What Are Oak Galls? Natural Dyeing, Ink Making, and More

Collected on
daily walks

oak galls have inspired a summer of creative experiements.

If you follow me on Instagram, you may have seen my stories when I spot a fallen oak gall. It’s always a small thrill—on most days, I’m lucky if I find one every few weeks during my daily dog walks. But this summer has been different. I’ve been finding them in bunches, almost daily.

So what exactly is an oak gall? These intriguing little spheres are formed when a gall wasp injects its eggs into the tissue of an oak bud. As Doug Tallamy explains in his excellent book The Nature of Oaks, “...the plant responds with an explosive, cancer-like growth of the cells surrounding the egg and the resulting cynipid larva” (p. 60). This growth becomes a protective home and food source for the developing larvae. The outer shell is hard and packed with bitter tannins—defenses that keep predators at bay.

Once the wasps exit the gall, leaving behind a tiny, telltale exit hole, the gall is safe to harvest. Thanks to their high tannin content, oak galls have long been prized by natural dyers. They’re traditionally used as part of the mordanting process for plant fibers, helping natural dyes adhere more effectively. Historically, they were also a key ingredient in iron gall ink—the very ink used to write the Declaration of Independence.

With my current bounty, I couldn’t resist experimenting. I made my first batch of oak gall ink, though it turned out a bit light—likely because I added too much water. My second attempt was more successful, yielding a rich, beautiful tone (you can see it in the photo below). I’ll keep refining the process, especially the iron ratio. More iron leads to a deeper, almost black color, but too much can damage paper or fabric.

Have you ever worked with oak galls? I’d love to hear about your experiments!