page_title: Medieval stained glass
section_title: Inherent colour
hierarchical_section_title: Medieval stained glass / Composition, manufacture and distribution / Colour / Inherent colour
caption_attribution_description: English: Part of a panel in the Jesse Tree window in York Minster, England. It may be the oldest stained glass in England, circa 1170, or possibly as early as 1150. Français&#160;: Partie d'un vitrail de la cathédrale d'York (Angleterre) représentant l'arbre de Jessé. Ce vitrail, datant des environs de 1170, voire 1150, est peut-être le plus ancien d'Angleterre.
context_page_description: Medieval stained glass is the coloured and painted glass of medieval Europe from the 10th century to the 16th century. For much of this period stained glass windows were the major pictorial art form, particularly in northern France, Germany and England, where windows tended to be larger than in southern Europe. In some countries, such as in Sweden and in England, only a fragment of an originally large amount of stained glass have survived to this day.
  Stained glass windows were used predominantly in churches, but were also found in wealthy domestic settings and public buildings such as town halls, though surviving examples of secular glass are very rare indeed. The purpose of stained glass windows in a church was both to enhance the beauty of their setting and to inform the viewer through narrative or symbolism. The subject matter was generally religious in churches, though "portraits" and heraldry are often included, and many narrative scenes give valuable insights into the medieval world.
context_section_description: Inherent colour refers to the colours that may be formed in the molten glass by manipulating the furnace environment. Theophilus describes molten glass changing to a ‘saffron yellow colour’ which will eventually transform to a reddish yellow on further heating, he also refers to a ‘tawny colour, like flesh’ which, upon further heating will become ‘a light purple’ and later ‘a reddish purple, and exquisite’.
  These colour changes are the result of the behaviour, under redox conditions, of the iron and manganese oxides which are naturally present in beech wood ash.
  In the glass melt the iron and manganese behave as follows:
   
  In an oxidising environment metal (and some non-metal) ions will lose electrons. In iron oxides, Fe²⁺ (ferrous) ions will become Fe³⁺ (ferric) ions. In molten glass this will result in a change in glass colour from pale blue to yellow/brown. In a reducing environment the iron will gain electrons and colour will change from yellow/brown to pale blue. Similarly manganese will change in colour depending on its oxidation state. The lower oxidation state of manganese (Mn²⁺) is yellow in common glass while the higher oxidation states (Mn³⁺ or higher) is purple. A combination of the two states will give a pink glass.
  As the manganese and iron may each be in different states of oxidation, the combination of the two can result in a broad range of attractive colours. Manganese in its fully oxidised state, if not present in too great a mass, will also act as a decolourant of glass if the iron is in its yellow, ferric form. The two colours in effect cancel each other out to produce a clear glass.
  Experimental manufacture of potash glass emulating Theophilus’ recipes has resulted in colours ranging from colourless to yellow, amber, brown, green, blue, pink and purple. Variation in colour hue and depth would also probably be affected by the source of the beech wood ash, depending on the soil chemistry where the beech tree grew, the age of the tree and the climate conditions.
  Some of the stronger reds, blues and greens that are a feature of medieval stained glass rely on the addition of copper oxides.
caption: Detail of the Jesse Tree panel from York Minster
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