Those of us that paint are always in awe of painters in the past century. They had to work under much tougher conditions. They could not go down to the local art store and buy a canvas pre-stretched. When I decide what size canvas I need, it is a simple trip to the art supply store. There I can purchase canvas of any size or type. On the other hand, many of the old masters paintings were painted on board. Frequently the canvases were of various sizes due to the hand work of making and stretching canvas.
Recently I visited the Houston Museum of Art where they had a Edgar Degas exhibit. The museum had a large showing of many of his early works. He is well known for painting groups, mostly famously dancers. One of his frequent group subjects was also race horses.
While at the exhibit I learned one of his techniques that he used to save time and add variety. I always thought of these artist as purest. I did not realize that they were always thinking of ways to make a painting better without adding a large amount of time to the process.
What Degas did was so simple that I wonder why I did not realize it before. He would use tracing paper and draw a dancer on it and then reverse the paper and trace it. What he would have then is two dancers that did not look alike but were in effect the same. They were being viewed from a different angle. Of course, I cannot do this, as I am never painting duplicates. Each animal I paint has a distinct look and personality that I need to capture.
However now have discovered this, I wonder what other labor saving techniques were used. I feel fairly certain that other painters have used tracing paper that is reversed for repetitive images. It will be interesting for me and maybe you to try to look at paintings with repetition of images and see if it is an example of the techniques of using tracing paper.