|Volume 12 Number 2/3
|[L10] Plexiglas (TIGHAR Artifact 2-3-V-2)
||February 1996 during TIGHAR’s NIKU III Preliminary expedition.
||Winterthur Museum Analytical Laboratory
||February 22, 1996
||This is an irregularly shaped sheet of transparent polymethyl methacrylate
(PMMA), trade name Plexiglas. It measures nominally 4.75 inches long by 2.5
inches wide and is 1/8 inch thick. A second fragment is roughly 1.75 inches
long by 1.5 inches wide and fits a fractured edge of the larger piece. Both
pieces exhibit a slight but uniform curvature over the surface.
||The convex surface of the sheet exhibits a number of shallow scratches, while
the concave surface has only a few. One edge appears to be an original manufactured
edge. The others exhibit saw marks. There is no evidence of heat damage. Because
PMMA must be heated to at least 90°C to be formed, the curve of the surface
on this sheet is probably original.
||This appears to be a scrap from Lockheed Model 10 Part Number
40552 – Window Glass, Fuselage, Cabin.
||Lockheed engineering drawings show that the material, the curvature, and
the thickness of the artifact match those specified for the cabin windows of
the Electra. A number of changes were made to the material and thickness specifications
for the windows over the production-life of the Model 10 (1934 to 1941). Of
particular interest is a change specified for January 15, 1937 at which time
the window thickness was reduced from 5/32 to 1/8 inch. The date is of special
interest because it was just at that time that the cabin windows in Earhart’s
airplane were replaced and additional special windows were installed as part
of her world flight preparations. The curvature and thickness of the Plexiglas
found on Nikumaroro exactly matches Lockheed’s specifications for Electra cabin
windows at exactly the time Earhart’s new windows were installed. They do not
match any window on the B-24.