….this special dye allowed those who saw through treated lenses, to see the “spiritual world”, or more like, the dark side, or the underworld.  The dye was banned in the USA despite there being no health concerns but can still be gotten in overseas markets, for “laboratory use only”.  
There’s another way to have this type of vision, to view dark entities and the underworld, that are supposedly “all around us”, and that is to take the old paper 3D movie glasses, that can still be bought on Amazon today, for a couple bucks each, the type with the one blue lens and one red lens.  You get 4 pair, then cut out the red lenses and toss them away, then insert one blue lens over the other blue lens, in one eye piece, and insert the two other blue lenses where the red lens used to be… so you have a pair of glasses where each eye piece has double blue lenses.  Put these on.  Then open your eyes.  Then, freak the fuck out, when you see demons and creepy hobgoblins near by, eye balling you.  No thanks.  Or as a wise man once put it: “Fuck that shit”.