Oak apples or galls were the main ingredient of one kind of ancient and medieval writing inks. The other kinds of ink were fine grained carbon suspensions; lampblack, ground charcoal, or soot from burned grapevines.

Crushing and fermenting the galls, then adding the resulting sludge to iron sulfate (or "green copperas") creates a dark blue-black ink. The sludge is thinned with water, wine, or vinegar.Gum arabic gave the ink a smooth thick consistency; if the ink is too thin, it spreads across the surface of paper or parchment before it has time to sink into the fibers.

It is easy to try this recipe; ferment the oak galls for a few days in a jar of water or vinegar, with a few rusty nails for your source of iron. You don't really need the gum arabic to get some good dark ink. When you first write with it, the ink will look pale, but it darkens as it dries.

Rules made by E.B. For his children to learne to write bye, 1571

"To make common yncke of Wyne take a quart,
Two ounces of gomme, let that be a parte,
Five ounces of galles, of copres take three,
Long standing dooth make it better to be;
If wyne ye do want, rayne water is best,
And as much stuffe as above at the least:
If yncke be to thick, put vinegar in,
For water dooth make the colour more dimme.
In hast for a shift when ye have a great nead,
Take woll, or wollen to stand you in steede;
which burnt in the fire the powder bette small
With vinegre, or water make yncke with all.
If yncke ye desire to keep long in store
Put bay salte therein, and it will not hoare.
Of that common yncke be not to your minde
Some lampblack thereto with gomme water grinde"