c. Testing For Instrument Sharpness. Two methods of testing instruments for
sharpness are available--the light test and the thumbnail test.
(1) The light test. This test requires that you look directly at the sharpened
edge. A shiny edge indicates that the instrument is dull, while a sharp edge will appear
as a black line. A sharp edge will not reflect light caused by the fine line that appears as
sharpness is achieved.
(2) The thumbnail test. This test is the more reliable of the two tests. Hold
the sharpened edge of the instrument at a 45 angle to the nail. Using light pressure,
push or pull the instrument (as dictated by the function of the instrument). If the
instrument slips or glides along the nail, it is still dull. If the instrument grabs or shaves
the nail, a sharp edge has been restored.
Figures 1-3 through 1-7 illustrate instrument sharpening.
Figure 1-3. Proper angulation for sharpening an instrument.