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516 XIV. DUPLICATION OF TRI-PACK COLOR FILMS
speed and a slight change in color balance, but the sum total of such variations does not appear to exceed the equivalent of the single filter step already mentioned. When film has been improperly stored or is old it is likely to be "off balance" by more than a single filter step. It is prudent to make an exposure and color balance test not only for every emulsion lot of film received, but also on every lot received at different times. A log with the results of such tests quickly shows up not only errors and variations, but also indicates when properly interpreted the magnitude of the exposure variation actually encountered in printing the tests.
Routine testing of filters in the arrangements in which they are used is helpful. The cost for several curves is no more than the price of a single 800-ft. roll of raw film. Testing of this kind is in reality inexpensive quality insurance.
Routine testing of the duplicates made commercially is readily accomplished if a test strip is attached to every roll of preprint material and printed as a part of the routine printing operation. The test strip can be designed to fit whatever situation is required. A simple yet informative test leader might include a few frames of each of the following:
(1) A fine-grain silver film (such as EK 5265) uniformly exposed to a density of 1.0.
(£) Clear leader (made by running EK 5365 through hypo).
(3) The 16-mm Kodak color test chart.
(4) Kodachrome printed through a Wratten 49 (blue filter) to yield a color density of 1.0.
(5) Same as (4) except through a Wratten 61 (green filter).
(6) Same as (4) except through a Wratten 29 (red filter).
(7) A resolving power test chart.
The test strip should be printed at " normal' ' exposure for the particular lot of raw film.
Sections 1, 2, 4, 5, and 6 of the strip can be read with an ordinary Eastman densitometer. The results of these readings can be plotted in a " scatter diagram" in accordance with the methods described in ASA Standards for Quality Control, Zl.l, Z1.2, and Z1.3. A check lasting over even a few weeks will indicate where the "tightening-up" process should be applied for quality improvement and in what amounts it should be applied. If more accurate results are required in specific cases, other checks such as per cent transmittance versus wavelength curves may be taken on the pertinent parts of the printed strip.