You can see how saturated the cooked-down version is compared with the cold-process one; and how the cold-process one improved as I let it evaporate down for another two months:

Start with black walnuts (the outer husks, and not the hard shells or nuts):

Wear heavy rubber gloves, or your fingers will look like this for weeks and weeks:

Soaking and cooking the husks down in water in a non-reactive pot:

Store finished ink in a glass bottle:

Writing sample of the cooked-down version:

What you'll need for either recipe:
Black walnuts
Water (distilled is probably best)
100-proof vodka
Whole cloves
Cooked-Down Black Walnut Ink (For Dip Pens Only)
Black walnuts have a green fruit-like exterior called a husk. This must be cut or torn away to reach the actual hard walnut shell (with its edible nutmeat inside). It's the husk you want for ink, wood stain, fiber dye-baths, or for making medicinal tinctures and ointments-- and not the hard walnut shell. The husk has remarkable staining properties... as soon as it is exposed to air, it turns dark brown quickly. I wore rubber gloves while I de-husked the black walnuts-- some of the husks that were darker in color were easy to tear apart with my hands. The ones that had just dropped off the tree and were still fresh and green were hard enough that I had to use a knife to slice away the husk. Dehusking was hard on the gloves and they kept tearing on me... which is why I still ended up with stained fingers! (Yes, this stuff will stain countertops and everything else it touches, including the pots, strainers and other equipment that you need to process it with, so just be forewarned if you plan to try this. It's best to set aside equipment just for this purpose.)
While de-husking, I noticed quite a few had white worms in them. I could usually tell if worms had gotten inside the husks because those were already turning dark brown inside (and those were the easiest to tear apart with my fingers since they were already starting to break down). I actually took the time to pick out the worms. I'm vegetarian and couldn't stand the thought of bugs in my ink... it would've been a lot simpler just to boil the husks whole, but I knew a lot of worms would've been inside them and that would've bothered me to kill them. I felt a lot like those Buddhists in that Brad Pitt movie, Seven Years in Tibet, where they wouldn't build on the ground until they'd removed all the worms safely from the soil, for fear of killing any. Also, if I'd left them whole, then the nuts inside would have been ruined for food. (Edited after the fact: I've since learned these white worms are actually Walnut Husk Maggots! It still bothers me to kill them, though!)
After the husks were removed, I simply put them into my large canning pot and covered them with our well water. I homeschool, so I couldn't do anything more with them that day. They soaked for about 24 hours before I could get back to them again. Then I brought them to a boil, lowered the heat, and gently simmered them with the lid on for several hours. I threw in a piece of steel wool for about an hour towards the end. This adds iron and is said to darken the color (though I think I will skip this next time... I prefer a reddish brown, and the steel wool seems to make a blackish brown and dulls the color a bit. Also, our well water has a bit of iron in it anyway.) I turned off the heat, and then let the husks soak overnight because I was too busy to get to the next stage.
The next day, I strained all the solids out. I lined a large colander with a "flour sack" dish towel to strain the liquid through. I returned the strained liquid to the rinsed-out canning pot and brought it to a boil on the stove for the last time. Then I lowered the heat to barely a simmer (with no bubbling at all, with just a little steam rising from the top). After a few hours, it reduced down enough to a nice dark brown color. I kept making writing samples every hour or so, to see if the ink was the right color and consistency (not too runny, not too thick). When it was finished, I added 8% alcohol by volume for a preservative (80-proof vodka, to be exact). In later batches, I went with 10% alcohol and 100-proof vodka, which is easier to figure out mathmatically. (For a 10% concentration of alcohol with 100-proof vodka, take the number of ounces of ink you have and divide it by 4 to obtain the amount of alcohol to add. Ex. If you have 32 ounces of ink, divide that by 4 = 8 ounces of alcohol to add). My cooked-down black walnut batches have never molded over, and some of them are 2 years old now.
When all was said and done, I had created about a gallon of homemade ink. I didn't count how many black walnuts I started out with, but I filled a large canning pot about 3/4 full with husks and water, if that gives any indication. I used dozens of black walnut husks. Maybe around 50 or so.
This ink is meant for dip-pen use only, and not for fountain pens. It would likely ruin a fountain pen. It is especially well-suited to glass dip pens. I recommend gold-plated metal nibs to resist corrosion by the acidic ink.
Observations for the Cooked-Down Ink:
I notice this cooked-down ink tends to form a thick pigmented sludge that sinks to the bottom of the bottles over time. It can't be shaken back in, though it can be stirred back in (carefully) with a popsicle stick. It doesn't seem to affect the ink adversely (like precipates would for an iron gall ink), though if you don't stir the sludge back in, your ink won't be as saturated and might come across as a bit watery and thin.
Sunlight tests have shown this ink to be fade-resistant. The longer the ink dries on the paper, the more waterproof it becomes, too.
Slow, Cold-Process Variation (Works in Some Fountain Pens)
In the quest to create a black walnut ink that would not form a thick pigmented sludge at the bottom of the bottle (as the cooked-down version is prone to doing), and in the interest of creating an ink that could be used in a fountain pen, instead of repeatedly cooking down the husks, I soaked the husks in water for months, strained, and then let it evaporate down to strength as follows.
1. Fermentation stage: Fill a non-reactive container with husks (remove nuts and black walnut maggots first). If you have a large amount, a plastic paint bucket works great. Fill with distilled water to cover and then put a lid on. Allow to ferment for 2 months (I forgot about mine and fermented it for 5 months and it developed a manure smell, and then later a yeast smell during the evaporation stage. It still turned out fine!)
2. Filter/strain the ink with a paint strainer or through a few layers of cloth in a strainer. Squeeze out as much of the liquid as you can.
3. Evaporation stage: Make a writing sample log. With a glass or dip pen, make a writing sample and note the date. Notice the strength of the ink. Now allow the ink to evaporate down until it is the strength you want. This can take weeks or months, depending on your quantity and how hot/dry it is and the type of container you use (I recommend a glass baking dish or cat litter box or some other shallow non-reactive container). I tape paper towel across the top to keep the dust, pollen and insects out, while still allowing evaporation to happen. Every so often make another writing sample to see how your ink is doing.
4. When your ink is dark enough, boil it covered for 10 minutes to kill the ink beasties. Watch it carefully or it will boil over in a huge foamy mess (speaking from personal experience here!) This is a rather stinky process, so ventilate the room. The odor of the ink should improve a little bit with boiling (a little less manurey).
5. Black walnut is naturally anti-fungal, but I definitely recommend adding 10% alcohol; basically, for a 10% concentration of alcohol, and if using 100-proof vodka, take the number of ounces of ink you have and divide it by 4 to obtain the amount of alcohol to add. Ex. If you have 32 ounces of ink, divide that by 4 = 8 ounces of alcohol to add). Add several whole cloves as an added preservative. The cloves will help improve the odor, too, somewhat.
6. Bottle in sterile glass bottles, preferably amber glass, with no air space inside (this will help prevent mold growth, too).
Observations for the Cold-Process Variation
This ink is pretty forgiving and hard to mess up. I’ve been able to use this ink in Parker Vector, Pilot 78G, and Pilot Parallel fountain pens so far. The cold-process version is a tad less saturated than the cooked-down version, but less prone to forming pigmented sludge on the bottom of the bottle, which is probably why I'm able to use it in a fountain pen (the cooked kind clogs fountain pens). This kind can be used with dip pens, too.
I did notice my working jar of ink grew a kind of film on top (mold?) when the ink level became low and there was a lot of air space inside the jar, and after not using it for a couple of weeks. My other full bottles are fine. So I recommend keeping this cold-process ink in jars small enough to contain it, with no air space inside. Or, if you've made a very large quantity of ink, use those storage tanks from photography darkroom suppliers with a floating lid:
Ink on tap!

The floating lid:

or a collapsible bottle such as the Arista Air-Evac Bottle... this would be well-suited for iron gall inks, too:

Edited by fiberdrunk, 02 November 2012 - 17:46.