Having purchased a hone, the first thing to do is to see that it is perfectly true; that is, that its surface is a perfect plane. If hollow or twisted, it is useless until made straight. It may be tested by means of two steel or wood straight-edges, and the method of doing this, which is very simple but difficult to describe, the microscopist can learn from any cabinet maker or carpenter. If the hone be not true it must be made so, and this is best done by grinding it with emery on a slab of marble or, better still, a plate of cast iron which has been planed true. (Waste castings with planed surfaces may be found in most machine shops, and may be either borrowed or purchased for a small sum.) If the hone is very uneven, coarse emery may be used at first; then finer must be taken, and so on until the surface of the hone is not only true but very smooth. This involves considerable labor, but it cannot be avoided if a true edge as well as a sharp one is desired, and hence our advice to use the hone for nothing but section knives. Accuracy in a penknife or a razor for shaving is of no consequence; in a section-knife it is a sine qua non.
The surface of the hone must not only be true and smooth, it must also be clean and free from dust and grit, a single particle of which may spoil the work of hours. It should therefore, when not in use, be kept constantly covered. It is always used with oil, and this oil should be of a kind that does not readily dry up. Good sperm is excellent, and so is purified neat’s-foot oil. Avoid kerosene, soap and water, and similar fluids, which are so frequently recommended, especially under the guise of new discoveries. They have all been tried and found wanting. After use, the stone should be carefully wiped clean, fresh oil being applied when it is next used. It must never be used without a liberal supply of oil, otherwise it will become glazed and will no longer act on the steel.
The hone being in good order, the blade is laid flat on it and moved over its surface with circular sweeps. The method of doing this is easily acquired, and is best learned by watching an expert cutler at work. If we could only hit it, the perfection of this operation would be to wear down the sides of the blade until they just met; they would then form a keen and perfect edge. Unfortunately we cannot always hit this point exactly; we are apt to overdo the matter just a little, and then comes up the bête noir of beginners—the “wire edge.” This is caused by the metal of the blade bending away from the hone as soon as it becomes of a certain degree of thinness. Once it does this it cannot be worn off by the hone, and the only way to remove it is to draw the edge of the knife or razor across a piece of horn or hard wood. After removing the wire edge in this way, give the blade one or two sweeps on the hone and then strop it. If the blade be very soft, the wire edge comes very quickly and easily, and is very hard to get rid of. On very hard blades the wire edge is not so apt to make its appearance. It comes, however, on very excellent blades. It may be avoided in a measure by driving the blade edge-first over the hone, and indeed the blade should always be sharpened most in this way. And since the backward and forward strokes are always nearly equal, as regards space passed over, this is accomplished by exerting a greater pressure on the forward than on the backward stroke.
This wire edge is a nasty thing when it breaks off on the hone. Unless removed it will very speedily ruin a fine knife, therefore look out for it and wipe off the hone carefully if you have any suspicion that particles of steel have broken off the blade and got on to it.
In honing, as in everything else, however, nothing but practice will impart skill, and he who intends to become an expert should practice on a few old razors, grinding, honing and stropping them himself, until he has acquired the art of giving them an edge far keener than most of the razors ordinarily used for shaving.
The last operation to which the knife is subjected is that of stropping, and as the blade should be stropped after every section, it becomes important that our tools should be good and that we should know how to use them. By having two or three knives we can always avoid grinding and honing the blades ourselves, for it is then easy to hire the work done, and half a dozen knives will last a careful worker a long time with merely the aid of a good strop. But the strop he must use himself. Fortunately no great skill is required in stropping, but the strop must be a good one and is best home-made.
Our readers have doubtless seen the “Cheap John” strop-vendors take a rough table knife, strop it on one of their “patent” strops and cut a hair with it. Nevertheless such a knife, sharpened in that way, would not cut good sections, and such a strop is not just the thing for giving the finishing touch to a section-knife, even though the label does say that it is “intended for surgical instruments.”[[21]]
[21]. The finest emery paper, glued on a strip of wood and used as a strop, will impart to a razor an edge sufficiently keen to enable it to remove the beard, and if paper three or four degrees coarser be used, a very dull knife or razor may be sharpened, and afterwards stropped on the finer emery until it is keen enough to cut a hair. But it will be found that cutting edges produced in this way are not smooth enough for section-cutting.
The strop should never be used with the intention of removing metal so as to thin the edge of the knife. This is the proper function of the hone, and those who depend most on the hone and least on the strop, will always succeed best. The strop is used in the first place for smoothing off the edge, and in the second for removing that incipient dullness which always comes from even the slightest use. It is true that in the latter case the strop trespasses somewhat on the functions of the hone, but only to a very slight extent, and stropping should never be carried so far as to require more than a very few strokes.
