Both wood blocks and metal blocks intended to illustrate printed books were always made of the same depth as the type, so that they could all be printed together, and that is done to-day in the case of process or half-tone blocks, which are actually wooden blocks faced with the soft metal bearing the design. There is always some interest in the question as to whether a certain print has been cut on a wood block or on a metal block, and if the print is in perfect condition it is a very difficult matter to decide. But it is rarely that some small defect or peculiarity does not appear by help of which a tolerably certain judgment can be arrived at. Early engraved blocks were often used again and again until they became quite old, and at last they were got at by insects who ate small holes in them. If therefore a print shows little white circular marks upon it there is no doubt that it was made from a wood block. Instances are by no means unknown in which experts have decided that a certain block had been cut on metal, and a later impression has turned up _with worm holes in it_! The grain of wood will sometimes show on an old print, or a broken edge will show a sharp fracture indicating wood, in contradistinction to a rounded one, indicating metal. The blacks on prints from an engraved metal plate always show very even spaces, and there are usually plenty of them, often broken, however, by small white dots, the presence of which denotes the style known as Pointille, the finest examples of which can be found among the French Horæ printed for Pigouchet in the fifteenth century. The metal used was probably a sort of pewter, lead and tin, very easy to engrave upon, and strong enough to bear many printings. But in many instances these little blocks seem to have been roughly treated and have fallen about, and the result is that outer lines which show perfectly straight in early copies, show as slightly rounded lines on late ones. This is taken as a decided proof that the original block was made of soft metal, although I am by no means certain that it is impossible for a straight edge on wood to warp into a curved line. Prints from old wood cuts in outlines were frequently added to early printed books and painted over thickly with opaque colour so as to produce a different design. The original outline has only been used as a slight guide. Instances of these curious changes can be found in numbers of the fine vellum books illustrated in colour which were printed for Antoine Vérard at Paris in the fifteenth century. In other cases, particularly in Italy and France, ornamental printed borders and illustrations have been very carefully painted by hand just as if they belonged to ordinary illuminated manuscripts. But the art work in all these cases is not good. The true _illuminatores_ were obsolescent. A few instances of attempts at colour printing either by means of blocks or stencil plates were made by Erhard Ratdolt at Venice, and a few others.