|Doing some low-light writing? Grab a fig.|
Samuel van Hoogstraten, Self Portrait (1647-9)
"Letters that are not to be read but in the night, must be written with the Gall of a Tortois, or Fig milk, if you put it to dry at the fire, or else [with] Water of Glow-Wormes."
Johann Jacob Wecker, Eighteen Books of the Secrets of Art & Nature (1661)
If I may offer a recommendation: opt for the fig milk. The tortoise dissection might be a little messy on your writing desk.