The veneers being so thin, it is of course easy to cut through several layers of them at once, and this suggested, or at all events lent itself admirably to the design of the earlier examples, which are generally arabesques symmetrically disposed right and left of a central line. If two dark and two light veneers are put together, the whole of one panel, both ground and pattern, can be cut at one operation with a thin fret saw; the ornamental pattern drops into the space cut out of the ground, which it, of course, fits exactly except for the thickness of the saw-cut, and the two half-patterns thus filled in are "handed" right and left, and so complete the symmetrical design. The line given by the thickness of the saw is then filled in with glue and black colour so as to define the outline, and additional saw-cuts are made or lines are engraved, and in either case filled in with the same stopping, wherever additional lines are wanted for the design. It only remains to glue the whole down to a solid panel, and to polish and varnish the surface, and it is then ready to be framed into its place as the back of a church stall, or the lining of a courtly hall, library, or cabinet.
It was thus that the simpler Italian Intarsia was done, such as that in the dado surrounding Perugino's Sala del Cambio in his native city, where the design consists of light arabesques in box or some similar wood on a walnut ground, defined by black lines just as I have described.
But like all true artists the Intarsiatore did not stand still. Having successfully accomplished simple outline and accurate drawing, he was dissatisfied until he could carry his art farther by introducing the refinement of shading. This was done at different times and by different artists in a variety of ways; either by inlaying the shadow in different kinds of woods, by scorching it with fire, or by staining it with chemical solutions. In the book desks of the choir at the Certosa or Charterhouse of Pavia, the effect of shading is got in a direct but somewhat imperfect way by laying strips of different coloured woods side by side. Each flower or leaf was probably built up of tolerably thick pieces of wood glued together in position, so that they could be sliced off in veneers and yield several flowers or leaves from the same block, much in the way of Tunbridge Wells ware, though the Italian specimens are, I believe, always cut _with_ the grain and not across it. The designs thus produced are very effective at a short distance, but the method is, of course, suitable only to bold and simple conventional patterns.