A method of preparing a security document which comprises printing on at least one side of a security paper and thereafter applying to at least one side of the printed security paper over the printing a substantially transparent coating composition comprising an unpigmented polyurethane and/or polyacrylate, said coating composition being such as to provide a film, when cast on a glass surface, that has a König hardness of from 15 to 130 seconds, and also passes the water resistance test as defined by the following steps:

(a) the total formulation to be used in the coating is cast on a glass plate so as to produce a film with a dry weight of 80 g/m 2 ;
(b) the film is initially dried at 23 °C and once tack free dried for an additional hour at 80 °C;
(c) the film is weighed before being wetted and tested for tensile strength and Young's Modulus and is visually checked for any change in transparency;
(d) a sample of the film is boiled in water containing 10 g/litre Na 2 CO 3 for 30 minutes;
(e) the film is then rinsed in cold water and the steps (b) to (c) are then repeated;
wherein when the film is dried and re-weighed the film meets the following criteria:

(i) the wet tensile strength and Young's Modulus of the boiled film are not less that 90% of the initial film wet tensile strength and Young's Modulus;
(ii) the film shows no perceptible loss of transparency; and
(iii) the dried weight of the film is not less than 98% of the original weight.