A coloured appearance, under a determined light source with determined observation conditions, is analysed with 3 dimensions or 3 parameters: hue, chroma and lightness. This coloured appearance can be uniform and unchanging with the observation angle of the analysed surface or object: it is classically opaque colours, translucent colours or transparent colours. Special aesthetic effects colours are different from the previous ones, and their appearance changes with the observation conditions: light source and inclination of the surface or object. They are" out of the ordinary"... Depending of the respective geometric positions of the light source, the object and the observer, the metallized or nacreous or spangled effects lead to changes in hue and/or in chroma and/or in lightness with more or less glittering. The more recent effects allow changes almost continuously in hue, chroma and lightness, when the observation conditions are changing or when the observer looks at a very shapely surface. Here are some use examples: cosmetics (eyelids blushes, lipsticks, nails varnishes...), Paints (automotives, buses, bicycles, motorbicycles, head casques...), mobile phones, household appliances industry... The lecture will begin with the definitions of the Flip and Flop index and the respective geometric positions object I light source I observer, versus the type of light used. Then the measurements with the multiangles equipments and the meaning of the different angle will be explain. The different types of special effects pigments and their functioning mechanisms will be detailed: aluminium pigments, pigments based on transparent substrates (mica - silica - alumina - liquid crystals), pigments based on opaque substrates (aluminium, iron oxide). The parameters influencing the Flop index and the colour matching will concern the last part of the presentation.
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