If they made of natural fibres, i. e. linen or cotton, wash in high temp and soak in hot very warm water with added bleach to it. Amount of bleach depends on amount of linen. Keep for 1-2 hours, rinse VERY WELL. bleach contains chlorine which is by its nature discolours anything. It is often added in different cleaning product under different names and brands and can cost £££. Dont be fooled. Use any supermarkets bleach for £0. 90