You will also need 

WATER 

to make your ink.

Ink from the last batch I made.

If your ink turns out a funny color, or does something else weird, you might have contaminants in your water. My hometown sends out a water quality report once a year, so I pretty much know there's not much in there that will affect my ink. If you've got well water, or just aren't sure what's in your local water, maybe use distilled or bottled water. I've also seen some ink recipes that call for wine or some other liquid. I haven't tried any of those yet, so I'm sticking with tap water this time.

Here's a little online booklet from Yale University containing medieval ink recipes:

https://travelingscriptorium.files.wordpress.com/2014/06/scopa-recipes-booklet_web-june-2014.pdf

There is a lot of information about making ink and some recipes here:
https://irongallink.org/igi_indexc33a.html

Ian the Green has been making ink for quite some time. Here's a link to his blog:
https://scribescribbling.wordpress.com/

More info about medieval ink at Stefan's Florilegium Archive:
http://www.florilegium.org/

There are tons of ink recipes online, and even more in actual treatises from the middle ages. If you find any good recipes that have worked for you, please share!