Tapered tube & Wire

I have never had any particular interest in tapered wire or tube until now, when I was shown some bangles and ear-rings, and realised I didn't know how they were made.  I recently posted a query on Orchid / Ganoksin, and am currently waiting for information from more experienced metalsmiths.  The picture above left shows a solid silver-plated copper hoop, tapered smoothly in both directions, two solid tapered nickel silver finger rings, and a hollow 0.5mm-thick sterling ear hoop.  The picture on the right shows the ear hoop sawn in half, it can plainly be seen to have seams around the interior and exterior periphery.  However I have also been shown one that has only an interior seam.  Anyone give me some ideas of how these are made? By way of experiment, I hammered a 30x10mm cylindrical sprue of pewter into a double-ended spindle shape reminiscent of some of the crescent designs above, although I've not yet worked out how to hammer or press it into a crescent without damaging the cross section.