Many insurance companies' TV advertisements like to portray a little boy or girl playing with soap bubbles. The ads will then say 'Think about your future' or something. The soap bubbles appear to be the ideal simplistic game that touches both parents and children. However, when soap bubbles become more than a game to an adult, the latter may spend eleven years experimenting with them. And one of the reasons may be because that adult wants to make the soap bubbles coloured.

The adult we are discussing is Tim Kehoe, who is featured in the November issue of Popular Science magazine. He had the idea of making coloured bubbles. Kehoe admits that he thought that it would all be easy.

Turns out that it is far from easy to make a coloured bubble. If food colouring is mixed with the soap, for instance, the resulting bubble will not be coloured but rather translucent, with a spot of the colouring at the bottom.

To be able to blow a true coloured bubble, the chemistry of the bubble itself has to be clearly understood. A bubble wall is made up of three layers: a layer, comprising water molecules, which is held in place by the other two layers of surfactant molecules — a surfactant substance typically being one which lowers the surface tension of the substance (in this case water) that it is mixed with.

More than a year and hundreds of experiments after Tim Kehoe began this project, he had managed to produce soap bubbles that would explode very loudly, soap bubbles that would bounce really high up in air and ultimately coloured bubbles (blue in colour). His mixing and heating of dyes and colourings had finally paid off. Well, not quite so.

The bubble was coloured and that was in itself an achievement. The toy companies, however, did not want it. This was because when the coloured bubble exploded, its dye would spill onto everything and everybody nearby. And mums definitely hate that.

The chemistry behind Kehoe's first coloured bubbles is pretty simple. The molecules of the dye he had concocted had bonded with the molecules of the surfactant, which were evenly spread everywhere on the bubble's surface. The dye molecules were thus also distributed around the bubble in an evenly manner.

But the point remained that Kehoe's coloured bubbles were staining everything and everybody. These bubbles would not make it. What was needed was a coloured bubble which would somehow turn colourless on explosion.

To get this done, Kehoe employed Ram Sabnis, a chemist. His mission was to manufacture a water-soluble disappearing dye that could colour the very thin wall of a bubble. This might well appear impossible, although it wasn't.

The 'magic' coloured bubble that was formed some time after made use of a very obscure branch of chemistry. A branch which had never been experimented and played with — yet. Ram Sabnis built a dye molecule from the unstable lactone ring. This molecule is fabulous. On the bubble, the ring is open and all visible light passes through it, save that required for the bubble's colour, which is reflected. With exposure to air, water or pressure, the bubble explodes. However, the ring closes and visible light passes through. The colour quite literally fades away and the bubble thus appears invisible on explosion.

According to the Popular Science article, the coloured bubbles, branded 'Zubbles', will be on the market in February 2006, if not sooner. Zubbles may well be a best-seller, but in any case, it is one of the wittiest inventions of this year. I can't wait to try it out.

This work is licenced under a Creative Commons Licence.

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