Very useful models, both on a small scale for book illumination, and on an enlarged one for wall decoration, are now prepared by several of the artists' colour-men, for teaching amateurs the different modes of shading, &c. They consist of outline plates partially coloured by hand. The beginner will find it a very useful exercise to complete a few of these before trying his hand upon more original works upon vellum. The greatest care must be taken to have every implement perfectly clean. Experience alone can teach the artist the value of what are called glazing or transparent colours, such as the lakes, carmine, madders, gamboge, &c. Some tints may be used either as glazing colours, or as body-tints, according to their preparation, and according to the degree of thickness with which they are applied. As a general principle, all shades should be painted in transparent colour, all lights in opaque. Reflected lights may often be best given by scumbling thin body-colour over transparent shade. In order to prepare the tints for these operations, it may be well to use a little of Newman's or Miller's preparations with them. The less tints are retouched after the first application, the more clear and brilliant they are likely to remain. Above all things never let the paint-brush go near the mouth, and never attempt to correct or retouch a tint while it is in process of drying, as doing so will infallibly make it look streaky and muddy. In all these processes of manipulation, however, practice, good example, and good tuition, must teach what the minutest directions would fail to satisfactorily convey. The principal colours having been applied, the next difficulty will be to heighten them with gold and silver. Any large surfaces of gilding it will be well to apply previously to commencing colouring, and as much as possible intended for burnishing. The principal metallic preparations used in illumination may be enumerated as follows:--gold leaf, gold paper, shell gold, saucer gold, gold paint, silver leaf, shell silver, and shell aluminium. Of these, the leaves, paper, and paint, are of English, and the shells and saucers of French manufacture. Occasionally gold and silver powder and German-metal leaf are employed, though too rarely to make them important enough to claim general notice.