You need to know you rim's outside and inside diameter in order to fit your pattern and also in order to make a paper mask. Choose an image you want to use and step and repeat the image as necessary to complete a circle that will fit on your bowl's rim. In this case I chose to engrave with a vector pattern, but the same would apply for a rastered pattern.
You need to know the foot diameter in order to make the positioning fixture. This simple fixture will hold the bowl in position so that you can use the paper masks to check your pattern, without the risk of moving the bowl.