Have you heard or seen the book, “500 BOWLS” by the Lark books? I was fortunate enough that my bowl is in this book. This books features many great bowls. This bowl has a connection to Kodak. I use the Kodak film container for my circle decoration. If I remember correctly, I first saw this technique from the book, Warren MacKenzie: American Potter, that influenced my pottery greatly, that another story, and thought to use the Kodak film container as a sign of ex-Kodak potter. Kodak's container is black, not the semi-transparent film container.
After throwing the pottery, you hold the film container outside the bowl, and push the clay toward outside in circular motion from inside with a finger. If you thrown the shape of bowl right, this makes very nice complement to the bowl. After making these circles, I turn the wheel and reshape the edge of bowl with a chamois to reshape to be round.