I bought one of the Astrid and Miyu advent calendars last year and was pleased with the assortment and the materials. They work in sterling silver, brass, and some fine gold and have added lab diamonds to the mix as well.

Not sure why they wouldn’t have opted for seed pearls for this, as they aren’t expensive, but they went with faux pearls instead. The metal is sterling silver plated in gold, and the ring sells for USD$100.