| 摘要 |
The invention relates to improvements in security substrates and in particular to fibrous security substrates, such as paper, incorporating a watermark. The security substrate comprises a fibrous base layer, having a normal base fiber density, said base layer incorporating a watermark consisting of a plurality of alphanumeric characters. Each character comprises dark and/or light regions, the dark regions being formed by more densely deposited fibers than the normal base fiber density and the light regions being formed by less densely deposited fibers than the normal base fiber density. The density of the fibers in any region is substantially uniform such that there is no gradual change of tone between the light and dark regions. Each dark and light region adjoins at least one light and dark region respectively and an area of normal fiber density. |
