I just found a great list of practical sympathetic inks ("invisible inks") and gawd look at this source. this is great!

It's basically a manual for people wanting to debunk phony spiritualists, giving detailed explanations of the various tricks and gimmicks that they used in their seances.

Dilute cupric nitrate solution is mentioned as an option, apparently producing red Cu₂O upon heating.

@mxchara link?

@nautilus https://www.gutenberg.org/ebooks/61871 here!

@mxchara thanks, I'm an avid PG volunteer and reader so I'll check this out

@nautilus cool. are you thinking of organizing a seance? =p or at least a spiffy magic show

@mxchara no I just like occult stuff