I recently travelled to the USA from Asia. When I arrived in Detroit they marked my E-cigarette with a clear colorless liquid using a small paint brush used for water colors.

What chemical(s) do they use as markers?

  • 1
    As a related question what is the purpose of the marking?
    – Phil
    Commented May 27, 2014 at 23:59
  • 3
    @Phil: "marking" is to elicit a chemical reaction with compounds of explosives that most likely makes the clear liquid change color.
    – Jonas
    Commented May 28, 2014 at 8:52
  • 1
    @Jonas, thanks. I wasn't aware they did that with liquids too. Whenever I've been checked it's been with the cloth in in the wand thing
    – Phil
    Commented May 28, 2014 at 16:00
  • This question appears to be off-topic because it is about science/chemicals - not a travel question.
    – Mark Mayo
    Commented May 29, 2014 at 13:51
  • 7
    @MarkMayo But the fact that something similar may be experienced by travellers makes it relevant right? Commented May 31, 2014 at 15:48

1 Answer 1


They are known as taggants. I found an article about them on Wikipedia.

Hope it helps.

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