I'm about to order some inks, and a thought crossed my mind. What if they were to sit in a 100 degree mailbox all day? Would they somehow become denatured? A lot has been said about ink's ability to withstand water/chemical tampering, but I haven't heard much on how they deal with heat.

Never had a problem with it down here in Texas and it gets pretty darn hot.

I've wondered this myself, being a cook I stand at the stove for hours a day, than stand in the walkins for a while... How do I choose an ink and pen that can withstand these conditions ?

There aren't any proteins in standard FP ink to become denatured. The majority of it is simply water and the rest are small organic molecules. The worst thing that is likely to happen is that one of Noodler's full to the brim bottles will leak everywhere as it expands in the heat.

Denaturing is only prevalent in large polymers with tertiary structures, like proteins. In other words, if it's not full of big, complex, and twisty molecules, you're probably safe. My guess is that pen inks contain pretty basic compounds, so I would assume that, as long as the paper doesn't catch fire (at 451 degrees), you're probably safe with most basic, dark inks. (some off-kilter inks may discolor at higher temperatures, but I doubt that 100 degrees will cause significant problems.)