As I worked on a piece today, I stopped to check on a technical detail. The question was about protective coatings. Specifically, if an alien artifact turned up that had a protective coating, what would that tell you about the aliens that made it? You could infer a few things from the level of technology required to make such a coating, but what would it tell you about the aliens themselves?
If it were being used in a purely protective or purely decorative manner, perhaps not much. However, if it were intended to protect a written message underneath (as in my piece), the fact that the aliens were able to regard it as clear should tell you a few things about the wavelengths of light they see with. What part of the energy spectrum they regard as "visible" would approximate the maximal output range of their sun. You can derive all kinds of information from that, from the temperature and class of the star, to some preliminary information about the chemical composition of their atmosphere.
The most durable coating would be diamond, laid on by vapor-deposition. So... what's the transmission profile of diamond? It turns out that diamond is transparent from the far-infrared all the way up into the far-ultraviolet. Not much help in figuring out the physiology (or physiognomy) of my bug-eyed friends.
I should note that checking these details as I was trying to write the story was A Big Mistake, one I make on a disturbingly regular basis. I should have just marked it with TKTK, or (CHECK THIS) of some other notation, and gotten on with the story. It wouldn't have mattered one way or the other, really, since it was a throwaway detail, spouted by Dr. Science on the way to his lab. If it had turned out to be contradictory, I could have straightened it out later with different dialogue.
This is just another bad writing habit I need to break, and an associated good writing habit I need to develop. Namely, just get on with the writing.