Cristallo in artistic glass production is transparent glass, homogeneous, absolutely colorless. The secret of quality in cristallo, which is glass, is the purity of the raw materials, the use of bleaching agents, the preparation of the vitrifiable mixture, the fusion process. In the middle of the XVth century Murano invented a pure and colorless glass, which for the first time in history was called cristallo and was later imitated in other European countries.In contrast with Nordic crystal, which has a concentration of lead oxide and today must be subject to strict controls of the fumes deriving from its fusion, its contact with foods and its waste disposal, Murano cristallo is a sodic-calcic glass whose principal components, aside from silica, are sodium oxide and calcium oxide. Murano has always remained faithful to sodic cristallo because it is most suitable for the production of particularly light blown objects which require long working processes.Opaque colored glass is obtained on the basis of the same principles but with a base of white opaline glass and a larger amount of raw coloring agents.