Ref the fonts or markings on the Aluminium, rather than go around the houses shouldn't we be looking for documentary evidence as to the standards used? i.e a document that tells employees that this is the stamp that is to be used. Then if you have s piece with divergent markings you may have a piece that has been labelled twice or am I just being simple. Surley there was a set procedure for this kind of thing.
Well, it's a tricky problem. The available texts are limited, and many needed references are not available on Google Books or Hathitrust.org due to copyright. Alcoa documents would obviously be ideal.
However, the general history of aluminum markings can be deduced from the available reference materials:
Phase 1: Proprietary Markings -- Prior to the massive increases in aircraft production in the early 1940s, the markings were defined by the aluminum manufacturer. Numerous books and manuals state "AL" and "ALC" were the standard abbreviations for Alclad.
Photographs show Alclad aluminum was marked with the prefix "ALC", e.g., "ALC 24ST".
Phase 2: QQ Specification, 1941 -- In the early 1940s, Federal government QQ specifications are issued for major metal types. Specifically in 1941, specification "QQ-A-362" is issued covering Alclad 24 Aluminum. ( Ref: National Directory of Commodity Specifications: Classified and ..., Issue 178. By United States. National Bureau of Standards, Paul A. Cooley, Ann Elizabeth Rapuzzi.
http://books.google.com/books?id=h6iOBWpe0ogC or hathitrust.org.) Although the QQ-A-362 specification is not available, the above source states the specification included marking and labeling requirements of the Alclad aluminum ("packaging, packing, and marking for shipment"). [See Attachment 1 below.]
At this time, photographs start to show aluminum marked with more extensive labeling including the word "ALCLAD".
War Department Technical Manual TM 1-424, "Aircraft Hardware and Materials", June 1942 describes the markings expected to be found on aluminum.
(
http://babel.hathitrust.org/cgi/pt?id=uc1.b3241791;view=2up;seq=16 ) [See Attachment 2 below.]
Phase 3: AN-A-13 Specification, 1943 -- The AN-A-13 (Army Navy Aeronautical Specification) is issued in 1943 covering Alclad 24. A second version AN-A-13-2 is released in 1944. ( Ref: National Directory of Commodity Specifications listed above.) [See Attachment 3 below.]
Photographs of aluminum sheet begin to show "AN-A-13" markings.
Phase 4: Post-WW2 -- Equally fascinating, but does not concern us here.