Inlaid, or mosaic work, is used only in the higher branches of bookbinding. Formerly books were not inlaid, but painted with various colours. Grolier used a great deal of black, white, and green. Tuckett employed a method of extracting one colour from leather and substituting another by chemical action, thus: - Take dark chocolate colour, trace the design thereon, and pick it out or pencil it in with suitable chemicals, say dilute nitric acid; this will change the. chocolate, leaving the design a bright red on a chocolate ground.

To lay on the various colours with leather is, no doubt, by far the better plan. Paint has a tendency in time to crack, and, if acids are used, they will to a certain extent rot or destroy the leather; but if leather is used it will always retain both colour and texture. To choose the proper colours that will harmonise with the ground, give tone, and produce the proper effect, requires a certain amount of study. Morocco is generally used, but in Vienna calf has given very good results. If the pattern to be inlaid be very small, steel punches are used, the pattern being worked in blind on the side of the book. Take morocco of a different colour from the ground it is to decorate, pare it down as thin as possible, and lay it on a slab of lead. With a steel punch the exact facsimile of the pattern that is to be inlaid, punch out from the leather the required number of pieces. These are pasted and laid very carefully on the exact spot made by the blind tooling; press each down well into the leather either with a folding-stick or the fingers, so that it adheres properly. When dry, the book is pressed between polished plates, so that the raised pieces, or the pieces that have been laid on, may be forced well into the ground leather.

When it has been pressed, the whole of the leather must be prepared as for morocco, and finished in gold. The tools in the working will hide all the edges of the various inlaid pieces, provided they are laid on exactly.

If interlacing bands are to be of various colours, the bands must be cut out. Pare the leather thin, and after working the pattern through the paper on to the leather on the side of the book, lay it on the thinly pared leather; with a very sharp and pointed knife, cut through the paper and leather together on a soft board. Or, the design may be worked or drawn on a thin board, and the various bands cut out of the board as patterns. Lay these on the thin leather and cut round them. Keep the board templates for any future use of the same patterns. The various pieces are pasted, carefully adjusted in their places, and well rubbed down. The leather is then prepared and worked off in gold.

Another method is to work the pattern in blind on the sides, pare the morocco thin, and while damp place it upon the portion of the pattern to be inlaid, and press it well with the fingers, so that the design is impressed into it. Lay the leather carefully on some soft board, and cut round the lines made visible by the pressure with a very sharp knife. When cut out, paste and lay them on the book and prepare as before, and finish in gold. This last method is not of much value, though it is sometimes chosen; for any good work, where accuracy is required, the plans mentioned previously are to be preferred.

The Viennese work their calf in the same way that the cabinet-makers inlay woodwork. With a very sharp and thin knife, they cut right through two leathers laid one on the other. The bottom one is then lifted out and replaced by the top one. By this method the one fits exactly into the other, so that, if properly done, the junctions are so neatly made that no finishing is required to cover the line where the two colours meet.