ABSTRACT
Metal nanoparticles have been made since antiquity. One example is the fourth-century. Lycurgus. cup,. which. features. a. curious. optical. property:. in reflected light it appears green, but in transmission it appears red [1]. Recent. transmission. electron. microscopy. (TEM). studies. revealed. metal.nanoparticles. embedded. in. the. glass. are. responsible. for. the. colouring..The. nanoparticle. sizes. range. from. 20. to. 100. nm,. and.most. are.made. of. alloyed gold and silver. Although there are many other examples of Roman and medieval coloured glass, these are due to metal compounds or oxides and not metal nanoparticles. The addition of silver and gold to a glass mix may.have.been.accidental.or.part.of.a.more.traditional.colouring.method..The.technique.does.not.seem.to.have.outlasted.the.fourth.century.and.was.not.rediscovered.until.the.seventeenth.century,.with.the.invention.of.ruby. glass [1]. Unlike the Lycurgus cup process the ruby glass process was well understood.and.widely.used..Another.form.of.metal.nanoparticles,.colloidal. gold solutions, was known from the fourth or fifth century BC. However, it was.not.until.the.nineteenth.century.that.causes.of.the.colour.of.ruby.glass.were.attributed.to.the.size.of.the.gold.nanoparticles..
