Editing Stained glass (section)

==Techniques==

==="Pot metal" and flashed glass===
The primary method of including colour in stained glass is to use glass, originally colourless, that has been given colouring by mixing with metal oxides in its melted state (in a crucible or "pot"), producing glass sheets that are coloured all the way through; these are known as "pot metal" glass.<ref>[https://boppardconservationproject.wordpress.com/2013/02/10/facts-about-glass-creating-coloured-glass-pot-metal-glass/ "Facts about Glass – Creating Coloured Glass; Pot-metal glass"], Boppard Conservation Project – Glasgow Museums</ref> A second method, sometimes used in some areas of windows, is [[flashed glass]], a thin coating of coloured glass fused to colourless glass (or coloured glass, to produce a different colour). In medieval glass flashing was especially used for reds, as glass made with gold compounds was very expensive and tended to be too deep in colour to use at full thickness.<ref>''Investigations in Medieval Stained Glass: Materials, Methods, and Expressions'', xvii, eds., Brigitte Kurmann-Schwarz, Elizabeth Pastan, 2019, BRILL, {{ISBN|9004395717}}, 9789004395718, [https://books.google.com/books?id=1UueDwAAQBAJ&pg=PA4 google books]</ref>

===Glass paint===
[[File:Magi Herod MNMA Cl23532.jpg|thumb|[[Grisaille]] stained glass (15th century)]]
Another group of techniques give additional colouring, including lines and shading, by treating the surfaces of the coloured sheets, and often fixing these effects by a light firing in a furnace or kiln. These methods may be used over broad areas, especially with silver stain, which gave better yellows than other methods in the Middle Ages. Alternatively they may be used for painting linear effects, or polychrome areas of detail. The most common method of adding the black linear painting necessary to define stained glass images is the use of what is variously called "glass paint", "vitreous paint", or "[[grisaille]] paint". This was applied as a mixture of powdered glass, iron or rust filings to give a black colour, clay, and oil, vinegar or water for a brushable texture, with a binder such as [[gum arabic]]. This was painted on the pieces of coloured glass, and then fired to burn away the ingredients giving texture, leaving a layer of the glass and colouring, fused to the main glass piece.<ref>[https://boppardconservationproject.wordpress.com/2013/05/03/facts-about-glass-early-glass-painting/ "Facts about Glass: Early Glass Painting"], Boppard Conservation Project – Glasgow Museums; Historic England, 287-288</ref>

===Silver stain===
"Silver stain", introduced soon after 1300, produced a wide range of yellow to orange colours; this is the "stain" in the term "stained glass". [[Silver]] compounds (notably [[silver nitrate]])<ref>{{Cite book|url=https://books.google.com/books?id=hFQ4AQAAIAAJ&q=Silver+compounds+(notably+silver+nitrate)+are+used+as+stain+applied+to+the+surface+of+glass+and+fired+on|title=Ceramic Industry|last=Steinhoff|first=Frederick Louis|date=1973|publisher=Industrial Publications, Incorporated|language=en}}</ref> are mixed with binding substances, applied to the surface of glass, and then fired in a furnace or kiln.<ref>{{Cite book|url=https://books.google.com/books?id=X2fQAAAAMAAJ&q=Silver+compounds+(notably+silver+nitrate)+are+used+as+stain+applied+to+the+surface+of+glass+and+fired+on|title=Chambers's encyclopaedia|date=1967|publisher=Pergamon Press|language=en}}</ref> They can produce a range of colours from [[Orange (colour)|orange]]-red to yellow. Used on blue glass they produce greens. The way the glass is heated and cooled can significantly affect the colours produced by these compounds. The chemistry involved is complex and not well understood. The chemicals actually penetrate the glass they are added to a little way, and the technique therefore gives extremely stable results. By the 15th century it had become cheaper than using pot metal glass and was often used with glass paint as the only colour on transparent glass.<ref>[https://boppardconservationproject.wordpress.com/2013/07/28/facts-about-glass-silver-stain/ "Facts about Glass: Silver Stain"], Boppard Conservation Project – Glasgow Museums; Historic England, 290</ref> Silver stain was applied to the opposite face of the glass to silver paint, as the two techniques did not work well one on top of the other. The stain was usually on the exterior face, where it appears to have given the glass some protection against weathering, although this can also be true for paint. They were also probably fired separately, the stain needing a lower heat than the paint.<ref>''Modern Methods for Analysing Archaeological and Historical Glass'', section 7.3.3.5, 2013, ed. Koen H. A. Janssens, Wiley, {{ISBN|1118314204}}, 9781118314203, [https://books.google.com/books?id=9OunNskEvXYC&pg=PT803 google books]</ref>

==="Sanguine" or "Cousin's rose"===
"Sanguine", "carnation", "Rouge [[Jean Cousin the Elder|Jean Cousin]]" or "Cousin's rose", after its supposed inventor,<ref>In fact  [[Jean Cousin the Elder]] was only born in 1500, at the same time as the tehnique; claims that he was the first French painter in oils might be more valid.</ref> is an iron-based fired paint producing red colours, mainly used to highlight small areas, often on flesh. It was introduced around 1500.<ref>[https://boppardconservationproject.wordpress.com/2013/07/21/facts-about-glass-sanguine-and-carnation/ "Facts about Glass: Sanguine and Carnation"], Boppard Conservation Project – Glasgow Museums; Historic England, 288</ref> Copper stain, similar to silver stain but using copper compounds, also produced reds, and was mainly used in the 18th and 19th centuries.<ref name="auto">Historic England, 290</ref>

===Cold painting===
"Cold paint" is various types of paint that were applied without firing. Contrary to the optimistic claims of the 12th century writer [[Theophilus Presbyter]], cold paint is not very durable, and very little medieval paint has survived.<ref name="auto"/>

===Scratching techniques===
As well as painting, scratched [[sgraffito]] techniques were often used. This involved painting a colour over pot metal glass of another colour, and then before firing selectively scratching the glass paint away to make the design, or the lettering of an inscription. This was the most common method of making inscriptions in early medieval glass, giving white or light letters on a black background, with later inscriptions more often using black painted letters on a transparent glass background.<ref>[https://boppardconservationproject.wordpress.com/2014/12/09/examples-of-writing-in-stained-glass/ "Examples of Writing in Stained Glass"], Boppard Conservation Project – Glasgow Museums</ref>

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File:Détail vitrail st Etienne photo.png|Detail from a 13th-century window in the [[Basilica of Saint-Quentin]] depicting the creation of a stained-glass window in Middle Ages.
File:Roundel with Saint Lambrecht of Maastricht MET cdi32-24-48.jpg|Renaissance roundel using only black or brown glass paint, and silver stain. The bishop-saint [[Lambrecht of Maastricht]] stands in an extensive landscape, 1510–20. Diameter {{cvt|8+3/4|in|cm}}. Designed to be placed low, close to the viewer.
File:Stained Glass Panel with the Visitation MET MED700.jpg|Detail of German panel (1444) of ''[[Visitation (Christianity)|Visitation]]''; pot metal, including white glass, black vitreous paint, yellow silver stain, and olive-green enamel. The plant patterns in the red sky are formed by scratching away black paint from the red glass before firing. Restored with new lead cames.
File:Ecce Homo (one of a pair) MET DT279321 (cropped).jpg|German glass, [[Nuremberg]], after a drawing by [[Sebald Beham]], c. 1525. Silver stain produces a range of yellows and gold, and painted on the reverse of the blue sky, gives the dark green of the cross.<ref>Barbara Butts, Lee Hendrix and others, ''Painting on Light: Drawings and Stained Glass in the Age of Dürer and Holbein'', 183, 2001, Getty Publications, {{ISBN|089236579X}}, {{ISBN|9780892365791}}, [https://books.google.com/books?id=kiA2AgAAQBAJ&pg=PA196 google books]</ref>
</gallery>