Wood Finishing

Wood Finishing is the process of applying to the surface after it has been prepared, by filling and smoothing, or otherwise, a thin coating of varnish or other substance, to render it durable, enhance its beauty or change its appearance. There are numerous methods of finishing, and a variety of materials are used; the varieties of varnish being the principal. The distinctive qualities of these varieties are treated under their proper headings.

In their natural state all woods are more or less porous, consist-of bundles of hard fibres, with interstices filled with a softer sub-stance. These constitute the grain, and as the hard or soft parts predominate the wood is said to be hard, fine, or close-grained, or soft and open-grained. To fill these softer parts, or pores, and give to the whole an even, uniform surface, hard, and capable of a brilliant polish, is the object of the finishers' art. This hard, firm surface was formerly gained by the successive application of several coats of varnish, at least three preliminary coats being required to fill the pores; the inequalities were then reduced by fine sand or glass-paper, and several additional coats laid on, the last, after becoming thoroughly hard, being polished if desired. In this operation, however, a great quantity of varnish is absorbed by the open pores of the wood, and it is consequently so expensive that it is now seldom used. Recourse is therefore had to various plans to render the wood non-absorbent before applying varnishes, and certain compounds called fillers are largely used for this purpose.

Richness of effect may be gained in decorative woodwork by using woods of different tone, such as amaranth and amboya, or inlaying and veneering. The Hungarian ash and French walnut afford excellent veneers, especially the burls or gnarls. A few useful notes on the subject are given by a recent American authority. In varnishing, the varnishes used can be toned down to match the wood, or be made to darken it, by the addition of coloring matters. The patented preparations, known as " wood fillers," are prepared in different colors for the purpose of preparing the surface of wood previous to the varnishing. They fill up the pores of the wood, rendering the surface hard and smooth. For polishing mahogany, walnut, etc., the following is recommended : Dissolve beeswax by heat in spirits of turpentine until the mixture becomes viscid; then apply, by a clean cloth, and rub thoroughly with a flannel or cloth. A common mode of polishing mahogany is by rubbing it first with linseed oil, and then by a cloth dipped in very fine brickdust; a good gloss may also be produced by rubbing with linseed oil, and then holding trimmings or shavings of the same material against the work in the lathe.

Glass-paper, followed by rubbing, also gives a good lustre.

Logwood, lime, brown soft-soap, dyed oil, sulphate of iron, nitrate of silver exposed to the sun's rays, carbonate of soda, bichromate and permanganate of potash, and other alkaline preparations, are used for darkening the wood; the last three are specially recommended. The solution is applied by dissolving one ounce of the alkali in two gills of boiling water, diluted to the required tone.

The surface is saturated with a sponge or flannel, and immediately dried with soft rags. The carbonate is used for dark woods. Oil tinged with rose madder may be applied to hard woods like birch, and a red oil is prepared from soaked alkanet root in linseed-oil. The grain of yellow pine can be brought out by two or three coats of japan, much diluted with turpentine, and afterwards oiled and rubbed. To give mahogany the appearance of age, lime water used before oiling is a good plan. In staining wood, the best and most transparent effect is obtained by repeated light coats of the same. For oak stain a strong solution of oxalic acid is employed; for mahogany, dilute nitrous acid. A primary coat or a coat of wood-fillers is advantageous. For mahogany stains, the following are given : 2 oz. of dragon's blood dissolved in one quart of rectified spirits of wine, well shaken, or raw sienna in beer, with burnt sienna to give the required tone; for darker stains, boil half a pound of madder and 2 oz. of logwood chips in one gallon of water, and brush the decoction while hot over the wood; when dry, paint with a solution of 2 oz. of potash in one quart of water.

A solution of permanganate of potash forms a rapid and excellent brown stain.

The Processes

Finishing, although comprehending many minute sub-divisions, may be divided into four principal processes, i. e., " Filling," "Varnishing," "Rubbing," and " Flowing," "Polishing," etc. Each of them are treated at length in their proper order, and for full information regarding the successive operations, the learner must refer to these heads; here we shall give a general view of the entire operation without details. The process described is for fine work. First make the article to be finished quite clean and free from dust; then apply the proper filler with a brush; rub it well into the grain with excelsior or tow, rubbing across the grain when practicable, then clean all the surplus filler from the surface with rags; after filling, allow the article to stand for several hours, during which time the filler should become quite hard and dry. Before proceeding to apply the varnish, if necessary, make the surface of the filler quite smooth with sand-paper; then apply a coat of varnish, allowing it to get quite hard; after the last coat of varnish, with fine sand-paper, sand-paper the surface sufficiently to make it entirely smooth and remove any lumps or irregularities.

The number of coats required depends greatly upon the quality of filler used, regarding which some remarks will be found under the head of Fillers. It is said that with some fillers one coat of varnish is sufficient, but this can scarcely be the case with fine work, as it is nut possible for one coat of varnish to give sufficient body to rub a four, or possibly three coats are more desirable. When the last coat of varnish has been applied, the article is ready for "rubbing" with pumice stone, moistened with linseed oil and applied with a bit of hair-cloth or coarse rag. This is for the purpose of making the varnish perfectly smooth and preparing it for the polishing. After rubbing, if a dead finish is desired, the work is complete, but the body of the work is generally cleaned up with a little oil well rubbed in, which gives it a lustre, afterward rubbed with a cloth dampened with alcohol, which removes the surplus oil from the surface. The veneered panels are either "flowed" or " polished," which processes are described under these heads.