Optics: interference phenomena, exhibited by diffraction gratings. Coloured mezzotint by M. Rapine [1883], after B. Desgoffe. https://www.rawpixel.com/image/13968649/image-background-pattern-circleFree Image from public domain licenseOptics: a soap bubble exhibiting interference colours. Colour mezzotint by M. Rapine, c. 1883, after B. Desgoffe. https://www.rawpixel.com/image/14019333/image-art-circle-lightFree Image from public domain licensePeinture représentant une partie des regalias du Royaume de France, la couronne de Louis XV et l'épée Joyeuse dit de… https://www.rawpixel.com/image/11761646/image-person-art-vintageFree Image from public domain license