely cooled to take it out. This will prevent it from cracking.