Section-Cutting / A Practical Guide to the Preparation and Mounting of Sections for the Microscope, Special Prominence Being given to the Subject of Animal Sections

by Sylvester Marsh

A slight knowledge of geometry will enable any one to see that these statements are strictly accurate.

As regards other points in the form of the knife, we refer to what has been previously said when discussing the general principles which should govern the construction of cutting tools.

We now proceed to give a few practical directions for sharpening knives and razors and keeping them in order.

Section knives, during the process of sharpening, are subjected to three distinct processes: 1, Grinding; 2, Honing; 3, Stropping.

Grinding is one of the most important, though it is probable that it will rarely be undertaken by the microscopist himself. More knives and razors are spoiled in grinding than in any other way. We have now in our possession an excellent knife, which in an evil hour we entrusted to a New York cutler, and received it back utterly ruined, the temper being entirely taken out of the blades! Some of our readers may wonder at this, but unfortunately it is too true. The cutler, to save time and trouble, too frequently holds the blade against the stone with such force that it becomes over-heated, especially when he is a little careless and allows the supply of water to fall short.[^[20]] The owner does not find this out until he discovers that the knife is ruined, because nothing is more easy than to cool the blade and grind off the tell-tale blue spots. When charged with his rascality, the cutler always denies it and lays the blame on a “soft spot in the steel”—a miserable subterfuge—too transparent to deceive the least experienced.

[20]. Nothing is more easy than to heat a thin rod or stout wire red hot by holding it against a dry grindstone rapidly revolving. We have often kindled fire in this way.

The only protection against this is either to entrust the knife to a man of known carefulness and integrity, or to stand over him while he does it. If the knife be ground under the owner’s eye, no fear need be entertained, because it is easy to insist upon the use of plenty of water.

The grindstone used for section knives should be of fine grain, and it should run true and be very straight across the face, otherwise it will be impossible to grind the knife true, and this, as we have seen, is a necessity.

Every microscopist that expects to do much at cutting sections must learn to hone his own knife or razor. Of the various hones in use the famous Turkey oilstone is said to be altogether the best. It is, however, very difficult to get it genuine and in sufficiently large pieces. We therefore use the German hone-slate, a softer, yellow stone of wonderful fineness and cutting power. The ordinary whetstones are altogether too coarse, and as for artificial stones and strops, they may do for coarse work and common razors for scraping, but they will not do for knives used for section-cutting. If any of our readers should be so fortunate as to possess a good, old-fashioned Turkey oilstone with a fair sized surface, let them think much of it. It is invaluable. Years ago, when working on some investigations that required the use of very sharp knives, we were offered, by an old English carpenter, the use of a real Turkey stone. We have never since found anything that did its work so quickly and so well.

To merely mention the substitutes for Turkey oilstone would fill some pages. We therefore confine ourselves to the German hone. It is obtained from the slate mountains in the neighborhood of Ratisbon, where it occurs in the form of a yellow vein running vertically into the blue slate, sometimes not more than an inch in thickness, and varying to twelve to eighteen inches. After being quarried it is sawed into thin slabs, which are usually cemented to a similar slab of the blue slate as a support, and the combined stones are then set in a wooden frame and fitted with a cover, also of wood. Unlike the Turkey oilstone, the Arkansas stone, and some others, the German hone is soft and easily scratched and worn. It must therefore be carefully preserved, and as the flatness of the hone is an important point, it should never be used for anything but section knives.