Pre-Flashing: How to do it

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In order to estimate the degree of pre-flashing needed for a duplication procedure, prepare a pre-flash exposure series by

• 1 Exposing a number of film strips of the duplication material or print stock in a sensitometer to a wedge in the usual exposure conditions to produce a conventional characteristic curve.
• 2 Process one strip conventionally without any pre-flashing and plot the curve.
• 3 Expose the remainder in a continuous rotary contact printer, for example a Bell and Howell Model C, to a series of neutral densities filters placed in the filter holder in the light beam, - a range of 1.00, 2.00, 3.00 is suggested to start. Use a trim setting suggested by the normal LAD set-up system for this stock, as a starting point. Process the strips in the same standard process and plot the characteristic curves.
• 4 A comparison of the curves will show the degree of contrast reduction achieved by each exposure level. If the film stock is colour and if the three curves are no longer parallel to each other the colour of the exposing light must be adjusted to compensate. This can be done by using subtractive filters but is more easily achieved by adjusting the trim settings of an additive printer lamp house.
• As a guide for negative-positive duplication:
• Red contrast lower than rest - lower the red exposure - reduce the red trim value
• Green contrast lower than rest - lower the green exposure - reduce the green trim value
• Blue contrast lower than rest - lower the blue exposure - reduce the blue trim value
• If the duplication process is copying onto a reversal film the trim values shown above are increased.
• 5 Repeat the series until the curves are parallel. Some stocks do not behave uniformly when pre-flashed and colour negative films and negative type duplicating films are easier to set up than reversal films.
• 6 Use the estimated trim values for all pre-flashed material. All pre-flashing can be done on just one printer only regardless of the printer to be used for the image. Always use a continuous printer with full frame gate [or the Academy gate removed], which produces a uniform flash over a band between the perforations. This pre-flashed stock can then be used on any other printer - step or continuous.
• 7 The degree of flashing needed for any particular restoration is almost impossible to estimate without making a test.

Pre-flashing will not be needed for black and white duplication but will be probably needed for the following:

• 1 Making a colour internegative from a stencilled print
• 2 Making an internegative from a duplitized two colour print
• 3 Making an internegative from high contrast positives such as Kodachrome, Kodachrome prints, early Ektachrome and Agfacolor prints, and Technicolor prints.
• 4 Making a combined duplicate colour negative from some Technicolor protection masters and almost all Technicolor optical fades and dissolves.

The most commonly pre-flashed film is Eastman Colour Internegative, but also some colour camera negative films give good results when pre-flashed. Fuji Negative film and Eastman Colour Negative films have been successfully used and seem to be good at handling pastel colours of early stencilled and hand coloured prints.