PREPARATION OF WOOD AS A FOUNDATION FOR PAINTINGS
MAHOGANY wood, since the Twelfth Century, has been a great favorite with painters, but an Oak panel is just as good. It is absolutely necessary, however, to reinforce the reverse side of a wood panel, either by means of a cradle or by means of cleats.
Cleats are very dangerous. Pictures split and buckle alongside of cleats, and when such buckling takes place, the picture ought to be taken off and cradled.
If the wood panel is sufficiently heavy, these cleats may be screwed on, but at all events they should be glued on with a proper glue, such as can be purchased in the United States under the name of LePage’s Glue, or Russia Cement; but, in any event, it is quite important, in addition to gluing these strips, to fasten them by means of fine wire nails which may go through to the outer surface, and then be cut off and sandpapered to a smooth finish. A very good preparation of a wood foundation is to fill the wood first with what is known as wood filler. This is a material called Silex, or Silica, mixed in a quick drying varnish. It is thinned down with Spirits of Turpentine, applied across the grain of the wood panel, and after ten or fifteen minutes it is rubbed off lightly, the fine grain of the wood becomes filled up with this Silica or wood filler; and, after twenty-four or forty-eight hours, the surface is then rubbed with very fine sandpaper, which makes it perfectly smooth. Then a thin application of Shellac Varnish is applied; and Shellac Varnish for this purpose is manufactured by taking two pounds of any Orange Shellac to three-quarters of a gallon of Denatured Alcohol. This should not be mixed in a metal container, but should be mixed in a stone jar or glass bottle. In a few hours it will have dissolved, if shaken occasionally. A coat of this is applied to the wood after the fill has become thoroughly dry. Three hours afterwards it should again be lightly sandpapered. After this another coat of Shellac Varnish is applied, both to the front and the back of the wood panel. Three hours after that, it can again be lightly sandpapered, and then it is ready for painting. The sandpaper is essential because it roughens the surface and forms a bond between the pigment and the wood. If you paint on a highly polished surface, whether it be glass, metal, wood or canvas, there is very little bond between two glossy coats, and the chances of peeling are very great; but, if you roughen the surface upon which you are going to paint, there is a contact between the paint and the surface, due to the roughness just mentioned.
Shellac used in priming wood is essential, in order to prevent the resinous matter from evaporating into the painting. But, if a painting should crack, which has been based on Shellac, and a restorer applied alcohol, it is quite obvious that the painting would become badly damaged.