Improvements in watermarking

A watermark formation element 20 has an integrated body comprising a watermark forming surface, which has one or more watermark forming regions, and a drainage surface. The watermark formation element is formed from a plurality of layers 30-33 which are fused together to form an integrated body, each layer having drainage apertures. Drainage apertures in each layer at least partially overlap the apertures of adjacent layers. Multiple apertures in an overlying layer overlap fewer apertures in an underlying layer, providing drainage channels 22 extending from front surface apertures in the watermark forming surface to the drainage surface. Drainage apertures in each layer thus have an increased cross sectional area compared to those of an overlying layer, such that the cross sectional area of the drainage channels increases as the drainage channels extend towards the drainage surface. The element is preferably formed by 3D printing.