What are the ingredients in making a homemade ink?

A pinkish-purple ink can be made from Pokeweed berries that are crushed and allowed to sit a while. You can use the juice right away but it becomes darker purple if it ferments a while. The ink will turn from pinkish-purple to light brown over time. The Declaration of Independence was written with pokeweed ink and that is why it is so faded to light brown now.
A blackish ink can be made from Oak galls and Iron sulfate. Boil a bunch of Oak galls in water and let it simmer for quite a while until the solution is as brown as possible, then add Iron sulfate and mix it. The ink is pale brown when applied and then darkens over the next several days, then lasts longer than your lifetime. You only make a small amount of the ink at a time because it darkens by itself and you want it to do that on what you write on. This kind of ink was used for hundreds of years until better ink was made in the 20th Century.
You can also buy fabric dye and use that as ink.