Paragraph 55. We have already learned that the surface of a piece of wood is porous and that it is ready to absorb any sort of liquid which is applied. The stain which we have been discussing penetrates the wood through the pores and changes the color a little deeper than merely on the surface, but inasmuch as the stain is very thin, or as the painter would say, has "no body," it does not fill the pores of the wood, therefore even though the desirable color has been obtained on a piece of wood, the surface still presents innumerable open mouths ready to drink up any other liquid which at any time might touch it. The next step in our finishing process is to fill all of these tiny pores, and to do it without destroying the color or the beauty of the surface. A great many different kinds of filler have been devised, for different kinds of wood require different kinds of filler. Some wood has very large open pores - chestnut, for example - other wood is very close grained and has tiny pores, maple being a good example. Of course we would not expect that chestnut would require the same kind and quantity of filler material as maple. We must take into consideration the nature of the wood to be filled in order to determine the kind of filler to be used; the principles are so similar that it is not difficult to get a general idea of the process.

Wood filler is simply some sort of pasty material which can be made sufficiently thin to enter the pores. Then when the liquid dries the body, or substance of the paste remains in the pores and fills them up level with the surface. Various materials are used for this paste. In the cheaper fillers such material as starch is used, but in the better fillers a harder material, such as silex or ground stone, is employed. This is possibly the best filler, because the silex is composed of tiny crystals of stone which presents a great many sharp corners. If we could examine this filler with a microscope we could probably see that it is made up of innumerable crystals. The liquid of the filler would carry these crystals down into the tiny pores of the wood, then when the wood shrinks the crystals would be held fast because of their rough shape. This is the reason that ground stone makes such an excellent filler, because it makes the surface of the board so hard and solid that it is almost impossible for it to absorb any other liquid. Fillers are mixed with different sorts of material, sometimes oil and turpentine; sometimes a little alcohol or gasoline is used. The liquid is not a very important portion of the fillers because its principal purpose is to thin the filler so it will enter the pores of the wood. In your work you will find it best to use a good brand of ready-mixed filler and follow the directions for its use.

The filler should be applied with a stiff brush and it should be well rubbed. Since the filler is not to remain on the surface, you do not have to give any attention to avoiding brush marks. After the filler has stood for a few moments, or until it begins to lose its gloss, it is then time to rub it off with a piece of burlap or coarse cloth, rubbing first crosswise of the grain, to rub as much as possible into the wood, then afterward rub in the direction of the grain until all of the surplus is removed from the surface. A sharp stick should be used to remove the surplus filler from the corners and angles of your work. Always be sure that all of the filler on the surface is rubbed off before leaving a piece of work. If the filler is allowed to dry over night it will become hard and it will be almost impossible to remove it. After the filler has had time to become thoroughly hard, which usually requires several hours, you are then ready to take up the next step of your finishing process.

The work thus far (getting the desired color by staining or dyeing and stopping the pores by rubbing in the filler) might be called the foundation work of any sort of wood finish. No difference what sort of finish you desire, these steps should be carefully executed. After you have reached this place or completed the foundation work you should then decide what sort of finish you are going to make. There are three general classes which will be of interest to you: the wax finish, varnish finish and the shellac polish. Regardless of which you use, if you expect fine results the foundation work should be done as already explained.