ACETATE ~ TRANSPARENCY SHEET
Many of your 1950s/ 60s annuals have illustrations that were 'coloured in'
at the printing stage by having a sheet of thick transparency laid over the
b&w line drawings. This sheet had been painted onto. You will note
that sometimes the colouring does not correspond with image, and is 'all
over the shop' ! This is when the quality control was slack, and the
sheet was not aligned correctly in correspondence with the drawing!
You would have noticed that some coloured artwork does include black
and white block-strips adhered to the borders. These are Registration Marks, for
the use of aligning / synchronizing the colours employed. This is because each
colour (black, red, blue, yellow) is a separate process:
For those who want more technical information on this, the following is as
stated on the freepatentsonline website:
** In colour printing with a colour registration system for the registration of
plural colour images on an image bearing surface, such as a photoreceptor belt
of a colour printer, registration marks are imaged on the image bearing surface,
which registration marks correspond to the colour images and are sensed by a
registration marks sensor. In an initial gross registration mode the system
first automatically images first registration marks, in the form of expanded
chevron targets, which are greatly expanded in the process direction so as to
avoid overlapping marks even if there is initial gross misregistration, to thus
provide wider initial misregistration latitude for the sensor. When an
acceptable initial registration is achieved, the system automatically switches
to imaging more closely spaced and more frequent second registration marks,
preferably regular chevron targets, providing higher registration accuracy.
These registration targets may be generated along opposite sides of the image
areas, on opposite sides of the photoreceptor or other image bearing surface in
the process direction.