[Brightcolours]

ThO2 browns glass over time reducing the transmission of light through it.

 

While we're on the subject, don't eat IC chips from the 70s. There were traces of radioactive elements that would emit alpha particles....

You can get rid of the yellowing easily, if it occurs.

 

And on the subject of radioactive elements. When elements decay, they become other isotopes/elements, which may emit other radiation when they decay. So more than likely, they will emit gamma, alpha and beta radiation.

 

And on ICs from the 70's, I have not heard of radioactive elements in those. As far as I know, they used the same stuff as they do now (silicon, gold).