Marking
Black Oxide
Most black oxide coatings can be easily marked. A problem
arises due to the irregularity of the thickness of the coating.
Naturally, the thicker the coating, the harder it is to penetrate,
and some newer coatings are harder yet.
It is essential that when etching black oxide surfaces, there
is firm contact between the stencil and the piece to be etched.
If the pressure is not very firm, the part will re-oxidize
itself and a deep dark etch will result instead of a white
etch.
Vast improvements have recently been made in this area with
electrolytes which tend to stop the re-oxidation action,
thus resulting in a clear white etch and usually a saving
of time. For round surfaces, rolling will not produce good
white etches. Contour blocks are necessary. In addition to
using firm pressure, and direct current (DC), voltage should
be kept low, five to ten volts. The contour block should
be well soaked with electrolyte. In most cases a deep etch
pad must be used. Time dwell needed to obtain proper results
varies from one to thirty seconds depending upon the thickness
of oxide coating to be penetrated.
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