This will actually work...

Take some dry (very DRY) mushrooms... and use 190 proof or 99% ethanol everclear would work as well... soak in a amber glass...  lid closed... in the fridge crisper for a few weeks... take  out strain your mark. the ethanol will turn blue you will find.

this is the nefarious blue juice of legend...

take this blue juice... place in freezer... crystals will precipitate... and there you go...

learned trick from a trusted chemist...