National Science Week 2021 – Science in the laundry

How did people make their shirts so bright?

Q. In the days when state of the art laundries all featured coppers, mangles and cement tubs, just how did people make those shirts so bright.
A. They used an optical brightener – Reckitt’s Starch.

The science:

Optical brighteners absorb energy from ultra-violet light. This energy ‘pushes’ some of the electrons in the atom to higher energy levels or states. This is described as going from S₀(ground state) to S₁ (excited state).

Eventually the electrons ‘fall’ back to the original energy state (S₀) and as this happens this releases some of the energy as a photon of light in the visible light range. This is governed by the First Law of Thermodynamics which states that energy cannot be created or destroyed by can be converted from one form to another, in this case from the ultra-violet light energy to the visible light energy.

Reckitt’s Bag Blue was a common sight in laundries where it was added to the end of the wash to make clothes appear brighter, especially whites.

Reckitt’s Bag Blue was also used to soothe insect bites and stings. Another component of the product, sodium bicarbonate, helped to neutralise the acids in a sting.