One-point Lesson : Making 'Bokuju'
Lesson #2: Making bokuju (sumi 'juice') ...
(information from Mr. Keizaburo Matsuzaki - paraphrased into English by David)
Sumi sticks used by calligraphers produce a rich and black ink, but we woodblock printmakers need such a large quantity of sumi that it is not practical for us to sit there rubbing the stick back and forth on a stone to produce it. Instead, we make it from 'ore- zumi' (broken sumi).
Go to your local calligraphy supply shop and ask for a bag of 'ore-zumi'. They will sell you a paper bag full of broken and otherwise sub-standard sumi sticks, ones that cannot be sold to their usual customers. The more different types of stick that are in the bag, the better. Get out your hammer and smash them up into pea-size fragments. (This is difficult, as the pieces tend to fly all over the room. Do the smashing with the sumi inside a strong bag of some kind.)
Put the fragments in a jar, pour in water to cover, and let them stand for a couple of months. (If you start off with hot water, it tends to help the process speed up.) Once the sumi has become good and soft, put the black mass into a mortar, and grind it into a smooth paste. When you think it is as smooth as you can make it, strain it through a cloth two or three times. (Dumping it into a sock and squeezing it out through the toe section works well.) Put the left-over mud back into the jar, add more smashed fragments, and start the process again for next time ...
Take the strained fluid and add water and 'nikawa' (melted gelatin) to 'taste'. A typical ratio might be sumi '1', water '1.5', nikawa 'a few spoonfulls', although these numbers are completely flexible. Less water will obviously produce a thicker fluid; more nikawa will produce a more glossy black. Let it sit for a day or so before using it, to let the components blend together well.
There is always a jar of sumi fragments soaking in a printer's workshop, and the sumi smell in the room is one of the 'badges' of our trade.