Duplex printing is used for the brilliant rendition of black-and-white photos. It is printed with two colours, a dark colour for the dark shades (black in greyscale pictures) and a light colour for the light and medium shades. The second colour consists of a light, usually neutral grey. However, this shade can also be varied from brownish to greenish, allowing the character of an old photo to be created.
Black-and-white photos must be appropriately converted in the repro for high-quality duplex printing. This entails the special colour separation of the photo.
When printing particular care must be taken that the special colour is not mixed too dark. Too dark a colour weakens the contrast and causes a grey fog on the photo. The special colour consists of 90% gloss print varnish, which emphasises the brilliance of the photos. In order to achieve a high density in the depth, a highly pigmented black colour is used with a colour density of 2.5. Thanks to this high-contrast printing a photo can be illustrated very photo-realistically.
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