Thanks Jeff Carter, interesting. 1947 and more automated process than we've seen in earlier photos of sheets being hand-rolled.
The question I wrestle with is that the forum has discovered numerous examples (over 20) of labelled 1930s aluminum from books, research reports, and factory photographs.
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All show labels of "ALC24ST" or "24SO" or "24ST"
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No examples show the word "ALCL
AD" in any way.
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All show
serif font (similar in many ways to a typewriter-style font)
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No examples show a
san-serif font.
These photos include examples from different major manufacturers located in different parts of the United States:
1. Douglas
2. Lockheed
3. Seversky
4. North American Aviation (assembled the test samples in the Caltech thesis)
5. Boeing
6. Curtiss Aeroplane Division
The "ALC24ST" marking has been found in Perdue library photos on three different areas on Earhart's Electra (a part in the engine mount, a part in the left wing bottom, and inside the engine cowlings).