Continuous tone printing in silicone from CNC milled
\nmatrices

The researchers at the Centre for Fine Print Research (CFPR) have been reappraising 19th Century print processes for the last fifteen years and Hoskins has published on the continuous tone properties of Woodburytype and its relation to other 19thC processes such as photo-ceramics in previous \npapers to the IS&T PICT (1) and EI in 2003 (2). Since the invention of Walter Bentley Woodbury’s ‘Woodburytype process in 1865 (3), it has been possible to autographically print a true continuous tone black and white \nphotographic image. New research at CFPR builds upon previous research to combining 19th Century Photomechanical techniques with digital technology to reappraise the potential of these processes CNC milled relief printing blocks from which casts are taken will enable a physical and tactile surface quality that more closely resembles the \nautographic surface of the Woodburytype and the three colour carbon printing processes. Therefore this latest research aims to explore the potential of creating coloured pictorial imagery from a continuous tone relief surface. The specific context for the research is to create a surface \nquality and visual appearance that retains the character of the earlier autographic processes, such as letterpress and screen printing, which are undergoing a revival, This is happening for two reasons, one, for their hand crafted content, and secondly, because they create a physical and \ntactile surface that has a subjective quality, hard to define using standard testing methodologies. To prove the potential the research team have been using CNC milled \nimages where the height of the relief image is dictated by creating a tone curve and then milling this curve into a series of relief blocks from which the image is cast in a silicone ink. A translucent image is cast from each of the colour matrices and each colour is assembled - one on top of \nanother - resulting is a colour continuous tone print, where colour tone is created by physical depth of colour. \nA number of factors have come together to enable a reappraisal of continuous tone printing. Software is now readily available that will split a photographic image into a bump map image where the Z-axis corresponds to a set of height steps on a tonal step wedge from black to white. This software is easily transcribed to either a DXF for processing in G Code to CNC (Computer Numeric control) in order mill an image. In addition new silicone materials have become more readily available that can be precisely coloured. The aim is to create a digitally initiated, physical tactile surface that retains the qualities of arlier autographic process which is capable of being transferred to a range of substrates and demonstrates the potential for future research into new methods of continuous tone printing. This research is part of a larger parallel research project to investigate the potential of creating a physically printed relief surface that better \nrepresents the autographic mark making requirements of visual artists and designers. \n(1) Thirkell, Paul, Hoskins, Stephen, 2003, A reassessment of past colour collotype printing achievements as a model for current digital, archival printing practice. IS&T SPIE PICS Digital Photography Conference, Rochester New York \n(2) Hoskins, Stephen, Thirkell Paul, 2003 The relevance of 19th Century continuous tone photomechanical printing techniques to digitally generated imagery IS&T SPIE Electronic Imaging Conference, Santa Clara, California \n(3) Nadeau, Luis, Encyclopedia of printing, photographic and \nphotomechanical processes, 1989-1990 Atelier Luis Nadeau, Canada. ISBN 0969084153

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