RIT 2081 386 - Gravure Process Lab assignment

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2081-386 (786) Gravure Process Lab Assignment — Digital File to Engraving to Proof R. Chung, Professor (083b) 1.0 Introduction Gravure cylinder is a core component of the gravure printing process. We will take a close look at the gravure engraving and proofing workflows. In addition, we will determine screen rulings, %dot area, and %dot growth of a mid-tone cell from digital file to gravure cell to cylinder proof. 2.0 Objectives 2.1 Describe gravure imaging workflows from digital file, Ballard shell engraving, to proofing 2.2 Measure gravure cell configurations by means of photomicrography 2.3 Determine dot growth from digital value to engraving to print 3.0 Materials and equipment used 3.1 CMS and Gravure Research Library (7B-1294) 3.1.1 GRL contents have been cataloged and are searchable via wally.rit.edu. You can browse the collection and use the collection on site. 3.1.2 ProScope (a microscope that captures enlarged images using a CCD camera) 3.1.3 “Gravure Research Agenda: The Journey of a Test Form from Engraving to Proofing,” Gravure, February 2006, pp. 42-47. 3.1.4 Textbook and web sites of key equipment manufacturers 3.2 The instructor will provide the following materials 3.2.1 A digital file of the monochrome test page (from myCourses) 3.2.2 A Ballard shell of the test page (available during lab) 3.2.3 A cylinder-based proof of the test page 3.2.4 A screen ruling indicator 3.3 For report writing, use desktop publishing software packages, e.g., Word, Excel, Acrobat Distiller, etc. Ten 8.5” x 11” color pages are without charge at DPC. 4.0 Gravure digital engraving workflows (Objective 1) 4.1 Read the article, “Gravure Research Agenda: The Journey of a Test Form from Engraving to Proofing,” Gravure, February 2006, pp. 42-47. 4.2 Consult relevant web sites including (a) MDC at www.daetwyler.com for electromechanical engraver and Collage, packaging layout system; and (b) jmheaford at www.jmheaford.com for rotogravure proof press, etc.Lab - Digital File to Engraving and Proofing / Chung 2 4.3 Construct two workflow diagrams to show (a) how a digital file is transformed into an engraved cylinder, and (b) how a cylinder is transformed to an ink-on-paper print. Use information found from section 4.1 and 4.2 to describe key components of the flow charts. 5.0 Close-up view of gravure cells from digital file to Ballard shell to proof (Objective 2) 5.1 Observe with a high-power magnifier and describe characteristics of the gray scale from the supplied digital file, Ballard shell, and its proof. a) The highlight cell is indicated by the proof that renders the smallest printable dots in the gray scale. b) The midtone cell corresponds to the 50% dot area from the digital file. c) The flood point is indicated by the proof that prints like a solid (no more halftone pattern). Typically, the flood point corresponds to 70-80% region of a gray scale. d) The shadow cell corresponds to the 100% dot area from the digital file. 5.2 Use either the Epson scanner or the ProScope microscope to capture highlight, midtone, and shadow steps of an engraved Ballard shell with a (mm) scale included. a) Build a 3 x 3 illustration to show how highlight, midtone, and shadow look like in a digital file, a Ballard shell, and a cylinder proof (Appendix A). b) Describe key components of the illustration in terms of engraving and proofing. c) Explain how rotogravure prints differently than offset from halftone and continuous-tone point of view. 5.3 Screen angle and screen ruling a) Open the highlight of the photomicrograph of Ballard Shell in Photoshop with the distance (in mm) indicated (Figure 1). Figure 1. Highlight of a Ballard Shell photomicrograph b) The baseline is the engraving raster. Screen angle is the angle between the baseline and the line that passing through its shortest distance between cells. Describe the engraving direction and show how to calculate screen angle.Lab - Digital File to Engraving and Proofing / Chung 3 c) Screen ruling is the number of halftone cells per inch or per centimeter. If you measure the distance between two adjacent cells in the screen angle direction, the reciprocal of the distance is its screen ruling. Show how you calculate screen ruling in terms of lines per inch (lpi). d) Verify the screen ruling with the use of a film-based screen-ruling indicator. 6.0 Dot growth or tonal value increase (Objective 3) 6.1 Dot growth is the difference between %dot area of ink-on-paper and the corresponding cell area of the engraving. Dot growth is also called tonal value increase (TVI). When the dot growth is negative, it is dot loss or tonal value decrease. TVI is generally determined by measuring the midtone of a gray scale. 6.2 To determine %dot area from the 50% tint of the engraving (Figure 2), measure the unit area (X, and Y are two sides of the unit area), and the cell area (x and y are two sides of a cell). Figure 2. %cell area (or dot area) of a 50% Ballard shell 6.3 Assuming that the cell approaches to a square, then the % dot area is equal to (xy/XY) x 100. 6.4 Repeat the above step and determine the %dot area of 50% tint from an ink-on-paper proof. Note: Paper dot is poorly defined in comparison to the gravure cell. Thus, measurement errors are inevitable. 6.5 Report the dot growth (a) between the engraved cell and the digital value, (b) between the printed dot and the engraved cell. 7.0 Further notes 7.1 Offer your thoughts about the value of this homework assignment. What would you do additionally to enhance your learning experiences? Citing references used to support your documentation. 7.2 Your homework should be typewritten and double-spaced. The length of your text should be 6~8 pages (8.5” x 11”).Lab - Digital File to Engraving and Proofing / Chung 4 7.3 Bonus (20 points): (1) collect print samples containing letter ‘a’ in 12 point Times printed by offset, gravure, flexo, electro-photographic, and inkjet printer, (2) make microphotographs of each, and (3) place them in a 8.5 x 11 page with captions. 7.4 Submit your lab report on time in hard copy in the class and digitally in myCourses drop box. Appendix A. Enlarged view of digital data, engraved cell, and proof at highlight, midtone, and


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