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which used slightly radioactive thorium glass. By now this will have decayed a bit, and the glass will have a yellowish tint.

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I doubt you'll notice any colour change caused by decay of the thorium salt - the half life of the naturally occurring isotope, Thorium-232, is 14.05 billion years!

The glass may well have a slight yellow tint - surely this is a built-in "minus violet" filter and would have been regarded as desirable in the days when monochrome ruled.

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