These are placed relatively to the design as shown in fig. 13.
The corner of the print fits into the notch at A, and one edge of the print lies against the straight notch at B.
The register marks may be even closer to the space covered by the design, but must not actually touch it, as some margin of paper is necessary in printing: they should also be cut always on the long side of the printing block. It will be seen from the drawing on page 70 that these register marks correspond to the position of the thumb of each hand in laying the paper on the block for printing.
[Illustration: FIG. 13.--Position of register marks.]
[Illustration: FIG. 14.--Register marks.]
The corner mark, ABC, is made by cutting from A to B and B to C, with the knife held perpendicularly, and its flat side against the line, then the shaded portion is cut with a flat chisel, sloping from the surface of the block at AC to a depth of about 1/16 inch along AB and BC. The straight notch, EF, is similarly cut, first with a perpendicular knife along EF, and then the shaded portion is chiselled sloping down to the line EF.
[Illustration: FIG. 15.--Register marks (section of).]
In section the two register marks would be as above.
The register marks must be smoothly and evenly cut so that the paper, in printing, may slide easily home to its exact place.
When the design of the key-block and the two register marks have been cut and cleared, the trace of paper and paste on the uncut parts of the wood should be carefully washed off with a piece of sponge and warm water. The block is then finished and ready for use. The key-block, however, is only one of the set of blocks required for a print in colour, but the colour blocks are simpler and require, as a rule, far less labour.
The colour blocks are planned and established by means of impressions taken from the key-block. For this purpose the register marks are inked[2] for printing as well as the design on the block, and the impressions must include both. These impressions are taken on thin Japanese paper, but not necessarily the thinnest tissue. If the thinnest is used, it should be pasted at the corners to a sheet of stiffer paper for convenience in handling.
[2] The preparation of the ink for printing is described on p. 54.