Operating Manual

OPERATING MANUAL
24.2 Measuring patterns
The pattern measurement should take place on the same homogeneous background (e.g. white
cardboard) as that used for comparison between the pattern and the color reproduced.
Only unit types with small measuring field: When measuring coarsely structured patterns, multiple
measurements must be carried out. By observing the average value continuously displayed on
the screen, you can judge when enough measurements have been made. As a rule of thumb, you
can quit when the Lab average displayed deviates by less than dE = 0.2.
24.3 Colorant calibration series
24.3.1 General
The colorants used for mixing a pattern have to be made known to the computer in the form of
colorant calibrations. A colorant calibration consists of a certain number of proportionately different
mixtures of a colorant with transparent white (varnish, binder, thinner, etc) on a substrate
(print carrier). In a colorant calibration series, we combine a selection of calibrations of different
colorants in which the same substrate, the same transparent white and the same manufacturing
process were used. As a rule, one colorant calibration series is allocated to one assortment.
Colorant calibrations should correspond as closely as possible to normal printing conditions. For
example, the ink film thickness used in the colorant calibrations should be in the same order of
magnitude as that applying in ordinary printing. It is clear that colorant calibrations play a vital
role. Incorrect or inaccurate calibrations usually result in unsatisfactory recipes. Reproducibility
is also crucial. Unless the printing process remains constant, the recipe calculation is a waste
of time.
24.3.2 Absorption and scattering of an ink
The physical characteristics of an ink are determined by absorption and scattering capacity. If an
ink (pigment, dye) has only the property of absorption, the measuring values (remissions) of the
concentration grades on white substrate are sufficient for calculation of the optical data.
An ink with no scattering (only absorption) is characterized by the fact that it is invisible if applied
to a black substrate.
If an ink (pigment) possesses scattering capacity (e.g. opaque white), measured values of
concentration grades on black substrate are required to calculate the optical data. It is then
recommended to carry out colorant calibration on a contrast substrate.
182
24 • Application notes