Clearing depth: two to three times the thickness of the paper you are printing on. For a typical damped washi that is well under a millimetre. Some beginner kits teach a single paper thickness — shallower still, and not wrong for a simple print.
The guide line itself: a vertical cut on the line, about one eighteenth of an inch deep — roughly 1.4 mm.
The guide is not a raised wall. It is the uncut wood left standing where the block surface around it has been shaved down.
What a kento actually is
A kento is a pair of stops carved into the block itself, so the sheet is placed the same way every time without measuring anything. There are two of them and they do different jobs.
The kagi is the right-angle corner. Traditionally it sits at the lower right of the block. You push the corner of the sheet into it, and that fixes the paper in two directions at once.
The hikitsuke is a straight side stop, sitting a short distance in from the lower left along the same edge. It fixes the sheet's rotation. Without it the corner is a pivot and the far end of a large sheet can swing several millimetres.
Both marks must be in exactly the same position on every block in the set. That is the whole point, and it is the reason it is worth drawing them once at full size rather than measuring them onto each block by hand.
Why the depths differ
The two cuts are doing two unrelated things, which is why one number does not cover both.
The guide line is the edge the paper actually meets. It needs to be a crisp vertical wall — deep enough that a sheet cannot ride up over it, shallow enough that it does not weaken the wood. The traditional figure is a first vertical cut on the line at one eighteenth of an inch. If you are working in millimetres, call it 1.4 mm and cut it cleanly rather than deeply.
The clearing is the area beside the guide, taken away so the sheet has somewhere to sit. Here the reference is the paper, not the block: two to three times the paper's thickness. The logic is straightforward once you see it. Clear too little and the paper cannot lie flat against the stop. Clear too much and you have made a trench that fills with pigment and prints a mark.
It is worth saying that the sources do not fully agree on this one. Beginner woodblock kits commonly instruct you to clear to the depth of a single sheet — two to three times shallower than Yoshida. I do not think either is a mistake. A kit print is two blocks on dry paper in an afternoon; Yoshida is describing professional practice where the sheet is damped and registered many times over, and wants a little more room. If you are working simply, err shallow. The figure that actually matters is not the number at all: the cleared area must be flat and smooth, and the way to check it is a folded scrap of your own paper rather than a ruler.
A depth of two to three millimetres instead of two to three paper thicknesses is roughly five times too deep. It is an easy slip, the block looks fine, and the problem only shows up as unexplained marks near the edge of the print.
The guide sits below the surface, not above it
This is the part that is most often built backwards, and it matters more than the numbers.
The guides are not grooves cut for the paper to drop into. A shallow margin is cleared away around each guide, leaving a small ridge of wood standing. The sheet lies on the block, its edge reaches out across the cleared strip, and it stops against the inner face of that ridge.
The tops of those ridges are then shaved a fraction below the face of the block. That is the part worth getting right: if a guide stood proud of the block face, the baren would ride over it and either crush it or lift the paper off the image.
Because they sit low and slope away, the baren passes over the whole area without ever touching the guide. The paper still registers against the vertical face, because the sheet is positioned before the baren goes anywhere near it.
One consequence worth knowing: the strip of wood between the guide and the carved image area will pick up pigment as you brush. That is normal. It is also why the clearing should not be deeper than it needs to be — the deeper the trench, the more pigment collects in it.
Cutting them
The traditional method is deliberately unhurried:
- Cut the hikitsuke first, then the kagi. The side stop is the easier of the two and gets your hand in.
- Hold the chisel upright, flat face towards you, with the flat face on the line you want to keep.
- Press straight down, roughly 2 mm, and rock the blade gently rather than levering it. Levering chips the vertical face, and the vertical face is the entire function.
- Then clear the waste beside it, checking the depth against a folded scrap of your actual printing paper rather than a ruler.
One detail from the traditional sources that is easy to miss: the kagi's cleared area should fall away very slightly towards the corner. It gives the sheet somewhere to go as it is pushed home, instead of bunching.
The chisel for this — a kento-nomi — is a hand tool. It is not meant to be struck with a mallet. The cut is shallow and controlled; force is not what produces the clean face.
If you are not cutting into the block
Kento notches assume a block you are willing to carve into, and a paper you place by hand. Not everyone is working that way. If you are printing lino on a press, Ternes-Burton registration pins do the same job with a pin bar and punched tabs, and are easier to keep identical across a set of blocks because the jig is separate from the block entirely.
Some printmakers also abandon cut-in kento for a floating L-shaped jig that carries the marks on a separate piece of board. It sacrifices the elegance of having the registration built into the block, and gains the ability to move it.
Kento works out both kinds of registration for you and prints the layout at full size, so you can lay it straight on the block instead of measuring. It handles kento notches and Ternes-Burton pins, and takes account of the paper size, the image area and the margins you actually want.
Where these figures come from
- Toshi Yoshida & Rei Yuki, Japanese Print-Making (1966) — the depths, the positions of kagi and hikitsuke, and the slight fall towards the corner. Read as an extract reprinted by McClain's Printmaking Supplies. This is a secondhand extract hosted by a retailer rather than the book itself; the figures are consistent with everything else I have found, but I have not checked them against a first edition.
- Dave Bull, Encyclopedia of Woodblock Printmaking — the construction: guides shaved below the block level and bevelled away from the brushing area, and the warning about pigment collecting on the wood between the guide and the carved area.
- McClain's, Kento Registration tip, August 2005 — the cutting method: chisel upright, flat face towards you, pressed down about 2 mm and rocked gently, hikitsuke first.
- Hikosaka Woodblock Print Studio, How to Make「ANPAN」on Woodblock Print — an undated instruction leaflet supplied with a beginner moku hanga kit. The dissenting figure on clearing depth (one paper thickness), and an independent confirmation that the kagi sits at the corner with the hikitsuke a short way in along the same edge.