There is a lot of debate about the correct method. What temperature to use, how long to leave them in, do you put the plates in while it's pre-heating or wait?
So I decided to find out for myself if it was possible to make the permanent marker actually stay permanent. I bought two white plates at the dollar store then spent the next 4 weeks testing different temperatures and time. I would place a plate in while the oven was pre-heating then put the other in once the oven hit the desired temperature.
It became a pretty normal routine in my house. Draw, bake, wash, wash, wash. Draw, bake, wash, wash, wash. I would put the plates in my dishwasher and leave them there wash after wash until the marker would come off.
The Verdict: First of all, it has to be a regular Sharpie pen. Any other sort of Sharpie doesn't stand a chance. And secondly, it's never going to be permanent. No matter what temperature you do, or how long you bake it, the marker will eventually come off. The longer you bake it the more washes you get, but I ever got more then 6 washes before the marker came off.
If I hand washed it with a scrubber then it always came off immediately. The only way to get more then 10 washes out of it is to use a very soft sponge and treat it as though it's a bomb about to explode.
But what was really interesting, and I didn't see this on any other sites, was how the color faded and changed. The higher the temperature the oven was, the more the colors faded and changed.
So I started to experiment with really low temperatures. You have to get below 250 degrees for the colors to stay untouched. Unfortunately, it comes off with one quick wash.
So basically you have two options. Have bright colors that don't stay, or have faded colors that last a while. Or you could always just decorate them and have them on display.