However, I found that the lettering washed off in the dishwasher.
So, I researched a little more and found a helpful article that listed a number of helpful hints to add some permanency to the design:
1. Use an inexpensive mug. Apparently, the better quality mugs also have a better glaze that prevents the lettering adhering well.
2. Ensure you have cleaned the outside of the mug thoroughly. It was suggested that rubbing alcohol and a soft cloth be used to clean the mug.
3. Bake the finished mug for longer and at a higher temperature than most instructions suggest.
I followed these instructions carefully... and the design still washed off. So... my suggestions?
It's certainly a great idea for a gift and if you still would like to create them, keep a couple of things in mind. First, you can buy ceramic pens that are a little expensive but easy to use and will not wash off. Check with your local art and craft store (as I did) for these pens. There are also ceramic paints that could be used, too, which will look attractive but perhaps will not be as easy to use for quotes and text. My second suggestion is to create your designed mug with permanent markers but pot a little plant in the mug rather than use it as a regular coffee cup. I planted some little 'heartsease' in the mug which combined nicely with my quote.