Fig. 21
a Comparison of the original purple glass with a probable later addition. b Comparison of four stained yellows, characterized by a shift of the silver nanoparticles band from 420 (light yellow) to 450 nm (intense yellow); c Comparison of blue glass, stained yellow and the combined layers. d Comparison of green glass, stained yellow and the combined layers. The band’s position of the main chromophores are indicated. Figure 20a shows the points where the spectra were taken