Silver retention techniques have been developed to “create a distinguishing visual style” for some photographers. Some labs refer to the technique as silver retention, bleach bypass, or skip bleach. In all of these processes, varying amounts of silver are left in the print or negative film stock. And, no matter what it is called, the end results are very similar.
Silver Retention refers to a process with selected bleaching of the silver image, where the film is NOT bleached at all, or where the film is left with varying amounts of silver. During the development process, the exposed silver halide is developed up and the oxidized developer forms dyes. There is a silver plus dye image in those areas. In the skip bleach process, some of the non-converted silver remains in the film where there is dye formation.
This technique produces a certain ‘look’, which in some circumstances is very desirable.
Color Negative films that go through a bleach bypass, have:
- Higher contrast and
- Less saturation
- Blown-out whites and highlights, and
- Loss of shadow detail
The left image is the bleach bypass image which is higher in contrast and the colors are very desaturated. On the right, the colors are vibrant and realistically reproduced.
This plot shows the effect of bleach bypass on color negative film. The dashed line is the normally processed color negative, and the straight line is the sensitometry from film that was processed using bleach bypass in an C-41 process.
There is little effect in the Dmin area, but for the film that went through the bleach bypass, the RGB curves are much higher in contrast. Because of the increased contrast in the negative, the densities overall are higher. To print this back to a normal level of density, the photo printer needs to be turned up. The shadow areas will get more light so the blacks will be blacker, and the highlights will be blown up because they are on the straight line portion of the curve. There is no shouldering off. The final result will be higher contrast and less saturation in the image.
Retained silver will increase the density of the negative. If this density is too high, it may be too difficult to photo print successfully. Therefore, underexpose the negative by one stop or more.
Bleach bypass can be achieved by reducing the bleach time in C-41 process, if you are using tank processing. However, when using machine processing, it may be difficult for the processing lab to just change the bleaching time.