_Tempering Knife Blades._—To heat the blades lay them in a clear charcoal fire, with the _cutting edge downwards_, and heat very slowly. It is not particular if the back of the blade, which is _uppermost_, is so very hot or not. Harden in clean luke-warm water. If many blades are to be hardened at once, lay a number in the fire and remove one at a time as they are properly heated. To temper, brighten one side on a grindstone or emery wheel so that the temper color can be seen, and lay the blades in the fire, or on an iron plate heated over the fire, with the backs _down_ and the cutting edges _uppermost_. On the plate place wood ashes or fine sand to help keep the blades in proper position, and also facilitate even drawing. When the proper color is seen on the brightened portion of the cutting edge, remove and cool in cold water. When an extra tough blade is wanted, after it is hardened, handle it so that it will not draw any lower after removing from the fire, and let it cool without putting in water. Long blades, when they are being drawn, can be straightened, if necessary, by putting them between two pins in the anvil or pins fixed in an iron block and bending between these until straight, wetting the blade with a cloth or sponge saturated with water, when the blade is thus straightened. Surprising as it may seem, when hardened steel is being drawn, it can be bent to quite an extent, and when cooled will remain as bent. File makers straighten files in this manner. Sword blades and blades of butchers’ knives undergo the same process of manipulation to be made straight. _The Lead Bath for Tempering._—Among the many secrets of tempering is the employment of the lead bath, which is simply a quantity of molten lead, contained in a suitable receptacle and kept hot over a fire. The uses of this bath are many. For instance, if it be desired to heat an article that is thick in one portion and thin in another, every one who has had experience in such work knows how difficult it is to heat the thick portion without overheating the thin part. If the lead bath be made and kept at a red heat, no matter how thick the article may be, provided sufficient time be given, both the thick and thin parts will be evenly and equally heated, and at the same time get no hotter than the bath in which they are immersed. For heating thin cutting blades, springs, surgical instruments, softening the tangs of tools, etc., this bath is unequaled.