Point III

Engravers and Statuaries may so harden their Tools, that they may hold their points long, if they be to cut stones.

That Iron may be hardened by Cementation with Salts, so that it may serve instead of Steel, is now openly known; but the iron or steel is to be kept in cementation as long as need shall be, not with common salt alone, but mixed with the powder of coals and salt of ashes; then the Iron grows as hard as steel, but steel is rendered harder than it was before.