While stained glass had been used in French churches in the Romanesque period, the Gothic windows were much larger, eventually filling entire walls.

Their function was to fill the interior with a mystical colored light, representing the Holy Spirit, and also to illustrate the stories of the Bible for the large majority of the congregation who could not read.

[1] The rose window was a particularly important feature of the major French cathedrals, beginning with Notre Dame de Paris.

The medieval French church, Following the doctrine of Saint Augustine, associated light with the power of God, the Son and the Holy Spirit.

[4] Suger described the finished work at Saint-Denis as "a circular string of chapels, by virtue of which the whole church would shine with the wonderful and uninterrupted light of most luminous windows, pervading the interior beauty".

Pierre de Roissy, a dignitary of the Chapter of Chartres Cathedral, wrote in about 1200 that the stained glass windows being installed in the nave "would transmit the clarity of the sunlight, signifying the Holy Scriptures, which push evil away from us, as they illuminate us.

The Abbey also had a Tree of Jessé window, depicting the genealogy of Christ, which became a common feature at Gothic cathedrals for the next century.

[5] They introduced the famous Chartres blue, glass colored with Cobalt(II) oxide, which cooled and balanced the vivid reds and yellows of the windows.

Important early examples include the west rose window of Notre-Dame de Paris, the chapel of the Virgin of the Abbey of Saint-Germain-des-Prés (destroyed in the 18th century, but some of the glass was preserved).

[9] The most important and influential work in this style is the upper royal chapel of Sainte-Chapelle (1234–1244), built for Louis IX to display his recently acquired collection of sacred relics.

The important figures and scenes are placed in additional quadrilateral settings of mosaic-like decoration, dominated by red and blue colors.

[14] Other major examples of Rayonnant stained glass are the great north and south rose windows of the transept of Notre-Dame de Paris, whose construction was sponsored by King Louis IX of France.

He preserved the original windows in the disambulatory, but reconstructed the central sanctuary and built a large new transept to replace the Carolingian nave.

Between 1255 and 1260 another new tendency appeared in French windows; large panels surrounding the colored figures were filled with grisaille, or grey or white glass.

[18] In the second part of the 13th century, the grisaille portions were animated by quadrille panes illustrating biblical stories and bordered with delicate foliage.

[19] In the Fourteenth century France was engaged in the Hundred Years' War with England, and also faced a series of deadly epidemics of the Plague.

[21] One distinctive feature of the flamboyant was a curvilinear design of the stone mullions within the arched top of windows which, with some imagination, resembled flames agitated by the wind.

It had two components; the upper element, called the soufflet, which resembled an elongated four-leaf clover; which was flanked by two mouchettes, undulating spindle-shaped forms decorated with cusps in designs.

The court helped introduce Renaissance artistic ideas such as realism and perspective into French art, including stained glass.

Stained glass workshops were located in the major European cities, and began to dedicate more and more of their time to the maintenance of existing windows.

The Duc Jean de Berry, brother of King Charles V, commissioned stained glass windows for his residence in Bourges.

[27] Bourges, under The Duke Jean du Berry, the brother of King Charles V of France, was a major center for stained glass in the 15th century.

The Gothic style, which began in France, worked with elongated figures and vibrant colors, while the Renaissance set for a more naturalistic stance for the art, beginning in Italy.

Artists that did commission work on stained glass windows outside of public and religious buildings would carry around “cartoons” of their proposed designs.

The first stained glass window to portray its patron is at the Basilica of Saint Denis, where an image of the Abbot Suger is shown at the feet of Christ.

One variety of the process was described in detail at the beginning of the 12th century by the monk Theophile in a tract called "Schedula Diversarum Artium" or "Treatise on the Diverse Arts".

The glass was continually rotated and gradually pushed and flattened into a circular disk or plate, with a slight rise in the center where the tube had been inserted.

With the use of silver stain, the windows gradually lost the appearance of a mosaic of colored glass pieces and increasingly looked like illustrations of illuminated manuscripts.

Part of this resulted from optics; in the dark churches of the 12th century, the colors of the small windows, with their thick glass, and greater contrast and seemed more vivid.

The mullions of Notre-Dame de Paris spread outwards from the center like the rays of the sun, giving Rayonnant style its name.