Gold ruby glass and lustre ceramics are the almost unique examples of physical colors in the cultural heritage. The main physical effect at the origin of their color is the excitation of surface plasmon modes in metal nanoparticles. Moreover, in lustre, interference effects due a multilayer structure add a bright iridescence. The principle of plasmons is recalled in detail and applied to Gold ruby glass. The case of luster ceramics is treated in more detail due to the complexity of the effects involved: plasmon, scattering, interference between specular reflected light beams and also between scattered beams.