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This is probably a rather unusual question for this forum. The review of the movie Metropolis (made in 1926) by Roger Ebert shows what I assume is a still frame from the movie:

picture

The shield looks very thin and has the typical small scratches that I would expect from a transparent thermoplastic.

My question: What material is this? If this is a silica-based glas and not a thermoplastic (did that exist in 1926?), what characteristics does it have? Is it flexible?

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    $\begingroup$ Possibly still ordinary glass. If you think about e.g., the canopy of a Spitfire, this likely was acrylate which by Wikipedia was developed by 1928 and really entered production in the 1930s to cast large panels ready to mold after heating. Perhaps a cheaper soda-lime glass (less high melting temperature than modern borosilicate glass, easier to bring into this shape). $\endgroup$
    – Buttonwood
    Sep 7 at 20:33
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    $\begingroup$ Perhaps cellophane? $\endgroup$
    – Jon Custer
    Sep 7 at 23:59
  • $\begingroup$ When we still had a laboratory glass shop, they could make amazing glass structures. $\endgroup$ Sep 8 at 16:10
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Most synthetic plastics were commercialized after 1930s, I think. But semi-synthetic cellulose derivatives like cellulose acetate and especially cellulose nitrates were around from the middle of 19nth century. Both were used at some point to produce thin film, in particular photographic film.

My first bet would be that it is a celluloid plate, made from mixture of nitrocellulose and camphor. It was one of the first thermoplastics and can be made transparent.

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  • $\begingroup$ Indeed, if it is a movie, then it must have been made on a photographic film, so it surely was available. $\endgroup$ Sep 8 at 6:57

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