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Material World
Object

Stained glass window

Metal oxides dissolved in glass, held in lead, and the reason medieval Europe knew a great deal about colouring materials.

Stained glass is coloured in the melt rather than on the surface: metal compounds dissolve in the batch and colour the glass throughout. Cobalt gives blue at very low concentrations, copper gives red or turquoise depending on the furnace atmosphere, manganese gives purple, iron gives green and brown, and gold gives the deep ruby known as cranberry glass.

The pieces are cut and joined with lead cames, which is a structural choice as much as an aesthetic one: lead is soft enough to be worked around irregular shapes and to accommodate the movement of a large panel in wind and temperature. Painted detail is applied as a vitreous enamel and fired on.

History

Coloured glass is ancient; architectural stained glass on a large scale belongs to Gothic Europe from the twelfth century, and depends on the architecture as much as the glass — flying buttresses moved the load off the walls and left space for windows the size of a building's side.

Chartres and Sainte-Chapelle are the surviving demonstrations. The blue of Chartres has been the subject of long argument about whether the recipe was lost; the current understanding is that the medieval glass differs in composition and in the way it has weathered rather than in a secret that vanished.

Cultural significance

It was a medium of instruction before it was decoration, in a period when most of the audience could not read. That is a real materials fact: the windows had to be legible from thirty metres, which sets the palette, the scale of the figures and the width of the lead lines.

It is also where a great deal of practical knowledge about colouring materials was accumulated and transmitted, centuries before any of it could be explained. A glassmaker who knew that copper gives red in a reducing furnace and green in an oxidising one had a working theory of something that would not be understood until the twentieth century.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is made of

  • Soda-lime glass — material · coloured in the melt by metal oxides rather than painted on the surface
  • Lead — element · the cames holding the pieces, soft enough to work around irregular shapes and to move with the panel
  • Cobalt — element · the blue, at concentrations low enough that a very little went a very long way and was traded accordingly

Sources

  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Stained glass window back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Stained glass window → is made of (the blue, at concentrations low enough that a very little went a very long way and was traded accordingly) → Cobalt → is sourced from (much of world supply arrives as a by-product of copper mining rather than from cobalt-first operations) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Stained glass window → is made of (coloured in the melt by metal oxides rather than painted on the surface) → Soda-lime glass → is produced by (drawn off the tin bath as a sheet flat on both surfaces) → Float glass process → takes as input (with difficulty, which is why flat borosilicate costs several times what window glass does) → Borosilicate glass → is produced by (with boron oxide replacing most of the soda, which is what drops the thermal expansion to a third and lets a hot dish go into water) → Glass melting → takes as input (as the stabiliser, and without it a soda-silica glass would slowly dissolve in water) → Limestone
  • Stained glass window → is made of (the cames holding the pieces, soft enough to work around irregular shapes and to move with the panel) → Lead → is produced by (as the oxide, from galena, by the same route) → Roasting → takes as input (a copper sulfide; roasting drives off the sulfur that would otherwise prevent reduction) → Chalcopyrite
  • Stained glass window → is made of (coloured in the melt by metal oxides rather than painted on the surface) → Soda-lime glass → is composed of (as silica sand, the principal former) → Quartz
  • Stained glass window → is made of (coloured in the melt by metal oxides rather than painted on the surface) → Soda-lime glass → is produced by (drawn off the tin bath as a sheet flat on both surfaces) → Float glass process → takes as input (the batch is essentially sand, with soda ash to lower the melting point and limestone to stop the result dissolving in water) → Sand → is sourced from (the ultimate source of most of it — granite weathers, the feldspar becomes clay and washes out, and the quartz survives as grains) → Granite → is composed of (by volume, alongside feldspar and lesser mica) → Quartz
  • Stained glass window → is made of (the blue, at concentrations low enough that a very little went a very long way and was traded accordingly) → Cobalt → is sourced from (much of world supply arrives as a by-product of copper mining rather than from cobalt-first operations) → Copper → is extracted from (the principal copper ore worldwide) → Chalcopyrite

These are the most distinct paths back. Stained glass window can be traced through others besides.