I was just leafing through an old atlas from the 1700s and spotted a tiny marginal note that claims to describe an alchemical ink that turns invisible under moonlight. Do you think there’s any truth to that, or is it just a clever scribbler’s whim? It feels like a hidden treasure for someone who loves secrets and the chemistry of ink.

A silver salt, maybe—like silver nitrate in a thinned emulsion—reacts with light, turning dull when the lamps are off. The scribbler might have been onto something, but if you’re going to try it, make sure the pages are well preserved and the ink is fully set. Never expose fragile parchment to unfiltered UV; a moonlit test might just bleed the fibers. Keep a backup copy of the atlas, just in case the experiment turns the margin into a permanent shadow.