Tinsel Electrons

Tinsel – it is that time of year again when brightly coloured garlands of tinsel find themselves draped across Christmas trees, picture frames and the occasional staircase banister. This year the tinsel I will be digging out of the garage is made of plastic, which is not only pretty but also fire resistant and nontoxic. However, tinsel hasn’t always been so safe…

In the 1950s and 1960s aluminium tinsel was used to make beautiful Christmas trees, but whilst pretty, placing thin strips of aluminium in close contact with lights created a fire hazard. In much the same way that thin pieces of aluminium should not be placed in the microwave, the thin strips of metal in close contact with fairy lights could produce a short circuit. Although not combustible, the aluminium could not dissipate heat quickly causing it to sometimes melt. Additionally, tiny crinkles in the foil could lead to sparks. Melting, sparking Christmas trees was not the festive look.

So aluminium tinsel was replaced with a lead core material covered in a thin top coating of tin to give the glittering sparkle. Whilst this material offered better fire resistance, the lead core presented a toxic hazard. Again not ideal, especially around small children.

With aluminium and lead both ruled out, manufactures swapped to plastic. The plastics used in tinsel today are non-toxic with an atomic structure that naturally guards against fire. For a current to flow, electrons in the atoms need to be able to move; the electrons need to be able to become excited. In an insulator, such as plastic tinsel, the electrons occupy an area called the valence band. This region is a long way below the conduction band, where the electrons are excited and able to move. To get from the valence to conduction band, the electrons would need a lot of energy. This means that the plastic tinsel cannot easily support an electric current, making the material an ideal festive decoration.

This year, as I try to work out how to tastefully decorate my house with multi-coloured tinsel, I’ll spare a thought for the trapped electrons in the valence band, helping to protect my home from fire!