Iron inks are fun. They're pretty stable, stain like crazy, but some of them will eat away at thin things like paper, so they're best used on leathers, velours,

Iron inks are fun. They're pretty stable, stain like crazy, but some of them will eat away at thin things like paper, so they're best used on leathers, velours, and other tanned materials. I make a blue using ferric ammonium sulfate and sodium ferrocyanide mixed in water.