Characterizing Paper: darkroom printing

Procedures:

Determine general exposure (determine first image white)

Set enlarger to standard position. Enlarger high enough so that with lens stopped down you can estimate an exposure of between 10-20 seconds. Beseler 45 at top and 150mm lens stopped to f45 .. Using step test exposure (cardboard style or) make exposures in 1/4 stop steps. This is very easily done with an F-stop style timer. I use the RH timer. If you don’t make many prints, then your typical timer will suffice, just use a conversion chart to adjust your printing times.

  • 1/2 stop sequence: 8 / 11.3 / 16 / 22.6 / 32 / 45.3 seconds
  • 1/4 stop sequence: 13.5 / 16 / 19 / 20.2 / 22.6 / 25.4 seconds

Evaluate contrast of paper

The contrast of the paper is shown by the number of steps visible on the step wedge test print. To calculate the range multiply the number of steps difference from the ‘dark grey’ to the ‘light grey’ by the value of the wedge steps.

In this case, the step wedge is graduated in 1/2 stop, .15 increments.

6*15 = 90

scn_bp3_character2
1 stop exp diff

Note that the 2 different prints show the same range (same number of steps)- their difference is in which numbers are shown. The 1 stop exposure difference at the enlarger time move the steps in the scale, not the difference between the H and L steps.

What You can’t see, is the effect of changing the developer dilution (in my earlier tests). The effect of altering dilution of Moersch SE-1 Sepia developer from 1+9 ro 1+14 is an increase shadow difference – the 3 darker steps are more distinctly seen at 1+14. The range from darkest to lightest is only increase about 1/4 “stop” — my value for the R of this paper didn’t change significantly, but the shadow detail is improved with higher dilution.

 Meaning, if I want to have ‘bang’ prints, I use 1+9. If I want to pull ? from the shadows, I use the 1+14 dilution.

  • Rapid shadow progression = bang
  • Shallow progression = ?

What I learned –

Using Slavich Bromoportrait #3 paper in Moersch SE1 Sepia developer at 2 different dilutions changes the shadow separation, but not the paper’s tonal range. I am now able to switch between papers (Bromoportrait, or Ilford Warmtone) being certain of prints matching within quarter stop (my characterization goals). Further, since I use Bromoportrait for lith-printing, I know how much exposure a negative requires. The range check provides an estimate of ratios of lith chemicals.

Using the same general process, I can characterize the negative needed for solarizations. None of these efforts uses much paper (1 or 2 sheets cut into test sizes) or time – between 1 and 4 hours to do all the tests for standard prints, lith-prints, solarization…

Stouffer wedges provide other levels between steps than the “15s” —

characterizingpaper-005
stouffer wedges

summary of ISO interpretation-

* the ISO-P rating gives the speed of the paper: double ISO value means half of the exposure time. Unfortunately exposure meters that are calibrated in ISO-P values are hard to find. This ISO-P value has nothing to do with the ISO rating of your rolls.

* the ISO-R rating gives the grade of the paper: ISO-R divided by 100 is equal to log(D), which defines the contrast behavior of the paper. E.g. Ilford Multigrade IV has an ISO-R range of 130 for grade 1 and 90 for grade 3  The higher the ISO-R value, the lower the contrast of the print.