Blue visually and Electro-magnetically detectable plasters. Blue is a colour not naturally found in food ingredients. It is an offence to contaminate food. Under The Food Safety Act 1990 it shall be a defence for the person charged to prove that he took all reasonable precautions and excercised due diligence to avoid the commission of the offence by himself or by a person under his control. Hence blue plasters are widely used in catering, food processing and food manufacturing. Made from strong stretchy washproof material, with a hypoallergenic adhesive, they have an aluminium strip under the lint pad for detection by metal detectors.