Pewter moves when you work with it so if the background is not kept flat throughout the process one can easily feel that the pewter is controlling you and the pattern might get lost.
This is an example of what NOT to do.
Tip: Don't use too much pressure when tracing the pattern. If you are heavy handed, take a deep breath, relax and go slowly. Before you begin to push out the low or high relief, flatten the background with your finger so that you can see the pattern clearly.