This process uses a flat aluminium printing plate and works on the
principle that oil and water do not mix. The image is transferred onto
the plate photographically through ultra-violet light shining through
a negative. The plate is then washed with a chemical that makes the
image area attractive to the oily ink. The non-image area is later
dampened with water to repel the ink. To lengthen the life of the
printing plate and prevent the paper becoming damp through contact
with the water, a rubber blanket transfers the ink from the plate to
the paper. This is called offset lithography and is used for most
commercial printing such as books, magazines, brochures etc. If rolls
of paper are used rather than flat sheets the process can be speeded
up and higher volumes printed. This is called web offset lithography.
* 4 colours(process colours) - black, cyan, magenta and yellow - are
used to build up all other colours and tones.
* Ready mixed (spot colours) are used for one, two or three colour
* Additional spot colours are sometimes used for special colours
such as gold.
* Economical for between 1,000 and 1,000,000 copies.
* Good quality can be achieved.
This uses an engraved plate where the printing surface is lower than
the main area of the plate. The image is photo-etched onto
copper-faced printing cylinders which are expensive but will stand up
to very long print runs. The engraved recesses are then filled with
ink, the surface is scraped clean and then the ink is transferred to
an impression cylinder in much the same way as lithography. The
process can be sheet fed or roll fed, as used for higher quality
printing and very high volumes such as magazines and books. Limited
edition fine art prints and postage stamps can be done this way but
are reflected in the high costs.
* 4 colours (process colours) - black, cyan, magenta and yellow -
are used to build up all other colours and tones.
* Excellent for half tones.
* Economical for between 500,000 and 5,000,000 copies.
* High quality can be achieved.
This type of printing is much less common these days but is still
economical for small print runs. It uses a raised surface for printing
off, usually made of aluminium sheet. The ink is rolled onto the plate
and this is transferred directly to the paper. The quality is very
good but the range of available type is very limited. It is used for
items such as invitation cards, and short runs of books.
* Colours generally limited to one or two ready mixed colours.
* Economical for between 500 and 5,000 copies.
* High quality in terms of sharpness.
* Limited typefaces available.
* Used mainly for text only - not suitable for half tone