Medieval stained glass
The subject matter was generally religious in churches, though "portraits" and heraldry were often included, and many narrative scenes give valuable insights into the medieval world.
The thick opaque glass consisted of basic colors such as red, blue, and green, creating geometric designs instead of detailed pictures.
The glass was made from heating sand, lime, and soda ash in a furnace which created a murky color that limited light exposure.
[2] The glass pieces were held together by thick lead strips, creating a graphic and sometimes blocky look compared to later styles.The windows often showed scenes from the Bible and the lives of saints.
[2] While there are not many surviving examples of Romanesque stained glass, some can still be found in churches like Saint-Denis in France and Saint-Sernin in Toulouse.
The late medieval period, often referred to as the Gothic Era, ranged from the 14th to the 16th century and marked a significant evolution in stained glass artistry.
Artists began to employ more refined methods of shading and highlighting, enhancing the three-dimensionality of figures depicted in the glass.
[9] As well as containing potash, beech ash comprises an assortment of compounds including iron and manganese oxides, which are particularly important for generating colour in glass.
Forest glass was manufactured in Burgundy and Lorraine near the Rhein; in Flanders; and in Normandy, in the Seine and Loire Valleys.
It is also possible that 'impurities' could be introduced at the fritting stage within the glass furnace, leading to the addition of further alumina, silica and iron oxides.
[13] These color 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.
Manganese in its fully oxidised state, if not present in too great a mass, will also act as a decolorant of glass if the iron is in its yellow, ferric form.
Experimental manufacture of potash glass emulating Theophilus' recipes has resulted in colors ranging from colorless to yellow, amber, brown, green, blue, pink and purple.
[17][18] Some of the stronger reds, blues and greens that are a feature of medieval stained glass rely on the addition of copper oxides.
In France, in Chartres Cathedral and St Denis in Paris, soda glass has also been found,[21] and no doubt there must be many other examples.
Evidence of recycling Roman tesserae to produce window glass in the 9th century has been identified at the Benedictine Monastery of San Vincenzo, Molise, Italy.
Cox suggests that the examples analysed at York could indeed be 'Roman, or slightly later, glass re-melted in France and imported into England'.
Producing a strong clear yellow could be difficult in early stained glass as it relied upon the careful control of furnace conditions in order to create the appropriate reducing or oxidising environment.
[30] The introduction of silver stain in the early 14th century not only provided a solution to this difficulty, but also allowed greater flexibility in the way in which color could be used.
