We"ve heard of black...

We"ve heard of black ice before, but never pink! French scientists have developed an intelligent varnish that changes colour when the temperature drops below one degree Celsius.

This colour-coded warning system is intended to be used on road surfaces to warn drivers of slippery conditions and invisible ice patches. While the technology is still in the development stage at present, it has already been put through a winter of vigorous testing.

The company behind the coating, Eurovia, painted metre-square patches of the new substance on a variety of different roads across France.

When the temperature approached freezing, the colourless square – which has been painted on a white background in our pictures – turned pink. Then, as the thermometer rose back above two degrees Celsius, the colour disappeared again. The secret ingredient of the paint is a polymer which contains a thermo-chromic pigment – similar to that found in bath thermo-meters, frozen food packaging and temperature-sensitive labels on beer bottles.

This is the first time a coating of this type has been used to monitor the temperature of a road. One of the major advantages of the system is that it can be used anywhere that gets icy in the winter, such as pavements to warn ped-estrians of a slippery walking surface.

The two major challenges now facing the inventors are improving the night-time visibility of the varnish, and ensuring that it’s rugged enough to survive the summer months – when it will be exposed to increased levels of ultraviolet rays which fade the pigment.