Page 153 - DLIS006_INFORMATION SOURCES AND SERVICES

Information Sources and Services

Notes Offset Duplicating

Offset machines require a trained operator because the ink and water used in the process have to
be carefully mixed and because the machine must be cleaned regularly. For these reasons, offset
equipment is usually located in a centralized reprographics department.
Although offset masters can be prepared in various ways, the two major types are:
1. Direct Imaging: Typewriting or imprinting directly on the master
2. Imaging on Presensitive Masters: Using aluminium-based or plastic paper sensitized with
a coating that accepts a photographic image
Figure 7.4: Stencil Duplication

Figure 7.5: An Electronic Stencil Image

Source: 210.46.97.180/zonghe/book/197-office%20procedure/chapter6.htm
Direct-image masters are easy to prepare, and corrections can be readily made with a soft pencil
eraser. Imaging on presensitive masters can be accomplished on some electrostatic copiers.
Other methods of master preparation include the use of special master-maker machines as well
as electronic stencil scanner equipment.

A paper master can be used for about 2,500 copies, while an aluminium plate can be used for up
to 50,000 copies, depending on the process used. Because of [he large volume, economy, and
high-quality copy, offset is the favoured method of duplication for companies whose work
warrants the employment of an operator with special skills. Offset will print more clearly than
is possible for any other duplicating or copying method mentioned thus far. The process will

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