Topic – Controlling Contrast

Experimenting with split grade processing on my Durst M670 enlarger with dichroic head continues.

The full process of split grade processing entails a test strip for finding the highlights with yellow light (what I call a base exposure) and then another test strip with magenta for determining the shadows. The final print is then made out of these two exposures after each other. The method of course works but all these test strips are a bit tedious and time consuming to do.

A simplified approach has been tested which shows some decent results. The idea is to save time by finding a ‘suitable’ amount of magenta expressed in exposure stops in relation to the first base exposure which is regarded as 0 (zero).

During my first tests of the full process I noticed how, more often than not, the amount of magenta needed turned out to be roughly the same as the base exposure. A typical exposure is 8 secs yellow at f/8 and then another 8 secs magenta at f/8. As the two exposures are the same I call this magenta exposure 0 stops relative to the base exposure. I use the colour heads maximum yellow (Y) setting of the Durst of 170 and the same number goes for the magenta (M).

Below is a test run with four different exposures with this method.

All prints below have all undergone a base exposure of 8 secs Y170. They are then subjected to contrast enhancement by adding exposure stops of magenta, M170.


The top left is with no contrast enhancement i.e. no magenta exposure at all. The bottom left has -2 exposure of M170 (-2 = 8/4 =  2 secs). Top right is with -1 magenta exposure (-1 = 8/2 = 4 secs) and the bottom right has +/- 0 magenta (0 = 8/1 = 8 secs).

The results contain no surprises really but give some fuel to the idea of expressing the second exposure (M) in stops relative to the first one (Y) and that this ‘stops number’ can be directly related to the resulting contrast grade.

In my case I tend to like the result of a second (magenta) exposure of -1 or 0.

The benefit is that contrast can be fairly well controlled without the second test strip (the one for the shadows). And that saves time in the darkroom.


Note: I also tried the method on a colour negative (C-41 process). It was much trickier, and the resulting print dismal, probably because colour negatives have much orange colour on them by themselves which offset any attempt to control contrast with yellow and magenta.

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