only granulated charcoal, and bring to a dull red heat. Remove from overt, open box, and dump contents instantly into water with the chill taken off. This treatment brings out a dense, tough, close-grained and very hard surface, and the parts will be much stronger than if made of tool steel.
Note: When dumping parts into water, carry the box very close to the surface of water, so that parts are quenched in water without the air striking them. This applies to all methods of case-hardening.
CASE-HARDENING WITHOUT COLOR: The foregoing process may or ma/ not result in some color, but cannot be depended upon to produce the brilliant colors often desired. A method that produces no color, but gives a hard, even grained surface, follows:
In the bottom of box place a layer of granulated raw bone 1./2 inch deep; on this arrange the parts to be hardened, then another layer of bone, and so on to within an inch or so of the top. Then fill up with old bone that has been used before. Put on cover and seal with fire clay. Heat to good cherry red three to four hours, then dump in clean cool soft water. Very small or thin pieces should be dumped in oil. This results in good even hardening, and the parts come out a clean steel gray, free from scale.
•CASE-HARDENING MALLEABLE IRON: Buttplates, pistol grip caps, and many other parts not essential to the mechanism of a gun may be made of malleable iron castings. If they are completely annealed in the making, they may be successfully case-hardened—otherwise results are doubtful.
For this work use one part granulated raw bone, well mixed with three parts granulated charcoal. For Bessemer steel or very small parts, slightly reduce the prooortion of bone. Pack in boxes or parts as previously described, sprinkle charcoal dust over the top, and heat to cherry red two to four hours. Dump in clean soft water.
CASE-HARDENING WITH COLORS: This involves the use of charred bone, prepared as previously described. It is essential that the parts be well polished—the better the polish, the more brilliant the colors. Burnishing and buffing is not advised, as it closes and fills the pores and retards the process. Polish the parts with fine abrasives as described in chapter on polishing, and dean by boiling in lye solution as for bluing, or by pickling; after cleaning, handle the parts only with clean, white cocton gloves that have been washed and boiled. A single touch with the bare finger will leave a spot that will mar the final finish.
Pack the work in layers as before, having the layers of charred bone about 3/4 inch deep, leaving about 2 inches at top which is filled with charred bone. Put on lid and seal with fire clay. Be sure that none of the parts are nearer than 1/2 inch from sides of box, and that the parts do not rouch each other. Bring the box to a nice cherry red and hold uniform at this heat two to four hours. Too high a heat will result in no color.
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