Silver halide printing

Printing on silver halide (AgX) based Colour Negative (CN) media is frequently thought of as old-fashioned. Coated paper dates back about a hundred years – a respectable history, during which some of the biggest and best-known global brands (including FujiFilm and Kodak) have spent many tens of millions and many man-years developing a huge range of media for different applications.

LumeJet has taken the traditional 'C-Type' silver halide process and married it to the best of modern digital technology. We call the resultant image the 'L.Type'. For more on what makes our prints different, go to Technology & Quality

 

Why Print with Silver Halide?

  • True contone images
  • RGB colourspace, offering more colours than CMYK
  • Colour fidelity, matches metallics and hard-to-print Pantone® spot colours
  • Flawless, intense blacks
  • Durable, archive quality, light-safe prints
 

How does silver halide printing work?

 
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Silver halide (AgX) printing with Colour Negative (CN) photographic media works by subtracting colours from white light (subtractive colour system).

Silver halide (AgX) media has three layers of light-sensitive coatings, one each for Red, Green and Blue, placed one on top of the other like transparency foils, on a backing sheet (white paper for photographic paper, clear substrate for film).

The three coating layers are a gelatine mix, containing grains of dye-sensitised silver halide (∆) that reacts to Red, Green and Blue wavelengths, surrounded by a large number of colourless “colour couplers” (o).

 
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When the paper is exposed to light, the sensitized silver halide grains in the appropriate layer form a “latent image”, or a small activation of Ag+ ions along the grain edge (●).

Imagine an RGB image with a single pixel of solid Green (R=0, G=100, B=0).  As the paper is colour negative, this is inverted before exposure (R=100, G=0, B=100). Or in other words, there is maximum exposure in Red and Blue layers, and none in the Green layer.

 
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After the paper has been exposed, it is processed in developer. Developer attacks any grains where there is a latent speck (●), reducing the grain to a tangle of filamentary silver. 

This reaction oxidises the developer, which in turn reacts with the colourless colour couplers around each exposed grain to produce a cloud of coloured dye. The couplers are the complementary colour to the exposing light – Cyan for Red, Magenta for Green and Yellow for Blue.

 
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Once development is complete, the paper goes into bleach fixer, which bleaches the filamentary silver, stops further oxidisation and makes any remaining unexposed silver halide grains inert. 

Then the print is washed in clean water, removing any residue of the coatings, including the silver, which is recovered via the recycling process.