The investigation examined the printing characteristics of the association product plate, a continuous tone lithographic process which utilizes a synthetic, light-sensitive coating variably ink-receptive according to the degree of exposure it receives. The methodology was designed to determine (1) the printing range of the plate, (2) the effective sensitivity of the coating to varying amounts of exposure within this range, and (3) the degree to which adherence to ideal tone reproduction could be achieved through systematic variation of exposure. The plate is not commercially available, therefore it was necessary to consult patent literature and prior research to obtain details of the coating composition and plate manufacture. A number of pre-trial tests were conducted to optimize the manufacturing process and achieve a desirable balance of coating resiliency and printability. After optimizing plate manufacture, equal-interval continuous tone gray scales were printed on a conventional lithographic press to determine the printing characteristics of the plate. The characteristic curves which were generated by plotting printed densities against negative densities revealed low highlight contrast and high midtone and shadow contrast within a relatively narrow log exposure range of .75-1.10. Faulty tone reproduction can often be corrected by modifying the contrast gradients of the film negative(s) used for plate exposure. In halftone lithography, this procedure selectively alters dot area to achieve desired print reflectance. In the case of continuous tone processes, tone corrected negatives selectively modify the ink receptivity of the plate coating. VIII In order to test the effects of exposure modulation on the tone reproduction characteristics of the plate, an optical matrix was sensitometrically generated from continuous tone panchromatic film. Various film development techniques were used to alter negative contrast and obtain gray scales with diverse equal-interval log E increments within the response range of the plate. The matrix was used for exposing plates of similar manufacture to generate print data for analysis. Printed densities obtained from the matrix were used to construct conventional characteristic curves, as well as response profiles relating printed density differences to log exposure increments. A mathematical model of the Jones tone reproduction diagram was used to calculate tone correction factors in terms of relative log exposure and to reconstruct tone corrected negative scales. Printed densities obtained from the test matrix were used to gauge the effect of the corrected scales on tone reproduction. This method, in essence, emulated the Jones-type approach to tone correction in a single print run, thereby reducing manufacturing and printing variables. The data revealed a high degree of success in correcting mid-tone and shadow reproduction through exposure modification. Although some areas of non-linear plate response were persistent, these were primarily due to shortcomings in the methodology rather than plate failure. Optical tone correction of the low highlight contrast was significantly more problematic. Given the relatively short printing range of the plate, the required negative gradient eliminates many original tonal values. Other means physical and/or chemical are required to lengthen the tonal range and raise highlight contrast in order to improve overall plate performance.

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School of Print Media (CIAS)


Silver, Julius


Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: TR940.D385 1988


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