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Alternative Photographic Processes - (Hand made photographic -emulsions and processes)

Exposure tests - Van Dyke Brown


Take the step wedge and carry out a series of exposure tests to establish an exposure that produces a D max ( darkest tone or black) - density while recording as many other tones as possible. You might need to make several tests to establish this.


We can see here that as the exposure is increased the tones on the scale become denser.

Take into account that different papers and light sources will give quite different results.

On the top is a test on Hahnemuhle fine art paper below Arches -

the transparent step wedge is below this.

If we look at the top test we can see that the tone from about 80% to 100% is blocked up and records as the same tone.



You will most likely find that while the result gives a Dmax several of the adjacent ones block up and produce the same tone as Dmax. Like wise while the test produces a Dmin or white, several of the adjacent tones also record as white. So if you had an image in photoshop and printed it using this exposure some of the light tones and some of the dark tones that had blocked up would be lost. This is because the tonal scale of the Van Dyke emulsion is on as long as that of the scale.

So if we want these tones to print we need to adjust the tonal scale with curves and carry out further tests.

Mouse over


Go to - Layer - New Adjustment Layer - Curves

This will bring up a graph with a straight line - the lower end of the line represents D Max or the darkest tones while D min is represented by the high end of the graph.

Each division is 10% so what we need to do is click on the line and move the line to draw a curve that will reference the missing tones. The steeper the curve the greater the contrast between tones - the flatter the curve the lower the contrast.


When we look at the straight test, we can get a good idea of how to adjust the curve - we need to make it steeper from DMax or black to about 80% and do the same from White to 10% the reset the points in between to create an elegant curve that is always climbing.

We don't want the curve to flatten out or worse go down at any point.

So if we move the lower points on the graph so they form a steeper angle this will give these tones more contrast.


So the tones on the original step wedge will look quite different than the one with the adjustment curve.


Mouse over to see step wedge with curve adjustment


This allows us to drop the curve into any image and it will readjust the image to suit the tonal scale of the process.

Mouse over to see negative with curve

When we make a print from each negative at the exposure time we established through the original step wedge we can see how the unadjusted image looks over exposed.

Mouse over to view image made with cruve adjusted negative


A Van Dyke Brown print made from the original negative with no curve adjustment. The exposure time was established with the step wedge.


A print made from the readjusted negative with the curve added.

If you are making prints with no curve adjustment, the tendency with an image like this is to reduce the exposure to compensate for the apparent over exposure, but in the process, there is a compression of tone in both the high lights and shadows.

A Print made from the original negative with no readjusted curve but a reduced exposure.



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