Hi Bart, I Am Making A Stained Glass Window!

a detail of a stained glass window where two scenes are separated by thick arched bands of red and black, forming a v. on the left, two workers assemble a panel of stained glass in a workshop. it is upright and has the same scalloped design as this window. on the right, two other workers load the flat panel into a kiln. from a window of the martyrdom of st stephen at the basilica in saint quentin, in northern france, posted to wikipedia by jojomarg
Detail from a 13th-century window in the Basilica of Saint-Quentin depicting the creation of a stained-glass window in Middle Ages, posted to wikipedia by JojoMarg

Looking something up about the history of stained glass, I found this detail of a 13th century window of stained glass makers making the stained glass window, which,

marge simpson standing in front of a loom at a renn faire or something, looking back over her shoulder with a pleased look on her face, having just woven a tapestry that reads, "Hi bart i am weaving on a loom!" via acme archives direct, because rather than go with the cropped reddit version, i decided to post the full production cel that includes the 20th century fox seal and serial number of authenticity in the lower left corner.
an original production cel from The Simpsons, Season 6, ep 2F15, “Lisa’s Wedding,” via Acme [d’oh, sold]