The last bit of carving on the Keyblock involves cutting the all-important registration marks, called "Kentos." Carved into the lower corner and along the side, these marks serve as channels that the paper will slip into. They will be identical on each block, so that the paper lines up exactly in the same place on each color block.
The finished keyblock, ready to be inked for the first run of Artists Proofs, or "APs". These proofs will be used to cut the color blocks from, and will be used to test and adjust each color block before it is used to print a "real" print run from. I personally like to use Japanese Gampi paper for my AP's. It's thin, but very strong.
A boar hair/deer hair traditional brush, hand-made from a split piece of bamboo, is used to ink the keyblock up with black ink for the first run of proofs. The ink is applied directly to the plate, and is brushed around the block.
The keyblock, all inked up, ready for the first piece of paper. Oh! The excitement!
The first run of Artists Proofs: