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P. 121
INSTRUMENT MAKING 89
8. Hardening.—Cover with soap, heat to a full cherry
red color and plunge immediately in cold water. Be careful
not to overheat the blank. Better underheat it, for if over-
heated the carbon is burned out and the instrument will not
take a fine edge.
9. Testing.—Test with a file for proper hardness. If the
file attacks the metal it is too soft. If this is the case, reheat
as before and again plunge.
10. Secondary Polish.—Polish again according to the
directions already given.
11. Tempering.—Place the shank of the instrument in
the flame and heat to a faint yellow or straw color, plunging
immediately in cold water or other media as indicated.
12. Tertiary Polish.—Polish again to remove .the oxides
formed on the surface, so that the colors may again be seen
to appear in case of subsequent tempering.
13. Spring Temper for Shank.—Cover with soap and
place the blade of the instrument in contact with a hammer or
some other large piece of metal, so that it will conduct away
the heat and prevent drawing the temper already given the
blade. Place that portion of the shank back of where the
temper is required in the flame, heat and watch closely for
the blue color , on the appearance of which, plunge immediately
as before.
14. Sharpening and Final Polish.—Again polish, and
sharpen the blade for use.
Technic Work in Brass.—If the instruments are made in
brass, practically the same procedures are followed, except
that no hardening or tempering is required and the polish-
ing is done only on completion of the work. The brass
should be first annealed, when it is ready for the various
manipulations (Fig. 123).
8. Hardening.—Cover with soap, heat to a full cherry
red color and plunge immediately in cold water. Be careful
not to overheat the blank. Better underheat it, for if over-
heated the carbon is burned out and the instrument will not
take a fine edge.
9. Testing.—Test with a file for proper hardness. If the
file attacks the metal it is too soft. If this is the case, reheat
as before and again plunge.
10. Secondary Polish.—Polish again according to the
directions already given.
11. Tempering.—Place the shank of the instrument in
the flame and heat to a faint yellow or straw color, plunging
immediately in cold water or other media as indicated.
12. Tertiary Polish.—Polish again to remove .the oxides
formed on the surface, so that the colors may again be seen
to appear in case of subsequent tempering.
13. Spring Temper for Shank.—Cover with soap and
place the blade of the instrument in contact with a hammer or
some other large piece of metal, so that it will conduct away
the heat and prevent drawing the temper already given the
blade. Place that portion of the shank back of where the
temper is required in the flame, heat and watch closely for
the blue color , on the appearance of which, plunge immediately
as before.
14. Sharpening and Final Polish.—Again polish, and
sharpen the blade for use.
Technic Work in Brass.—If the instruments are made in
brass, practically the same procedures are followed, except
that no hardening or tempering is required and the polish-
ing is done only on completion of the work. The brass
should be first annealed, when it is ready for the various
manipulations (Fig. 123).
