Re-using glass from a 1908s sliding door - toughened?

I am considering re-using glass from an old 1980s sliding door to cut a piece for an internal window above an internal door.

The question being - would glass from a 1980s sliding doors be toughened? I assume nowadays that it would have to be, but then?

I looked at the glass through polarised lenses and cannot see any dark lines from annealing. I think it is 4mm, and I cannot see the edges as it is still in the old aluminium frame. There are no obvious marks or stamps on the glass.

Any tips on how to check it is not toughened?

Thanks

Andy


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