The technique is old. As early as the first quarter of the twelfth century, the Benedictine monk Theophilus Presbyter described it in Schedula diversarum artium, a treatise on the various art techniques of his time. Numerous medieval masters worked with glass to effectively exploit the interplay of color and light. Their skillful use of grisaille and, from the fourteenth century onward, of silver-yellow largely contributed to their fame. The earliest of these artists remain unknown, but some of the later ones became famous and played a major role in art history. In thirteenth-century Siena, for example, they were still overshadowed by Duccio di Buoninsegna (1255–1318/19), who supplied them with the cartoon (the preparatory design) for the stained-glass window in the apse of the cathedral around 1287/88. In the seventeenth century, however, artists like Engrand Leprince (died 1531) and Arnaud de Moles (1470–1520) were as famous as the fresco or panel painters of the time. This was due to the fact that they no longer created glass paintings from other artists’ cartoons but works based on their own designs.
In the early modern period, interest in glass painting waned: far fewer large-scale works on historical themes were created, and the rare glass painters still active in Europe preferred to reproduce famous prints. Antoine-Joseph Pernety (1716–1796), a monk of the Congregation of Saint Maur who came to be known as Dom Pernety, lamented this trend in Traité pratique des différentes manières de peindre. Published in 1757, this book confirmed the decline of glass painting, underscored that hardly any painters of the time mastered this art, and endeavored to describe the technique.
In those days, creating a glass painting began with the production of colored plate glass, which was subsequently cut in the desired shapes for later assembly using lead cames. The artists painted exclusively with black and used hatchings or dots to create shades of gray. Another technique consisted in covering the entire glass surface with a mixture of gum arabic and black enamel paint, and subsequently fashioning the intended motif on the dried layer using a feather with a rounded tip. Just like on engravings, the artist could create varied shading effects using the hatching technique. The final step involved placing the glass plate in a kiln to fix the picture. Drawing with a feather required extreme care, however: removing too much of the black layer damaged the sharpness of the image, and a wrong move meant starting afresh.
Thilo Westermann still masters the art of handling black color and possesses the required dexterity to successfully uphold the tradition. Like the old masters, he covers the glass plate with a black layer from which he carefully etches his motifs. He renders the light and shading effects not with hatching, but with dots—a myriad of dots of light that, at the end of the drawing process, compose flowers, crystal or porcelain vases, and scholar’s rocks. The effect is striking not only because Westermann works exclusively with light, but also because he succeeds in perfectly rendering the lightness of the petals, the tenderness of the corollas, and the transparency of faceted glass.
In his endeavor to imitate nature, Thilo reminds me of Wenceslaus Hollar (1617–1677), a seventeenth-century artist born in Prague who also created stunning trompe l’oeil images, but using a technique that boasts similarities with glass painting: etching. A polished and stripped metal plate is covered with varnish and then blackened with smoke. Using a needle, the artist draws on this prepared surface, incising the varnish to expose the bare metal beneath. During the process, the drawing stands out against the blackened area and thus can be modified. The plate is then dipped in a bath of water and nitric acid, allowing the mordant to corrode the metal and to create recesses at the exposed areas (i.e., those not covered by varnish). Subsequently, the metal plate is cleaned with water and dried with blotting paper. In a final step, the varnish is removed and the plate can be coated with ink for printing on paper. The result is the opposite of Westermann’s work, since the drawing appears in black instead of being generated by light and the transparency of the supporting material.
Between 1642 and 1647, Hollar created a series of excellent etchings depicting fur muffs. Just like trompe-l’oeil still lifes, these works perfectly render the bright and silky surface of the fur. The subtle shades of gray, the delicate contrast with the white or cream background, and the shadows emphasizing the contours of the muff give the fur such a realistic appearance that we are irresistibly tempted to touch the sheet of paper to determine whether this is an illusion or not. Doesn’t the same happen when we stand before a work by Thilo Westermann? Hollar played with black, Thilo plays with light. Hollar used hatching, Thilo uses dots. So, let’s challenge him to create the counterpart to Hollar’s muffs—using only light.
Translation: Mark Kyburz
Published in Thilo Westermann et l'art de dessiner sous verre, ed. Vitromusée Romont (Berlin/Boston: De Gruyter, 2022), pp. 179–181.