Files and Sand-papers.
HAVING now examined the analogies between the cutting, boring, striking and grasping tools of Nature and Art, we come to those finishing tools which smooth and polish the surface.
The first is the File, an instrument which needs but little description. It consists of a surface of hardened steel, broken up into rough-edged teeth of infinite variety, according to the work which the file has to do. It is rather remarkable, by the way, that at present the English files are infinitely superior to those produced in any other part of the world; that their teeth are all made by hand; and that a genuine Sheffield file will first cut its way through a piece of iron in half the time that would be occupied by a file of any other nation, and then would easily cut its antagonist in two.
As long as the File is intended to work upon metal, there is little difficulty in its manufacture, except that no machinery has yet been invented which can give the peculiar edging of the ridges, and to which is owing the unmistakable “bite” of a real English file.
But there are occasions when the hand of the most cunning file-maker is baffled, and when it is necessary to cut files so delicate that the unaided human eye cannot trace their teeth. Art, therefore, has recourse to Nature, and the cabinet-maker, who cannot obtain any file made by human hands which will answer his purpose in the higher branches of his trade, makes great use of the “Dutch Rush,” as he calls it. It is not a rush at all, but simply a species of Mare’s Tail, or Equisetum, a plant which fills in profusion almost every marshy spot in England.
The peculiar fitness of the Equisetum for this purpose cannot be appreciated even by those who use it until it has been viewed under the microscope. I have now before me a small piece of Equisetum, placed under a half-inch power, and viewed by direct illumination, it being treated as an opaque object.
The microscope reveals at a glance the source of the power which the ingenuity of man has taken advantage of. The surface of the Equisetum is seen to be composed of myriads of tiny parallel ridges, each ridge bristling with rows of flinty spicules, looking very much like the broken glass upon the top of a wall. Minute as they are, these spicules can do their work, and they enable the joiner to finish off work in a manner that could not be accomplished by any tool made by human hands.
I find, by recent inquiries, that modern joiners scarcely, if ever, use the Equisetum, preferring emery-paper as cheaper and more expeditious, and knowing that the popular eye is not able to appreciate the difference of the surface obtained by the Equisetum from that which is given by the finest emery-paper ever made. Wood-carvers, however, if they be of the conscientious kind, and love their work for its own sake, adhere to the Dutch Rush, and are all the happier for it.
Pass we now to the coarser kinds of polishers, the chief of which is popularly known as Sand-paper, and is made by coating some tissue with glue, and scattering upon it sand of different qualities, according to the work to be done. Sometimes, when the work is rough, the sand is large, rough, and coarse, and sometimes, when the work is fine, the sand is so carefully sifted before it is scattered on the glued paper, that there is little distinction between the sand-paper and emery-paper. Linen, by the way, is generally used instead of paper, as being more enduring, less liable to crack, and capable of being folded so as to obtain access to crevices which paper could not touch.
Again in Nature we find a parallel, and the coarse Sand-paper of modern Art has long been anticipated in the scale-clad skins of many fishes.
The accompanying illustration is taken from the skin of a Picked Dog-fish found by myself lying dead on the rocks in Bideford Bay. I cut off a piece for transmission to the draftsman, and found that not only did it feel exactly like cutting through a piece of very common sand-paper, but that it blunted the edge of a new knife in exactly the same manner as would have been done by the roughest of sand-paper.
This kind of skin is common to all the shark tribe (including the Dog-fishes, which are but sharks in miniature), and to the Skate, Saw-fish, &c. I have now before me a small, but perfect example of the Saw-fish, the surface of which is covered with flinty scales like those of the Dog-fish, but very much smaller, requiring the aid of a magnifying lens to distinguish them. Even to guess at the number of them is impossible, for they cover the whole of the body, and extend to the very end of the beak, in some places glittering in a strong light as if pounded glass had been sprinkled all over the fish. One of the most interesting points in their structure is the manner in which they reach the rounded jaws, and there become converted into teeth powerful enough to crush the animals on which the fish live. The structure of these jaws will be explained in a future chapter.
Some of the skates and sharks have these scales of great size, so as to show their formation almost without the aid of a magnifying-glass. This is the case with a species of skate, the skin of which is used by the Japanese for wrapping round the handles of their best swords, and which is greatly valued by that nation, the sword being an almost sacred article in the eyes of a Japanese.
There is a well-known museum in which these swords are labelled as having handles of “granulated ivory.” Now, in the first place, there is no such thing as granulated ivory; and, in the next, a mere glance ought to tell the observer that the so-called ivory is a skin of some sort, worked upon the handle while wet, and kept in its place by copper studs. Even the junction of the edges is perceptible, and yet the authorities of the museum in question, although they have been repeatedly corrected, still persist in calling the skate-skin by the absurd title of granulated ivory.
However, if ivory could be granulated, it would certainly look very much like the skate-skin. When examined closely, the scales, whether of Dog-fish, Skate, Shark, or Saw-fish, are seen to resemble hexagonal cones, not coming quite to a point, but truncated, so as to have an hexagonal flattened tip. They are almost of a flinty hardness, especially at their tips, and on inspection of them the observer is not surprised at the use of Dog-fish skin in place of sand-paper.
Perhaps the reader may ask why the Equisetum should be taken as the prototype of the file, and the skin of the Dog-fish as that of sand-paper. The reason is this. The flinty points of the Equisetum are set upon parallel ridges something like those of a file, while the scales of the Dog-fish are without any apparent order, being crowded against each other like the cutting particles upon the sand-paper. That there should not be an order, and that a definite one, is out of the question. But it has not yet been detected by human eyes, and therefore may be practically treated as non-existent.