Medieval Stained Glass
One of the most documented examples of nanotechnology known in history is medieval stained glass artisans. They were the first nanotechnologists, as they, although unaware, trapped gold nanoparticles in the 'glass matrix' in order to generate the ruby red colour in the windows. They also trapped silver nanoparticles which gave it a deep yellow colour. As in today's finding it is the size of the metal (whether it be gold or silver) nanoparticles that define the variations in colour [Refer to Figure 1.1 for a chart of the different colours and according sizes]. This example of colour change is a testimony to the dramatic change in material properties at the nanoscale.
The Lycurgus Cup
The Lycurgus Cup was made by the Romans at around the fourth century (AD). An interesting factor about the cup is that the colours of the cup can change. When it is looked at in reflected light or daylight, it appears green. However, when light is shone into the cup and transmitted through the glass, it changes colour to red. What gives it these unusual optical properties is due to the glass containing tiny amounts of colloidal gold and silver. Colloidal gold is nanoparticles of pure gold suspended in water or a solution.