| Titre : |
Shades of difference : Visual and instrumental methods of colour assessment analysed |
| Type de document : |
texte imprimé |
| Auteurs : |
Werner Rudolf Cramer, Auteur |
| Année de publication : |
2018 |
| Article en page(s) : |
p. 34-39 |
| Langues : |
Anglais (eng) |
| Catégories : |
Colorimétrie
Evaluation visuelle
Mesure -- Instruments
vision des couleurs
|
| Index. décimale : |
667.9 Revêtements et enduits |
| Résumé : |
Methods of assessing colour and colour differences visually and instrumentally are discussed and compared. Preferred methods of carrying out visual colour assessment are described and explanations are offered for why visual and instrumental assessments may sometimes seem to give conflicting results. |
| Note de contenu : |
- Measurement angles and correlation problems
- An organised approach to visual matching
- The principle of reversibility - and some exceptions
- Instrumental assessment : geometrical considerations
- Angle-dependent behaviour of effect pigments
- Appearance of metallic and effect pigments compared
- Visual and instrumental aspects summarised
- Fig. 1 In this example of visual observation, the starting position at the window is + 15° for illumination and -15° for observation, i.e. the difference angle between illumination and observation is 30°C
- Fig. 2. Tilting the panel up, the angle of illumination increases and the aspecular (difference angle between observation and gloss) also increases
- Fig. 3. The observation angle increases when tilting the panel down. In the first steps the aspecular angle is negative, i.e. the observation angle is opposite to the gloss angle
- Fig. 4. Tilting the panel further down, the aspecular angle increases. The difference angle between illumination and observation remains the same
- Fig. 5. Tilting a panel up and down at a window produces the same colour travel
Fig. 6. When tilting a panel by the window, the highest lightness is observed near the gloss and will decrease when the panel is tilted away from this. The same or similar values occur due to principle of the reversibility of light ; deviations reveal the orientation of the effect pigments
- Fig. 7. A portable instrument illuminates at 45°. Measurement is made at -15°, +15°, 25°, 45°, 75° and 10° off gloss
- Fig. 8. If coloured transparent interference pigments are applied to a white background, the colour change from the reflection to the transmission colour is shown when measuring the gloss line. The transition range is between 20° and 30° from the gloss angle
- 9. Application also influences behaviour with regard to lightness. The same coating was applied with and without an additional effect layer. Close to the gloss, the effect layer produces a brighter shade
- 10. Tilting a sample panel at the window or in a light cabin shows the same colour gradient for both tilting down and tilting up. The colour gradient that current portable devices describe corresponds to the gradient when the gloss angle is changed. In all cases, different colour gradients arise from those of the interference |
| En ligne : |
https://drive.google.com/file/d/1TQwGB5nfx6DUSG2me8WmaEWhw62SxsnE/view?usp=drive [...] |
| Format de la ressource électronique : |
Pdf |
| Permalink : |
https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=30494 |
in EUROPEAN COATINGS JOURNAL (ECJ) > N° 4 (04/2018) . - p. 34-39
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Shades of difference in EUROPEAN COATINGS JOURNAL (ECJ), N° 4 (04/2018)
