Fact 1: Lead crystal is made up of at least 20% lead.
Fact 2: Superman can not see through lead.
Question: Can Superman see through lead crystal?

This was a real conversation that came up at work about a month ago.

At first, it sounded plausible that Superman wouldn’t be able to see through lead crystal, and if a bad guy gave Superman a lead crystal box with kryptonite inside, he’d have no idea, even though the humans around him would be able to see it plain as day. It even sounded possible that if the bad guy had all of the windows in his base made out of lead crystal, Superman would not be able to see inside (even though everyone else would).

However, it was determined in the end that it was only Superman X-ray vision that was affected by lead. His regular vision would be able to see right through it, and any bad guy that tried this lead crystal technique would end up feeling pretty stupid.

Incidentally, a bad guy wouldn’t be much better off making his base out of pencils. Pencil “lead” is not actually lead. It’s graphite, which is a dense form of a carbon.

Moral: Don’t make Superman angry. Vague loopholes in his superpowers never quite work the way you hope they will.