COLOURED SILVER IMAGES.

Today’s print film emulsions processed in a modern developer formula such as Kodak D19 produce a neutral grey image. However the film emulsions and developer formulae used prior to 1930 all appear to produce “warmer”, slightly brown images, which can only be copied on a modern film stock by using an old formula developer process, which commercial laboratories are unhappy to use as modern customers prefer cold neutrals. Very little investigation of this aspect of archive film restoration has occurred. It is one reason why quality checking of restored images is difficult - it is almost impossible to judge the accuracy of a restoration when the image colours of the original and the restoration are different.

Some developing agents produced markedly warm brown image colours, partly because of the developing agent decomposition products laid down with the silver, and partly because the different granular dispersal of the silver image alters the colour of the image.

One technique widely used on paper was to used developing agents, such as chloroquinol, that produce naturally brown tones [in this case, due to insoluble oxidation products laid down with the silver image]. The images obtained by this method may be slightly coloured by reflected light, and are therefore very suitable for paper prints, but the image is generally opaque and appears neutral by transmitted light.