STAINED GLASS. 490 STAINED GLASS. (q.v.). in that the glass to be made iridescent is not allowed to lose its high degree of heat. It is continually returned to the furnace at very brief intervals, and the lajers of glass become a solid mass, although close examination will often reveal their once separate existence and their number. The idea may have been taken from the Greco-Eoman pieces, which are often amber or violet in the natural state of the glass, like mod- ern pot metal, and rendered opaque and iridescent by the gradual decay of the exterior surface. In the course of experiments upon iridescent and lustrous surfaces, much was done in the way of depositing iron, tin, and other metals in a nearly pure state. By way of producing tours de force for exhibition pieces, these metallic de- posits were sometimes carried to surprising ex- tremes; thus about 1890 a vase was exhibited which was of glass within, but had its outside almost wholly non-vitreous and showing only an opaque and rough surface of warm brown ; and this piece was described by the exhibitor as con- taining as much iron as glass could possibly re- ceive and retain. Stained Glass Windows. By far the most important use of stained glass is its application to the artistic decoration of windows, usually termed glass painting, though properly speaking it is not painting at all. Originally, there was but one method of making ornamental glass win- dows, and that was to produce the pattern in out- line with finely made leaden frames, into the grooves of which pieces of colored or stained glass were fitted. It appears to have been a branch of art unknown to antiquity and to have been used in a primitive fashion in churches of the fourth and following centuries, the diff'erent colors forming not figures, but ornamental pat- terns. These are described by early authors such as Prudentius, Sidonius, Apollinaris, and Gregory of Tours, but nothing of this period has been pre- served. The majority of windows up to the ele'enth century were closed by thin slabs of alabaster or other translucent material often pierced by holes arranged to form patterns, as at Santi Vincenzo ed Anastasio and other Roman chuijches. One of the best known of the early examples of the use of figures in glass windows is of the eleventh century in the former monastery of Tegernsee (Bavaria) ; like all of the first at- tempts, they were only tasteful arrangements of colored glass in imitation of the stone mosaics used for floors, etc. Shortly afterwards in the twelfth century the monk Theophilus describes in his treatise the method of making such windows as the earliest ones at Chartres, Saint Denis, and Vendome. The centre of the steady progress throughout the twelfth and thirteenth centuries was in Northern France, where the use of Gothic architecture, with its immense increase in the size of the windows, suddenly brought stained glass windows into prominence, not only as one of the most important acces.sories of architecture, but as the one prominent color factor in the great Gothic interiors. As the windows occupied the entire wall-space between the piers, both in the aiale-walls and clerestories of the churches, they afforded the same opportunity for composi- tion that the solid walls had previously offered to fresco-painting. The French cathedrals of the thirteenth century at Le Mans, Chartres, Bourges, and to a less degree Rheims and Rouen, pre- serve whole series of contemporary windows, which gave the type to other countries and to the succeeding eentur.v. Those of the Sainte Clia- pelle in Paris are also of extreme beauty. The cliaraeteristics of the earliest Gothic windows are: multiplication of small figures in many sep- arate compositions grouped in tiers or rows of framed medallions; rich and dark coloring; wide decorative borders; heavy leads bent so as to outline the figures or cut them in the deep shad- ows. The development during the fourteenth century was toward lighter coloring, larger figures, nar- row borders, more ornamentation in the body of the windows, more delicate gradations of color, and increase of modeling, loss of simplicity, and tendency to mannerisms, while in the fifteenth century much clear glass was introduced into the backgrounds, and inscribed ribbons and archi- tectural accessories became conspicuous, whereas the earlier windows are composed of many small and distinct pictures set in a groundwork of grisaille or of color ornament, the later ones comprising a single figure or picture for each light or even a composition occupying the whole window. The designers of the Gothic age did not, to any great extent, give the details of their pictures on glass as their successors — Renais- sance and modern — mistakenly attempted to do, but obtained their superb effects by a clear know'l- edge of the interaction of colors, by juxtaposition of complementary colors, and the effect of dis- tances; the technique being that of glass colored not on the surface, but in the mass either by stain or incorporation. This branch of art w-as, therefore, governed by totally different artistic principles from those governing opaque painting (fresco, oil, tempera, tapestry, etc.), and these principles were thoroughly understood. The practice of painting on glass, i.e. of ap- plying color with the lirush on fusible pigments fixed by heat, began in the use of grisaille, a browning pigment, for cross-hatching and outlin- ing on clear glass the ornamental details of the backgrounds, in order to soften the glare of the clear glass without introducing disturbing color- elements. It was then applied, even in early French windows, to the faces and hands to indi- cate the features and fingers; and its use ex- tended gradually to all the shaded details, the inscriptions and ornaments, of the later windows. The perfection of the French work of the thir- teenth century has never been equaled. These series of cathedral windows were also one of the principal branches of Christian iconography (q.v.), joining with sculpture in expressing the subjects of religious thought in art. During the latter part of the thirteenth cen- tury the art was carried to England, Germany, and Italy, where it did not really flourish before the following century. In Italy the imperfect understanding of Gothic methods did not allow of the use of such immense windows, and the art never became thoroughly acclimated. At Arezzo Cathedral are some windows by a French artist, Guillaume de Marcillati, proving the transmis- sion from France. Other interesting examples are in San Francesco at Assisi. San Petronio in Bologna, and the Cathedral and Santa Croce in
