Computer Imaging Technology: The Process of Identification
Narelle Jarry
Introduction
In 1930, not anticipating the advent of the computer, Paul Valery said that the arts could no longer escape the influence of modern science and technologies. Great innovations would change all techniques of the arts influencing creativity and perhaps going so far in the end as to transform the concept of art itself (1). Today, with it's wide spread use, the computer appears to have become an innovation of this sort.
Over time, many technological innovations have influenced the arts. No one would have anticipated how far reaching Senefelder's laundry list dashed off on an inking slab in 1796 would be, yet today we think of lithography not only as a means of commercial printing but also as a fine art print-making process. Similarly, with the advent of photography, the challenge of justifying an art which relied so heavily on a machine became real. Edward Weston said of photography "Wouldn't it be funny, if one could pierce the future, and find that [photography] was accepted as a great art form, because the mind-- 'intelligence', that is --could be directed through a machine in a purer form, without the bungling interference of the hand!" (2). Warhol went further - not only did he advocate the use of modern technology in art, but commented that he'd actually like to be a machine. Unselfconscious about his reliance on machines, Warhol's soup cans and Coke bottles, both in their everyday subject matter and mechanical methods of execution, are prime examples of an artist working with, and reacting to, the technology afforded him by the time in which he worked.
The rapid growth of the computer graphics field, and the dramatic changes it has undergone, make it impossible to identify all of the processes one can employ. At times it is impossible to even ascertain if the computer has been used at all. Initially, output or hard copy was not of importance for computer artists, who in the 50's merely photographed their computer screen. By the 80's, many artists were outputting onto 35mm film and either projecting the image onto canvas, having it photoengraved or printing in traditional photographic format.
It will be, and for some of us already is, the responsibility of the conservator to maintain and care for these collections. To do that effectively we must understand, first of all, what we're looking at. The 'digital imaging' profession classifies these print technologies in a similar manner to traditional print-making processes -- relief, intaglio, planographic and serigraphic. The four digital systems investigated here are: thermographic, ink jet, electrographic and fujix printing systems.
Thermographic Printing Systems
These systems rely on the application of heat to form an image. Specifically, thermal transfer systems, introduced in the late 1970's and early 80's, employ heat to transfer colorant from a carrier to a final substrate. Each color is transferred individually, the paper passing under the printhead three times allowing for the transfer of cyan, magenta and yellow colorants. There are a number of processes which fall into this broad class of printers. The two currently investigated are only related in their use of heat to transfer colorant.
Direct Thermal Transfer (commercially known as: thermowax)
This is an inexpensive system which produces fairly low resolution images. A sheet of smooth paper and a donor ribbon with a thermoplastic, wax containing ink layer, move in contact under a thermal printhead. The application of heat through the donor ribbon causes the ink to release and transfer onto the paper.
Identification
The opaque thermoplastic ink has a high wax component, and under raking light the surface looks waxy.
The image is visibly made up of cyan, magenta, yellow and often black dots, arranged in a pattern relating to the movement of the printhead.
Figure 1: Detail of direct thermal transfer print at 50x magnification.
The individual colors can be seen laid down beside one another, requiring your eye to mix them (similar in concept to off set lithography). (See Figure 1)
Dye Diffusion Thermal Transfer (commercially known as: dye sublimation)
Dye diffusion thermal transfer prints are billed as near photographic in quality. A ribbon, carrying dye based colorants, and a sheet of chemically-coated paper, move in contact under a thermal printhead. The application of heat makes the colorant gaseous, which then condenses on the support. The amount of dye transferred from the ribbon is determined by the amount of heat supplied by the printhead, allowing for what the industry terms: 'continuous' tonality.
Identification
These prints have a gloss.
Figure 2: Dye diffusion thermal transfer print in specular light.
There is a distinct topography revealed in specular light. (See Figure 2)
Poor registration in the transfer of dye layers may cause one color to be visible at an edge.