A set of blocks consists of a key-block and several colour blocks. The block that must be cut first is that which prints the line or "key" of the design. By means of impressions from this key-block the various other blocks for printing the coloured portions of the design are cut. The key-block is the most important of the set of blocks and contains the essential part of the design.

A drawing of that part of the design which is to be cut on the key-block should first be made. This is done on the thinnest of Japanese tissue paper in black indelible ink. The drawing is then pasted face downward on the prepared first block with good starch paste. It is best to lay the drawing flat on its back upon a pad of a few sheets of paper of about the same size, and to rub the paste on the surface of the block, not on the paper. The block is now laid down firmly with its pasted side on the drawing, which at once adheres to the block. Next turn the block over and lay a dry sheet of paper over the damp drawing so as to protect it, and with the baren, or printing rubber, rub the drawing flat, and well on to the block all over.

The drawing should then be allowed to dry thoroughly on the block.

With regard to the design of the key block, it is a common mistake to treat this as a drawing only of outlines of the forms of the print. Much modern so-called decorative printing has been weak in this respect. A flat, characterless line, with no more expression than a bent gaspipe, is often printed round the forms of a design, followed by printings of flat colour, the whole resulting in a travesty of "flat" decorative treatment.

The key design should be a skeleton of all the forms of a print, expressing much more than mere exterior boundaries. It may so suggest form that although the colour be printed by a flat tint the result is not flat. When one is unconscious of any flatness in the final effect, though the result is obtained by flat printing, then the proper use of flat treatment has been made. The affectation of flatness in inferior colour printing and poster work is due to a misapprehension of the true principle of flat treatment.

Plate V