I'm down to 2 last bottles of handmade iron gall ink. 

Time to make a new batch of ink! 

If you kids want to follow along, https://irongallink.org/ has TONS of information on ink & recipes.
Ian's blog also has lots of info along with his personal experiences in ink-making:
https://scribescribbling.wordpress.com/

Not sure which recipe I want to try yet, but I'm collecting the materials needed. The first ingredient is
Oak Galls

An oak gall is a growth on an oak tree caused by insect damage. Tannic acid is concentrated in these galls and is the first basic ingredient in this type of ink. 

Aleppo oaks (Quercus infectoria) are supposed to produce the best ink - having a larger amount of tannic acid in the galls than other oaks. Galls from this species of oak are caused by wasps laying eggs in the tree. The resulting galls have been used in ink-making for centuries. 

Aleppo oak tree - native to Greece & can be found in parts of southern Europe.

If you look closely at oaks in your area, you may also see lumps or round growths caused by similar insect damage. Several years ago, I made a small batch of ink from oak galls collected in Missouri. It was a good solid black ink, so feel free to experiment. (You may want to check with the owner of the oak tree(s) before you harvest galls. Might be a little embarrassing to be charged with trespass or property damage in your quest for ink.) I have no idea how to measure the amount of tannic acid in a given batch of oak galls. You might have to adjust your recipe if you're using galls from another species of oak.

SOURCES FOR OAK GALLS

Kremer Pigment sells aleppo oak galls: http://shop.kremerpigments.com/en/

Ancient Earth Pigments also sells them: https://www.ancientearthpigments.com/product/aleppo-gallnuts/

Yay! Oak galls.