Sun on a hot day is way safer than oven, and ceramic chips between every chip, not just the ends of a barrel. I just F-ed up a whole barrel of THC sunbursts!
If the sun doesn't get hot enough, try putting them in a black grill, unlit of course. Definitely monitor the temp. I wasn't paying attention and my oven got up to 140. The clay got pushed into the mold in the adjacent chip and now I have what looks to be double hats and canes molds.