New Star Software Collection/NSS_Collection.iso/3-251 oo2 english program/1.ima/RR.ZIP/PPRINTIN.SEQ

Text File | 1991-06-30 | 4.6 KB | 85 lines

Few inventions have exerted such an enormous influence on the
course of world history as printing. Until its development some
500 years ago, books had been both scarce and expensive, for two
main reasons. First, the paper used in books (parchment) was
made from animal skins and so was neither cheap nor abundant.
Second, books had to be written by hand or else printed using a
very primitive method with wooden blocks. The former problem was
solved by the introduction into Europe of a method of making
paper from rags. The latter problem was solved in the 15th
century by the invention of movable type, which led to the
development of the printing press. Although the exact origins of
this invention are not clear, it was probably first perfected by
a German named Johannes Gutenberg.

Before Gutenberg's time, printing was done by cutting out
letters, words and sentences on wooden blocks which were then
dipped in ink . Once the printing job was finished, the blocks
were thrown away. It is not hard to understand why such a method
would be wasteful and costly. Gutenberg developed a method of
using reusable, independently movable type characters made of
metal and set into a forme, or metal frame. This process is,
therefore, called typesetting. These type characters could be
assembled for a particular printing job, separated, then re
assembled for the next job. With this invention, books could be
printed cheaply, quickly, and in large numbers.

The process developed by Gutenberg is still used today and is
known in the printing industry as letterpress. It is no longer
the only, or even the major, method by which printing is done,
however. Two other processes--offset lithography (sometimes
simply called "offset" or "lithography") and gravure--are also
widely used. Whereas letterpress prints from the raised surfaces
of metal type, lithography uses plane surfaces

which are divided chemically into printing and non-printing
areas. The gravure technique uses recessed surfaces: thousands
of tiny cells hold in ink on the gravure plate until contact is
made with the paper. These cells are produced photochemically or
electronically. In all three processes, the printing may be done
either on cut sheets of paper or on paper in continuous reels.
The printing surface, as distinct from the printed surface, may
be flat or cylindrical in letterpress; in gravure or offset
lithography, it is almost always a cylinder.

The letterpress technique has several advantages. It is ideal
for printing texts when an extremely sharp, clear image is
needed. What is more, corrections are possible, and easy to
make, right up until press time. Finally, whereas other
processes require the making of plates, which may be time
consuming and costly, letterpress printing does not.

The major advantage of offset lithography is that it may take
almost any printed image as its starting point. Thus, the book
you are now reading, with its illustrations, can be reproduced
directly by means of the offset process, and no further typing
or typesetting is required. Offset plates are prepared by
photographic techniques. Many printers also prefer lithography
because its thin aluminium plates are more easily and cheaply
stored than letterpress formes.

Gravure printing, like offset, uses plates rather than formes.
It is especially well-suited for the printing of colour
illustrations and produces extremely sharp images. However, the
preparation of gravure plates is a long and expensive process.
Gravure is still used for the printing of stamps, bank-notes,
security certificates, some colour magazines and mail order
catalogs, but offset printing has improved to the point that it
may soon replace gravure altogether.

Now, new technology Is available and the printing industry has
started to use it. The current growth areas in printing rely
heavily on photographic and electronic techniques; in none of
them is direct printing from metal type involved. Lithography,
for example, is one way in which conventional typesetting has been bypassed.
Computers are also entering the industry as never before:
optical character recognition can now be used for scanning
typewritten or handwritten material and translating it
instantaneously into printed form. Other new and revolutionary
techniques include inkjet printing (such as that used for some
computer printouts) and electronic colour scanners (for accurate
colour reproduction). The latest computer printing technology
uses laser printers. On the whole, the printing industry is now
increasingly reliant on photographic and electronic, rather than
purely mechanical, processes.