In the Book of Kells, verdigris was used for green. It's brilliant, not as toxic as some(looking at you, Orpiment!) but it had the drawback of being rather caustic, much like oak gall could be. Like gall ink, it's not hard to make, but I didn't like the thought of all this effort, only to have it eat through the paper and destroy my art.
So I looked to see if there was a period alternative. And there was: Iris Green.
Iris green ink was made from the blue iris common in Europe, but any blue or purple iris will do. The flowers are collected, and either boiled or(nowadays) frozen, then mashed, squeezed and strained.
Then alum is added. Initially this will change the dark purple liquid to a dark teal. Historically, cloths were dipped in this liquid and dried, then wetted with a bit of water, much like with cheap water paints. Sometimes this was done in a shell dish and this was credited with bringing the green out. Certainly, a lake of the alum mixture will produce a deep vivid forest green. But it is very useful to have a pigment that doesn't require grinding and mixing with a binder.
There are a couple of problems with Iris Green. Firstly, it's not as colorfast as verdigis. Secondly, the ink will not keep. There's a third problem in that you are completely at the mercy of the Iris growing season May to June, though I was lucky to get some in late April. And they don't all bloom at once. And when they do bloom, you might find, the blue and purple ones are taking their time. White irises are very pretty, but useless for these purposes. So you must pick them when you can then freeze them until there's enough to work with.
I put my batch of irises in a small pot with just enough water to barely cover them. The colors are surprisingly heat resistant, but I don't like to reduce more than I have to. Then boil, simmer, until the flowers are pale and washed out. mash them to get every last bit of pigment out, strain, squeeze and transfer the deep purple liquid to a glass container.
Now the alum, diluted in a little water, is added. The color change is instant.
At this point some people report being able to use the ink immediately. Personally I find the green too weak with concentrating it by inspissation (technical word for letting it sit and evaporate). Also prefer to add a drop of soda ash to shift the color.
I was finally able to make quite a bit, but, without even a design finished or a draft, I had to put the jar in the freezer to keep.
Iris lake made out of another batch:
Of course, the lake has the advantage of being stored safely in dry form.
