text: Tollens' reagent is also used to apply a silver mirror to glassware; for example the inside of an insulated vacuum flask.  The underlying chemical process is called silver mirror reaction.  The reducing agent is glucose (an aldehyde) for such applications.  Clean glassware is required for a high quality mirror. To increase the speed of deposition, the glass surface may be pre-treated with tin(II) chloride stabilised in hydrochloric acid solution.
  For applications requiring the highest optical quality, such as in telescope mirrors, the use of tin(II) chloride is problematic, since it creates nanoscale roughness and reduces the reflectivity.
  Methods to produce telescope mirrors include additional additives to increase adhesion and film resilience, such as in Martin's method, which includes tartaric acid and ethanol.