To make a beautiful golden brown walnut ink that was used by the great Old Masters follow these instructions.
In early fall as you travel the countryside, keep an eye out for tall walnut trees heavy with large green hulled walnuts. Revisit those trees later in the fall as the walnuts begin to drop. Collect the largest walnuts in a large five-gallon bucket. If the hulls are starting to rot and turn brown, it is all the better. As you gather the walnuts, you can speculate about just how many drawings each walnut contains. Leave the bucket of walnuts in hulls under a shed cover for a week to ten days. If not already, the green hulls will begin to turn dark brown and soft.
Find a large pot from the kitchen, or better, get one of those large turkey fryer pots with a gas grill. Outside the house, place the completely rotten walnuts and hulls into the pot and cover with a generous amount of water. If you do not use a gas grill, a hot plate will work. The idea is to slow cook the brown hulls over the weekend at low heat, stirring every so often. If the water cooks down, just add some more.
Eventually the walnut hulls will completely break down and beautiful brown ink will begin to form. Start testing the color strength with a stick and some white paper. It should be very dark brown, almost black when used straight and a beautiful golden brown when thinned with water as a wash.
Let cool and strain the entire mixture though nylon stocking to remove the nuts and heavy fiber. You can now heat again and boil down to the desired darkness and thickness. A very dark ink, just slightly thicker than water is desired. Last, you must add an ounce or two of formaldehyde to keep the ink from rotting. Do not reheat or cook after adding formaldhyde because of the toxic fumes. Also, as with any art material, the ink will be toxic because of the formaldehyde and should not be used by small children. A five-gallon bucket of walnuts should generate about a gallon of ink. Enough for many beautiful drawings and plenty left over for art friends until next fall.