| 摘要 |
<p>The technique for copying a photographic document is suitable for making a long term reproduction on a metallic backing. The first stage consists of taking a copper plate (10), applying a flexible film (20) of phto-sensitive material and then coating it with a transparent film (30) with clear (31,33,35,37) and opaque (32,34,36) sections alternately, formed by the photographic negative of the picture. The assembly is then illuminated by an actinic lamp (L), the photosensitive film is converted into resistive portions (21,23,25,27) and "window" portions (22,24,26,27). The later stages consist of immersing the plate (10) in a bath (13) of a chemical etching agent, for example perchlorate of iron. The etched regions are subsequently filled by an electrolytic deposit, typically of chrome, which gives a black appearance after interaction with the copper. The final surface is polished.</p> |
