So, I won't go into all the details, but in a medieval setting, an individual character has discovered a new extension of my world's magic system, where by using an ability that resembles 'telekinesis', she can change the kinetic energy of the molecules of any substance, in order to heat it or cool it. This is an incredibly advanced ability, that requires immense concentration. The physics of the universe are functionally the same as ours, aside from the ability of 'telekinesis'. What kinds of materials would she be able to make using her ability to change an objects temperature to any temperature, that would not be obtainable by a typically medieval blacksmith? For example, I have already considered how she could make obsidian by heating and rapidly cooling stone.
Edit: thanks to everyone for their answers! I've never used this site before and everyone's been so incredibly kind. Her ability to heat stems from a telekinetic like ability that is more common, so for example she could suspend something in the air whilst heating it, and could shape it without touching it whilst still hot. Absolutely, I take the point that the kind of stone used will only form obsidian with a high enough silicate content. Yes, she is not fully aware of how physics works, and doesn't have a great understanding of how heat works so most things she would have to learn through trial and error - she does have access to the Imperial Library, but that only allows her a Medieval-esque understanding of how the world works. Roughly a thousand years prior to the story, there were others with the same ability as her, and although it has been forgotten about there may be some old records/myths about it to explain where she might get ideas for techniques that might have required generations of experimentation to come up with - like the cold welding, freeze powdering and vacuum ideas.