Wooden shapers are a great low-tech way to dome your metal bases for enamelling. You can learn how to do that with my class on the subject.
In the class I explain how to make the shapers out of branches or dowels, but if you prefer to get a ready-made one, here you can purchase one made by me. The tool is two sided, with a medium round side and a small oval side. I find these two shapes to be the most useful for the job.
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The tools are made out of beech, and made with hand tools. Branded with the Enamel Workshop logo. The shaft of the tool is finished with a non-toxic oil.