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Rochester Institute of Technology RIT Scholar Works Theses Thesis/Dissertation Collections 5-1-1986 Black & white continuous tone printing using multiple negative working plates, so that each plate prints an equal segment of a determined density range Frank C. Forti Follow this and additional works at: http://scholarworks.rit.edu/theses Recommended Citation Forti, Frank C., "Black & white continuous tone printing using multiple negative working plates, so that each plate prints an equal segment of a determined density range" (1986). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. School of Printing Rochester Institute of Technology Rochester, New York CERTIFICATE OF APPROVAL MASTER'S THESIS This is to certify that the Master's Thesis of Frank C. Forti with a major in Printing Technology has been approved by the Thesis Committee as satisfactory for the thesis requirement for the Master of Science degree at the convocation of May, 1986 This is to certify that the Master's Thesis of Frank C. Forti with a major in Printing Technology has been approved by the Thesis Committee as satisfactory for the thesis requirement for the Master of Science degree at the convocation of May, 1986 Thesis Committee: -----------------------------­ Thesis Advisor Graduate Coordinator Director or Designate BLACK & WHITE CONTINUOUS TONE PRINTING USING MULTIPLE NEGATIVE WORKING PLATES, SO THAT EACH PLATE PRINTS AN EQUAL SEGMENT OF A DETERMINED DENSITY RANGE by Frank C. Forti A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the School of Printing in the College of Graphic Arts and Photography of the Rochester Institute of Technology May, 1986 Thesis Advisor: Dr. Julius Silver THESIS RELEASE PERMISSION FORM ROCHESTER INSTITUTE OF TECHNOLOGY COLLEGE OF GRAPHIC ARTS AND PHOTOGRAPHY Title of Thesis: BLACK & WHITE CONTINUOUS TONE PRINTING USING MULTIPLE NEGATIVE WORKING PLATES, SO THAT EACH--rLATE PRINTS AN EQUAL SEGMENT OF A DETERMINED DENSITY~G~ I, Frank C. Forti, herby grant permission to the Wallace Memorial Library of R.I.T., to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit. ---- - .-- --... -.- ... .. ... ~ ... ..... -. I, Frank C. Forti, herby grant permission to the Wallace Memorial Library of R.I.T., to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit. ACKNOWLEDGEMENTS I would like to thank my advisor, Dr. J. L. Silver, for his ideas and suggestions. I would also like to thank Mr. Sven Ahrenkilde, who was always there to help me, and to Professor Frank Cost, Professor Joseph Noga, and the rest of the School of Printing faculty for their support. Special thanks to the T&E Center for the use of their equipment, and their willingness to help. And finally, I thank my parents and my whole family for their constant support and encouragement. 11 TABLE OF CONTENTS PAGE LIST OF TABLES v LIST OF FIGURES vi ABSTRACT vii CHAPTER ONE INTRODUCTION Screenless vs. Halftone Printing 1 Collotype Process 2 Random Dot Printing 2 Subtractive Positive Working Screenless System 3 Negative Working Plates 5 Statement of The Problem 7 Hypothesis 7 Footnotes for Chapter One 9 CHAPTER TWO RELATED LITERATURE Screenless Lithography in Relation to Plate Grain 10 Tone Reproduction in Screenless Lithography 11 Footnotes for Chapter Two 14 CHAPTER THREE -- METHODOLOGY Film and Plate Preparation 15 Evaluation of Results 21 Footnotes for Chapter Three 22 CHAPTER FOUR PRESS TEST AND EXPERIMENTAL RESULT Evaluation of Press Run 24 Second Press Run and Test Evaluation 32 in CHAPTER FIVE CONCLUSIONS AND RECOMENDATIONS Summary and Conclusions 41 BIBLIOGRAPHY 43 IV LIST OF TABLES TABLE 1 Exposure and Developement Times to Produce the Negatives 19 TABLE 1A Photographic Masks 19 TABLE 2 Density Readings of Negatives 20 TABLE 3 Plate Exposures/First Press Run 21 TABLE 4 Density Readings From Printed Step Wedge 28 TABLE 5 Exposure and Developement Times for Negatives for Press Run Two 30 TABLE 5A Photographic Masks 30 TABLE 6 Density Readings From Negatives 31 TABLE 7 Plate Exposure Times/Second Press Run 32 TABLE 8 Density Readings From Second Press Run 34 TABLE 9 Densities of DuPont Scales used in Plate Test... 39 LIST OF FIGURES FIGURE 1 Grained Positive Plate 4 FIGURE 2 Positive Plate Exposed 5 FIGURE 3 Processed Positive Plate 5 FIGURE 4 Grained Negative Plate 6 FIGURE 5 Negative Plate Exposed 6 FIGURE 6 Processed Negative Plate 6 FIGURE 7 Effective Tone Reproduction in Screenless Lithography 12 FIGURE 8 Mask Representation for Plate One 18 FIGURE 9 Mask Representation for Plate Two 18 FIGURE 10 Mask Representation for Plate Three 18 FIGURE 11 Plate One/ First Press Run 25 FIGURE 12 Plate Two/ First Press Run 26 FIGURE 13 Plate Three/ First Press Run 27 FIGURE 14 Tone Reproduction Curve/lst Press Run 29 FIGURE 15 Tone Reproduction Curve/2nd Press Run 35 FIGURE 16 Plate One/ Second Press Run 36 FIGURE 17 Plate Two/ Second Press Run 37 FIGURE 18 Plate Three/ Second Press Run 38 FIGURE 19 Plate One. Plate Exposure Test 40 FIGURE 20 Plate Two. Plate Exposure Test 40 FIGURE 21 Plate Three. Plate Exposure Test 40 FIGURE 22 Plate Four. Plate Exposure Test 40 VI ABSTRACT Continuous tone printing, either collotype or screenless lithography, are processes that are in limited use. The halftone method of reproduction is still the most economical way to reproduce a continuous tone original. This study dealt with the mechanism of screenless lithography, more specifically on how to make the use of negative working plates a feasible alternative to positive working plates. It is known that the positive working plate can print a longer range of tones than a negative working plate. So the main point of the experiment dealt with how to extend the range of a negative working plate. A negative plate is of high contrast, and so multiple negative working plates were used to print one image. Each plate in itself can print three to four steps of a continuous tone step wedge. In this experiment, three plates were used in the hopes of printing twelve steps in a continuous gradation. A continuous tone step wedge along with a black and white photograph were divided among the three plates. Twelve steps on the step wedge were identified, and so each film had four of the possible thirty steps which existed on the step wedge. These films were exposed to plates, and mounted on the press. Each image was run in registration with one another, and the solid ink density was varied to produce the continuous tone vii effect. From the press sheets examined, in which there are examples in this report, a high contrast image was produced. One of the main problems in the experiment was differences in emulsion coating on each individual plate. Which resulted in inconsistent exposure times from one plate to another. From repeated continuous plate testing using a .15 density increment tone step wedge as a control guide, it was found that for the same exposure a hardening of the plate coating (and consequently of ink receptivity) corresponding to two steps equaling .30 density difference was to be expected. This made it virtually impossible to get a handle on the correct exposure time needed for the plate. Results from this experiment show, that it is not possible to effectively print a continuous tone image with a negative working plate and or multiple negative plates. This is due to the high contrast of the negative working plate, thus making it suitable for mainly halftone lithographic purposes. vm CHAPTER ONE INTRODUCTION Screenless vs . Halftone Printing Today almost all pictures that are reproduced economically are reproduced using the halftone method. This conversion of a continuous tone original into a pattern of dots degrades the image and introduces problems in the reproduction process. The resolution of the image is limited by the size of the dot, thus were fine detail is needed the use of the halftone process will not achieve the desired results. A effect is also a problem with the halftone process, caused by overprinting halftone images, or by screen interference with irregular shaped images in the subject. Another example of degradation is experienced in color reproduction when pastel colors in originals (which are always continuous tone) usually turn out grayer or less saturated in the halftone reproduction. That this saturation loss is due to the halftone structure can be demonstrated by exposing both continuous and halftone scales onto a photographic color film. The continuous tone highlight steps will have higher saturation than the halftone even though they are matched for lightness and produced by the same dyes. These problems can be eliminated through the use of the screenless process, but the use of the screenless process is limited because of problems controlling the process. There are two systems of continuous tone printing, the collotype process, and random dot printing. These two processes will be explained in the following two sections. Through out this printing" paper, the terms "random dot and "screenless lithography" will be used in reference to the same process. COLLOTYPE PROCESS The collotype plate consists of a differentially light- "image" hardened that picks up ink in direct proportion to the degree of hardening of the gelatin. The plate is coated with a dichromate gelatin, which is applied while the plate is spinning on a plate whirler. This process has not been that popular, because it is very involved, and also the number of impressions off one plate is limited to about two thousand.

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