It sounds like something from a horror film...a valuable collector's doll, stored in an air-tight display case with other dolls, begins to warp and buckle, its face becomes bloated and discoloured and a sticky brown liquid starts to build up inside it. And more sinister yet, the dolls stored with it begin to `catch' the disease!

In fact this is not a scene from a video nasty, but a phenomenon known as 'Pedigree' or 'Hard Plastic Dolls Disease' observed by real-life doll collectors and museum staff, which a team of scientists from the University are helping to understand using state-of-the-art technology.

Dr Howell Edwards, Professor Tony Johnson and postgraduate student Ian Lewis studied two cellulose-acetate dolls produced in the 1940s and 1950s by the 'Pedigree' company suffering from the disease. They used the sophisticated technique of Raman spectroscopy, which is an ideal means of examining valuable or historically important artefacts, because it involves examining an object scientifically with laser radiation without having to dismantle or damage it in any way.

The team discovered that the disease was attributable to the tiny iron hooks used to hold the dolls together and found in their eye mechanisms, reacting with the poly vinyl-acetate material from which the dolls were made: a similar reaction has led to the degradation of many old cellulose movies stored in iron cans. A by-product of the degradative process is acetic acid which gives rise to the 'vinegar syndrome' by which the disease is also known because of the distinctive smell caused by the reaction; the acetic acid speeds up the degradation process by attacking the iron.

Dr Edwards explained how the disease could be prevented : "We recommend removing iron components from hard plastic dolls made from poly vinyl-acetate, or, if this proves too destructive, washing them in soap and water to remove any acids produced by the reaction. But collectors must take care to dry them thoroughly afterwards, since remaining traces of moisture would rust the iron and speed up the on-set of the disease."

University Of Bradford.