Back in the Middle Ages, glass artists used to produce yellowish colorations in soda-lime glasses using mixtures that contained silver salts, clay composites and natural oils. The resulting colour was a characteristic pale yellow known as silver-stain. This coloration is mainly caused by the extinction – absorption and, to a lesser extent, scattering – of light occasioned by silver nanoparticles formed inside the glass. This colouring technique comprises a heat treatment divided in two stages: in the first one, an ion exchange between the silver ions in the mixture and the alkali ions in the glass takes place. This process is called nucleation of silver nanoparticles. The second stage consists of a reduction process that causes the growth of these nanoparticles and the development of colour. This is known as growth and aggregation of nanoparticles. In our work, systematic working procedures have been developed with the aim of reproducing silver-stain in modern soda-lime glasses formed by flotation.
