The spectacularly colourful solutions of alkali metals in liquid ammonia have attracted attention of researchers since the 19 th century (for a comprehensive review see Ref. 1, 2). At lower alkali metal concentrations, the resulting deep blue solutions contain localised solvated electrons and dielectrons, 1,3-5 which found practical application as reducing agents for the hydrogenation of aromatic hydrocarbons within the Birch reduction process. At higher concentrations, as the excess electrons become delocalised, the solution turns into a liquid metal with a characteristic golden metallic sheen and conductivity comparable to that of copper. Models of the nonmetal-to-metal transition in liquid systems go back to the work of Landau and Zeldovich in the 1940s and have been experimentally tested on supercritical mercury or alkali metals numerous times. The emerging picture has been that of a sharp transition occurring around the critical point, at which metal clusters of sufficient size are formed in the dense supercritical vapour. However, the behaviour of alkali metals dissolved in liquid ammonia is qualitatively different. In these systems, the nonmetal-to-metal transition happens gradually, merely with an increase of the concentration of electrons dissolved in a dense liquid.