Here's what I found out:
Baking at 350 for 30 min does NOT work.
Colors change when baked! Especially Yellow...it turns a yucky pinkish color.
It is nearly impossible to find a ceramic enamel or sealer that is food grade (that doesn't require a kiln...)..I'm still looking.
Drawing freehand one a surface that is not flat, is not easy.
These are so freakin cool!
So, if you want the drawing or writing to last I suggest:
Use only BLACK or SILVER Sharpies.
Bake at 400 for at least 40 minutes.
Put your pieces in the oven while it is cold. DO NOT preheat.
Let them cool COMPLETELY in the oven as well.
After I followed these few rules, I tested a piece by running it through my dishwasher, and the image stayed put!
I would recommend handwashing even so.
I would also make these few recommendations:
Cheap dishes are better as the finish is not as good and the ink can get into it. (Nicer dishes don't hold the paint)
Put your images or text in the areas least likely to come in contact with utensils or lips. (ie the wrong side of the cup and the outer edges of the plates.)
Mistakes are very easy to erase.
I suggest a q tip with a bit of alcohol or if that doesn't get it off, a paste made from baking soda and water. A bit of scrubbing and it will come off.
Because I freehand my drawings and text I made it hard on myself, but really enjoyed making these. I assume one could use transfer paper to get "neater' results.
I really would like to make a bunch of these for gifts next Christmas, but I want to test mine a bit more to see how long they will last before I do.
I'm not expert on this stuff, but I am seriously considering buying a few pens that are actually made for writing on glass and trying it again :)
*One month later and the owl cups still looks the same! It's been through the dishwasher probably 5 times because I never seem to remember not to stick it in there, but none of the ink has come off :D