Glass Wax was a window cleaning product that was applied to windows and let dry. It dried to a whitish film and then was polished off. Some bright person realized that this whiteness could be used for another purpose and voila, Glass Wax stencils were born. Glass Wax produced these in all sorts of Christmas motifs-nativity, Santas, snowflakes, bells, angels…all the popular images of the day.
The stencil was taped to the window. You dabbed the Glass Wax on with a dry sponge and when Christmas was over, you wiped the images off. A side benefit was a clean window. There are memoirs on various blogs that say that a few drops of food coloring added to the glass wax resulted in colored images.
Here’s an old TV commercial that features Glass Wax Stencils.