Mounting large sheets of paper is a
specialist's job. It is inadvisable to attempt it without training in bookbinding and the appropriate equipment, including the press. Badly mounted paper comes unstuck in places, causing blisters and loose corners, mistakes which cannot afterwards be rectified and which can ruin the whole effect of a picture. Mounting is thus better left to a bookbinder or mounter. The small expense involved is preferable to the losses sustained from spoiled material.
Sized and primed boards of large size must sometimes be stiffened with a frame glued onto the back. To make the wooden frame stick securely, the priming or backing must be removed from around the edges where the frame is to be glued. This is most easily done with a tooth plane.
The construction of the frame and the mounting is a carpenter's job. After mounting, the frame and board must be put in a veneer press for at least half a day; no glue holds permanently without pressure. With a sufficient number of clamps and some experience of carpentry you can do the mounting yourself; it is not as difficult as mounting paper.
Even the best paper containing no wood pulp will yellow if exposed constantly to sunlight and will become as fragile as when it is stored in perpetual dry heat. Continuous damp causes mildew, which results in permanent stains. Damp storage also softens the glue of both ground and paint; it may begin to rot, at which point the picture cannot be saved. If these dangers are avoided, paper is very durable. There are papers which have survived in good condition from the time when paper was first invented. The best quality paper thus provides both an ideal surface for all glue and pastel colors and, with a suitable ground, a good covering for inferior boards.
Hardboard sheets, which are obtainable in many varieties, are very similar in character to good rag pasteboards. They usually have one rough and one smooth side. The rough side generally has a rather disagreeable wire grating texture which must be entirely eliminated by the priming if it is not to spoil the effect of the picture. The smooth side always has a slight residue of the paraf
fin which is used in the press to prevent the board from sticking to the metal. Since paraffin prevents the priming from adhering, it must be removed with sandpaper. Smooth surfaces are rubbed with a wooden block with mitered edges, covered with sandpaper.
A board thus prepared provides a very good support, especially for backing paper or canvas. Unlike plywood or massive panels of glued planks, it does not warp.
Wood is a living material, and even after centuries it never quite comes to rest. Absorbing moisture at different rates it always warps in quite unforeseen ways. The illustration shows how various are the pulls in each board cut from the same stem. This pull never quite ceases. Wood must season for at least ten years in the air before it can be worked into boards for painting. And apart from this fact, not all woods are suitable, particularly those which are resinous. Only de
ciduous woods are to be considered; walnut and pear are the best.
In earlier centuries painters used wood frequently, simply because they had nothing better. In spite of the fact that boards were prepared according to all the rules of the art, every old painting on wood is now a problem for the restorer. The board must be protected from warping by inlay, which is the only way to counteract the constant working of the wood.
Plywoods have definite advantages over boards made from planks glued together. There are basically two kinds. One consists of laminations glued together so that the grains run in different directions, the other of veneer surfaces with wooden bars between them. The latter, called "block board," is less likely to warp. Avoid plywoods having roundcut veneers as their outer layer. These always develop fine hair cracks which cannot be hidden even by the thickest priming and painting. The round-cut veneer can be recognized by its unnatural graining. Only plank-cut veneers can be used for painting.
A ground is easily applied to wood without using a lining, and this is about the only convenience that wood has to offer. Boards of synthetic fiber are much more suitable as supports for painting.