For making medieval glass windows, medieval glass is used. Medieval glass is the painted or colored glass, which was found in medieval, Europe between 10th and 16th century. Medieval Stained glass windows were the chief pictographic art form during medieval period, especially in northern France, Germany and England where windows tended to be big in comparison to southern areas. The frescos technique of painting is less common than in Italy. Mostly the stained glass windows were used in churches, but these were also found in rich domestic setting and public building like town halls.

The reason behind using medieval stained glass windows in churches was not only to enhance the beauty of the church but also to tell the stories to viewers through symbolic representation. The matter of subject in churches is generally religious, though portrayals and heraldry is often added and many story scenes give valuable imminent to the medieval period.

Window glasses are in use from first century AD and medieval stained glass windows having colored and painted glass were manufactured at an early date. Each medieval glass was made up with soda; however, the soda glass in northern Europe was almost replaced by forest glass after 1000 A.D. There were many examples of a rich blue colored glass, which was produced in the medieval period by using soda as the alkali.

The paint, which was used on medieval stained glass windows, was a kind of enamel. This enamel is mostly dark brown or black, which is formed by mixing the ground copper or iron oxide, wine, urine or vinegar and gum Arabic. Other ingredients may include sugar, treacle or vegetable oil. This paint was applied in a sequence of washes and superior constituents were added in last. Both the external and internal sides could be painted to add depth on overall artwork. The enamel was fixed by processing the glass in an annealing oven.

It is difficult to produce a bright and clear yellow color in medieval stained glass windows as it depends upon the careful control of furnace condition for creating an appropriate oxidized environment. The early fourteenth century not only provided the solution to this difficulty but also facilitated great flexibility for using colors. Silver stain was a blend of silver nitrate and silver sulphite mixed with pipe clay, which was applicable on clear glass. This technique provided more flexibility to glass painting. For example, the hair of the stature could be painted on the same piece of the glass as the head. Silver stain was also used to highlight the fine points of copy work and grisaille, and later it was added to the base of colored glass for creating a larger variety of glass hues.

Today, stained glass conversation follows moral principles that are completely different from medieval stained glass windows. Importance is now given to the historical material such as glass, lead and iron work. To conserve medieval stained glass windows, it is required to clean the windows carefully. Protective glazing, which are introduced and produced in market, should be used for preserving these windows.