| From the 10th or 11th century, when
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| | commercially produced and widely used
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| stained glass began to flourish as an
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| | today, under the name of cathedral glass,
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| art, glass factories were set up where
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| | although it was not the type of glass
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| there was a ready supply of silica, the
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| | favoured for stained glass in ancient
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| essential product of glass manufacture.
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| | cathedrals. It has been much used for
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| Glass was usually coloured by adding
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| | lead lighting in churches in the 20th
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| metallic oxides to the glass while in a
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| | century.
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| molten state in a clay pot over a
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| | Flashed glass Red pot metal glass was
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| furnace. Glass coloured in this way was
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| | often undesirably dark in colour and
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| known as pot metal. Copper oxides were
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| | prohibitively expensive. The method
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| added to produce green, cobalt for blue,
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| | developed to produce red glass was called
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| and gold was added to produce red glass.
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| | flashing. In this procedure, a
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| Cylinder glass This glass was then
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| | semi-molten cylinder of colourless glass
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| collected from the pot into a molten
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| | was dipped into a pot of red glass so
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| globule and blown, being continually
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| | that the red glass formed a thin coating.
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| manipulated until it formed a large
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| | The laminated glass thus formed was cut,
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| cylindrical bottle shape of even diameter
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| | flattened and heat annealed.
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| and wall-thickness. It was then cut open,
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| | There were a number of advantages to this
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| laid flat and annealed to make it stable.
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| | technique. It allowed a variety in the
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| This is the type of glass most commonly
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| | depth of red, ranging from very dark and
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| used for ancient stained glass windows.
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| | almost opaque, through ruby red to pale
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| Crown glass This glass was partly blown
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| | and sometimes streaky red that was often
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| into a hollow vessel, then put onto a
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| | used for thin border pieces. The other
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| revolving table which could be rapidly
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| | advantage was that the red of
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| spun like a potter's wheel. The
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| | double-layered glass could be engraved or
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| centrifugal force caused the molten
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| | abraded to show colourless glass
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| material to flattened and spread
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| | underneath. In the late Medieval glass
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| outwards. It could then be cut into small
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| | this method was often employed to add
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| sheets. This glass could be made coloured
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| | rich patterns to the robes of Saints. The
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| and used for stained glass windows, but
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| | other advantage, much exploited by late
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| is typically associated with small paned
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| | Victorian and early 20th century artists,
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| windows of 16th and 17th century houses.
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| | was that sheets could be flashed in which
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| The concentric, curving ripples are
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| | the depth of colour varied across the
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| characteristic of this process. The
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| | sheet. Some stained glass studios,
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| center of each piece of glass received
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| | notably Lavers and Barraud, made
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| less force during the spinning, and thus
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| | extensive use of large segments of
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| produced was a thicker piece. These were
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| | irregularly flashed glass in robes and
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| sometimes used for the special effect
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| | draperies.
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| created by their lumpy, refractive
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| | There still exist a number of glass
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| quality. They are known as bull's eyes
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| | factories, notably in Germany, USA,
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| and are feature of late 19th century
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| | England, France, Poland and Russia which
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| domestic lead lighting and are sometimes
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| | continue to produce high quality glass by
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| used with cathedral glass or quarry glass
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| | traditional methods primarily for the
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| in church windows of that date.
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| | restoration of ancient windows. Modern
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| Table glass This glass was produced by
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| | stained glass windows often use machine
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| tipping the molten glass onto a metal
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| | made glass, slab glass, which as its name
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| table and sometimes rolling it. The glass
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| | suggests is very thick, and so-called
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| thus produced was heavily textured by the
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| | cathedral glass which is sometimes
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| reaction of the glass with the cold
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| | heavily textured.
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| metal. Glass of this appearance is
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