Coloristics
Under coloristic refers to the evaluation and approval of color (lat.-English. Colors ).
Originally it was only understood to mean visual assessment. In the meantime, the term coloristic mostly refers to visual and / or colorimetric evaluations.
General
Before reliable colorimetric measurement methods were developed, visual assessment was the only way to assess a color. Nowadays, more reliable measurement methods are available, but these, for example with effect pigments , quickly reach their limits. In these cases a visual assessment must be made.
"Colourists are employees in textile dyeing works, lacquer factories and other coloring industries who are responsible for assessing the dyes and sometimes also the color combinations."
methodology
Basics
In the coloristic evaluation, the respective sample is always compared with a defined standard. Such standards can be, for example:
- Colors from a color fan , such as RAL Classic or NCS
- Defined standard samples from a previous production
- Other predetermined color samples, often the case with first-time productions or laboratory settings
Depending on the production effort of the samples and the type of standard, these are colored anew each time, stored as a standard color or saved as an electronic standard in the colorimetry software. The latter method can logically only be used if a reproducible measurement can be obtained colorimetrically.
For the visual assessment of colorants , the new coloration is useful, since in this way the standard and sample can be applied to the same base. This eliminates the optical barrier at the edge and differences can be better assessed. This is not practical in the following cases:
- Color fans - are only available as a colored sample
- Elaborate sample production, for example with powder coatings - the costs are too high
- Mixtures of colorants - would have to be adjusted in terms of color yourself
- Technical limits - in the case of powder coatings or plastics , application on the same test specimen is not possible
Assessment of colors
When assessing colors, the color of the current sample is compared with the standard and, if there is a discrepancy, a nuance is made. This can be done in different ways depending on the color location of the standard and the color order system used.
Assessment of colorants
Colorants, i.e. coloring substances, are mainly tested during their manufacture or as an incoming inspection at the processor (e.g. in a paint factory). The actual concentration in the end use differs depending on the formulation, i.e. it is still unknown at the time of the test. It is therefore not enough to check just one pigment concentration, as the difference between different batches can in turn depend on the depth of color .
In practice, a white lightening (mixture with white) and a full shade ( opaque coloring) are usually checked. Whitening can, but does not have to be, based on a standard color depth .
In the manufacture of colorants, shading is only sensible if the assessment is based on the hue angle .
The assessment should be carried out under a standard light type (mostly D65 - northern daylight). Depending on the application, a second type of light (such as types of light A - incandescent light or F11 - neon tube light) can be added to rule out metamerism .
Evaluation methods according to color range
Achromatic shades, strong to medium lightening
In these areas one usually relies on colorimetric measurement values, as these work very reliably. However, a visual evaluation is often added for information.
Color tones close to full tone
In the area with high chroma (C *) , especially with yellow colors, colorimetrically high deviations can hardly be seen visually. In other color areas (such as blue ) this is the other way around. In principle, these differences can also be seen in white blends, but the effect is less serious.
Transparent shades
Particularly in the case of not completely opaque colors (especially in the yellow, orange and red areas ), the influence of the substrate must be taken into account. Even with completely identical, standardized substrates, small differences in the layer thickness can have a major impact on the measurement. This is also difficult with the visual assessment.
Metallic shades
Metal effect pigments can not be recognized by conventional color measuring devices due to their mode of action ( reflection ). As a result, although the basic color (without effect pigment) can be set, differences in the effect are not recognized. In most cases, an additional visual assessment is used here.
Shimmering colors
It becomes even more difficult if interference pigments are used that change their color depending on the viewing angle (e.g. as a security feature on the 50 euro note ). There are now measuring devices with the option of angle-dependent color measurement, but color adjustment based on the data obtained is still difficult. Here, too, the visual assessment is usually used.
Individual evidence
- ↑ Manfred Richter: Introduction to colorimetry . Walter de Gruyter, Berlin / New York 1981. ISBN 3-11-008209-8