We are working on some sintered ceramic samples that have different surface colours. Energy dispersive X-ray spectroscopy does not yield surface compositions that would explain a change in colour. We can see that some samples have different surface roughness that is associated to surface porosity due to incomplete sintering and grain growth. Some of the samples appear to have have grain/pore size on the same scale as the red portion of the visible spectrum. Thus I am thinking that some samples appear blue as the longer wavelengths may be being absorbed, whereas the shorter blue wavelengths are being reflected to give a blue appearance under natural light. I have searched literature for surface roughness induced colour shift but have not found anything useful. Can anybody point me to some relevant references? Thank you.
Dear Dr. Jacob Ross Bowen,
I suggest to have a look at the following interesting papers that could confirm your hypothesis:
-The effects of surface gloss and roughness on color constancy for real 3-D objects
Jeroen J. M. Granzier; Romain Vergne; Karl R. Gegenfurtner
Journal of Vision, Vol.14, 16 (2014). doi:https://doi.org/10.1167/14.2.16
Available at: https://jov.arvojournals.org/article.aspx?articleid=2121504
-Experimental Relationships between Surface Roughness, Glossiness and Color of Chromatic Colored Metals
Makiko Yonehara, Tsutomu Matsui, Koichiro Kihara, Hiroaki Isono, Akira Kijima Toshio Sugibayashi
MATERIALS TRANSACTIONS 45(4):1027-1032 (2004). DOI: 10.2320/matertrans.45.1027
Available directly in Research Gate at: https://www.researchgate.net/publication/240795139_Experimental_Relationships_between_Surface_Roughness_Glossiness_and_Color_of_Chromatic_Colored_Metals
Best regards, Pierluigi Traverso
Dear Dr Jacob Ross Bowen,
The seemingly paradoxical chemical-independant color variation is an interesting observation, which we have also encountered when sintering multiphase aluminium zinc oxide ceramic targets at various sintering temperatures.
https://www.researchgate.net/publication/337091819_Microstructure_evolution_in_high_density_AZO_ceramic_sputtering_target_fabricated_via_multistep_sintering
As Mr Pierluigi Traverso has pointed out, the surface roughness can alter the reflected optical profile. In addition, it is plausible that chemical nonhomogenity, band gap variation as well as the porosity itself can all lead to alterations in how we percieve the color of the ceramic sample.
In fact, porosity is sometimes purposefully applied for engineering nanoporous alumina photonic crystals, for which the Maxwell Garnett approximation can provide a general explanation.
https://www.researchgate.net/publication/303771151_Introduction_to_the_Maxwell_Garnett_approximation_Tutorial
https://www.researchgate.net/publication/258736162_Constrained_Order_in_Nanoporous_Alumina_with_High_Aspect_Ratio_Smart_Combination_of_Interference_Lithography_and_Hard_Anodization
Good luck
Ali
Dear Pierluigi Traverso and Ali Reza Jahangiri,
Thank you both for the prompt replies and suggestions for for reading! I will take a look at these papers.
Kind regards
Jacob
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