Playing with Gradations in Film Development
The more light that reaches the film, the greater the blackening after development in the negative, because the more silver halide is converted into metallic silver. This is true for all films, because even with color, the silver image is the foundation on which the color image is built. The silver is only bleached out later, leaving the pure dye image behind. Different exposure to light leads to different densities the negative or even the slide is covered to different degrees in different places. If you now measure all the densities that can be achieved with a film material and arrange the values in a graph, the result is a curve – the blackening or gradation curve. At its base, it shows the formation of veils without image traces, then the threshold, and then the part running upwards at an angle in a straight line, in which all the image information is contained at different densities. At the top, the curve flattens in its shoulder, reaches maximum density and thus its usable end.
If the curve runs steeply, one speaks of hard gradation. All brightness values are graded within a narrow space, are gathered in their course, and there is little room for intermediate tones. If, on the other hand, the curve runs flatter, the space creates a much more extensive graduated scale of brightness values between the extremes of black and white can be recorded, the transitions are softer. And softer is the gradation.
With slide material, which always works steeper than normal negative film, it doesn’t help you much if you have low light contrast in the subject – the density in the midtones must be right if the image is to work. And that requires the right amount of exposure.
If, on the other hand, you take a picture on negative film of soft gradation and have a subject with low contrast between light and dark, then it is relatively unimportant on which part of the rising gradation curve you place the short range of brightness values in this case – at the bottom, in the middle or at the top: As long as you hit the rising part of the curve with the entire subject range – with the shadows, in other words, not “drowning” in the foot of the curve, with the highlights drowning in the maximum density – your negative remains copyable in all its tone or color value gradations. It’s just a little thinner or denser, and the exposure you need when enlarging is correspondingly short or long.