Viridian is the colour between green and cyan on the colour wheel, and in hexidecimal code for computer display is #40826D. Pure chromium oxide has excellent stability but make a dull pigment: viridian is a hydrated chromium (III) oxide i.e. with water molecules which turn the chromium ions to a more attractive hue.The Parisians Pannetier and Binet first prepared the blue-green pigment known as vert émeraude (viridian) in 1838. In 1859 the French chemist C.E. Guignet developed an alternative method of manufacture which lead to the pigment's use by artists on a larger scale: it was adopted by the Impressionist painter Paul Cézanne (1839-1906) in paintings such as Mountains seen from L'Estaque and House of the Hanged Man. George Field described it as:
Field's Chromatography or Treatise on Colours and Pigments as Used by Artists
"Viridian... a still later addition to the palette, and the only permanent green which can be described as gorgeous, being not unlike the richest velvet. Pure and clear as the emerald, it may be called the Prussian Blue of Greens, of such richness, depth, and transparency is it. In hue of a bluish-green, its deepest shades verge on black, while its light tints are marked by transparent clearness unsurpassed. No compound of blue and yellow will afford a green at once so beautiful and stable, so gifted with the quality of light, and therefore so suited for aerial and liquid effects. Used with aureolin, it gives foliage greens sparkling with sunshine; and, fitly compounded, will be found invaluable for the glassy liquidity of seas, in painting which it becomes incumbent to employ pigments more or less transparent.
"The general failing in the representation of the sea is, that instead of appearing liquid and thin, it is made to bear the semblance of opacity and solidity. In order to convey the idea of transparency, some object is often placed floating on the wave, so as to give reflection; and it is strange that we find our greatest men having recourse to this stratagem. To say it is not true in all cases, is saying too much; but this we do assert, that as a general principle it is quite false, and we prove it in this way: water has its motion, more or less, from the power of the wind; it is acted upon in the mass, and thus divided into separate waves, and these individually have their surface ruffled, which renders them incapable of receiving reflection. The exception to this will be, where the heaving of the sea is the result of some gone-by storm, when the wind is hushed, and the surface becomes bright and glassy. In this state, reflections are distinctly seen. Another exception will be in the hollow portion of the waves, as they curl over, and dash upon the shore."