Hi, the covering is mica insulation, this is now standard on all new toasters, health and safety have been at work here it is so it is not possible to touch the element wires on your toaster. If the element is fitted with the mica still in situ, you will find that the bread facing that element takes longer to brown. it is possible to remove it but great care should be taken as you can damage the element wire in the process, you could buy new elements for all your slots and replace the lot.
As a registered domestic electrician and competent person I advise you do not attempt this yourself but send your toaster to me for repair. Dualit toaster can be difficult to re-assemble and if not done correctly can be dangerous.
regards
jim.fortress@blueyonder.co.uk
p.s I repair dualit toasters
Jim Fortress Electrics Ltd, Aintree Village, Merseyside, April 2008