Xerography and Preservation: Problems and Potential
| Published date | 01 January 1983 |
| DOI | https://doi.org/10.1108/eb047484 |
| Pages | 69-73 |
| Date | 01 January 1983 |
| Author | Nancy J. Bell |
| Subject Matter | Information & knowledge management,Library & information science |
Xerography and Preservation:
Problems and Potential
NANCY J. BELL
A recent issue of the Association of Research
Libraries' Newsletter reported that 70.3 percent of
United States libraries have photocopying machines
for interlibrary loan and on-site user services, pro-
ducing an average of 273,000 page impressions an-
nually.1 This figure, added to the number of copies
made by patrons using coin-operated machines,
copies made for in-house duplication of disserta-
tions,2
and those made as a conservation alternative
for items printed on badly deteriorated or embrittled
paper, indicates our reliance on photoduplication as
a means of transmitting and preserving our cultural
records.
Photoduplication technology dramatically aug-
ments our ability to reproduce, and possibly preserve,
at a reasonable cost research materials for future
scholars. Yet, how permanent are the results of this
process? Will we find that Xerography
—
the innova-
tive technology that started the copying revolution
in 1938 — to be the preservation nightmare of the
future?
Research indicates that in general, the photo-
duplicated image is as stable and permanent as the
paper on which it is printed. This, however, is not
the whole answer to a question complicated by tech-
nology dependent on several inter-related factors.
To best appreciate these mechanisms it is useful to
understand the basic principles of photoduplication
or electrophotography.3
Twenty-one years after the initial patent was
issued for Xerography, the first convenient office
copier capable of making multiple copies was mar-
keted in 1959. This machine harnessed two natural
processes about which much was already known: the
attraction of opposite electrical charges and the in-
crease of electric conductivity in the presence of
light. These basic principles make possible photo-
duplicated copies. The two methods of photoduplica-
tion commonly employed are "transfer," which uses
plain paper, and "direct process," which depends
upon a coated surface paper.
Transfer Method
An image is produced by the transfer method in
the following manner:
1.
A photoconductive surface4 is given a positive
electrical charge by means of a high voltage
power supply.
2.
The image of the document to be copied is ex-
posed by optical means to the photoconductor.
This causes the charge to drain from the surface
in all but the image area which remains unex-
posed and charged.
3.
Negatively charged powders or toners, often a
carbon pigment, are cascaded over the surface.
This pigment or toner electrostatically adheres to
the positively charged image area making a visible
image.
4.
A piece of plain paper is placed over the charged
surface and given a positive charge.
5.
The negatively charged powder image is electro-
statically attracted to the positively charged
paper.
6. The powder image is fused to the paper by heat-
ing, or by the application of a solvent vapor
which partially dissolves the toner and causes it to
fuse to the paper. Xerographic images can also be
fixed by applying pressure to force the powder
into the surface. Non-fusible toner images can be
fixed by applying a coating of transparent plastic
or fixative by spraying the surface.
7.
After the photoconductive surface is cleaned, the
process can be repeated.
Xerographic images produced by the transfer
method just described are considered to be stable5
providing that the photoduplication equipment is
operating properly. Equipment which has not reached
optimum temperatures may produce an image in
which the toner is inadequately fused to the paper
Nancy Bell is an Apprentice Bookbinder at the
Eisenhower Library, Johns Hopkins University. She
serves as LHT Assistant Editor responsible for Pre-
servation Technology.
SUMMER 1983 69
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