Coprinus comatus 'ink' does make a reasonable ink as one image on the botanic gardens website shows. You can get to it by using the following address: http://www.anbg.gov.au/fungi/images-misc/coprinus-ink-large.jpg
Josh, I used the ink straight up. To get the ink, put an ink cap into a tub and leave it alone to dissolve. After a day you'll find the tub has black liquid plus solids. Carefully pour off the liquid and there's your ink. You can keep it in a fridge for ages, but it has a sort of musty/yeasty smell. There's liquid plus spores in the ink and the latter will settle out. You want them mixed in, so shake the jar a little if you see any sign of settling. You can also keep dry ink. Pour fresh ink into a shallow tray, so as to get a thin film of ink and let it dry out. You'll get a black crust. Scrape it off and save those dried flakes. They keep out of the fridge. I've had a couple of vials for some years. When I want ink I pour some flakes into a thimble-sized cup and add a tiny amount of water and stir - there's the ink. Be careful! Too much water and you get a very pale ink.