They're also pretty awful if you try to use them for safety purposes. Like... how blue can purple be before it's not purple anymore, idk. Last year it was very purple, but now the test is a year older, or is the product non-uniform and that's why it's different...

Basically, if you inject enough suspicion into any situation, colorimetric tests will eventually lead you to believe that you're in trouble. And then later if you bring the sample to somebody with access to real equipment it often turns out there was no trouble besides the sort you were looking for in the first place.

I honestly think we could save a lot of lives by just putting a gas chromatography machine in the library next to the 3d printers and training people to use it.