Envelopes and fluorescence

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Specifically white envelopes. Has anyone ever seen a blue fluorescence when opening the glued flap?
What causes this and why only on white envelopes (but not all white envelopes)
Best viewed in a darker room for those about to try it

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thank you

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Simpo Two said:

Now you need to ask yourself why you're opening envelopes in a darkened room...


Gottit. You need to keep opening envelopes to create light so you can read the contetns of the first one!

aye, that's it.
or i'm a tight Scot who uses street lights when possible. purely to save the planet though

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an X-ray from sellotape! that's impressive