The DARKROOM COOKBOOK, Third Edition

94 THE DARKROOM COOKBOOK
How it Works
Pre and Post Flashing to Control Contrast
Les McLean
The initial exposure to white light will produce no tone on enlarging paper—it simply
eliminates the paper’s inertia to light. Therefore, when exposing the paper with a negative
in the enlarger a certain amount of the exposure is not producing tone, and more
importantly, detail. Flashing is a method of controlling contrast by pre-sensitizing the
paper with an exposure to white light that overcomes the paper’s inertia.
When fl ashing is employed, all units of image-forming exposure passed through the
negative will produce tone, therefore less exposure is required. Consequently, because
of the reduced image forming exposure the lower values are less likely to block up,
resulting in better separation in the shadows. At the other end of the tonal scale, the
highlight detail is improved because, in effect, the paper is getting more exposure to
the image-forming light that produces tone and detail. Because the inertia is overcome
by the white light fl ashing exposure all light transmitted through the negative is “working”
to ensure that the detail on the negative is recorded on the paper, hence the lowering
of overall contrast and the improvement of detail throughout.
In describing how I make the prints illustrating this method, I use two terms to
describe the light: White light and Image-forming light. White light is any source of light
that can be used for fl ashing, for example an enlarger with no negative in the carrier, or
the Paper Flasher® that I use. However, it is important that you can accurately control
the time of the exposure and that the light source will provide consistent illumination.
Image-forming light is the light projected on to the baseboard by the enlarger with the
negative in place.
A second light source is required, preferably attached to an accurate timer to make the
fl ashing exposure. A second enlarger will do but I prefer the Paper Flasher manufactured
by RH Designs, which can easily be attached to the enlarger. I fi nd it quick, convenient
and accurate (see Resources).
A second method is to leave the negative in the carrier and place a piece of diffusing
material, such as Opal Perspex under the lens, similar to the procedure used when
employing a color analyzer in color printing. This method will make the fl ashing exposures
quite lengthy.
Making the Pre-Flash Test Strip
Use a full 8 � 10 inch sheet of enlarging paper to make your pre-fl ash test strip or cut
a piece into 1 � 10 inch strips. With the paper held fl at in an easel, use a black card to
cover a 1 inch section of the test strip—this strip will receive no exposure and remain
paper-base white.
With a pencil put indicator marks at about 1 inch intervals along the edge of the
test strip, 8 to 10 should be suffi cient. Expose the test strip to white light in the same
way as you would when making a normal test strip, I use 1- or 2-second intervals. Move
the card in sequence through each of the remaining indicator marks exposing for the