What is Glass?
Glass is a natural material and in its simplest form is silica, which occurs in sand, quartz, and siliceous lava. Glass is actually a super-cooled liquid, which is so viscous (i.e. stiff) at room temperature that it effectively behaves like a solid.
Man-made glass has evolved over several thousand years and most glass today is produced with various additives such as a flux of soda or soda ash and a stabiliser such as lime heated together with the raw silica to produce a bubbling liquid as silica melts (which gives off various gases). This liquid can be rolled, floated, pressed, blown and cast into a multitude of shapes and forms.
The cooling of the glass is carefully controlled to ensure that tensions that can cause breakage are not set up within the material. This important process is called ‘annealing’.
Stained glass is usually created from a blown bubble of molten glass which is then spun and flattened (bullion or crown) or moulded and stretched into a cylinder, the ends of which are cut off, then split down one side and opened out to form a sheet. A pure mix of silica, soda ash and lime will produce clear colourless glass. By adding various oxides in the ‘melt’ wavelengths of light will be prevented from passing through the glass. The wavelengths of light not stopped by the glass will give it its colour.
What is the Origin of Glass?
Exactly where glass originated is not known, although there is evidence of Egyptians using decorative glass as early as three thousand years BC. Their discovery of glass is thought accidental, but the Egyptians were instrumental in discovering a process for making clear glass, which could be cast or fused.
Expensive vessels and jewellery were made from the new prestigious material. The technology for making and treating glass spread from the Near East to all parts of the Mediterranean and the advent of glass-blowing using a metal pipe, and use of the furnace, meant a wide variety of bottles, dishes, vases, etc. could be produced easily. In the first century AD glazed (i.e. clear) windows were employed in the houses of the wealthy Romans and Byzantines, particularly in Northern Europe. Some of the earliest examples of copper lights have been excavated in Pompeii.
Where did Stained Glass Originate?
Stained glass only came into being when Christian beliefs had spread to Europe and architecture advanced to the point where the possibility of vistas or windows in church buildings became a reality.
In the meantime glass art forms such as mosaic had come to the fore. Expression of faith inspired these new art forms. In the sixth century coloured glass glazing was used in St Martin of Tours in France. This glass was not painted however, and we have to look to examples from four centuries later in Germany, including excavations at Lorsch Abbey and Ausburg cathedral to find painted and coloured glass with discernible style and technique along with leaded framework, thought to have derived from goldsmiths’ techniques.
So it can be said that the origins of stained glass as an authentic art form began in Europe inspired by Christian imagery and evolving glass technology, including addition of oxides in manufacture – such as copper, cadmium and cobalt to create greens, reds and blues. The art flourished as a beautiful and powerful visual means of story telling for the illiterate populace to convey the gospel in cartoon form and became more prolific and refined as the architecture progressed.
The Gothic period allowed the creation of large curtain walls of stained glass in many colours and applied techniques such as glass painting, requiring sections to be painted and then fired in a kiln. With the discovery of silver oxide it was possible to create a wide palette of hues from pale yellow to bright orange and artists could for the first time ‘apply’ colour to individual elements in a design and not be confined just to the colours of the glass sections chosen at the start of the design process. It is from this application of yellow stain using oxide of silver that we have derived the term ‘stained glass’ and it is because of the use of glass paints in this context and in particular yellow stain within a leaded glass design that we can describe a panel or window truly as Stained Glass.