HONE, or HONE-SLATE

HONE, or HONE-SLATE. These are various slaty-stones wrought into the form of straight slabs, and used for whetting or sharpening the edges of tools after they have been ground. They consist chiefly of the following:—1. Norway rag-stone, the coarsest variety of the hone-slates; it gives a finer edge than the sandstones. 2. Charnley Forest stone, which is used as a substitute for Turkey oil-stone. 3. Ayr stone, Scotch stone, or slate stone, used for polishing marble, and copper plates, but the harder kinds for whetstones. 4. Idwell, or Welsh oil-stone, used for small articles of cutlery. 5. Devonshire oil-stone, for sharpening thin-edged broad tools. 6. Cutters' green-stone, from Snowdon, which is very hard and close, and is used for giving the last edge to lancets, &c. 7. German razor-hone, used almost entirely for razors. It is obtained from the slate mountains near Ratisbon, where it forms a yellow vein in the blue slate. It is sawn into thin slabs, and cemented to a slab of slate which serves as a support. 8. Blue polishing stone, a dark slate of uniform texture, used by workers in silver and some other metals, for polishing off the work. 9. Gray polishing-stone, somewhat coarser than the blue. 10. Welsh clearing-stone, a soft variety of hone-slate used by curriers for giving a fine edge to their broad knives. 11. Peruvian hone, for sharpening large tools. 12. Arkansas stone, from North America. 13. Bohemian stones—used by jewellers.

Turkey oil-stone is superior to every other substance as a whetstone; it will abrade the hardest steel, and is sufficiently compact to resist the pressure required for sharpening a graver. The black variety is somewhat harder than the white. These stones are imported from Turkey in irregular masses, seldom exceeding three inches square, and ten inches long, and are cut up by means of the lapidary's splitting-mill, and diamond powder, then rubbed smooth with sand or emery on an iron plate, inlaid in wood, and secured by glazier's putty. Sperm or neat's foot oil, or some oil which does not readily thicken, should be used with them. Oil-stone powder is used for grinding together the brass or gun-metal fittings of mathematical instruments, and also instead of pumice-stone for polishing superior brass-work.

The following analyses throw an interesting light on the nature of polishing stones:—