The process of staining, usually by greasy materials sticking to the surface or by the absorption and adhesion of dust and particles to the cotton A banknote security feature incorporated randomly during the manufacture of the paper. The fibres can be made of silk, plastic or metal, and may be visible, invisible, or fluorescent under UV light. of which the A banknote (or ‘bill’ as it is often referred to in the US) is a type of negotiable promissory note, issued by a bank or other licensed authority, payable to the bearer on demand. is made. It is one of the main reasons for banknote deterioration and their subsequent destruction.