Quick Dips

Glowing Sheep and Perfect Pelts

By Vicki Hyde

Why should a sheep's skin fluoresce? Researchers aren't sure, but both they and sheepskin users are interested in finding out, as the glowing skins can not only tell us something about the state of health in sheep, but also provide better quality pelts for processors.

This intriguing property of pelts was discovered by accident when researchers were testing new ways of looking at pelts as they pass through the production line at fellmongeries. The Imaging and Sensing Team at Industrial Research Limited have developed a machine vision system which sweeps a high-intensity laser across a pelt passing below, taking three images of the pelt at once.

The reflection image is like looking at the pelt under top lighting conditions, providing an overall impression of the quality of the pelt and showing up old scars and ribbing. The transmission image is produced by the light passing through the pelt, akin to holding it up against a strong backlight. It helps to show holes, strain and dog bites, distinguishing between these and ordinary pigmentation marks.

These images are comparable to what a human pelt grader would see. The fluorescent image, however, shows up defects that are invisible to the naked eye. The entire pelt fluoresces when exposed, and areas of scarring, such as from cockle, stand out brightly against the ordinary fluorescence levels of the pelt.

Research into the biochemistry of such scarring continues in an effort to find out why this reaction should take place and what it means in the healing process for the animal.

Whatever is happening at basic science level, the fluorescent images are already proving their worth to industry, allowing graders to identify areas of weaknesses in a pelt and, hence the proper grading for pelts. While the defects are not ordinarily visible at the early stages of processing, they do show up when the pelts are tanned, meaning large losses in both product and profits.

Being able to spot these invisible glowing points on pelts means that fellmongeries have fewer rejected pelts and penalties for misgrading. A 10% increase in recovered value, for example, is worth about $30 million in simply grading from first to third grade, not counting reduced costs of penalty payments for incorrectly graded material.

Peter Hilton, of the IRL machine vision group, is hoping that the fluorescent properties will assist in another area, that of pelt identification. By tracking which pelts come from which farm, and what sort of grade they are, farmers will be able to get feedback on their stock handling methods and make any changes that will help increase the value of the pelts.

By exposing the pelt to specific high intensity ultraviolet light, Hilton has found that he can create dark marks on the pelt which show up in the fluorescent image. He'd like to learn more about the biochemistry behind the reaction.

"If we knew more about it, we might be able to improve our images," notes Hilton.

Vicki Hyde is the editor of New Zealand Science Monthly.