from Aurei Velleris, (Hamburg: bei Christian Liebezeit, in der St. Joh. Kirch, 1708)
The Black Ravenshead
That is the black and stinking earth of the wise, wherein awaken worms. There one swallows the other; there one thing destroyed is the other thing born. Then this earth is at the bottom of the vessel, and wholly dissolves itself in the water as before.
Here it is asked how long it takes to turn the stone black, and what the sign is of the right decomposition. I answer: when the black color appears, then is the same darkness a certain sign of the right putrefaction and decomposition of the stone, but when the darkness wholly disappears, then is it a sign that the stone has wholly decomposed and putrefied.