Reference Book
The primary advantage of a multi colour press is that more than one colour can
be printed in a single pass through the press. Without a multi colour press, the
press sheet would have to be printed with one colour, then replaced on the
infeed table and run through the press again for each additional colour required.
Not only is this a time-consuming operation, but it can lead to mis-register
problems. Paper is not diamensionally stable. When passed through the press,
each piece of paper is subjected to both ink and water. Moisture from the
dampening system tends to make the paper stretch, then shrink as it dries.
When a single-colour press is used for a multi-colour job, some time will
elapse before the paper is put through the press for the next colour. During
this time, the paper may shrink, stretch, or warp slightly owing to humidity
and other environmental conditions in the printing plant. The overall effect is
that on the second pass through the press, the paper is not exactly the same
size as it was on the first pass through the press. This makes critical registration
more difficult and sometimes impossible. A multi-colour press can reduce
this problem.
One additional advantage of a multi-colour press is that the press operator can
judge the quality of the printed sheet immediately as it comes off the press,
and he can make press adjustments based on this evaluation. When printing
process colour, all four colours must be printed with the correct press settings
if the colours on the final job are to be correct. When a single-colour press is
used to print process colour, improper press adjustments during the printing of
the first colour may only be discovered as the fourth colour is being printed.
By this time, all of the sheets have been printed with three colours and it is too
late to make any corrections. The whole job will have to be scrapped and
reprinted.Sequence of colours
Process colour involves overprinting of four seperate images. During printing
the sequence of colours can vary depending on the type of ink, paper, or press
or on the preference of the operator. There are several common sequences.
The sequence of cyan, then magenta, yellow and finally black is often used.
Yellow, magenta, cyan and black is another frequent colour order. If cyan is
first printed on the sheet, details will usually be carried across the sheet
whereever the final image appear and it is relatively easy to fit all colours after
cyan into their proper position. One disadvantage of using cyan as first colour
is with the quality of ink laid down on the first pass through the press. All
following colours will tend to dry slowly because the paper has already absorbed