Etsuko Ichikawa writes with hot glass on paper. They’re called glass pyrographs.
In the words of the artist:
“I see this process as a metaphor of my daily life in terms of encounters and impressions relating directly to my work. Meeting someone, seeing some event, hearing a piece of music – these encounters are fleeting moments, but sometimes the impressions of these moments take on their own lives.”
Hat tip: Forrest Loder
r3ckon 
Traces of the Molten State on YouTube: http://www.youtube.com/watch?v=cbQucVqJ3Rk
Very cool to see the videos of the process. I hadn’t seen those. Thanks for sharing!