Exploring the bronzing effect at the surface of ink layers (Orale)

Mathieu Hébert (1) , Maxime Mallet (1) , Alexis Deboos (1) , Pierre Chavel (1, 2) , Deng-Feng Kuang (1) , Jean-Paul Hugonin (3) , Mondher Besbes (3) , Anthony Cazier (1)

1 LHC - Laboratoire Hubert Curien
2 Laboratoire Charles Fabry / Spim
3 Laboratoire Charles Fabry / Naphel

We i nvestigate t he optical phenomenon responsible f or t he c olored shine that s ometimes a ppears at the surface of ink layers i n t he s pecular direction, o ften ca lled bronzing or gloss di fferential. I t seems to co me from the w avelength-dependent refractive i ndex of t he i nk, which i nduces a wavelength-dependent reflectance of t he i nk-air interface. Our experiments o n c yan and magenta i nkjet i nks confirm this t heory. C omplex refractive i ndices ca n b e ob tained from measurements of t he s pectral reflectance a nd transmittance of a t ransparency film coated with t he i nk. We pr opose a correction o f t he cl assical C lapper-Yule model in order to in clude th e c olored gloss in t he pr ediction of th e s pectral reflectance of an inked paper. We also explored effects of scattering by the micrometric or nanometric roughness of the ink surface. The micrometric roughness, easy to model with a geometrical optics model, can predict the spreading of the colored gloss ov er a l arge cone. E lectromagnetic models a ccounting for t he e ffect of t he na nometric roughness of t he surface also predict the attenuation of short wavelengths observed under collimated illumination.

Mots clés: gloss; ink; printing; Bronzing; complex refractive index

Domaines: Optique / photonique; Optique [physics.optics]

Mathieu Hébert, Maxime Mallet, Alexis Deboos, Pierre Chavel, Deng-Feng Kuang, et al.. Exploring the bronzing effect at the surface of ink layers (Orale). Conference on Measuring, Modeling, and Reproducing Material Appearance 2015, Feb 2015, San Francisco, United States. pp.93980U, ⟨10.1117/12.2076446⟩. ⟨hal-01160299⟩