The first step in finishing an article after it has been assembled is to sand it smooth. This not only removes small irregularities in the surface, but also cleans the wood for the final treatment. Sandpaper is surfaced with small particles of flint, garnet or quartz and comes in a number of textures. The flint and garnet papers are generally considered best. Three grades are sufficient for most work, No. 0 (fine), No. 1/2 (medium) and No. 11/2 (medium coarse). Sanding should always be done with the grain and for flat surfaces the paper should be wrapped around a block (fig. 90). Always dust the surface of the wood carefully after sanding.
There are many types of finishes which protect the surface of the wood and enhance its beauty. The commonest are discussed briefly below and will fill the needs of the average worker. In some cases, as in painting and enameling, step-by-step instruction has been omitted as this information is given by the manufacturer on the container.
Regardless of the finish used, the following suggestions may help. Always work in as clean a room as possible. Small particles of dust will adhere to a tacky surface and make it extremely difficult to get a smooth finish. Fill all holes with putty or plastic wood before applying finishing substances. Powdered pumice mixed with water (or linseed oil) to a creamy paste can be rubbed over almost any type of finish to dull it and remove too high a shine. If you wish to heighten the lustre, on the other hand, polish the surface with rottenstone mixed with crude or sweet oil to the consistency of light cream. It is applied with a pad of soft cotton waste very slightly dampened and should always be rubbed in long strokes with the grain of the wood.
Paint and enamel are both opaque finishes which hide the grain of the wood and which come in a variety of colors. Enamel is a little more difficult to apply than paint, but gives a higher lustre and a harder surface. Before applying either of these to new wood, be sure to shellac all knots in the lumber or they will bleed through the finish. When applying several coats of paint or enamel, allow each to dry thoroughly and sand lightly with No. 00 sandpaper between coats.
Five kinds of wood stains are water, chemical, spirit, oil, and varnish. The last two are easiest to use and are recommended for the beginner. All types are transparent and add color to the wood without hiding the grain. Except in the case of varnish stain, they do not protect the surface of the wood and must be covered with one of the finishes below. Several coats of stain are generally needed, and the wood should be sanded lightly between each.
Shellac provides a very satisfactory transparent finish which is durable and easy to apply. White shellac is used over plain wood or over light stains, orange shellac over stains of dark color. Shellac dries fast and must be applied skillfully with long brush strokes. It is important that the surface be completely covered at each stroke since it cannot be touched up afterwards as with paint. Shellac should also be sanded lightly between coats.
Like shellac, varnish provides a transparent protective coat which may be applied over raw wood or stains. When used on raw wood, the grain should be sealed with a prepared wood filler, a colorless paste that is mixed with turpentine. On either stained or raw wood, the varnish should be preceded by a thin coat of shellac as a base. Several coats of rubbing varnish are then brushed on. Each coat is rubbed down when dry with the pumice and water mixture described above. If a dull finish is desired, no further treatment is necessary; for a high lustre, a final coat of finishing varnish is applied. The latter contains slightly more oil than the rubbing varnish and requires more time to dry. Varnishing should always be done in a warm room of at least 65° F.
Oil polishing may be done over a stain or on either filled or unfilled raw wood. It is heat and water resistant and gives a lasting semigloss finish. Equal parts of linseed oil and turpentine are mixed and applied with a pad of cotton waste. Use the oil sparingly and rub in vigorously. The process should be repeated several times at 24-hour intervals.
Wax in either liquid or paste form is one of the best protective coverings for wood. It is easy to apply and may be renewed at intervals without special preparation. It is frequently used over varnish or shellac and may also be applied to either filled or unfilled wood. Paste wax is generally considered preferable to liquid wax. It can be rubbed on with the fingers or a small lump of it may be folded inside a cheesecloth pad. As the pad is rubbed over the wood enough wax comes through to leave a thin coat on the surface. When this has dried, it must be polished vigorously with a soft cloth. Second and third coats are applied in the same way.
One of the finest of all finishes and one of the most difficult to handle successfully is the shellac process known as French polishing. While it takes time and skill to do, it results in a beautiful soft lustre which cannot be duplicated by simpler methods.
The initial step is to fill the pores of the wood with the wood filler described above under varnishing. Three coats are brushed on, each being sanded lightly with 00 sandpaper when dry. This provides the necessary base on which to work.
Three rubbers are now prepared by wrapping handfuls of soft cotton waste in pieces of clean muslin. Dip the stuffing of the first of these in shellac, wring it out and wrap it in its muslin cover. Rub it over the entire surface of the object with a circular motion, never permitting the pad to stop or rest on the surface at any time. As soon as this coat is dry, dust on a little powdered pumice and sprinkle a few drops of linseed oil over it. Then polish the surface with the second rubber using the same circular motion. When the coat has been evenly dulled, clean off the excess pumice mixture with a dry cloth.
At least two more coats of shellac must be applied in the same way, polished with pumice and cleaned as above. The most difficult step is the final one. Pour a little wood or denatured alcohol into a plate and dip the third rubber in it. Squeeze out the excess liquid on a scrap board and, with very little alcohol on the rubber, quickly wipe over the entire surface to remove all marks of polishing. Use a circular motion without pausing and lift the pad from the wood the instant the rubbing is finished. If too much alcohol is used or if the rubber rests for a moment in one spot, the alcohol will burn through the shellac and the entire finish is spoiled. If this happens there is no remedy. One can only scrape off the entire finish and start again from the beginning.
Many craftsmen feel that the rubbers used in French polishing improve with use and age. To keep them, remove the inner wads and store in tightly covered mason jars. The muslin covers should be washed in strong borax, rinsed, dried, and put away for future use.