Interesting, I had ruled out silver as I my initial searches were showing about $80 for a large enough piece of sheet, but you've prompted me to look again and I've found a much cheaper supplier. Would you suggest fine, sterling or argentium silver? Also, does 0.5 mm sound about right?
For some extra context, I've included a snip of the design (though it yet may be tweaked a bit). Sorry, I ought to have included this in the first post.
I thought the ring on top may look like the bird has a blob on top of its head, but perhaps if it's not soldered on the edge of the sheet, but instead on the back extending over the top this might preserve the shape of the front edge.
I wouldn't mind the colour contrast between brass/copper and silver at all, but I suspect the silver would present less of a problem with tarnishing (and therefore re-polishing) over time. Would that be correct?
Alistair
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