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|  MIL-E-24763A(SH)
w/INT. AMENDMENT 1
photograph all of the test panels (include a gray color scale in all photos and develop photographs to the scale).
After a test period of 1 year (365 days), the test panels shall be examined for chalking in accordance with ASTM
D4214, Fig. 2 after the test panels are rinsed with cold tap water at nominal tap pressure for a period of 5 to 10
minutes without rubbing the surface in a manner that would disturb any chalking. Then wash the panels with a
warm soap solution using a soft sponge to remove any chalking or dirt. The test panels shall then be dried for 24
hours at ambient laboratory conditions and examined for film deterioration and color as follows:
Property
ASTM Test Method
Color
E97
Gloss 60
D523
Checking
D660
Cracking
D661
Blistering
D714
Color difference
D2244
The test results shall conform to the requirements of 3.7.4.
4.6.16. Impact resistance. The impact resistance of the enamel shall be determined in accordance with
ASTM D2794. A suitable instrument is the Gardco Model 172 Universal Impact tester with Model 172-GE Impact
tester adapter complete with indenter plate, fixture plate, and rubber anvil pad. The GE impacter weighs 3.6 pounds
and has formed on each end four convex spherical segments which are of different radii and extensions. Test panels
shall be in accordance with 4.5.1.1. With an uncoated panel in place on the rubber anvil pad, determine the height
of the drop for each end of the impacter to shown on the panel slight evenly spaced segment marks of the impacter
circumference. The heights so determined will always be used. Place the coated panel, film downward, on the
rubber anvil pad at the bottom of the impacter guide. Drop the impacter from the above previously determined
height. Drop the impacter end and drop it on the panel adjacent to the first area of impact. Remove the panel from
the tester and inspect the coating. Use 10 power magnification to detect fine surface cracking. Record the
maximum percent increase corresponding to the largest spherical impression at which no cracking occurs or other
failure.
4.6.17. Compatibility test. The thoroughly mixed enamel shall be allowed to stand undisturbed for 5
minutes. On one clear plate-glass panel, prepared in accordance with ASTM D3891, brush a coat of the mixture to
approximately 25 m (0.001 in) dry film thickness and allow to dry at room temperature in a vertical position for 24
hours. While brushing, observe for streaks and pigment separation. On another panel prepared in the same way,
draw down a 51 m (0.002 in) wet film thickness on a glass panel. Allow to stand for 5 minutes in a horizontal
position. While the paint is still wet, rub-up an area using the index finger in a circular motion for a minimum of 20
revolutions. Exert light pressure of the finger while rubbing so as not to rub off the film. Allow enamel to dry for
24 hours and compare the rubbed-up area against the un-rubbed area. Any visual difference in color or gloss,
streaks, craters, or pigment floating of the dried film shall be cause for rejection due to incompatibility. The results
of the compatibility tests shall be evaluated for conformance in accordance with the requirements of 3.8.13.
4.6.18. 60-degree specular gloss. The thoroughly mixed enamel shall be drawn down on a plane, opaque
white glass panels as specified in ASTM D3891. Use a film applicator that will produce a nominal wet film
thickness of 0.075 mm (0.003 in). Dry for a minimum of 24 hours under referee conditions in a dust free
environment. Paint specimen shall be dry and hard before gloss test. Use longer cure time if required. When tested
as specified in table V, gloss shall conform to requirements of table IV as applicable, for class specified.
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