Lithographic Printing
How Offset Printing
Works
A Brief History of Printing
• The early " revolution" of moveable printing failed to
ignite the world.
• The process of producing printed versions of Chinese
texts was more time consuming than traditional handinscribing.
• Storing the thousands of characters in the Chinese
alphabet was a problem.
• Pen and oil-based ink was more efficient.
Johannes Gutenberg 1436
• Johannes Gutenberg,
1436 was a profit-minded
goldsmith from Southern
Germany.
• His motivation was
personal profit: he hoped
to get rich by massproducing the Church's
ever-popular
"indulgences".
The Printing Press
• The amount of
information in one
Sunday New York Times
is greater than the
amount of information
an 18th century person
in England would be
exposed to in his
lifetime.
The Passage of Time
• As the New World ( America ) grew in
importance so did the media of printed
communication.
• Gutenberg's technology did not change for
400 years.
• The next revolution was the invention of
continuous rolls of paper.
• Print availability to the public jumped
astronomically.
The Creative Process
Every print piece starts with the creative process.
Writers, editors, graphic designers and artists are the
initial step in the creation of magazines, newspapers,
brochures, flyers, catalogues and other print pieces.
When each article is written, edited and approved with final
art, the pieces are sent electronically to the director of
graphic design for page layout.
From a simple sketch
To a final colour
drawing
When each article is written, edited and
approved with final art, the pieces are sent
electronically to the director of graphic design
for page layout. The director determines what
page a story will appear on, where art will be in
relation to words and, in some publications,
where advertising will appear.
Lithography
• Lithography is a chemical process .
• Lithography depends on the principle that oil and
water do not mix
Images (words and art) are put on plates
which are dampened first by water, then
ink. The ink sticks to the image area, the
water to the non-image area. Then the
image is transferred to a rubber blanket,
and from the rubber blanket to paper.
Pre-Press Production
Before the job can be printed, the document must be converted to
film and "plates." Images from the negatives are transferred to
printing plates in much the same way as photographs are developed.
A measured amount of light is allowed to pass through the film
negatives to expose the printing plate. When the plates are
exposed to light, a chemical reaction occurs that allows an ink-
receptive coating to be activated.
Formatting the page by cutting
negatives and placing them in
place before the plate is made.
A blueprint of the negative and
plate layout, used to check image
positions before printing.
There are different materials for plates,
including paper (which produces a lowerquality product). The best plate material is
aluminium, which is more costly.
Each of the primary colours -- black, cyan
(blue), magenta (red), and yellow -- has a
separate plate. Even though you see many,
many colours in the finished product, only
these four colours are used
The Press Run
The printing process used to print our
newspapers is called web offset
lithography. The paper is fed through the
press as one continuous stream pulled from
rolls of paper. Each roll can weigh as much
as 2,000 pounds (1 ton). The paper is cut to
size after printing. Offset lithography can
also be done with pre-cut paper in sheet fed
presses.
Web presses print at very high speeds and use
very large sheets of paper. Press speeds can reach
up to 50,000 impressions per hour. An impression
is equal to one full press sheet (38 inches x 22 and
three quarters), which is 8 pages of the Express &
Star.
The press has to maintain a constant
balance between the force required to move
the paper forward and the amount of
backpressure (resistance) that allows the
paper to remain tight and flat while
travelling through the equipment..
The Inking Process
Ink and water do not mix -- this is the underlying
principle of offset lithography. The ink is distributed to
the plates through a series of rollers. On the press, the
plates are dampened, first by water rollers, then ink
rollers. The rollers distribute the ink from the ink
fountain onto the plates.
The image area of the plate picks up ink from the ink
rollers. The water rollers keep the ink off of the nonimage areas of the plate. Each plate then transfers its
image to a rubber blanket that in turn transfers the
image to the paper. The plate itself does not actually
touch the paper -- thus the term "offset" lithography.
All of this occurs at an extremely high speed.
Colour control is a process that involves the
way in which the ink blends together, and is
tied closely to the plate registration. The
amount of ink that is released into the units
depends on how much ink is needed to
achieve a desired look. The ink is adjusted
via the control panel that is part of the
overall control console.
Bindery
The bindery is where the printed product is
completed. The huge rolls of now-printed paper
are cut and put together so that the pages fall
in the correct order. Pages are also bound
together, by staples or glue, in this step of the
process.
The "stitcher" gathers, assembles and
staples the magazines (called books)
before they are sent for final
trimming.