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While this shows a specific pattern, it also shows the general technique. The most important tip here is that this uses "bullion wire" aka "French wire" which is a coiled extremely fine wire used in embroidery, which makes it very flexible and thus useful for this technique.

Bangles cut out from the plastic of a round plastic bottle (like a drink bottle). After applying heat to the sides of it, they become strong enough and rough edges have gone. Not sure if they are still too cheap-and-tacky to want to make, however, they might provide a good base for a silk-wrapped bangle etc.

How to make your own bangle bracelet form for molding in silicone - Resin Obsession This tutorial goes through how to make your desired shape for a bangle out of polymer clay (and bake and sand it) and then use that bangle form as the basis of a silicone mould.,