[SEVENTEENTH LESSON.]
TO REPAIR WOOD-CARVING—GLUE—NITRIC ACID GLUE—PREPARING DECAYED WOOD—ARTIFICIAL WOOD—FILLERS—SPRAYING—TO MAKE GLUE “TAKE.”
It will sometimes happen to a carver that, owing to bad wood or inadvertence, he splits away or breaks off a piece from his work. In this case he must have recourse to glue. This should be of the very best quality, perfectly light and clean. Glue is made in what alchemists used to call a balneum mariæ, that is, of a vessel containing hot water, within which is a smaller vessel. The glue, which is in the inner pot, is therefore to be boiled by the heat of warm water, and not of the fire directly. Before setting it to boil, break it into very small pieces, say of the size of a hazel nut, and let it stand in cold water for twelve hours. It will now be like a thick jelly. Pour off all the water not absorbed, and put the jelly into the inner pot, fill the outer with water and let it boil till the glue is like a thick cream. Use it while in this state.
If you add to the glue, while thus liquid, some nitric acid, say about a tea-spoonful to half a pint of glue, you will have a very superior cement, which holds faster than the plain glue, and is much less liable to crack or split. It dries more slowly, which makes it very valuable for veneering and for large surfaces, where glue often dries before the whole can be applied. Again, when an article fastened with common glue is detached, it is often almost impossible to stick it on again with the same. But with the acidulated glue this is easy.
The greatest advantage of this glue is, that if it be kept excluded from the air it will remain in a liquid state for at least a year, and can be used cold. Its disadvantages are a very pungent and not agreeable smell, and the fact that, when corked up, the cork is most certain to get glued to the bottle, and requires to be broken to get it out, rendering a new one necessary. This may be avoided, however, with great care. Stir the acid into the glue with a glass rod or tube.
It may happen that a rotten, broken place is found even in the best wood; or the carver may obtain possession of a piece of ancient, worm-eaten, half-decayed carving, and with a very little skill such pieces can be perfectly repaired. Take a piece of similar wood, and reduce it to fine sawdust by means of a rasp. For this purpose American walnut and dark old oak, or cocoa-nut shell, which is easily pulverized in a mortar, is excellent. Make this into a paste with glue, and repair with it any broken places. This, if properly made, is quite like wood itself, and may be moulded into any shape. It “takes hold” of the ground, and when dry it may be filed into uniformity with the rest. It may also be cut with ease or trimmed to shape, or, in fact, carved. If there is too little glue in it it will break too easily, if there is too much it will be too glazy. But a proper mixture makes it quite like wood.
Scratches and chance cuts may be remedied by merely melting them with hot water. But for such small defects a filler is useful. This is a kind of paint or liquid cement, the object of which is to fill up the pores of certain coarse woods and make the surface fine. The squeezing wax, described in the chapter on making moulds, is a filler. Others are made by mixing flour with varnish, etc. Any dealer in paints and varnishes will supply a filler suitable to any special work.