Abstract: A process for producing a flat product such as a coin includes the steps of forming a slurry comprising a suspension of particulate material in a film-forming cellulose derivative, depositing a quantity of this slurry onto a support surface, drying the slurry to form a self-supporting flat product, and removing the dried product from the support surface. The particulate material essentially comprises metallic particles and matter whose chemical composition and physical properties differ from those of the metallic particles such that the added matter is not or only partially taken into solution with the metallic particles on heat treatment of the product whereby the presence of the added matter can readily be detected following such heat treatment.